tools/objtool/check.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
   4  */
   5
   6 #include <string.h>
   7 #include <stdlib.h>
   8
   9 #include "builtin.h"
  10 #include "check.h"
  11 #include "elf.h"
  12 #include "special.h"
  13 #include "arch.h"
  14 #include "warn.h"
  15
  16 #include <linux/hashtable.h>
  17 #include <linux/kernel.h>
  18
  19 #define FAKE_JUMP_OFFSET -1
  20
  21 #define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
  22
  23 struct alternative {
  24         struct list_head list;
  25         struct instruction *insn;
  26         bool skip_orig;
  27 };
  28
  29 const char *objname;
  30 struct cfi_init_state initial_func_cfi;
  31
  32 struct instruction *find_insn(struct objtool_file *file,
  33                               struct section *sec, unsigned long offset)
  34 {
  35         struct instruction *insn;
  36
  37         hash_for_each_possible(file->insn_hash, insn, hash, sec_offset_hash(sec, offset)) {
  38                 if (insn->sec == sec && insn->offset == offset)
  39                         return insn;
  40         }
  41
  42         return NULL;
  43 }
  44
  45 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  46                                               struct instruction *insn)
  47 {
  48         struct instruction *next = list_next_entry(insn, list);
  49
  50         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  51                 return NULL;
  52
  53         return next;
  54 }
  55
  56 static struct instruction *next_insn_same_func(struct objtool_file *file,
  57                                                struct instruction *insn)
  58 {
  59         struct instruction *next = list_next_entry(insn, list);
  60         struct symbol *func = insn->func;
  61
  62         if (!func)
  63                 return NULL;
  64
  65         if (&next->list != &file->insn_list && next->func == func)
  66                 return next;
  67
  68         /* Check if we're already in the subfunction: */
  69         if (func == func->cfunc)
  70                 return NULL;
  71
  72         /* Move to the subfunction: */
  73         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  74 }
  75
  76 #define func_for_each_insn(file, func, insn)                            \
  77         for (insn = find_insn(file, func->sec, func->offset);           \
  78              insn;                                                      \
  79              insn = next_insn_same_func(file, insn))
  80
  81 #define sym_for_each_insn(file, sym, insn)                              \
  82         for (insn = find_insn(file, sym->sec, sym->offset);             \
  83              insn && &insn->list != &file->insn_list &&                 \
  84                 insn->sec == sym->sec &&                                \
  85                 insn->offset < sym->offset + sym->len;                  \
  86              insn = list_next_entry(insn, list))
  87
  88 #define sym_for_each_insn_continue_reverse(file, sym, insn)             \
  89         for (insn = list_prev_entry(insn, list);                        \
  90              &insn->list != &file->insn_list &&                         \
  91                 insn->sec == sym->sec && insn->offset >= sym->offset;   \
  92              insn = list_prev_entry(insn, list))
  93
  94 #define sec_for_each_insn_from(file, insn)                              \
  95         for (; insn; insn = next_insn_same_sec(file, insn))
  96
  97 #define sec_for_each_insn_continue(file, insn)                          \
  98         for (insn = next_insn_same_sec(file, insn); insn;               \
  99              insn = next_insn_same_sec(file, insn))
 100
 101 static bool is_static_jump(struct instruction *insn)
 102 {
 103         return insn->type == INSN_JUMP_CONDITIONAL ||
 104                insn->type == INSN_JUMP_UNCONDITIONAL;
 105 }
 106
 107 static bool is_sibling_call(struct instruction *insn)
 108 {
 109         /* An indirect jump is either a sibling call or a jump to a table. */
 110         if (insn->type == INSN_JUMP_DYNAMIC)
 111                 return list_empty(&insn->alts);
 112
 113         if (!is_static_jump(insn))
 114                 return false;
 115
 116         /* add_jump_destinations() sets insn->call_dest for sibling calls. */
 117         return !!insn->call_dest;
 118 }
 119
 120 /*
 121  * This checks to see if the given function is a "noreturn" function.
 122  *
 123  * For global functions which are outside the scope of this object file, we
 124  * have to keep a manual list of them.
 125  *
 126  * For local functions, we have to detect them manually by simply looking for
 127  * the lack of a return instruction.
 128  */
 129 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 130                                 int recursion)
 131 {
 132         int i;
 133         struct instruction *insn;
 134         bool empty = true;
 135
 136         /*
 137          * Unfortunately these have to be hard coded because the noreturn
 138          * attribute isn't provided in ELF data.
 139          */
 140         static const char * const global_noreturns[] = {
 141                 "__stack_chk_fail",
 142                 "panic",
 143                 "do_exit",
 144                 "do_task_dead",
 145                 "__module_put_and_exit",
 146                 "complete_and_exit",
 147                 "__reiserfs_panic",
 148                 "lbug_with_loc",
 149                 "fortify_panic",
 150                 "usercopy_abort",
 151                 "machine_real_restart",
 152                 "rewind_stack_do_exit",
 153                 "kunit_try_catch_throw",
 154         };
 155
 156         if (!func)
 157                 return false;
 158
 159         if (func->bind == STB_WEAK)
 160                 return false;
 161
 162         if (func->bind == STB_GLOBAL)
 163                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 164                         if (!strcmp(func->name, global_noreturns[i]))
 165                                 return true;
 166
 167         if (!func->len)
 168                 return false;
 169
 170         insn = find_insn(file, func->sec, func->offset);
 171         if (!insn->func)
 172                 return false;
 173
 174         func_for_each_insn(file, func, insn) {
 175                 empty = false;
 176
 177                 if (insn->type == INSN_RETURN)
 178                         return false;
 179         }
 180
 181         if (empty)
 182                 return false;
 183
 184         /*
 185          * A function can have a sibling call instead of a return.  In that
 186          * case, the function's dead-end status depends on whether the target
 187          * of the sibling call returns.
 188          */
 189         func_for_each_insn(file, func, insn) {
 190                 if (is_sibling_call(insn)) {
 191                         struct instruction *dest = insn->jump_dest;
 192
 193                         if (!dest)
 194                                 /* sibling call to another file */
 195                                 return false;
 196
 197                         /* local sibling call */
 198                         if (recursion == 5) {
 199                                 /*
 200                                  * Infinite recursion: two functions have
 201                                  * sibling calls to each other.  This is a very
 202                                  * rare case.  It means they aren't dead ends.
 203                                  */
 204                                 return false;
 205                         }
 206
 207                         return __dead_end_function(file, dest->func, recursion+1);
 208                 }
 209         }
 210
 211         return true;
 212 }
 213
 214 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 215 {
 216         return __dead_end_function(file, func, 0);
 217 }
 218
 219 static void init_cfi_state(struct cfi_state *cfi)
 220 {
 221         int i;
 222
 223         for (i = 0; i < CFI_NUM_REGS; i++) {
 224                 cfi->regs[i].base = CFI_UNDEFINED;
 225                 cfi->vals[i].base = CFI_UNDEFINED;
 226         }
 227         cfi->cfa.base = CFI_UNDEFINED;
 228         cfi->drap_reg = CFI_UNDEFINED;
 229         cfi->drap_offset = -1;
 230 }
 231
 232 static void clear_insn_state(struct insn_state *state)
 233 {
 234         memset(state, 0, sizeof(*state));
 235         init_cfi_state(&state->cfi);
 236 }
 237
 238 /*
 239  * Call the arch-specific instruction decoder for all the instructions and add
 240  * them to the global instruction list.
 241  */
 242 static int decode_instructions(struct objtool_file *file)
 243 {
 244         struct section *sec;
 245         struct symbol *func;
 246         unsigned long offset;
 247         struct instruction *insn;
 248         unsigned long nr_insns = 0;
 249         int ret;
 250
 251         for_each_sec(file, sec) {
 252
 253                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 254                         continue;
 255
 256                 if (strcmp(sec->name, ".altinstr_replacement") &&
 257                     strcmp(sec->name, ".altinstr_aux") &&
 258                     strncmp(sec->name, ".discard.", 9))
 259                         sec->text = true;
 260
 261                 if (!strcmp(sec->name, ".noinstr.text"))
 262                         sec->noinstr = true;
 263
 264                 for (offset = 0; offset < sec->len; offset += insn->len) {
 265                         insn = malloc(sizeof(*insn));
 266                         if (!insn) {
 267                                 WARN("malloc failed");
 268                                 return -1;
 269                         }
 270                         memset(insn, 0, sizeof(*insn));
 271                         INIT_LIST_HEAD(&insn->alts);
 272                         INIT_LIST_HEAD(&insn->stack_ops);
 273                         init_cfi_state(&insn->cfi);
 274
 275                         insn->sec = sec;
 276                         insn->offset = offset;
 277
 278                         ret = arch_decode_instruction(file->elf, sec, offset,
 279                                                       sec->len - offset,
 280                                                       &insn->len, &insn->type,
 281                                                       &insn->immediate,
 282                                                       &insn->stack_ops);
 283                         if (ret)
 284                                 goto err;
 285
 286                         hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
 287                         list_add_tail(&insn->list, &file->insn_list);
 288                         nr_insns++;
 289                 }
 290
 291                 list_for_each_entry(func, &sec->symbol_list, list) {
 292                         if (func->type != STT_FUNC || func->alias != func)
 293                                 continue;
 294
 295                         if (!find_insn(file, sec, func->offset)) {
 296                                 WARN("%s(): can't find starting instruction",
 297                                      func->name);
 298                                 return -1;
 299                         }
 300
 301                         sym_for_each_insn(file, func, insn)
 302                                 insn->func = func;
 303                 }
 304         }
 305
 306         if (stats)
 307                 printf("nr_insns: %lu\n", nr_insns);
 308
 309         return 0;
 310
 311 err:
 312         free(insn);
 313         return ret;
 314 }
 315
 316 /*
 317  * Mark "ud2" instructions and manually annotated dead ends.
 318  */
 319 static int add_dead_ends(struct objtool_file *file)
 320 {
 321         struct section *sec;
 322         struct rela *rela;
 323         struct instruction *insn;
 324         bool found;
 325
 326         /*
 327          * By default, "ud2" is a dead end unless otherwise annotated, because
 328          * GCC 7 inserts it for certain divide-by-zero cases.
