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_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, offset)
  38                 if (insn->sec == sec && insn->offset == offset)
  39                         return insn;
  40
  41         return NULL;
  42 }
  43
  44 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  45                                               struct instruction *insn)
  46 {
  47         struct instruction *next = list_next_entry(insn, list);
  48
  49         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  50                 return NULL;
  51
  52         return next;
  53 }
  54
  55 static struct instruction *next_insn_same_func(struct objtool_file *file,
  56                                                struct instruction *insn)
  57 {
  58         struct instruction *next = list_next_entry(insn, list);
  59         struct symbol *func = insn->func;
  60
  61         if (!func)
  62                 return NULL;
  63
  64         if (&next->list != &file->insn_list && next->func == func)
  65                 return next;
  66
  67         /* Check if we're already in the subfunction: */
  68         if (func == func->cfunc)
  69                 return NULL;
  70
  71         /* Move to the subfunction: */
  72         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  73 }
  74
  75 #define func_for_each_insn(file, func, insn)                            \
  76         for (insn = find_insn(file, func->sec, func->offset);           \
  77              insn;                                                      \
  78              insn = next_insn_same_func(file, insn))
  79
  80 #define sym_for_each_insn(file, sym, insn)                              \
  81         for (insn = find_insn(file, sym->sec, sym->offset);             \
  82              insn && &insn->list != &file->insn_list &&                 \
  83                 insn->sec == sym->sec &&                                \
  84                 insn->offset < sym->offset + sym->len;                  \
  85              insn = list_next_entry(insn, list))
  86
  87 #define sym_for_each_insn_continue_reverse(file, sym, insn)             \
  88         for (insn = list_prev_entry(insn, list);                        \
  89              &insn->list != &file->insn_list &&                         \
  90                 insn->sec == sym->sec && insn->offset >= sym->offset;   \
  91              insn = list_prev_entry(insn, list))
  92
  93 #define sec_for_each_insn_from(file, insn)                              \
  94         for (; insn; insn = next_insn_same_sec(file, insn))
  95
  96 #define sec_for_each_insn_continue(file, insn)                          \
  97         for (insn = next_insn_same_sec(file, insn); insn;               \
  98              insn = next_insn_same_sec(file, insn))
  99
 100 static bool is_static_jump(struct instruction *insn)
 101 {
 102         return insn->type == INSN_JUMP_CONDITIONAL ||
 103                insn->type == INSN_JUMP_UNCONDITIONAL;
 104 }
 105
 106 static bool is_sibling_call(struct instruction *insn)
 107 {
 108         /* An indirect jump is either a sibling call or a jump to a table. */
 109         if (insn->type == INSN_JUMP_DYNAMIC)
 110                 return list_empty(&insn->alts);
 111
 112         if (!is_static_jump(insn))
 113                 return false;
 114
 115         /* add_jump_destinations() sets insn->call_dest for sibling calls. */
 116         return !!insn->call_dest;
 117 }
 118
 119 /*
 120  * This checks to see if the given function is a "noreturn" function.
 121  *
 122  * For global functions which are outside the scope of this object file, we
 123  * have to keep a manual list of them.
 124  *
 125  * For local functions, we have to detect them manually by simply looking for
 126  * the lack of a return instruction.
 127  */
 128 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 129                                 int recursion)
 130 {
 131         int i;
 132         struct instruction *insn;
 133         bool empty = true;
 134
 135         /*
 136          * Unfortunately these have to be hard coded because the noreturn
 137          * attribute isn't provided in ELF data.
 138          */
 139         static const char * const global_noreturns[] = {
 140                 "__stack_chk_fail",
 141                 "panic",
 142                 "do_exit",
 143                 "do_task_dead",
 144                 "__module_put_and_exit",
 145                 "complete_and_exit",
 146                 "__reiserfs_panic",
 147                 "lbug_with_loc",
 148                 "fortify_panic",
 149                 "usercopy_abort",
 150                 "machine_real_restart",
 151                 "rewind_stack_do_exit",
 152                 "kunit_try_catch_throw",
 153         };
 154
 155         if (!func)
 156                 return false;
 157
 158         if (func->bind == STB_WEAK)
 159                 return false;
 160
 161         if (func->bind == STB_GLOBAL)
 162                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 163                         if (!strcmp(func->name, global_noreturns[i]))
 164                                 return true;
 165
 166         if (!func->len)
 167                 return false;
 168
 169         insn = find_insn(file, func->sec, func->offset);
 170         if (!insn->func)
 171                 return false;
 172
 173         func_for_each_insn(file, func, insn) {
 174                 empty = false;
 175
 176                 if (insn->type == INSN_RETURN)
 177                         return false;
 178         }
 179
 180         if (empty)
 181                 return false;
 182
 183         /*
 184          * A function can have a sibling call instead of a return.  In that
 185          * case, the function's dead-end status depends on whether the target
 186          * of the sibling call returns.
 187          */
 188         func_for_each_insn(file, func, insn) {
 189                 if (is_sibling_call(insn)) {
 190                         struct instruction *dest = insn->jump_dest;
 191
 192                         if (!dest)
 193                                 /* sibling call to another file */
 194                                 return false;
 195
 196                         /* local sibling call */
 197                         if (recursion == 5) {
 198                                 /*
 199                                  * Infinite recursion: two functions have
 200                                  * sibling calls to each other.  This is a very
 201                                  * rare case.  It means they aren't dead ends.
 202                                  */
 203                                 return false;
 204                         }
 205
 206                         return __dead_end_function(file, dest->func, recursion+1);
 207                 }
 208         }
 209
 210         return true;
 211 }
 212
 213 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 214 {
 215         return __dead_end_function(file, func, 0);
 216 }
 217
 218 static void clear_insn_state(struct insn_state *state)
 219 {
 220         int i;
 221
 222         memset(state, 0, sizeof(*state));
 223         state->cfa.base = CFI_UNDEFINED;
 224         for (i = 0; i < CFI_NUM_REGS; i++) {
 225                 state->regs[i].base = CFI_UNDEFINED;
 226                 state->vals[i].base = CFI_UNDEFINED;
 227         }
 228         state->drap_reg = CFI_UNDEFINED;
 229         state->drap_offset = -1;
 230 }
 231
 232 /*
 233  * Call the arch-specific instruction decoder for all the instructions and add
 234  * them to the global instruction list.