 329          */
 330         for_each_insn(file, insn)
 331                 if (insn->type == INSN_BUG)
 332                         insn->dead_end = true;
 333
 334         /*
 335          * Check for manually annotated dead ends.
 336          */
 337         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 338         if (!sec)
 339                 goto reachable;
 340
 341         list_for_each_entry(rela, &sec->rela_list, list) {
 342                 if (rela->sym->type != STT_SECTION) {
 343                         WARN("unexpected relocation symbol type in %s", sec->name);
 344                         return -1;
 345                 }
 346                 insn = find_insn(file, rela->sym->sec, rela->addend);
 347                 if (insn)
 348                         insn = list_prev_entry(insn, list);
 349                 else if (rela->addend == rela->sym->sec->len) {
 350                         found = false;
 351                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 352                                 if (insn->sec == rela->sym->sec) {
 353                                         found = true;
 354                                         break;
 355                                 }
 356                         }
 357
 358                         if (!found) {
 359                                 WARN("can't find unreachable insn at %s+0x%x",
 360                                      rela->sym->sec->name, rela->addend);
 361                                 return -1;
 362                         }
 363                 } else {
 364                         WARN("can't find unreachable insn at %s+0x%x",
 365                              rela->sym->sec->name, rela->addend);
 366                         return -1;
 367                 }
 368
 369                 insn->dead_end = true;
 370         }
 371
 372 reachable:
 373         /*
 374          * These manually annotated reachable checks are needed for GCC 4.4,
 375          * where the Linux unreachable() macro isn't supported.  In that case
 376          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 377          * not a dead end.
 378          */
 379         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 380         if (!sec)
 381                 return 0;
 382
 383         list_for_each_entry(rela, &sec->rela_list, list) {
 384                 if (rela->sym->type != STT_SECTION) {
 385                         WARN("unexpected relocation symbol type in %s", sec->name);
 386                         return -1;
 387                 }
 388                 insn = find_insn(file, rela->sym->sec, rela->addend);
 389                 if (insn)
 390                         insn = list_prev_entry(insn, list);
 391                 else if (rela->addend == rela->sym->sec->len) {
 392                         found = false;
 393                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 394                                 if (insn->sec == rela->sym->sec) {
 395                                         found = true;
 396                                         break;
 397                                 }
 398                         }
 399
 400                         if (!found) {
 401                                 WARN("can't find reachable insn at %s+0x%x",
 402                                      rela->sym->sec->name, rela->addend);
 403                                 return -1;
 404                         }
 405                 } else {
 406                         WARN("can't find reachable insn at %s+0x%x",
 407                              rela->sym->sec->name, rela->addend);
 408                         return -1;
 409                 }
 410
 411                 insn->dead_end = false;
 412         }
 413
 414         return 0;
 415 }
 416
 417 /*
 418  * Warnings shouldn't be reported for ignored functions.
 419  */
 420 static void add_ignores(struct objtool_file *file)
 421 {
 422         struct instruction *insn;
 423         struct section *sec;
 424         struct symbol *func;
 425         struct rela *rela;
 426
 427         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 428         if (!sec)
 429                 return;
 430
 431         list_for_each_entry(rela, &sec->rela_list, list) {
 432                 switch (rela->sym->type) {
 433                 case STT_FUNC:
 434                         func = rela->sym;
 435                         break;
 436
 437                 case STT_SECTION:
 438                         func = find_func_by_offset(rela->sym->sec, rela->addend);
 439                         if (!func)
 440                                 continue;
 441                         break;
 442
 443                 default:
 444                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 445                         continue;
 446                 }
 447
 448                 func_for_each_insn(file, func, insn)
 449                         insn->ignore = true;
 450         }
 451 }
 452
 453 /*
 454  * This is a whitelist of functions that is allowed to be called with AC set.
 455  * The list is meant to be minimal and only contains compiler instrumentation
 456  * ABI and a few functions used to implement *_{to,from}_user() functions.
 457  *
 458  * These functions must not directly change AC, but may PUSHF/POPF.
 459  */
 460 static const char *uaccess_safe_builtin[] = {
 461         /* KASAN */
 462         "kasan_report",
 463         "check_memory_region",
 464         /* KASAN out-of-line */
 465         "__asan_loadN_noabort",
 466         "__asan_load1_noabort",
 467         "__asan_load2_noabort",
 468         "__asan_load4_noabort",
 469         "__asan_load8_noabort",
 470         "__asan_load16_noabort",
 471         "__asan_storeN_noabort",
 472         "__asan_store1_noabort",
 473         "__asan_store2_noabort",
 474         "__asan_store4_noabort",
 475         "__asan_store8_noabort",
 476         "__asan_store16_noabort",
 477         /* KASAN in-line */
 478         "__asan_report_load_n_noabort",
 479         "__asan_report_load1_noabort",
 480         "__asan_report_load2_noabort",
 481         "__asan_report_load4_noabort",
 482         "__asan_report_load8_noabort",
 483         "__asan_report_load16_noabort",
 484         "__asan_report_store_n_noabort",
 485         "__asan_report_store1_noabort",
 486         "__asan_report_store2_noabort",
 487         "__asan_report_store4_noabort",
 488         "__asan_report_store8_noabort",
 489         "__asan_report_store16_noabort",
 490         /* KCOV */
 491         "write_comp_data",
 492         "__sanitizer_cov_trace_pc",
 493         "__sanitizer_cov_trace_const_cmp1",
 494         "__sanitizer_cov_trace_const_cmp2",
 495         "__sanitizer_cov_trace_const_cmp4",
 496         "__sanitizer_cov_trace_const_cmp8",
 497         "__sanitizer_cov_trace_cmp1",
 498         "__sanitizer_cov_trace_cmp2",
 499         "__sanitizer_cov_trace_cmp4",
 500         "__sanitizer_cov_trace_cmp8",
 501         "__sanitizer_cov_trace_switch",
 502         /* UBSAN */
 503         "ubsan_type_mismatch_common",
 504         "__ubsan_handle_type_mismatch",
 505         "__ubsan_handle_type_mismatch_v1",
 506         "__ubsan_handle_shift_out_of_bounds",
 507         /* misc */
 508         "csum_partial_copy_generic",
 509         "__memcpy_mcsafe",
 510         "mcsafe_handle_tail",
 511         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 512         NULL
 513 };
 514
 515 static void add_uaccess_safe(struct objtool_file *file)
 516 {
 517         struct symbol *func;
 518         const char **name;
 519
 520         if (!uaccess)
 521                 return;
 522
 523         for (name = uaccess_safe_builtin; *name; name++) {
 524                 func = find_symbol_by_name(file->elf, *name);
 525                 if (!func)
 526                         continue;
 527
 528                 func->uaccess_safe = true;
 529         }
 530 }
 531
 532 /*
 533  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 534  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 535  * But it at least allows objtool to understand the control flow *around* the
 536  * retpoline.
 537  */
 538 static int add_ignore_alternatives(struct objtool_file *file)
 539 {
 540         struct section *sec;
 541         struct rela *rela;
 542         struct instruction *insn;
 543
 544         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 545         if (!sec)
 546                 return 0;
 547
 548         list_for_each_entry(rela, &sec->rela_list, list) {
 549                 if (rela->sym->type != STT_SECTION) {
 550                         WARN("unexpected relocation symbol type in %s", sec->name);
 551                         return -1;
 552                 }
 553
 554                 insn = find_insn(file, rela->sym->sec, rela->addend);
 555                 if (!insn) {
 556                         WARN("bad .discard.ignore_alts entry");
 557                         return -1;
 558                 }
 559
 560                 insn->ignore_alts = true;
 561         }
 562
 563         return 0;
 564 }
 565
 566 /*
 567  * Find the destination instructions for all jumps.
 568  */
 569 static int add_jump_destinations(struct objtool_file *file)
 570 {
 571         struct instruction *insn;
 572         struct rela *rela;
 573         struct section *dest_sec;
 574         unsigned long dest_off;
 575
 576         for_each_insn(file, insn) {
 577                 if (!is_static_jump(insn))
 578                         continue;
 579
 580                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 581                         continue;
 582
 583                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 584                                                insn->offset, insn->len);
 585                 if (!rela) {
 586                         dest_sec = insn->sec;
 587                         dest_off = arch_jump_destination(insn);
 588                 } else if (rela->sym->type == STT_SECTION) {
 589                         dest_sec = rela->sym->sec;
 590                         dest_off = arch_dest_rela_offset(rela->addend);
 591                 } else if (rela->sym->sec->idx) {
 592                         dest_sec = rela->sym->sec;
 593                         dest_off = rela->sym->sym.st_value +
 594                                    arch_dest_rela_offset(rela->addend);
 595                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 596                         /*
 597                          * Retpoline jumps are really dynamic jumps in
 598                          * disguise, so convert them accordingly.
 599                          */
 600                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 601                                 insn->type = INSN_JUMP_DYNAMIC;
 602                         else
 603                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 604
 605                         insn->retpoline_safe = true;
 606                         continue;
 607                 } else {
 608                         /* external sibling call */
 609                         insn->call_dest = rela->sym;
 610                         continue;
 611                 }
 612
 613                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 614                 if (!insn->jump_dest) {
 615
 616                         /*
 617                          * This is a special case where an alt instruction
 618                          * jumps past the end of the section.  These are
 619                          * handled later in handle_group_alt().
 620                          */
 621                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 622                                 continue;
 623
 624                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 625                                   insn->sec, insn->offset, dest_sec->name,
 626                                   dest_off);
 627                         return -1;
 628                 }
 629
 630                 /*
 631                  * Cross-function jump.
 632                  */
 633                 if (insn->func && insn->jump_dest->func &&
 634                     insn->func != insn->jump_dest->func) {
 635
 636                         /*
 637                          * For GCC 8+, create parent/child links for any cold
 638                          * subfunctions.  This is _mostly_ redundant with a
 639                          * similar initialization in read_symbols().
 640                          *
 641                          * If a function has aliases, we want the *first* such
 642                          * function in the symbol table to be the subfunction's
 643                          * parent.  In that case we overwrite the
 644                          * initialization done in read_symbols().
 645                          *
 646                          * However this code can't completely replace the
 647                          * read_symbols() code because this doesn't detect the
 648                          * case where the parent function's only reference to a
 649                          * subfunction is through a jump table.
 650                          */
 651                         if (!strstr(insn->func->name, ".cold.") &&
 652                             strstr(insn->jump_dest->func->name, ".cold.")) {
 653                                 insn->func->cfunc = insn->jump_dest->func;
 654                                 insn->jump_dest->func->pfunc = insn->func;
 655
 656                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 657                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 658
 659                                 /* internal sibling call */
 660                                 insn->call_dest = insn->jump_dest->func;
 661                         }
 662                 }
 663         }
 664
 665         return 0;
 666 }
 667
 668 /*
 669  * Find the destination instructions for all calls.
 670  */
 671 static int add_call_destinations(struct objtool_file *file)
 672 {
 673         struct instruction *insn;
 674         unsigned long dest_off;
 675         struct rela *rela;
 676
 677         for_each_insn(file, insn) {
 678                 if (insn->type != INSN_CALL)
 679                         continue;
 680
 681                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 682                                                insn->offset, insn->len);
 683                 if (!rela) {
 684                         dest_off = arch_jump_destination(insn);
 685                         insn->call_dest = find_func_by_offset(insn->sec, dest_off);
 686                         if (!insn->call_dest)
 687                                 insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
 688
 689                         if (insn->ignore)
 690                                 continue;
 691
 692                         if (!insn->call_dest) {
 693                                 WARN_FUNC("unsupported intra-function call",
 694                                           insn->sec, insn->offset);
 695                                 if (retpoline)
 696                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 697                                 return -1;
 698                         }
 699
 700                         if (insn->func && insn->call_dest->type != STT_FUNC) {
 701                                 WARN_FUNC("unsupported call to non-function",
 702                                           insn->sec, insn->offset);
 703                                 return -1;
 704                         }
 705
 706                 } else if (rela->sym->type == STT_SECTION) {
 707                         dest_off = arch_dest_rela_offset(rela->addend);
 708                         insn->call_dest = find_func_by_offset(rela->sym->sec,
 709                                                               dest_off);
 710                         if (!insn->call_dest) {
 711                                 WARN_FUNC("can't find call dest symbol at %s+0x%lx",
 712                                           insn->sec, insn->offset,
 713                                           rela->sym->sec->name,
 714                                           dest_off);
 715                                 return -1;
 716                         }
 717                 } else
 718                         insn->call_dest = rela->sym;
 719         }
 720
 721         return 0;
 722 }
 723
 724 /*
 725  * The .alternatives section requires some extra special care, over and above
 726  * what other special sections require:
 727  *
 728  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 729  *    instruction at the end so that validate_branch() skips all the original
 730  *    replaced instructions when validating the new instruction path.
 731  *
 732  * 2. An added wrinkle is that the new instruction length might be zero.  In
 733  *    that case the old instructions are replaced with noops.  We simulate that
 734  *    by creating a fake jump as the only new instruction.
 735  *
 736  * 3. In some cases, the alternative section includes an instruction which
 737  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 738  *    jumps' destinations to point back to .text rather than the end of the
 739  *    entry in .altinstr_replacement.
 740  */
 741 static int handle_group_alt(struct objtool_file *file,
 742                             struct special_alt *special_alt,
 743                             struct instruction *orig_insn,
 744                             struct instruction **new_insn)
 745 {
 746         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 747         unsigned long dest_off;
 748
 749         last_orig_insn = NULL;
 750         insn = orig_insn;
 751         sec_for_each_insn_from(file, insn) {
 752                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 753                         break;
 754
 755                 insn->alt_group = true;
 756                 last_orig_insn = insn;
 757         }
 758
 759         if (next_insn_same_sec(file, last_orig_insn)) {
 760                 fake_jump = malloc(sizeof(*fake_jump));
 761                 if (!fake_jump) {
 762                         WARN("malloc failed");
 763                         return -1;
 764                 }
 765                 memset(fake_jump, 0, sizeof(*fake_jump));
 766                 INIT_LIST_HEAD(&fake_jump->alts);
 767                 INIT_LIST_HEAD(&fake_jump->stack_ops);
 768                 init_cfi_state(&fake_jump->cfi);
 769
 770                 fake_jump->sec = special_alt->new_sec;
 771                 fake_jump->offset = FAKE_JUMP_OFFSET;
 772                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 773                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 774                 fake_jump->func = orig_insn->func;
 775         }
 776
 777         if (!special_alt->new_len) {
 778                 if (!fake_jump) {
 779                         WARN("%s: empty alternative at end of section",
 780                              special_alt->orig_sec->name);
 781                         return -1;
 782                 }
 783
 784                 *new_insn = fake_jump;
 785                 return 0;
 786         }
 787
 788         last_new_insn = NULL;
 789         insn = *new_insn;
 790         sec_for_each_insn_from(file, insn) {
 791                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 792                         break;
 793
 794                 last_new_insn = insn;
 795
 796                 insn->ignore = orig_insn->ignore_alts;
 797                 insn->func = orig_insn->func;
 798
 799                 /*
 800                  * Since alternative replacement code is copy/pasted by the
 801                  * kernel after applying relocations, generally such code can't
 802                  * have relative-address relocation references to outside the
 803                  * .altinstr_replacement section, unless the arch's
 804                  * alternatives code can adjust the relative offsets
 805                  * accordingly.
 806                  *
 807                  * The x86 alternatives code adjusts the offsets only when it
 808                  * encounters a branch instruction at the very beginning of the
 809                  * replacement group.
 810                  */
 811                 if ((insn->offset != special_alt->new_off ||
 812                     (insn->type != INSN_CALL && !is_static_jump(insn))) &&
 813                     find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
 814
 815                         WARN_FUNC("unsupported relocation in alternatives section",
 816                                   insn->sec, insn->offset);
 817                         return -1;
 818                 }
 819
 820                 if (!is_static_jump(insn))
 821                         continue;
 822
 823                 if (!insn->immediate)
 824                         continue;
 825
 826                 dest_off = arch_jump_destination(insn);
 827                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 828                         if (!fake_jump) {
 829                                 WARN("%s: alternative jump to end of section",
 830                                      special_alt->orig_sec->name);
 831                                 return -1;
 832                         }
 833                         insn->jump_dest = fake_jump;
 834                 }
 835
 836                 if (!insn->jump_dest) {
 837                         WARN_FUNC("can't find alternative jump destination",
 838                                   insn->sec, insn->offset);
 839                         return -1;
 840                 }
 841         }
 842
 843         if (!last_new_insn) {
 844                 WARN_FUNC("can't find last new alternative instruction",
 845                           special_alt->new_sec, special_alt->new_off);
 846                 return -1;
 847         }
 848
 849         if (fake_jump)
 850                 list_add(&fake_jump->list, &last_new_insn->list);
 851
 852         return 0;
 853 }
 854
 855 /*
 856  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 857  * If the original instruction is a jump, make the alt entry an effective nop
 858  * by just skipping the original instruction.
 859  */
 860 static int handle_jump_alt(struct objtool_file *file,
 861                            struct special_alt *special_alt,
 862                            struct instruction *orig_insn,
 863                            struct instruction **new_insn)
 864 {
 865         if (orig_insn->type == INSN_NOP)
 866                 return 0;
 867
 868         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 869                 WARN_FUNC("unsupported instruction at jump label",
 870                           orig_insn->sec, orig_insn->offset);
 871                 return -1;
 872         }
 873
 874         *new_insn = list_next_entry(orig_insn, list);
 875         return 0;
 876 }
 877
 878 /*
 879  * Read all the special sections which have alternate instructions which can be
 880  * patched in or redirected to at runtime.  Each instruction having alternate
 881  * instruction(s) has them added to its insn->alts list, which will be
 882  * traversed in validate_branch().
 883  */
 884 static int add_special_section_alts(struct objtool_file *file)
 885 {
 886         struct list_head special_alts;
 887         struct instruction *orig_insn, *new_insn;
 888         struct special_alt *special_alt, *tmp;
 889         struct alternative *alt;
 890         int ret;
 891
 892         ret = special_get_alts(file->elf, &special_alts);
 893         if (ret)
 894                 return ret;
 895
 896         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 897
 898                 orig_insn = find_insn(file, special_alt->orig_sec,
 899                                       special_alt->orig_off);
 900                 if (!orig_insn) {
 901                         WARN_FUNC("special: can't find orig instruction",
 902                                   special_alt->orig_sec, special_alt->orig_off);
 903                         ret = -1;
 904                         goto out;
 905                 }
 906
 907                 new_insn = NULL;
 908                 if (!special_alt->group || special_alt->new_len) {
 909                         new_insn = find_insn(file, special_alt->new_sec,
 910                                              special_alt->new_off);
 911                         if (!new_insn) {
 912                                 WARN_FUNC("special: can't find new instruction",
 913                                           special_alt->new_sec,
 914                                           special_alt->new_off);
 915                                 ret = -1;
 916                                 goto out;
 917                         }
 918                 }
 919
 920                 if (special_alt->group) {
 921                         if (!special_alt->orig_len) {
 922                                 WARN_FUNC("empty alternative entry",
 923                                           orig_insn->sec, orig_insn->offset);
 924                                 continue;
 925                         }
 926
 927                         ret = handle_group_alt(file, special_alt, orig_insn,
 928                                                &new_insn);
 929                         if (ret)
 930                                 goto out;
 931                 } else if (special_alt->jump_or_nop) {
 932                         ret = handle_jump_alt(file, special_alt, orig_insn,
 933                                               &new_insn);
 934                         if (ret)
 935                                 goto out;
 936                 }
 937
 938                 alt = malloc(sizeof(*alt));
 939                 if (!alt) {
 940                         WARN("malloc failed");
 941                         ret = -1;
 942                         goto out;
 943                 }
 944
 945                 alt->insn = new_insn;
 946                 alt->skip_orig = special_alt->skip_orig;
 947                 orig_insn->ignore_alts |= special_alt->skip_alt;
 948                 list_add_tail(&alt->list, &orig_insn->alts);
 949
 950                 list_del(&special_alt->list);
 951                 free(special_alt);
 952         }
 953
 954 out:
 955         return ret;
 956 }
 957
 958 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 959                             struct rela *table)
 960 {
 961         struct rela *rela = table;
 962         struct instruction *dest_insn;
 963         struct alternative *alt;
 964         struct symbol *pfunc = insn->func->pfunc;
 965         unsigned int prev_offset = 0;
 966
 967         /*
 968          * Each @rela is a switch table relocation which points to the target
 969          * instruction.