 235  */
 236 static int decode_instructions(struct objtool_file *file)
 237 {
 238         struct section *sec;
 239         struct symbol *func;
 240         unsigned long offset;
 241         struct instruction *insn;
 242         unsigned long nr_insns = 0;
 243         int ret;
 244
 245         for_each_sec(file, sec) {
 246
 247                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 248                         continue;
 249
 250                 if (strcmp(sec->name, ".altinstr_replacement") &&
 251                     strcmp(sec->name, ".altinstr_aux") &&
 252                     strncmp(sec->name, ".discard.", 9))
 253                         sec->text = true;
 254
 255                 for (offset = 0; offset < sec->len; offset += insn->len) {
 256                         insn = malloc(sizeof(*insn));
 257                         if (!insn) {
 258                                 WARN("malloc failed");
 259                                 return -1;
 260                         }
 261                         memset(insn, 0, sizeof(*insn));
 262                         INIT_LIST_HEAD(&insn->alts);
 263                         clear_insn_state(&insn->state);
 264
 265                         insn->sec = sec;
 266                         insn->offset = offset;
 267
 268                         ret = arch_decode_instruction(file->elf, sec, offset,
 269                                                       sec->len - offset,
 270                                                       &insn->len, &insn->type,
 271                                                       &insn->immediate,
 272                                                       &insn->stack_op);
 273                         if (ret)
 274                                 goto err;
 275
 276                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 277                         list_add_tail(&insn->list, &file->insn_list);
 278                         nr_insns++;
 279                 }
 280
 281                 list_for_each_entry(func, &sec->symbol_list, list) {
 282                         if (func->type != STT_FUNC || func->alias != func)
 283                                 continue;
 284
 285                         if (!find_insn(file, sec, func->offset)) {
 286                                 WARN("%s(): can't find starting instruction",
 287                                      func->name);
 288                                 return -1;
 289                         }
 290
 291                         sym_for_each_insn(file, func, insn)
 292                                 insn->func = func;
 293                 }
 294         }
 295
 296         if (stats)
 297                 printf("nr_insns: %lu\n", nr_insns);
 298
 299         return 0;
 300
 301 err:
 302         free(insn);
 303         return ret;
 304 }
 305
 306 /*
 307  * Mark "ud2" instructions and manually annotated dead ends.
 308  */
 309 static int add_dead_ends(struct objtool_file *file)
 310 {
 311         struct section *sec;
 312         struct rela *rela;
 313         struct instruction *insn;
 314         bool found;
 315
 316         /*
 317          * By default, "ud2" is a dead end unless otherwise annotated, because
 318          * GCC 7 inserts it for certain divide-by-zero cases.
 319          */
 320         for_each_insn(file, insn)
 321                 if (insn->type == INSN_BUG)
 322                         insn->dead_end = true;
 323
 324         /*
 325          * Check for manually annotated dead ends.
 326          */
 327         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 328         if (!sec)
 329                 goto reachable;
 330
 331         list_for_each_entry(rela, &sec->rela_list, list) {
 332                 if (rela->sym->type != STT_SECTION) {
 333                         WARN("unexpected relocation symbol type in %s", sec->name);
 334                         return -1;
 335                 }
 336                 insn = find_insn(file, rela->sym->sec, rela->addend);
 337                 if (insn)
 338                         insn = list_prev_entry(insn, list);
 339                 else if (rela->addend == rela->sym->sec->len) {
 340                         found = false;
 341                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 342                                 if (insn->sec == rela->sym->sec) {
 343                                         found = true;
 344                                         break;
 345                                 }
 346                         }
 347
 348                         if (!found) {
 349                                 WARN("can't find unreachable insn at %s+0x%x",
 350                                      rela->sym->sec->name, rela->addend);
 351                                 return -1;
 352                         }
 353                 } else {
 354                         WARN("can't find unreachable insn at %s+0x%x",
 355                              rela->sym->sec->name, rela->addend);
 356                         return -1;
 357                 }
 358
 359                 insn->dead_end = true;
 360         }
 361
 362 reachable:
 363         /*
 364          * These manually annotated reachable checks are needed for GCC 4.4,
 365          * where the Linux unreachable() macro isn't supported.  In that case
 366          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 367          * not a dead end.
 368          */
 369         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 370         if (!sec)
 371                 return 0;
 372
 373         list_for_each_entry(rela, &sec->rela_list, list) {
 374                 if (rela->sym->type != STT_SECTION) {
 375                         WARN("unexpected relocation symbol type in %s", sec->name);
 376                         return -1;
 377                 }
 378                 insn = find_insn(file, rela->sym->sec, rela->addend);
 379                 if (insn)
 380                         insn = list_prev_entry(insn, list);
 381                 else if (rela->addend == rela->sym->sec->len) {
 382                         found = false;
 383                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 384                                 if (insn->sec == rela->sym->sec) {
 385                                         found = true;
 386                                         break;
 387                                 }
 388                         }
 389
 390                         if (!found) {
 391                                 WARN("can't find reachable insn at %s+0x%x",
 392                                      rela->sym->sec->name, rela->addend);
 393                                 return -1;
 394                         }
 395                 } else {
 396                         WARN("can't find reachable insn at %s+0x%x",
 397                              rela->sym->sec->name, rela->addend);
 398                         return -1;
 399                 }
 400
 401                 insn->dead_end = false;
 402         }
 403
 404         return 0;
 405 }
 406
 407 /*
 408  * Warnings shouldn't be reported for ignored functions.
 409  */
 410 static void add_ignores(struct objtool_file *file)
 411 {
 412         struct instruction *insn;
 413         struct section *sec;
 414         struct symbol *func;
 415         struct rela *rela;
 416
 417         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 418         if (!sec)
 419                 return;
 420
 421         list_for_each_entry(rela, &sec->rela_list, list) {
 422                 switch (rela->sym->type) {
 423                 case STT_FUNC:
 424                         func = rela->sym;
 425                         break;
 426
 427                 case STT_SECTION:
 428                         func = find_func_by_offset(rela->sym->sec, rela->addend);
 429                         if (!func)
 430                                 continue;
 431                         break;
 432
 433                 default:
 434                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 435                         continue;
 436                 }
 437
 438                 func_for_each_insn(file, func, insn)
 439                         insn->ignore = true;
 440         }
 441 }
 442
 443 /*
 444  * This is a whitelist of functions that is allowed to be called with AC set.