 970          */
 971         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 972
 973                 /* Check for the end of the table: */
 974                 if (rela != table && rela->jump_table_start)
 975                         break;
 976
 977                 /* Make sure the table entries are consecutive: */
 978                 if (prev_offset && rela->offset != prev_offset + 8)
 979                         break;
 980
 981                 /* Detect function pointers from contiguous objects: */
 982                 if (rela->sym->sec == pfunc->sec &&
 983                     rela->addend == pfunc->offset)
 984                         break;
 985
 986                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 987                 if (!dest_insn)
 988                         break;
 989
 990                 /* Make sure the destination is in the same function: */
 991                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 992                         break;
 993
 994                 alt = malloc(sizeof(*alt));
 995                 if (!alt) {
 996                         WARN("malloc failed");
 997                         return -1;
 998                 }
 999
1000                 alt->insn = dest_insn;
1001                 list_add_tail(&alt->list, &insn->alts);
1002                 prev_offset = rela->offset;
1003         }
1004
1005         if (!prev_offset) {
1006                 WARN_FUNC("can't find switch jump table",
1007                           insn->sec, insn->offset);
1008                 return -1;
1009         }
1010
1011         return 0;
1012 }
1013
1014 /*
1015  * find_jump_table() - Given a dynamic jump, find the switch jump table in
1016  * .rodata associated with it.
1017  *
1018  * There are 3 basic patterns:
1019  *
1020  * 1. jmpq *[rodata addr](,%reg,8)
1021  *
1022  *    This is the most common case by far.  It jumps to an address in a simple
1023  *    jump table which is stored in .rodata.
1024  *
1025  * 2. jmpq *[rodata addr](%rip)
1026  *
1027  *    This is caused by a rare GCC quirk, currently only seen in three driver
1028  *    functions in the kernel, only with certain obscure non-distro configs.
1029  *
1030  *    As part of an optimization, GCC makes a copy of an existing switch jump
1031  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
1032  *    jump) to use a single entry in the table.  The rest of the jump table and
1033  *    some of its jump targets remain as dead code.
1034  *
1035  *    In such a case we can just crudely ignore all unreachable instruction
1036  *    warnings for the entire object file.  Ideally we would just ignore them
1037  *    for the function, but that would require redesigning the code quite a
1038  *    bit.  And honestly that's just not worth doing: unreachable instruction
1039  *    warnings are of questionable value anyway, and this is such a rare issue.
1040  *
1041  * 3. mov [rodata addr],%reg1
1042  *    ... some instructions ...
1043  *    jmpq *(%reg1,%reg2,8)
1044  *
1045  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1046  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1047  *
1048  *    As of GCC 7 there are quite a few more of these and the 'in between' code
1049  *    is significant. Esp. with KASAN enabled some of the code between the mov
1050  *    and jmpq uses .rodata itself, which can confuse things.
1051  *
1052  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1053  *    ensure the same register is used in the mov and jump instructions.
1054  *
1055  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1056  */
1057 static struct rela *find_jump_table(struct objtool_file *file,
1058                                       struct symbol *func,
1059                                       struct instruction *insn)
1060 {
1061         struct rela *text_rela, *table_rela;
1062         struct instruction *dest_insn, *orig_insn = insn;
1063         struct section *table_sec;
1064         unsigned long table_offset;
1065
1066         /*
1067          * Backward search using the @first_jump_src links, these help avoid
1068          * much of the 'in between' code. Which avoids us getting confused by
1069          * it.
1070          */
1071         for (;
1072              &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
1073              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1074
1075                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1076                         break;
1077
1078                 /* allow small jumps within the range */
1079                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1080                     insn->jump_dest &&
1081                     (insn->jump_dest->offset <= insn->offset ||
1082                      insn->jump_dest->offset > orig_insn->offset))
1083                     break;
1084
1085                 /* look for a relocation which references .rodata */
1086                 text_rela = find_rela_by_dest_range(file->elf, insn->sec,
1087                                                     insn->offset, insn->len);
1088                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1089                     !text_rela->sym->sec->rodata)
1090                         continue;
1091
1092                 table_offset = text_rela->addend;
1093                 table_sec = text_rela->sym->sec;
1094
1095                 if (text_rela->type == R_X86_64_PC32)
1096                         table_offset += 4;
1097
1098                 /*
1099                  * Make sure the .rodata address isn't associated with a
1100                  * symbol.  GCC jump tables are anonymous data.
1101                  *
1102                  * Also support C jump tables which are in the same format as
1103                  * switch jump tables.  For objtool to recognize them, they
1104                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1105                  * have symbols associated with them.
1106                  */
1107                 if (find_symbol_containing(table_sec, table_offset) &&
1108                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1109                         continue;
1110
1111                 /*
1112                  * Each table entry has a rela associated with it.  The rela
1113                  * should reference text in the same function as the original
1114                  * instruction.
1115                  */
1116                 table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
1117                 if (!table_rela)
1118                         continue;
1119                 dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
1120                 if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1121                         continue;
1122
1123                 /*
1124                  * Use of RIP-relative switch jumps is quite rare, and
1125                  * indicates a rare GCC quirk/bug which can leave dead code
1126                  * behind.
1127                  */
1128                 if (text_rela->type == R_X86_64_PC32)
1129                         file->ignore_unreachables = true;
1130
1131                 return table_rela;
1132         }
1133
1134         return NULL;
1135 }
1136
1137 /*
1138  * First pass: Mark the head of each jump table so that in the next pass,
1139  * we know when a given jump table ends and the next one starts.
1140  */
1141 static void mark_func_jump_tables(struct objtool_file *file,
1142                                     struct symbol *func)
1143 {
1144         struct instruction *insn, *last = NULL;
1145         struct rela *rela;
1146
1147         func_for_each_insn(file, func, insn) {
1148                 if (!last)
1149                         last = insn;
1150
1151                 /*
1152                  * Store back-pointers for unconditional forward jumps such
1153                  * that find_jump_table() can back-track using those and
1154                  * avoid some potentially confusing code.
1155                  */
1156                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1157                     insn->offset > last->offset &&
1158                     insn->jump_dest->offset > insn->offset &&
1159                     !insn->jump_dest->first_jump_src) {
1160
1161                         insn->jump_dest->first_jump_src = insn;
1162                         last = insn->jump_dest;
1163                 }
1164
1165                 if (insn->type != INSN_JUMP_DYNAMIC)
1166                         continue;
1167
1168                 rela = find_jump_table(file, func, insn);
1169                 if (rela) {
1170                         rela->jump_table_start = true;
1171                         insn->jump_table = rela;
1172                 }
1173         }
1174 }
1175
1176 static int add_func_jump_tables(struct objtool_file *file,
1177                                   struct symbol *func)
1178 {
1179         struct instruction *insn;
1180         int ret;
1181
1182         func_for_each_insn(file, func, insn) {
1183                 if (!insn->jump_table)
1184                         continue;
1185
1186                 ret = add_jump_table(file, insn, insn->jump_table);
1187                 if (ret)
1188                         return ret;
1189         }
1190
1191         return 0;
1192 }
1193
1194 /*
1195  * For some switch statements, gcc generates a jump table in the .rodata
1196  * section which contains a list of addresses within the function to jump to.
1197  * This finds these jump tables and adds them to the insn->alts lists.
1198  */
1199 static int add_jump_table_alts(struct objtool_file *file)
1200 {
1201         struct section *sec;
1202         struct symbol *func;
1203         int ret;
1204
1205         if (!file->rodata)
1206                 return 0;
1207
1208         for_each_sec(file, sec) {
1209                 list_for_each_entry(func, &sec->symbol_list, list) {
1210                         if (func->type != STT_FUNC)
1211                                 continue;
1212
1213                         mark_func_jump_tables(file, func);
1214                         ret = add_func_jump_tables(file, func);
1215                         if (ret)
1216                                 return ret;
1217                 }
1218         }
1219
1220         return 0;
1221 }
1222
1223 static int read_unwind_hints(struct objtool_file *file)
1224 {
1225         struct section *sec, *relasec;
1226         struct rela *rela;
1227         struct unwind_hint *hint;
1228         struct instruction *insn;
1229         struct cfi_reg *cfa;
1230         int i;
1231
1232         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1233         if (!sec)
1234                 return 0;
1235
1236         relasec = sec->rela;
1237         if (!relasec) {
1238                 WARN("missing .rela.discard.unwind_hints section");
1239                 return -1;
1240         }
1241
1242         if (sec->len % sizeof(struct unwind_hint)) {
1243                 WARN("struct unwind_hint size mismatch");
1244                 return -1;
1245         }
1246
1247         file->hints = true;
1248
1249         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1250                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1251
1252                 rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
1253                 if (!rela) {
1254                         WARN("can't find rela for unwind_hints[%d]", i);
1255                         return -1;
1256                 }
1257
1258                 insn = find_insn(file, rela->sym->sec, rela->addend);
1259                 if (!insn) {
1260                         WARN("can't find insn for unwind_hints[%d]", i);
1261                         return -1;
1262                 }
1263
1264                 cfa = &insn->cfi.cfa;
1265
1266                 if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
1267                         insn->ret_offset = hint->sp_offset;
1268                         continue;
1269                 }
1270
1271                 insn->hint = true;
1272
1273                 switch (hint->sp_reg) {
1274                 case ORC_REG_UNDEFINED:
1275                         cfa->base = CFI_UNDEFINED;
1276                         break;
1277                 case ORC_REG_SP:
1278                         cfa->base = CFI_SP;
1279                         break;
1280                 case ORC_REG_BP:
1281                         cfa->base = CFI_BP;
1282                         break;
1283                 case ORC_REG_SP_INDIRECT:
1284                         cfa->base = CFI_SP_INDIRECT;
1285                         break;
1286                 case ORC_REG_R10:
1287                         cfa->base = CFI_R10;
1288                         break;
1289                 case ORC_REG_R13:
1290                         cfa->base = CFI_R13;
1291                         break;
1292                 case ORC_REG_DI:
1293                         cfa->base = CFI_DI;
1294                         break;
1295                 case ORC_REG_DX:
1296                         cfa->base = CFI_DX;
1297                         break;
1298                 default:
1299                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1300                                   insn->sec, insn->offset, hint->sp_reg);
1301                         return -1;
1302                 }
1303
1304                 cfa->offset = hint->sp_offset;
1305                 insn->cfi.type = hint->type;
1306                 insn->cfi.end = hint->end;
1307         }
1308
1309         return 0;
1310 }
1311
1312 static int read_retpoline_hints(struct objtool_file *file)
1313 {
1314         struct section *sec;
1315         struct instruction *insn;
1316         struct rela *rela;
1317
1318         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1319         if (!sec)
1320                 return 0;
1321
1322         list_for_each_entry(rela, &sec->rela_list, list) {
1323                 if (rela->sym->type != STT_SECTION) {
1324                         WARN("unexpected relocation symbol type in %s", sec->name);
1325                         return -1;
1326                 }
1327
1328                 insn = find_insn(file, rela->sym->sec, rela->addend);
1329                 if (!insn) {
1330                         WARN("bad .discard.retpoline_safe entry");
1331                         return -1;
1332                 }
1333
1334                 if (insn->type != INSN_JUMP_DYNAMIC &&
1335                     insn->type != INSN_CALL_DYNAMIC) {
1336                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1337                                   insn->sec, insn->offset);
1338                         return -1;
1339                 }
1340
1341                 insn->retpoline_safe = true;
1342         }
1343
1344         return 0;
1345 }
1346
1347 static int read_instr_hints(struct objtool_file *file)
1348 {
1349         struct section *sec;
1350         struct instruction *insn;
1351         struct rela *rela;
1352
1353         sec = find_section_by_name(file->elf, ".rela.discard.instr_end");
1354         if (!sec)
1355                 return 0;
1356
1357         list_for_each_entry(rela, &sec->rela_list, list) {
1358                 if (rela->sym->type != STT_SECTION) {
1359                         WARN("unexpected relocation symbol type in %s", sec->name);
1360                         return -1;
1361                 }
1362
1363                 insn = find_insn(file, rela->sym->sec, rela->addend);
1364                 if (!insn) {
1365                         WARN("bad .discard.instr_end entry");
1366                         return -1;
1367                 }
1368
1369                 insn->instr--;
1370         }
1371
1372         sec = find_section_by_name(file->elf, ".rela.discard.instr_begin");
1373         if (!sec)
1374                 return 0;
1375
1376         list_for_each_entry(rela, &sec->rela_list, list) {
1377                 if (rela->sym->type != STT_SECTION) {
1378                         WARN("unexpected relocation symbol type in %s", sec->name);
1379                         return -1;
1380                 }
1381
1382                 insn = find_insn(file, rela->sym->sec, rela->addend);
1383                 if (!insn) {
1384                         WARN("bad .discard.instr_begin entry");
1385                         return -1;
1386                 }
1387
1388                 insn->instr++;
1389         }
1390
1391         return 0;
1392 }
1393
1394 static void mark_rodata(struct objtool_file *file)
1395 {
1396         struct section *sec;
1397         bool found = false;
1398
1399         /*
1400          * Search for the following rodata sections, each of which can
1401          * potentially contain jump tables:
1402          *
1403          * - .rodata: can contain GCC switch tables
1404          * - .rodata.<func>: same, if -fdata-sections is being used
1405          * - .rodata..c_jump_table: contains C annotated jump tables
1406          *
1407          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1408          */
1409         for_each_sec(file, sec) {
1410                 if (!strncmp(sec->name, ".rodata", 7) &&
1411                     !strstr(sec->name, ".str1.")) {
1412                         sec->rodata = true;
1413                         found = true;
1414                 }
1415         }
1416
1417         file->rodata = found;
1418 }
1419
1420 static int decode_sections(struct objtool_file *file)
1421 {
1422         int ret;
1423
1424         mark_rodata(file);
1425
1426         ret = decode_instructions(file);
1427         if (ret)
1428                 return ret;
1429
1430         ret = add_dead_ends(file);
1431         if (ret)
1432                 return ret;
1433
1434         add_ignores(file);
1435         add_uaccess_safe(file);
1436
1437         ret = add_ignore_alternatives(file);
1438         if (ret)
1439                 return ret;
1440
1441         ret = add_jump_destinations(file);
1442         if (ret)
1443                 return ret;
1444
1445         ret = add_special_section_alts(file);
1446         if (ret)
1447                 return ret;
1448
1449         ret = add_call_destinations(file);
1450         if (ret)
1451                 return ret;
1452
1453         ret = add_jump_table_alts(file);
1454         if (ret)
1455                 return ret;
1456
1457         ret = read_unwind_hints(file);
1458         if (ret)
1459                 return ret;
1460
1461         ret = read_retpoline_hints(file);
1462         if (ret)
1463                 return ret;
1464
1465         ret = read_instr_hints(file);
1466         if (ret)
1467                 return ret;
1468
1469         return 0;
1470 }
1471
1472 static bool is_fentry_call(struct instruction *insn)
1473 {
1474         if (insn->type == INSN_CALL &&
1475             insn->call_dest->type == STT_NOTYPE &&
1476             !strcmp(insn->call_dest->name, "__fentry__"))
1477                 return true;
1478
1479         return false;
1480 }
1481
1482 static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
1483 {
1484         u8 ret_offset = insn->ret_offset;
1485         struct cfi_state *cfi = &state->cfi;
1486         int i;
1487
1488         if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
1489                 return true;
1490
1491         if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
1492                 return true;
1493
1494         if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
1495                 return true;
1496
1497         for (i = 0; i < CFI_NUM_REGS; i++) {
1498                 if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
1499                     cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
1500                         return true;
1501         }
1502
1503         return false;
1504 }
1505
1506 static bool has_valid_stack_frame(struct insn_state *state)
1507 {
1508         struct cfi_state *cfi = &state->cfi;
1509
1510         if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
1511             cfi->regs[CFI_BP].offset == -16)
1512                 return true;
1513
1514         if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
1515                 return true;
1516
1517         return false;
1518 }
1519
1520 static int update_cfi_state_regs(struct instruction *insn,
1521                                   struct cfi_state *cfi,
1522                                   struct stack_op *op)
1523 {
1524         struct cfi_reg *cfa = &cfi->cfa;
1525
1526         if (cfa->base != CFI_SP)
1527                 return 0;
1528
1529         /* push */
1530         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1531                 cfa->offset += 8;
1532
1533         /* pop */
1534         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1535                 cfa->offset -= 8;
1536
1537         /* add immediate to sp */
1538         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1539             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1540                 cfa->offset -= op->src.offset;
1541
1542         return 0;
1543 }
1544
1545 static void save_reg(struct cfi_state *cfi, unsigned char reg, int base, int offset)
1546 {
1547         if (arch_callee_saved_reg(reg) &&
1548             cfi->regs[reg].base == CFI_UNDEFINED) {
1549                 cfi->regs[reg].base = base;
1550                 cfi->regs[reg].offset = offset;
1551         }
1552 }
1553
1554 static void restore_reg(struct cfi_state *cfi, unsigned char reg)
1555 {
1556         cfi->regs[reg].base = initial_func_cfi.regs[reg].base;
1557         cfi->regs[reg].offset = initial_func_cfi.regs[reg].offset;
1558 }
1559
1560 /*
1561  * A note about DRAP stack alignment:
1562  *
1563  * GCC has the concept of a DRAP register, which is used to help keep track of
1564  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1565  * register.  The typical DRAP pattern is:
1566  *
1567  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1568  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1569  *   41 ff 72 f8                pushq  -0x8(%r10)
1570  *   55                         push   %rbp
1571  *   48 89 e5                   mov    %rsp,%rbp
1572  *                              (more pushes)
1573  *   41 52                      push   %r10
1574  *                              ...
1575  *   41 5a                      pop    %r10
1576  *                              (more pops)
1577  *   5d                         pop    %rbp
1578  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1579  *   c3                         retq
1580  *
1581  * There are some variations in the epilogues, like:
1582  *
1583  *   5b                         pop    %rbx
1584  *   41 5a                      pop    %r10
1585  *   41 5c                      pop    %r12
1586  *   41 5d                      pop    %r13
1587  *   41 5e                      pop    %r14
1588  *   c9                         leaveq
1589  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1590  *   c3                         retq
1591  *
1592  * and:
1593  *
1594  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1595  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1596  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1597  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1598  *   c9                         leaveq
1599  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1600  *   c3                         retq
1601  *
1602  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1603  * restored beforehand:
1604  *
1605  *   41 55                      push   %r13
1606  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1607  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1608  *                              ...
1609  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1610  *   41 5d                      pop    %r13
1611  *   c3                         retq
1612  */
1613 static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
1614                              struct stack_op *op)
1615 {
1616         struct cfi_reg *cfa = &cfi->cfa;
1617         struct cfi_reg *regs = cfi->regs;
1618
1619         /* stack operations don't make sense with an undefined CFA */
1620         if (cfa->base == CFI_UNDEFINED) {
1621                 if (insn->func) {
1622                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1623                         return -1;
1624                 }
1625                 return 0;
1626         }
1627
1628         if (cfi->type == ORC_TYPE_REGS || cfi->type == ORC_TYPE_REGS_IRET)
1629                 return update_cfi_state_regs(insn, cfi, op);
1630
1631         switch (op->dest.type) {
1632
1633         case OP_DEST_REG:
1634                 switch (op->src.type) {
1635
1636                 case OP_SRC_REG:
1637                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1638                             cfa->base == CFI_SP &&
1639                             regs[CFI_BP].base == CFI_CFA &&
1640                             regs[CFI_BP].offset == -cfa->offset) {
1641
1642                                 /* mov %rsp, %rbp */
1643                                 cfa->base = op->dest.reg;
1644                                 cfi->bp_scratch = false;
1645                         }
1646
1647                         else if (op->src.reg == CFI_SP &&
1648                                  op->dest.reg == CFI_BP && cfi->drap) {
1649
1650                                 /* drap: mov %rsp, %rbp */
1651                                 regs[CFI_BP].base = CFI_BP;
1652                                 regs[CFI_BP].offset = -cfi->stack_size;
1653                                 cfi->bp_scratch = false;
1654                         }
1655
1656                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1657
1658                                 /*
1659                                  * mov %rsp, %reg
1660                                  *
1661                                  * This is needed for the rare case where GCC
1662                                  * does:
1663                                  *
1664                                  *   mov    %rsp, %rax
1665                                  *   ...