 445  * The list is meant to be minimal and only contains compiler instrumentation
 446  * ABI and a few functions used to implement *_{to,from}_user() functions.
 447  *
 448  * These functions must not directly change AC, but may PUSHF/POPF.
 449  */
 450 static const char *uaccess_safe_builtin[] = {
 451         /* KASAN */
 452         "kasan_report",
 453         "check_memory_region",
 454         /* KASAN out-of-line */
 455         "__asan_loadN_noabort",
 456         "__asan_load1_noabort",
 457         "__asan_load2_noabort",
 458         "__asan_load4_noabort",
 459         "__asan_load8_noabort",
 460         "__asan_load16_noabort",
 461         "__asan_storeN_noabort",
 462         "__asan_store1_noabort",
 463         "__asan_store2_noabort",
 464         "__asan_store4_noabort",
 465         "__asan_store8_noabort",
 466         "__asan_store16_noabort",
 467         /* KASAN in-line */
 468         "__asan_report_load_n_noabort",
 469         "__asan_report_load1_noabort",
 470         "__asan_report_load2_noabort",
 471         "__asan_report_load4_noabort",
 472         "__asan_report_load8_noabort",
 473         "__asan_report_load16_noabort",
 474         "__asan_report_store_n_noabort",
 475         "__asan_report_store1_noabort",
 476         "__asan_report_store2_noabort",
 477         "__asan_report_store4_noabort",
 478         "__asan_report_store8_noabort",
 479         "__asan_report_store16_noabort",
 480         /* KCOV */
 481         "write_comp_data",
 482         "__sanitizer_cov_trace_pc",
 483         "__sanitizer_cov_trace_const_cmp1",
 484         "__sanitizer_cov_trace_const_cmp2",
 485         "__sanitizer_cov_trace_const_cmp4",
 486         "__sanitizer_cov_trace_const_cmp8",
 487         "__sanitizer_cov_trace_cmp1",
 488         "__sanitizer_cov_trace_cmp2",
 489         "__sanitizer_cov_trace_cmp4",
 490         "__sanitizer_cov_trace_cmp8",
 491         "__sanitizer_cov_trace_switch",
 492         /* UBSAN */
 493         "ubsan_type_mismatch_common",
 494         "__ubsan_handle_type_mismatch",
 495         "__ubsan_handle_type_mismatch_v1",
 496         "__ubsan_handle_shift_out_of_bounds",
 497         /* misc */
 498         "csum_partial_copy_generic",
 499         "__memcpy_mcsafe",
 500         "mcsafe_handle_tail",
 501         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 502         NULL
 503 };
 504
 505 static void add_uaccess_safe(struct objtool_file *file)
 506 {
 507         struct symbol *func;
 508         const char **name;
 509
 510         if (!uaccess)
 511                 return;
 512
 513         for (name = uaccess_safe_builtin; *name; name++) {
 514                 func = find_symbol_by_name(file->elf, *name);
 515                 if (!func)
 516                         continue;
 517
 518                 func->uaccess_safe = true;
 519         }
 520 }
 521
 522 /*
 523  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 524  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 525  * But it at least allows objtool to understand the control flow *around* the
 526  * retpoline.
 527  */
 528 static int add_ignore_alternatives(struct objtool_file *file)
 529 {
 530         struct section *sec;
 531         struct rela *rela;
 532         struct instruction *insn;
 533
 534         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 535         if (!sec)
 536                 return 0;
 537
 538         list_for_each_entry(rela, &sec->rela_list, list) {
 539                 if (rela->sym->type != STT_SECTION) {
 540                         WARN("unexpected relocation symbol type in %s", sec->name);
 541                         return -1;
 542                 }
 543
 544                 insn = find_insn(file, rela->sym->sec, rela->addend);
 545                 if (!insn) {
 546                         WARN("bad .discard.ignore_alts entry");
 547                         return -1;
 548                 }
 549
 550                 insn->ignore_alts = true;
 551         }
 552
 553         return 0;
 554 }
 555
 556 /*
 557  * Find the destination instructions for all jumps.
 558  */
 559 static int add_jump_destinations(struct objtool_file *file)
 560 {
 561         struct instruction *insn;
 562         struct rela *rela;
 563         struct section *dest_sec;
 564         unsigned long dest_off;
 565
 566         for_each_insn(file, insn) {
 567                 if (!is_static_jump(insn))
 568                         continue;
 569
 570                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 571                         continue;
 572
 573                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 574                                                insn->offset, insn->len);
 575                 if (!rela) {
 576                         dest_sec = insn->sec;
 577                         dest_off = arch_jump_destination(insn);
 578                 } else if (rela->sym->type == STT_SECTION) {
 579                         dest_sec = rela->sym->sec;
 580                         dest_off = arch_dest_rela_offset(rela->addend);
 581                 } else if (rela->sym->sec->idx) {
 582                         dest_sec = rela->sym->sec;
 583                         dest_off = rela->sym->sym.st_value +
 584                                    arch_dest_rela_offset(rela->addend);
 585                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 586                         /*
 587                          * Retpoline jumps are really dynamic jumps in
 588                          * disguise, so convert them accordingly.
 589                          */
 590                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 591                                 insn->type = INSN_JUMP_DYNAMIC;
 592                         else
 593                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 594
 595                         insn->retpoline_safe = true;
 596                         continue;
 597                 } else {
 598                         /* external sibling call */
 599                         insn->call_dest = rela->sym;
 600                         continue;
 601                 }
 602
 603                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 604                 if (!insn->jump_dest) {
 605
 606                         /*
 607                          * This is a special case where an alt instruction
 608                          * jumps past the end of the section.  These are
 609                          * handled later in handle_group_alt().
 610                          */
 611                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 612                                 continue;
 613
 614                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 615                                   insn->sec, insn->offset, dest_sec->name,
 616                                   dest_off);
 617                         return -1;
 618                 }
 619
 620                 /*
 621                  * Cross-function jump.
 622                  */
 623                 if (insn->func && insn->jump_dest->func &&
 624                     insn->func != insn->jump_dest->func) {
 625
 626                         /*
 627                          * For GCC 8+, create parent/child links for any cold
 628                          * subfunctions.  This is _mostly_ redundant with a
 629                          * similar initialization in read_symbols().
 630                          *
 631                          * If a function has aliases, we want the *first* such
 632                          * function in the symbol table to be the subfunction's
 633                          * parent.  In that case we overwrite the
 634                          * initialization done in read_symbols().
 635                          *
 636                          * However this code can't completely replace the
 637                          * read_symbols() code because this doesn't detect the
 638                          * case where the parent function's only reference to a
 639                          * subfunction is through a jump table.
 640                          */
 641                         if (!strstr(insn->func->name, ".cold.") &&
 642                             strstr(insn->jump_dest->func->name, ".cold.")) {
 643                                 insn->func->cfunc = insn->jump_dest->func;
 644                                 insn->jump_dest->func->pfunc = insn->func;
 645
 646                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 647                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 648
 649                                 /* internal sibling call */
 650                                 insn->call_dest = insn->jump_dest->func;
 651                         }
 652                 }
 653         }
 654
 655         return 0;
 656 }
 657
 658 /*
 659  * Find the destination instructions for all calls.
 660  */
 661 static int add_call_destinations(struct objtool_file *file)
 662 {
 663         struct instruction *insn;
 664         unsigned long dest_off;
 665         struct rela *rela;
 666
 667         for_each_insn(file, insn) {
 668                 if (insn->type != INSN_CALL)
 669                         continue;
 670
 671                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 672                                                insn->offset, insn->len);
 673                 if (!rela) {
 674                         dest_off = arch_jump_destination(insn);
 675                         insn->call_dest = find_func_by_offset(insn->sec, dest_off);
 676                         if (!insn->call_dest)
 677                                 insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
 678
 679                         if (insn->ignore)
 680                                 continue;
 681
 682                         if (!insn->call_dest) {
 683                                 WARN_FUNC("unsupported intra-function call",
 684                                           insn->sec, insn->offset);
 685                                 if (retpoline)
 686                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 687                                 return -1;
 688                         }
 689
 690                         if (insn->func && insn->call_dest->type != STT_FUNC) {
 691                                 WARN_FUNC("unsupported call to non-function",
 692                                           insn->sec, insn->offset);
 693                                 return -1;
 694                         }
 695
 696                 } else if (rela->sym->type == STT_SECTION) {
 697                         dest_off = arch_dest_rela_offset(rela->addend);
 698                         insn->call_dest = find_func_by_offset(rela->sym->sec,
 699                                                               dest_off);
 700                         if (!insn->call_dest) {
 701                                 WARN_FUNC("can't find call dest symbol at %s+0x%lx",
 702                                           insn->sec, insn->offset,
 703                                           rela->sym->sec->name,
 704                                           dest_off);
 705                                 return -1;
 706                         }
 707                 } else
 708                         insn->call_dest = rela->sym;
 709         }
 710
 711         return 0;
 712 }
 713
 714 /*
 715  * The .alternatives section requires some extra special care, over and above
 716  * what other special sections require:
 717  *
 718  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 719  *    instruction at the end so that validate_branch() skips all the original
 720  *    replaced instructions when validating the new instruction path.
 721  *
 722  * 2. An added wrinkle is that the new instruction length might be zero.  In
 723  *    that case the old instructions are replaced with noops.  We simulate that
 724  *    by creating a fake jump as the only new instruction.
 725  *
 726  * 3. In some cases, the alternative section includes an instruction which
 727  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 728  *    jumps' destinations to point back to .text rather than the end of the
 729  *    entry in .altinstr_replacement.
 730  */
 731 static int handle_group_alt(struct objtool_file *file,
 732                             struct special_alt *special_alt,
 733                             struct instruction *orig_insn,
 734                             struct instruction **new_insn)
 735 {
 736         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 737         unsigned long dest_off;
 738
 739         last_orig_insn = NULL;
 740         insn = orig_insn;
 741         sec_for_each_insn_from(file, insn) {
 742                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 743                         break;
 744
 745                 insn->alt_group = true;
 746                 last_orig_insn = insn;
 747         }
 748
 749         if (next_insn_same_sec(file, last_orig_insn)) {
 750                 fake_jump = malloc(sizeof(*fake_jump));
 751                 if (!fake_jump) {
 752                         WARN("malloc failed");
 753                         return -1;
 754                 }
 755                 memset(fake_jump, 0, sizeof(*fake_jump));
 756                 INIT_LIST_HEAD(&fake_jump->alts);
 757                 clear_insn_state(&fake_jump->state);
 758
 759                 fake_jump->sec = special_alt->new_sec;
 760                 fake_jump->offset = FAKE_JUMP_OFFSET;
 761                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 762                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 763                 fake_jump->func = orig_insn->func;
 764         }
 765
 766         if (!special_alt->new_len) {
 767                 if (!fake_jump) {
 768                         WARN("%s: empty alternative at end of section",
 769                              special_alt->orig_sec->name);
 770                         return -1;
 771                 }
 772
 773                 *new_insn = fake_jump;
 774                 return 0;
 775         }
 776
 777         last_new_insn = NULL;
 778         insn = *new_insn;
 779         sec_for_each_insn_from(file, insn) {
 780                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 781                         break;
 782
 783                 last_new_insn = insn;
 784
 785                 insn->ignore = orig_insn->ignore_alts;
 786                 insn->func = orig_insn->func;
 787
 788                 /*
 789                  * Since alternative replacement code is copy/pasted by the
 790                  * kernel after applying relocations, generally such code can't
 791                  * have relative-address relocation references to outside the
 792                  * .altinstr_replacement section, unless the arch's
 793                  * alternatives code can adjust the relative offsets
 794                  * accordingly.
 795                  *
 796                  * The x86 alternatives code adjusts the offsets only when it
 797                  * encounters a branch instruction at the very beginning of the
 798                  * replacement group.