1666                                  *   mov    %rax, %rsp
1667                                  */
1668                                 cfi->vals[op->dest.reg].base = CFI_CFA;
1669                                 cfi->vals[op->dest.reg].offset = -cfi->stack_size;
1670                         }
1671
1672                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1673                                  cfa->base == CFI_BP) {
1674
1675                                 /*
1676                                  * mov %rbp, %rsp
1677                                  *
1678                                  * Restore the original stack pointer (Clang).
1679                                  */
1680                                 cfi->stack_size = -cfi->regs[CFI_BP].offset;
1681                         }
1682
1683                         else if (op->dest.reg == cfa->base) {
1684
1685                                 /* mov %reg, %rsp */
1686                                 if (cfa->base == CFI_SP &&
1687                                     cfi->vals[op->src.reg].base == CFI_CFA) {
1688
1689                                         /*
1690                                          * This is needed for the rare case
1691                                          * where GCC does something dumb like:
1692                                          *
1693                                          *   lea    0x8(%rsp), %rcx
1694                                          *   ...
1695                                          *   mov    %rcx, %rsp
1696                                          */
1697                                         cfa->offset = -cfi->vals[op->src.reg].offset;
1698                                         cfi->stack_size = cfa->offset;
1699
1700                                 } else {
1701                                         cfa->base = CFI_UNDEFINED;
1702                                         cfa->offset = 0;
1703                                 }
1704                         }
1705
1706                         break;
1707
1708                 case OP_SRC_ADD:
1709                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1710
1711                                 /* add imm, %rsp */
1712                                 cfi->stack_size -= op->src.offset;
1713                                 if (cfa->base == CFI_SP)
1714                                         cfa->offset -= op->src.offset;
1715                                 break;
1716                         }
1717
1718                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1719
1720                                 /* lea disp(%rbp), %rsp */
1721                                 cfi->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1722                                 break;
1723                         }
1724
1725                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1726
1727                                 /* drap: lea disp(%rsp), %drap */
1728                                 cfi->drap_reg = op->dest.reg;
1729
1730                                 /*
1731                                  * lea disp(%rsp), %reg
1732                                  *
1733                                  * This is needed for the rare case where GCC
1734                                  * does something dumb like:
1735                                  *
1736                                  *   lea    0x8(%rsp), %rcx
1737                                  *   ...
1738                                  *   mov    %rcx, %rsp
1739                                  */
1740                                 cfi->vals[op->dest.reg].base = CFI_CFA;
1741                                 cfi->vals[op->dest.reg].offset = \
1742                                         -cfi->stack_size + op->src.offset;
1743
1744                                 break;
1745                         }
1746
1747                         if (cfi->drap && op->dest.reg == CFI_SP &&
1748                             op->src.reg == cfi->drap_reg) {
1749
1750                                  /* drap: lea disp(%drap), %rsp */
1751                                 cfa->base = CFI_SP;
1752                                 cfa->offset = cfi->stack_size = -op->src.offset;
1753                                 cfi->drap_reg = CFI_UNDEFINED;
1754                                 cfi->drap = false;
1755                                 break;
1756                         }
1757
1758                         if (op->dest.reg == cfi->cfa.base) {
1759                                 WARN_FUNC("unsupported stack register modification",
1760                                           insn->sec, insn->offset);
1761                                 return -1;
1762                         }
1763
1764                         break;
1765
1766                 case OP_SRC_AND:
1767                         if (op->dest.reg != CFI_SP ||
1768                             (cfi->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1769                             (cfi->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1770                                 WARN_FUNC("unsupported stack pointer realignment",
1771                                           insn->sec, insn->offset);
1772                                 return -1;
1773                         }
1774
1775                         if (cfi->drap_reg != CFI_UNDEFINED) {
1776                                 /* drap: and imm, %rsp */
1777                                 cfa->base = cfi->drap_reg;
1778                                 cfa->offset = cfi->stack_size = 0;
1779                                 cfi->drap = true;
1780                         }
1781
1782                         /*
1783                          * Older versions of GCC (4.8ish) realign the stack
1784                          * without DRAP, with a frame pointer.
1785                          */
1786
1787                         break;
1788
1789                 case OP_SRC_POP:
1790                 case OP_SRC_POPF:
1791                         if (!cfi->drap && op->dest.reg == cfa->base) {
1792
1793                                 /* pop %rbp */
1794                                 cfa->base = CFI_SP;
1795                         }
1796
1797                         if (cfi->drap && cfa->base == CFI_BP_INDIRECT &&
1798                             op->dest.reg == cfi->drap_reg &&
1799                             cfi->drap_offset == -cfi->stack_size) {
1800
1801                                 /* drap: pop %drap */
1802                                 cfa->base = cfi->drap_reg;
1803                                 cfa->offset = 0;
1804                                 cfi->drap_offset = -1;
1805
1806                         } else if (regs[op->dest.reg].offset == -cfi->stack_size) {
1807
1808                                 /* pop %reg */
1809                                 restore_reg(cfi, op->dest.reg);
1810                         }
1811
1812                         cfi->stack_size -= 8;
1813                         if (cfa->base == CFI_SP)
1814                                 cfa->offset -= 8;
1815
1816                         break;
1817
1818                 case OP_SRC_REG_INDIRECT:
1819                         if (cfi->drap && op->src.reg == CFI_BP &&
1820                             op->src.offset == cfi->drap_offset) {
1821
1822                                 /* drap: mov disp(%rbp), %drap */
1823                                 cfa->base = cfi->drap_reg;
1824                                 cfa->offset = 0;
1825                                 cfi->drap_offset = -1;
1826                         }
1827
1828                         if (cfi->drap && op->src.reg == CFI_BP &&
1829                             op->src.offset == regs[op->dest.reg].offset) {
1830
1831                                 /* drap: mov disp(%rbp), %reg */
1832                                 restore_reg(cfi, op->dest.reg);
1833
1834                         } else if (op->src.reg == cfa->base &&
1835                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1836
1837                                 /* mov disp(%rbp), %reg */
1838                                 /* mov disp(%rsp), %reg */
1839                                 restore_reg(cfi, op->dest.reg);
1840                         }
1841
1842                         break;
1843
1844                 default:
1845                         WARN_FUNC("unknown stack-related instruction",
1846                                   insn->sec, insn->offset);
1847                         return -1;
1848                 }
1849
1850                 break;
1851
1852         case OP_DEST_PUSH:
1853         case OP_DEST_PUSHF:
1854                 cfi->stack_size += 8;
1855                 if (cfa->base == CFI_SP)
1856                         cfa->offset += 8;
1857
1858                 if (op->src.type != OP_SRC_REG)
1859                         break;
1860
1861                 if (cfi->drap) {
1862                         if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
1863
1864                                 /* drap: push %drap */
1865                                 cfa->base = CFI_BP_INDIRECT;
1866                                 cfa->offset = -cfi->stack_size;
1867
1868                                 /* save drap so we know when to restore it */
1869                                 cfi->drap_offset = -cfi->stack_size;
1870
1871                         } else if (op->src.reg == CFI_BP && cfa->base == cfi->drap_reg) {
1872
1873                                 /* drap: push %rbp */
1874                                 cfi->stack_size = 0;
1875
1876                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1877
1878                                 /* drap: push %reg */
1879                                 save_reg(cfi, op->src.reg, CFI_BP, -cfi->stack_size);
1880                         }
1881
1882                 } else {
1883
1884                         /* push %reg */
1885                         save_reg(cfi, op->src.reg, CFI_CFA, -cfi->stack_size);
1886                 }
1887
1888                 /* detect when asm code uses rbp as a scratch register */
1889                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1890                     cfa->base != CFI_BP)
1891                         cfi->bp_scratch = true;
1892                 break;
1893
1894         case OP_DEST_REG_INDIRECT:
1895
1896                 if (cfi->drap) {
1897                         if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
1898
1899                                 /* drap: mov %drap, disp(%rbp) */
1900                                 cfa->base = CFI_BP_INDIRECT;
1901                                 cfa->offset = op->dest.offset;
1902
1903                                 /* save drap offset so we know when to restore it */
1904                                 cfi->drap_offset = op->dest.offset;
1905                         }
1906
1907                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1908
1909                                 /* drap: mov reg, disp(%rbp) */
1910                                 save_reg(cfi, op->src.reg, CFI_BP, op->dest.offset);
1911                         }
1912
1913                 } else if (op->dest.reg == cfa->base) {
1914
1915                         /* mov reg, disp(%rbp) */
1916                         /* mov reg, disp(%rsp) */
1917                         save_reg(cfi, op->src.reg, CFI_CFA,
1918                                  op->dest.offset - cfi->cfa.offset);
1919                 }
1920
1921                 break;
1922
1923         case OP_DEST_LEAVE:
1924                 if ((!cfi->drap && cfa->base != CFI_BP) ||
1925                     (cfi->drap && cfa->base != cfi->drap_reg)) {
1926                         WARN_FUNC("leave instruction with modified stack frame",
1927                                   insn->sec, insn->offset);
1928                         return -1;
1929                 }
1930
1931                 /* leave (mov %rbp, %rsp; pop %rbp) */
1932
1933                 cfi->stack_size = -cfi->regs[CFI_BP].offset - 8;
1934                 restore_reg(cfi, CFI_BP);
1935
1936                 if (!cfi->drap) {
1937                         cfa->base = CFI_SP;
1938                         cfa->offset -= 8;
1939                 }
1940
1941                 break;
1942
1943         case OP_DEST_MEM:
1944                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1945                         WARN_FUNC("unknown stack-related memory operation",
1946                                   insn->sec, insn->offset);
1947                         return -1;
1948                 }
1949
1950                 /* pop mem */
1951                 cfi->stack_size -= 8;
1952                 if (cfa->base == CFI_SP)
1953                         cfa->offset -= 8;
1954
1955                 break;
1956
1957         default:
1958                 WARN_FUNC("unknown stack-related instruction",
1959                           insn->sec, insn->offset);
1960                 return -1;
1961         }
1962
1963         return 0;
1964 }
1965
1966 static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
1967 {
1968         struct stack_op *op;
1969
1970         list_for_each_entry(op, &insn->stack_ops, list) {
1971                 int res;
1972
1973                 res = update_cfi_state(insn, &state->cfi, op);
1974                 if (res)
1975                         return res;
1976
1977                 if (op->dest.type == OP_DEST_PUSHF) {
1978                         if (!state->uaccess_stack) {
1979                                 state->uaccess_stack = 1;
1980                         } else if (state->uaccess_stack >> 31) {
1981                                 WARN_FUNC("PUSHF stack exhausted",
1982                                           insn->sec, insn->offset);
1983                                 return 1;
1984                         }
1985                         state->uaccess_stack <<= 1;
1986                         state->uaccess_stack  |= state->uaccess;
1987                 }
1988
1989                 if (op->src.type == OP_SRC_POPF) {
1990                         if (state->uaccess_stack) {
1991                                 state->uaccess = state->uaccess_stack & 1;
1992                                 state->uaccess_stack >>= 1;
1993                                 if (state->uaccess_stack == 1)
1994                                         state->uaccess_stack = 0;
1995                         }
1996                 }
1997         }
1998
1999         return 0;
2000 }
2001
2002 static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
2003 {
2004         struct cfi_state *cfi1 = &insn->cfi;
2005         int i;
2006
2007         if (memcmp(&cfi1->cfa, &cfi2->cfa, sizeof(cfi1->cfa))) {
2008
2009                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
2010                           insn->sec, insn->offset,
2011                           cfi1->cfa.base, cfi1->cfa.offset,
2012                           cfi2->cfa.base, cfi2->cfa.offset);
2013
2014         } else if (memcmp(&cfi1->regs, &cfi2->regs, sizeof(cfi1->regs))) {
2015                 for (i = 0; i < CFI_NUM_REGS; i++) {
2016                         if (!memcmp(&cfi1->regs[i], &cfi2->regs[i],
2017                                     sizeof(struct cfi_reg)))
2018                                 continue;
2019
2020                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
2021                                   insn->sec, insn->offset,
2022                                   i, cfi1->regs[i].base, cfi1->regs[i].offset,
2023                                   i, cfi2->regs[i].base, cfi2->regs[i].offset);
2024                         break;
2025                 }
2026
2027         } else if (cfi1->type != cfi2->type) {
2028
2029                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
2030                           insn->sec, insn->offset, cfi1->type, cfi2->type);
2031
2032         } else if (cfi1->drap != cfi2->drap ||
2033                    (cfi1->drap && cfi1->drap_reg != cfi2->drap_reg) ||
2034                    (cfi1->drap && cfi1->drap_offset != cfi2->drap_offset)) {
2035
2036                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
2037                           insn->sec, insn->offset,
2038                           cfi1->drap, cfi1->drap_reg, cfi1->drap_offset,
2039                           cfi2->drap, cfi2->drap_reg, cfi2->drap_offset);
2040
2041         } else
2042                 return true;
2043
2044         return false;
2045 }
2046
2047 static inline bool func_uaccess_safe(struct symbol *func)
2048 {
2049         if (func)
2050                 return func->uaccess_safe;
2051
2052         return false;
2053 }
2054
2055 static inline const char *call_dest_name(struct instruction *insn)
2056 {
2057         if (insn->call_dest)
2058                 return insn->call_dest->name;
2059
2060         return "{dynamic}";
2061 }
2062
2063 static int validate_call(struct instruction *insn, struct insn_state *state)
2064 {
2065         if (state->noinstr && state->instr <= 0 &&
2066             (!insn->call_dest || insn->call_dest->sec != insn->sec)) {
2067                 WARN_FUNC("call to %s() leaves .noinstr.text section",
2068                                 insn->sec, insn->offset, call_dest_name(insn));
2069                 return 1;
2070         }
2071
2072         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
2073                 WARN_FUNC("call to %s() with UACCESS enabled",
2074                                 insn->sec, insn->offset, call_dest_name(insn));
2075                 return 1;
2076         }
2077
2078         if (state->df) {
2079                 WARN_FUNC("call to %s() with DF set",
2080                                 insn->sec, insn->offset, call_dest_name(insn));
2081                 return 1;
2082         }
2083
2084         return 0;
2085 }
2086
2087 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
2088 {
2089         if (has_modified_stack_frame(insn, state)) {
2090                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
2091                                 insn->sec, insn->offset);
2092                 return 1;
2093         }
2094
2095         return validate_call(insn, state);
2096 }
2097
2098 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
2099 {
2100         if (state->noinstr && state->instr > 0) {
2101                 WARN_FUNC("return with instrumentation enabled",
2102                           insn->sec, insn->offset);
2103                 return 1;
2104         }
2105
2106         if (state->uaccess && !func_uaccess_safe(func)) {
2107                 WARN_FUNC("return with UACCESS enabled",
2108                           insn->sec, insn->offset);
2109                 return 1;
2110         }
2111
2112         if (!state->uaccess && func_uaccess_safe(func)) {
2113                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
2114                           insn->sec, insn->offset);
2115                 return 1;
2116         }
2117
2118         if (state->df) {
2119                 WARN_FUNC("return with DF set",
2120                           insn->sec, insn->offset);
2121                 return 1;
2122         }
2123
2124         if (func && has_modified_stack_frame(insn, state)) {
2125                 WARN_FUNC("return with modified stack frame",
2126                           insn->sec, insn->offset);
2127                 return 1;
2128         }
2129
2130         if (state->cfi.bp_scratch) {
2131                 WARN_FUNC("BP used as a scratch register",
2132                           insn->sec, insn->offset);
2133                 return 1;
2134         }
2135
2136         return 0;
2137 }
2138
2139 /*
2140  * Follow the branch starting at the given instruction, and recursively follow
2141  * any other branches (jumps).  Meanwhile, track the frame pointer state at
2142  * each instruction and validate all the rules described in
2143  * tools/objtool/Documentation/stack-validation.txt.
2144  */
2145 static int validate_branch(struct objtool_file *file, struct symbol *func,
2146                            struct instruction *insn, struct insn_state state)
2147 {
2148         struct alternative *alt;
2149         struct instruction *next_insn;
2150         struct section *sec;
2151         u8 visited;
2152         int ret;
2153
2154         sec = insn->sec;
2155
2156         if (insn->alt_group && list_empty(&insn->alts)) {
2157                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
2158                           sec, insn->offset);
2159                 return 1;
2160         }
2161
2162         while (1) {
2163                 next_insn = next_insn_same_sec(file, insn);
2164
2165                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2166                         WARN("%s() falls through to next function %s()",
2167                              func->name, insn->func->name);
2168                         return 1;
2169                 }
2170
2171                 if (func && insn->ignore) {
2172                         WARN_FUNC("BUG: why am I validating an ignored function?",
2173                                   sec, insn->offset);
2174                         return 1;
2175                 }
2176
2177                 visited = 1 << state.uaccess;
2178                 if (insn->visited) {
2179                         if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
2180                                 return 1;
2181
2182                         if (insn->visited & visited)
2183                                 return 0;
2184                 }
2185
2186                 if (state.noinstr)
2187                         state.instr += insn->instr;
2188
2189                 if (insn->hint)
2190                         state.cfi = insn->cfi;
2191                 else
2192                         insn->cfi = state.cfi;
2193
2194                 insn->visited |= visited;
2195
2196                 if (!insn->ignore_alts) {
2197                         bool skip_orig = false;
2198
2199                         list_for_each_entry(alt, &insn->alts, list) {
2200                                 if (alt->skip_orig)
2201                                         skip_orig = true;
2202
2203                                 ret = validate_branch(file, func, alt->insn, state);
2204                                 if (ret) {
2205                                         if (backtrace)
2206                                                 BT_FUNC("(alt)", insn);
2207                                         return ret;
2208                                 }
2209                         }
2210
2211                         if (skip_orig)
2212                                 return 0;
2213                 }
2214
2215                 switch (insn->type) {
2216
2217                 case INSN_RETURN:
2218                         return validate_return(func, insn, &state);
2219
2220                 case INSN_CALL:
2221                 case INSN_CALL_DYNAMIC:
2222                         ret = validate_call(insn, &state);
2223                         if (ret)
2224                                 return ret;
2225
2226                         if (!no_fp && func && !is_fentry_call(insn) &&
2227                             !has_valid_stack_frame(&state)) {
2228                                 WARN_FUNC("call without frame pointer save/setup",
2229                                           sec, insn->offset);
2230                                 return 1;
2231                         }
2232
2233                         if (dead_end_function(file, insn->call_dest))
2234                                 return 0;
2235
2236                         break;
2237
2238                 case INSN_JUMP_CONDITIONAL:
2239                 case INSN_JUMP_UNCONDITIONAL:
2240                         if (func && is_sibling_call(insn)) {
2241                                 ret = validate_sibling_call(insn, &state);
2242                                 if (ret)
2243                                         return ret;
2244
2245                         } else if (insn->jump_dest) {
2246                                 ret = validate_branch(file, func,
2247                                                       insn->jump_dest, state);
2248                                 if (ret) {
2249                                         if (backtrace)
2250                                                 BT_FUNC("(branch)", insn);
2251                                         return ret;
2252                                 }
2253                         }
2254
2255                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2256                                 return 0;
2257
2258                         break;
2259
2260                 case INSN_JUMP_DYNAMIC:
2261                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2262                         if (func && is_sibling_call(insn)) {
2263                                 ret = validate_sibling_call(insn, &state);
2264                                 if (ret)
2265                                         return ret;
2266                         }
2267
2268                         if (insn->type == INSN_JUMP_DYNAMIC)
2269                                 return 0;
2270
2271                         break;
2272
2273                 case INSN_EXCEPTION_RETURN:
2274                         if (handle_insn_ops(insn, &state))
2275                                 return 1;
2276
2277                         /*
2278                          * This handles x86's sync_core() case, where we use an
2279                          * IRET to self. All 'normal' IRET instructions are in
2280                          * STT_NOTYPE entry symbols.