 799                  */
 800                 if ((insn->offset != special_alt->new_off ||
 801                     (insn->type != INSN_CALL && !is_static_jump(insn))) &&
 802                     find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
 803
 804                         WARN_FUNC("unsupported relocation in alternatives section",
 805                                   insn->sec, insn->offset);
 806                         return -1;
 807                 }
 808
 809                 if (!is_static_jump(insn))
 810                         continue;
 811
 812                 if (!insn->immediate)
 813                         continue;
 814
 815                 dest_off = arch_jump_destination(insn);
 816                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 817                         if (!fake_jump) {
 818                                 WARN("%s: alternative jump to end of section",
 819                                      special_alt->orig_sec->name);
 820                                 return -1;
 821                         }
 822                         insn->jump_dest = fake_jump;
 823                 }
 824
 825                 if (!insn->jump_dest) {
 826                         WARN_FUNC("can't find alternative jump destination",
 827                                   insn->sec, insn->offset);
 828                         return -1;
 829                 }
 830         }
 831
 832         if (!last_new_insn) {
 833                 WARN_FUNC("can't find last new alternative instruction",
 834                           special_alt->new_sec, special_alt->new_off);
 835                 return -1;
 836         }
 837
 838         if (fake_jump)
 839                 list_add(&fake_jump->list, &last_new_insn->list);
 840
 841         return 0;
 842 }
 843
 844 /*
 845  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 846  * If the original instruction is a jump, make the alt entry an effective nop
 847  * by just skipping the original instruction.
 848  */
 849 static int handle_jump_alt(struct objtool_file *file,
 850                            struct special_alt *special_alt,
 851                            struct instruction *orig_insn,
 852                            struct instruction **new_insn)
 853 {
 854         if (orig_insn->type == INSN_NOP)
 855                 return 0;
 856
 857         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 858                 WARN_FUNC("unsupported instruction at jump label",
 859                           orig_insn->sec, orig_insn->offset);
 860                 return -1;
 861         }
 862
 863         *new_insn = list_next_entry(orig_insn, list);
 864         return 0;
 865 }
 866
 867 /*
 868  * Read all the special sections which have alternate instructions which can be
 869  * patched in or redirected to at runtime.  Each instruction having alternate
 870  * instruction(s) has them added to its insn->alts list, which will be
 871  * traversed in validate_branch().
 872  */
 873 static int add_special_section_alts(struct objtool_file *file)
 874 {
 875         struct list_head special_alts;
 876         struct instruction *orig_insn, *new_insn;
 877         struct special_alt *special_alt, *tmp;
 878         struct alternative *alt;
 879         int ret;
 880
 881         ret = special_get_alts(file->elf, &special_alts);
 882         if (ret)
 883                 return ret;
 884
 885         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 886
 887                 orig_insn = find_insn(file, special_alt->orig_sec,
 888                                       special_alt->orig_off);
 889                 if (!orig_insn) {
 890                         WARN_FUNC("special: can't find orig instruction",
 891                                   special_alt->orig_sec, special_alt->orig_off);
 892                         ret = -1;
 893                         goto out;
 894                 }
 895
 896                 new_insn = NULL;
 897                 if (!special_alt->group || special_alt->new_len) {
 898                         new_insn = find_insn(file, special_alt->new_sec,
 899                                              special_alt->new_off);
 900                         if (!new_insn) {
 901                                 WARN_FUNC("special: can't find new instruction",
 902                                           special_alt->new_sec,
 903                                           special_alt->new_off);
 904                                 ret = -1;
 905                                 goto out;
 906                         }
 907                 }
 908
 909                 if (special_alt->group) {
 910                         if (!special_alt->orig_len) {
 911                                 WARN_FUNC("empty alternative entry",
 912                                           orig_insn->sec, orig_insn->offset);
 913                                 continue;
 914                         }
 915
 916                         ret = handle_group_alt(file, special_alt, orig_insn,
 917                                                &new_insn);
 918                         if (ret)
 919                                 goto out;
 920                 } else if (special_alt->jump_or_nop) {
 921                         ret = handle_jump_alt(file, special_alt, orig_insn,
 922                                               &new_insn);
 923                         if (ret)
 924                                 goto out;
 925                 }
 926
 927                 alt = malloc(sizeof(*alt));
 928                 if (!alt) {
 929                         WARN("malloc failed");
 930                         ret = -1;
 931                         goto out;
 932                 }
 933
 934                 alt->insn = new_insn;
 935                 alt->skip_orig = special_alt->skip_orig;
 936                 orig_insn->ignore_alts |= special_alt->skip_alt;
 937                 list_add_tail(&alt->list, &orig_insn->alts);
 938
 939                 list_del(&special_alt->list);
 940                 free(special_alt);
 941         }
 942
 943 out:
 944         return ret;
 945 }
 946
 947 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 948                             struct rela *table)
 949 {
 950         struct rela *rela = table;
 951         struct instruction *dest_insn;
 952         struct alternative *alt;
 953         struct symbol *pfunc = insn->func->pfunc;
 954         unsigned int prev_offset = 0;
 955
 956         /*
 957          * Each @rela is a switch table relocation which points to the target
 958          * instruction.
 959          */
 960         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 961
 962                 /* Check for the end of the table: */
 963                 if (rela != table && rela->jump_table_start)
 964                         break;
 965
 966                 /* Make sure the table entries are consecutive: */
 967                 if (prev_offset && rela->offset != prev_offset + 8)
 968                         break;
 969
 970                 /* Detect function pointers from contiguous objects: */
 971                 if (rela->sym->sec == pfunc->sec &&
 972                     rela->addend == pfunc->offset)
 973                         break;
 974
 975                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 976                 if (!dest_insn)
 977                         break;
 978
 979                 /* Make sure the destination is in the same function: */
 980                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 981                         break;
 982
 983                 alt = malloc(sizeof(*alt));
 984                 if (!alt) {
 985                         WARN("malloc failed");
 986                         return -1;
 987                 }
 988
 989                 alt->insn = dest_insn;
 990                 list_add_tail(&alt->list, &insn->alts);
 991                 prev_offset = rela->offset;
 992         }
 993
 994         if (!prev_offset) {
 995                 WARN_FUNC("can't find switch jump table",
 996                           insn->sec, insn->offset);
 997                 return -1;
 998         }
 999
1000         return 0;
1001 }
1002
1003 /*
1004  * find_jump_table() - Given a dynamic jump, find the switch jump table in
1005  * .rodata associated with it.
1006  *
1007  * There are 3 basic patterns:
1008  *
1009  * 1. jmpq *[rodata addr](,%reg,8)
1010  *
1011  *    This is the most common case by far.  It jumps to an address in a simple
1012  *    jump table which is stored in .rodata.
1013  *
1014  * 2. jmpq *[rodata addr](%rip)
1015  *
1016  *    This is caused by a rare GCC quirk, currently only seen in three driver
1017  *    functions in the kernel, only with certain obscure non-distro configs.
1018  *
1019  *    As part of an optimization, GCC makes a copy of an existing switch jump
1020  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
1021  *    jump) to use a single entry in the table.  The rest of the jump table and
1022  *    some of its jump targets remain as dead code.
1023  *
1024  *    In such a case we can just crudely ignore all unreachable instruction
1025  *    warnings for the entire object file.  Ideally we would just ignore them
1026  *    for the function, but that would require redesigning the code quite a
1027  *    bit.  And honestly that's just not worth doing: unreachable instruction
1028  *    warnings are of questionable value anyway, and this is such a rare issue.
1029  *
1030  * 3. mov [rodata addr],%reg1
1031  *    ... some instructions ...
1032  *    jmpq *(%reg1,%reg2,8)
1033  *
1034  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1035  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1036  *
1037  *    As of GCC 7 there are quite a few more of these and the 'in between' code
1038  *    is significant. Esp. with KASAN enabled some of the code between the mov
1039  *    and jmpq uses .rodata itself, which can confuse things.
1040  *
1041  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1042  *    ensure the same register is used in the mov and jump instructions.
1043  *
1044  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1045  */
1046 static struct rela *find_jump_table(struct objtool_file *file,
1047                                       struct symbol *func,
1048                                       struct instruction *insn)
1049 {
1050         struct rela *text_rela, *table_rela;
1051         struct instruction *dest_insn, *orig_insn = insn;
1052         struct section *table_sec;
1053         unsigned long table_offset;
1054
1055         /*
1056          * Backward search using the @first_jump_src links, these help avoid
1057          * much of the 'in between' code. Which avoids us getting confused by
1058          * it.
1059          */
1060         for (;
1061              &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
1062              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1063
1064                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1065                         break;
1066
1067                 /* allow small jumps within the range */
1068                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1069                     insn->jump_dest &&
1070                     (insn->jump_dest->offset <= insn->offset ||
1071                      insn->jump_dest->offset > orig_insn->offset))
1072                     break;
1073
1074                 /* look for a relocation which references .rodata */
1075                 text_rela = find_rela_by_dest_range(file->elf, insn->sec,
1076                                                     insn->offset, insn->len);
1077                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1078                     !text_rela->sym->sec->rodata)
1079                         continue;
1080
1081                 table_offset = text_rela->addend;
1082                 table_sec = text_rela->sym->sec;
1083
1084                 if (text_rela->type == R_X86_64_PC32)
1085                         table_offset += 4;
1086
1087                 /*
1088                  * Make sure the .rodata address isn't associated with a
1089                  * symbol.  GCC jump tables are anonymous data.
1090                  *
1091                  * Also support C jump tables which are in the same format as
1092                  * switch jump tables.  For objtool to recognize them, they
1093                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1094                  * have symbols associated with them.
1095                  */
1096                 if (find_symbol_containing(table_sec, table_offset) &&
1097                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1098                         continue;
1099
1100                 /*
1101                  * Each table entry has a rela associated with it.  The rela
1102                  * should reference text in the same function as the original
1103                  * instruction.
1104                  */
1105                 table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
1106                 if (!table_rela)
1107                         continue;
1108                 dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
1109                 if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1110                         continue;
1111
1112                 /*
1113                  * Use of RIP-relative switch jumps is quite rare, and
1114                  * indicates a rare GCC quirk/bug which can leave dead code
1115                  * behind.
1116                  */
1117                 if (text_rela->type == R_X86_64_PC32)
1118                         file->ignore_unreachables = true;
1119
1120                 return table_rela;
1121         }
1122
1123         return NULL;
1124 }
1125
1126 /*
1127  * First pass: Mark the head of each jump table so that in the next pass,
1128  * we know when a given jump table ends and the next one starts.
1129  */
1130 static void mark_func_jump_tables(struct objtool_file *file,
1131                                     struct symbol *func)
1132 {
1133         struct instruction *insn, *last = NULL;
1134         struct rela *rela;
1135
1136         func_for_each_insn(file, func, insn) {
1137                 if (!last)
1138                         last = insn;
1139
1140                 /*
1141                  * Store back-pointers for unconditional forward jumps such
1142                  * that find_jump_table() can back-track using those and
1143                  * avoid some potentially confusing code.
1144                  */
1145                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1146                     insn->offset > last->offset &&
1147                     insn->jump_dest->offset > insn->offset &&
1148                     !insn->jump_dest->first_jump_src) {
1149
1150                         insn->jump_dest->first_jump_src = insn;
1151                         last = insn->jump_dest;
1152                 }
1153
1154                 if (insn->type != INSN_JUMP_DYNAMIC)
1155                         continue;
1156
1157                 rela = find_jump_table(file, func, insn);
1158                 if (rela) {
1159                         rela->jump_table_start = true;
1160                         insn->jump_table = rela;
1161                 }
1162         }
1163 }
1164
1165 static int add_func_jump_tables(struct objtool_file *file,
1166                                   struct symbol *func)
1167 {
1168         struct instruction *insn;
1169         int ret;
1170
1171         func_for_each_insn(file, func, insn) {
1172                 if (!insn->jump_table)
1173                         continue;
1174
1175                 ret = add_jump_table(file, insn, insn->jump_table);
1176                 if (ret)
1177                         return ret;
1178         }
1179
1180         return 0;
1181 }
1182
1183 /*
1184  * For some switch statements, gcc generates a jump table in the .rodata
1185  * section which contains a list of addresses within the function to jump to.
1186  * This finds these jump tables and adds them to the insn->alts lists.