2281                          */
2282                         if (func)
2283                                 break;
2284
2285                         return 0;
2286
2287                 case INSN_CONTEXT_SWITCH:
2288                         if (func && (!next_insn || !next_insn->hint)) {
2289                                 WARN_FUNC("unsupported instruction in callable function",
2290                                           sec, insn->offset);
2291                                 return 1;
2292                         }
2293                         return 0;
2294
2295                 case INSN_STACK:
2296                         if (handle_insn_ops(insn, &state))
2297                                 return 1;
2298                         break;
2299
2300                 case INSN_STAC:
2301                         if (state.uaccess) {
2302                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2303                                 return 1;
2304                         }
2305
2306                         state.uaccess = true;
2307                         break;
2308
2309                 case INSN_CLAC:
2310                         if (!state.uaccess && func) {
2311                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2312                                 return 1;
2313                         }
2314
2315                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2316                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2317                                 return 1;
2318                         }
2319
2320                         state.uaccess = false;
2321                         break;
2322
2323                 case INSN_STD:
2324                         if (state.df)
2325                                 WARN_FUNC("recursive STD", sec, insn->offset);
2326
2327                         state.df = true;
2328                         break;
2329
2330                 case INSN_CLD:
2331                         if (!state.df && func)
2332                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2333
2334                         state.df = false;
2335                         break;
2336
2337                 default:
2338                         break;
2339                 }
2340
2341                 if (insn->dead_end)
2342                         return 0;
2343
2344                 if (!next_insn) {
2345                         if (state.cfi.cfa.base == CFI_UNDEFINED)
2346                                 return 0;
2347                         WARN("%s: unexpected end of section", sec->name);
2348                         return 1;
2349                 }
2350
2351                 insn = next_insn;
2352         }
2353
2354         return 0;
2355 }
2356
2357 static int validate_unwind_hints(struct objtool_file *file)
2358 {
2359         struct instruction *insn;
2360         int ret, warnings = 0;
2361         struct insn_state state;
2362
2363         if (!file->hints)
2364                 return 0;
2365
2366         clear_insn_state(&state);
2367
2368         for_each_insn(file, insn) {
2369                 if (insn->hint && !insn->visited) {
2370                         ret = validate_branch(file, insn->func, insn, state);
2371                         if (ret && backtrace)
2372                                 BT_FUNC("<=== (hint)", insn);
2373                         warnings += ret;
2374                 }
2375         }
2376
2377         return warnings;
2378 }
2379
2380 static int validate_retpoline(struct objtool_file *file)
2381 {
2382         struct instruction *insn;
2383         int warnings = 0;
2384
2385         for_each_insn(file, insn) {
2386                 if (insn->type != INSN_JUMP_DYNAMIC &&
2387                     insn->type != INSN_CALL_DYNAMIC)
2388                         continue;
2389
2390                 if (insn->retpoline_safe)
2391                         continue;
2392
2393                 /*
2394                  * .init.text code is ran before userspace and thus doesn't
2395                  * strictly need retpolines, except for modules which are
2396                  * loaded late, they very much do need retpoline in their
2397                  * .init.text
2398                  */
2399                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2400                         continue;
2401
2402                 WARN_FUNC("indirect %s found in RETPOLINE build",
2403                           insn->sec, insn->offset,
2404                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2405
2406                 warnings++;
2407         }
2408
2409         return warnings;
2410 }
2411
2412 static bool is_kasan_insn(struct instruction *insn)
2413 {
2414         return (insn->type == INSN_CALL &&
2415                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2416 }
2417
2418 static bool is_ubsan_insn(struct instruction *insn)
2419 {
2420         return (insn->type == INSN_CALL &&
2421                 !strcmp(insn->call_dest->name,
2422                         "__ubsan_handle_builtin_unreachable"));
2423 }
2424
2425 static bool ignore_unreachable_insn(struct instruction *insn)
2426 {
2427         int i;
2428
2429         if (insn->ignore || insn->type == INSN_NOP)
2430                 return true;
2431
2432         /*
2433          * Ignore any unused exceptions.  This can happen when a whitelisted
2434          * function has an exception table entry.
2435          *
2436          * Also ignore alternative replacement instructions.  This can happen
2437          * when a whitelisted function uses one of the ALTERNATIVE macros.
2438          */
2439         if (!strcmp(insn->sec->name, ".fixup") ||
2440             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2441             !strcmp(insn->sec->name, ".altinstr_aux"))
2442                 return true;
2443
2444         if (!insn->func)
2445                 return false;
2446
2447         /*
2448          * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2449          * __builtin_unreachable().  The BUG() macro has an unreachable() after
2450          * the UD2, which causes GCC's undefined trap logic to emit another UD2
2451          * (or occasionally a JMP to UD2).
2452          */
2453         if (list_prev_entry(insn, list)->dead_end &&
2454             (insn->type == INSN_BUG ||
2455              (insn->type == INSN_JUMP_UNCONDITIONAL &&
2456               insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2457                 return true;
2458
2459         /*
2460          * Check if this (or a subsequent) instruction is related to
2461          * CONFIG_UBSAN or CONFIG_KASAN.
2462          *
2463          * End the search at 5 instructions to avoid going into the weeds.
2464          */
2465         for (i = 0; i < 5; i++) {
2466
2467                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2468                         return true;
2469
2470                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2471                         if (insn->jump_dest &&
2472                             insn->jump_dest->func == insn->func) {
2473                                 insn = insn->jump_dest;
2474                                 continue;
2475                         }
2476
2477                         break;
2478                 }
2479
2480                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2481                         break;
2482
2483                 insn = list_next_entry(insn, list);
2484         }
2485
2486         return false;
2487 }
2488
2489 static int validate_section(struct objtool_file *file, struct section *sec)
2490 {
2491         struct symbol *func;
2492         struct instruction *insn;
2493         struct insn_state state;
2494         int ret, warnings = 0;
2495
2496         /*
2497          * We need the full vmlinux for noinstr validation, otherwise we can
2498          * not correctly determine insn->call_dest->sec (external symbols do
2499          * not have a section).
2500          */
2501         if (vmlinux)
2502                 state.noinstr = sec->noinstr;
2503
2504         list_for_each_entry(func, &sec->symbol_list, list) {
2505                 if (func->type != STT_FUNC)
2506                         continue;
2507
2508                 if (!func->len) {
2509                         WARN("%s() is missing an ELF size annotation",
2510                              func->name);
2511                         warnings++;
2512                 }
2513
2514                 if (func->pfunc != func || func->alias != func)
2515                         continue;
2516
2517                 insn = find_insn(file, sec, func->offset);
2518                 if (!insn || insn->ignore || insn->visited)
2519                         continue;
2520
2521                 clear_insn_state(&state);
2522                 state.cfi.cfa = initial_func_cfi.cfa;
2523                 memcpy(&state.cfi.regs, &initial_func_cfi.regs,
2524                        CFI_NUM_REGS * sizeof(struct cfi_reg));
2525                 state.cfi.stack_size = initial_func_cfi.cfa.offset;
2526
2527                 state.uaccess = func->uaccess_safe;
2528
2529                 ret = validate_branch(file, func, insn, state);
2530                 if (ret && backtrace)
2531                         BT_FUNC("<=== (func)", insn);
2532                 warnings += ret;
2533         }
2534
2535         return warnings;
2536 }
2537
2538 static int validate_vmlinux_functions(struct objtool_file *file)
2539 {
2540         struct section *sec;
2541
2542         sec = find_section_by_name(file->elf, ".noinstr.text");
2543         if (!sec)
2544                 return 0;
2545
2546         return validate_section(file, sec);
2547 }
2548
2549 static int validate_functions(struct objtool_file *file)
2550 {
2551         struct section *sec;
2552         int warnings = 0;
2553
2554         for_each_sec(file, sec)
2555                 warnings += validate_section(file, sec);
2556
2557         return warnings;
2558 }
2559
2560 static int validate_reachable_instructions(struct objtool_file *file)
2561 {
2562         struct instruction *insn;
2563
2564         if (file->ignore_unreachables)
2565                 return 0;
2566
2567         for_each_insn(file, insn) {
2568                 if (insn->visited || ignore_unreachable_insn(insn))
2569                         continue;
2570
2571                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2572                 return 1;
2573         }
2574
2575         return 0;
2576 }
2577
2578 static struct objtool_file file;
2579
2580 int check(const char *_objname, bool orc)
2581 {
2582         int ret, warnings = 0;
2583
2584         objname = _objname;
2585
2586         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2587         if (!file.elf)
2588                 return 1;
2589
2590         INIT_LIST_HEAD(&file.insn_list);
2591         hash_init(file.insn_hash);
2592         file.c_file = find_section_by_name(file.elf, ".comment");
2593         file.ignore_unreachables = no_unreachable;
2594         file.hints = false;
2595
2596         arch_initial_func_cfi_state(&initial_func_cfi);
2597
2598         ret = decode_sections(&file);
2599         if (ret < 0)
2600                 goto out;
2601         warnings += ret;
2602
2603         if (list_empty(&file.insn_list))
2604                 goto out;
2605
2606         if (vmlinux && !validate_dup) {
2607                 ret = validate_vmlinux_functions(&file);
2608                 if (ret < 0)
2609                         goto out;
2610
2611                 warnings += ret;
2612                 goto out;
2613         }
2614
2615         if (retpoline) {
2616                 ret = validate_retpoline(&file);
2617                 if (ret < 0)
2618                         return ret;
2619                 warnings += ret;
2620         }
2621
2622         ret = validate_functions(&file);
2623         if (ret < 0)
2624                 goto out;
2625         warnings += ret;
2626
2627         ret = validate_unwind_hints(&file);
2628         if (ret < 0)
2629                 goto out;
2630         warnings += ret;
2631
2632         if (!warnings) {
2633                 ret = validate_reachable_instructions(&file);
2634                 if (ret < 0)
2635                         goto out;
2636                 warnings += ret;
2637         }
2638
2639         if (orc) {
2640                 ret = create_orc(&file);
2641                 if (ret < 0)
2642                         goto out;
2643
2644                 ret = create_orc_sections(&file);
2645                 if (ret < 0)
2646                         goto out;
2647
2648                 ret = elf_write(file.elf);
2649                 if (ret < 0)
2650                         goto out;
2651         }
2652
2653 out:
2654         if (ret < 0) {
2655                 /*
2656                  *  Fatal error.  The binary is corrupt or otherwise broken in
2657                  *  some way, or objtool itself is broken.  Fail the kernel
2658                  *  build.
2659                  */
2660                 return ret;
2661         }
2662
2663         return 0;
2664 }