1187  */
1188 static int add_jump_table_alts(struct objtool_file *file)
1189 {
1190         struct section *sec;
1191         struct symbol *func;
1192         int ret;
1193
1194         if (!file->rodata)
1195                 return 0;
1196
1197         for_each_sec(file, sec) {
1198                 list_for_each_entry(func, &sec->symbol_list, list) {
1199                         if (func->type != STT_FUNC)
1200                                 continue;
1201
1202                         mark_func_jump_tables(file, func);
1203                         ret = add_func_jump_tables(file, func);
1204                         if (ret)
1205                                 return ret;
1206                 }
1207         }
1208
1209         return 0;
1210 }
1211
1212 static int read_unwind_hints(struct objtool_file *file)
1213 {
1214         struct section *sec, *relasec;
1215         struct rela *rela;
1216         struct unwind_hint *hint;
1217         struct instruction *insn;
1218         struct cfi_reg *cfa;
1219         int i;
1220
1221         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1222         if (!sec)
1223                 return 0;
1224
1225         relasec = sec->rela;
1226         if (!relasec) {
1227                 WARN("missing .rela.discard.unwind_hints section");
1228                 return -1;
1229         }
1230
1231         if (sec->len % sizeof(struct unwind_hint)) {
1232                 WARN("struct unwind_hint size mismatch");
1233                 return -1;
1234         }
1235
1236         file->hints = true;
1237
1238         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1239                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1240
1241                 rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
1242                 if (!rela) {
1243                         WARN("can't find rela for unwind_hints[%d]", i);
1244                         return -1;
1245                 }
1246
1247                 insn = find_insn(file, rela->sym->sec, rela->addend);
1248                 if (!insn) {
1249                         WARN("can't find insn for unwind_hints[%d]", i);
1250                         return -1;
1251                 }
1252
1253                 cfa = &insn->state.cfa;
1254
1255                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1256                         insn->save = true;
1257                         continue;
1258
1259                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1260                         insn->restore = true;
1261                         insn->hint = true;
1262                         continue;
1263                 }
1264
1265                 insn->hint = true;
1266
1267                 switch (hint->sp_reg) {
1268                 case ORC_REG_UNDEFINED:
1269                         cfa->base = CFI_UNDEFINED;
1270                         break;
1271                 case ORC_REG_SP:
1272                         cfa->base = CFI_SP;
1273                         break;
1274                 case ORC_REG_BP:
1275                         cfa->base = CFI_BP;
1276                         break;
1277                 case ORC_REG_SP_INDIRECT:
1278                         cfa->base = CFI_SP_INDIRECT;
1279                         break;
1280                 case ORC_REG_R10:
1281                         cfa->base = CFI_R10;
1282                         break;
1283                 case ORC_REG_R13:
1284                         cfa->base = CFI_R13;
1285                         break;
1286                 case ORC_REG_DI:
1287                         cfa->base = CFI_DI;
1288                         break;
1289                 case ORC_REG_DX:
1290                         cfa->base = CFI_DX;
1291                         break;
1292                 default:
1293                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1294                                   insn->sec, insn->offset, hint->sp_reg);
1295                         return -1;
1296                 }
1297
1298                 cfa->offset = hint->sp_offset;
1299                 insn->state.type = hint->type;
1300                 insn->state.end = hint->end;
1301         }
1302
1303         return 0;
1304 }
1305
1306 static int read_retpoline_hints(struct objtool_file *file)
1307 {
1308         struct section *sec;
1309         struct instruction *insn;
1310         struct rela *rela;
1311
1312         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1313         if (!sec)
1314                 return 0;
1315
1316         list_for_each_entry(rela, &sec->rela_list, list) {
1317                 if (rela->sym->type != STT_SECTION) {
1318                         WARN("unexpected relocation symbol type in %s", sec->name);
1319                         return -1;
1320                 }
1321
1322                 insn = find_insn(file, rela->sym->sec, rela->addend);
1323                 if (!insn) {
1324                         WARN("bad .discard.retpoline_safe entry");
1325                         return -1;
1326                 }
1327
1328                 if (insn->type != INSN_JUMP_DYNAMIC &&
1329                     insn->type != INSN_CALL_DYNAMIC) {
1330                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1331                                   insn->sec, insn->offset);
1332                         return -1;
1333                 }
1334
1335                 insn->retpoline_safe = true;
1336         }
1337
1338         return 0;
1339 }
1340
1341 static void mark_rodata(struct objtool_file *file)
1342 {
1343         struct section *sec;
1344         bool found = false;
1345
1346         /*
1347          * Search for the following rodata sections, each of which can
1348          * potentially contain jump tables:
1349          *
1350          * - .rodata: can contain GCC switch tables
1351          * - .rodata.<func>: same, if -fdata-sections is being used
1352          * - .rodata..c_jump_table: contains C annotated jump tables
1353          *
1354          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1355          */
1356         for_each_sec(file, sec) {
1357                 if (!strncmp(sec->name, ".rodata", 7) &&
1358                     !strstr(sec->name, ".str1.")) {
1359                         sec->rodata = true;
1360                         found = true;
1361                 }
1362         }
1363
1364         file->rodata = found;
1365 }
1366
1367 static int decode_sections(struct objtool_file *file)
1368 {
1369         int ret;
1370
1371         mark_rodata(file);
1372
1373         ret = decode_instructions(file);
1374         if (ret)
1375                 return ret;
1376
1377         ret = add_dead_ends(file);
1378         if (ret)
1379                 return ret;
1380
1381         add_ignores(file);
1382         add_uaccess_safe(file);
1383
1384         ret = add_ignore_alternatives(file);
1385         if (ret)
1386                 return ret;
1387
1388         ret = add_jump_destinations(file);
1389         if (ret)
1390                 return ret;
1391
1392         ret = add_special_section_alts(file);
1393         if (ret)
1394                 return ret;
1395
1396         ret = add_call_destinations(file);
1397         if (ret)
1398                 return ret;
1399
1400         ret = add_jump_table_alts(file);
1401         if (ret)
1402                 return ret;
1403
1404         ret = read_unwind_hints(file);
1405         if (ret)
1406                 return ret;
1407
1408         ret = read_retpoline_hints(file);
1409         if (ret)
1410                 return ret;
1411
1412         return 0;
1413 }
1414
1415 static bool is_fentry_call(struct instruction *insn)
1416 {
1417         if (insn->type == INSN_CALL &&
1418             insn->call_dest->type == STT_NOTYPE &&
1419             !strcmp(insn->call_dest->name, "__fentry__"))
1420                 return true;
1421
1422         return false;
1423 }
1424
1425 static bool has_modified_stack_frame(struct insn_state *state)
1426 {
1427         int i;
1428
1429         if (state->cfa.base != initial_func_cfi.cfa.base ||
1430             state->cfa.offset != initial_func_cfi.cfa.offset ||
1431             state->stack_size != initial_func_cfi.cfa.offset ||
1432             state->drap)
1433                 return true;
1434
1435         for (i = 0; i < CFI_NUM_REGS; i++)
1436                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1437                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1438                         return true;
1439
1440         return false;
1441 }
1442
1443 static bool has_valid_stack_frame(struct insn_state *state)
1444 {
1445         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1446             state->regs[CFI_BP].offset == -16)
1447                 return true;
1448
1449         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1450                 return true;
1451
1452         return false;
1453 }
1454
1455 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1456 {
1457         struct cfi_reg *cfa = &state->cfa;
1458         struct stack_op *op = &insn->stack_op;
1459
1460         if (cfa->base != CFI_SP)
1461                 return 0;
1462
1463         /* push */
1464         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1465                 cfa->offset += 8;
1466
1467         /* pop */
1468         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1469                 cfa->offset -= 8;
1470
1471         /* add immediate to sp */
1472         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1473             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1474                 cfa->offset -= op->src.offset;
1475
1476         return 0;
1477 }
1478
1479 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1480                      int offset)
1481 {
1482         if (arch_callee_saved_reg(reg) &&
1483             state->regs[reg].base == CFI_UNDEFINED) {
1484                 state->regs[reg].base = base;
1485                 state->regs[reg].offset = offset;
1486         }
1487 }
1488
1489 static void restore_reg(struct insn_state *state, unsigned char reg)
1490 {
1491         state->regs[reg].base = initial_func_cfi.regs[reg].base;
1492         state->regs[reg].offset = initial_func_cfi.regs[reg].offset;
1493 }
1494
1495 /*
1496  * A note about DRAP stack alignment:
1497  *
1498  * GCC has the concept of a DRAP register, which is used to help keep track of
1499  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1500  * register.  The typical DRAP pattern is:
1501  *
1502  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1503  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1504  *   41 ff 72 f8                pushq  -0x8(%r10)
1505  *   55                         push   %rbp
1506  *   48 89 e5                   mov    %rsp,%rbp
1507  *                              (more pushes)
1508  *   41 52                      push   %r10
1509  *                              ...
1510  *   41 5a                      pop    %r10
1511  *                              (more pops)
1512  *   5d                         pop    %rbp
1513  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1514  *   c3                         retq
1515  *
1516  * There are some variations in the epilogues, like:
1517  *
1518  *   5b                         pop    %rbx
1519  *   41 5a                      pop    %r10
1520  *   41 5c                      pop    %r12
1521  *   41 5d                      pop    %r13
1522  *   41 5e                      pop    %r14
1523  *   c9                         leaveq
1524  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1525  *   c3                         retq
1526  *
1527  * and:
1528  *
1529  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1530  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1531  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1532  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1533  *   c9                         leaveq
1534  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1535  *   c3                         retq
1536  *
1537  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1538  * restored beforehand:
1539  *
1540  *   41 55                      push   %r13
1541  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1542  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1543  *                              ...
1544  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1545  *   41 5d                      pop    %r13
1546  *   c3                         retq
1547  */
1548 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1549 {
1550         struct stack_op *op = &insn->stack_op;
1551         struct cfi_reg *cfa = &state->cfa;
1552         struct cfi_reg *regs = state->regs;
1553
1554         /* stack operations don't make sense with an undefined CFA */
1555         if (cfa->base == CFI_UNDEFINED) {
1556                 if (insn->func) {
1557                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1558                         return -1;
1559                 }
1560                 return 0;
1561         }
1562
1563         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1564                 return update_insn_state_regs(insn, state);
1565
1566         switch (op->dest.type) {
1567
1568         case OP_DEST_REG:
1569                 switch (op->src.type) {
1570
1571                 case OP_SRC_REG:
1572                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1573                             cfa->base == CFI_SP &&
1574                             regs[CFI_BP].base == CFI_CFA &&
1575                             regs[CFI_BP].offset == -cfa->offset) {
1576
1577                                 /* mov %rsp, %rbp */
1578                                 cfa->base = op->dest.reg;
1579                                 state->bp_scratch = false;
1580                         }
1581
1582                         else if (op->src.reg == CFI_SP &&
1583                                  op->dest.reg == CFI_BP && state->drap) {
1584
1585                                 /* drap: mov %rsp, %rbp */
1586                                 regs[CFI_BP].base = CFI_BP;
1587                                 regs[CFI_BP].offset = -state->stack_size;
1588                                 state->bp_scratch = false;
1589                         }
1590
1591                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1592
1593                                 /*
1594                                  * mov %rsp, %reg
1595                                  *
1596                                  * This is needed for the rare case where GCC
1597                                  * does:
1598                                  *
1599                                  *   mov    %rsp, %rax
1600                                  *   ...
1601                                  *   mov    %rax, %rsp
1602                                  */
1603                                 state->vals[op->dest.reg].base = CFI_CFA;
1604                                 state->vals[op->dest.reg].offset = -state->stack_size;
1605                         }
1606
1607                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1608                                  cfa->base == CFI_BP) {
1609
1610                                 /*
1611                                  * mov %rbp, %rsp
1612                                  *
1613                                  * Restore the original stack pointer (Clang).
1614                                  */
1615                                 state->stack_size = -state->regs[CFI_BP].offset;
1616                         }
1617
1618                         else if (op->dest.reg == cfa->base) {
1619
1620                                 /* mov %reg, %rsp */
1621                                 if (cfa->base == CFI_SP &&
1622                                     state->vals[op->src.reg].base == CFI_CFA) {
1623
1624                                         /*
1625                                          * This is needed for the rare case
1626                                          * where GCC does something dumb like:
1627                                          *
1628                                          *   lea    0x8(%rsp), %rcx
1629                                          *   ...
1630                                          *   mov    %rcx, %rsp
1631                                          */
1632                                         cfa->offset = -state->vals[op->src.reg].offset;
1633                                         state->stack_size = cfa->offset;
1634
1635                                 } else {
1636                                         cfa->base = CFI_UNDEFINED;
1637                                         cfa->offset = 0;
1638                                 }
1639                         }
1640
1641                         break;
1642
1643                 case OP_SRC_ADD:
1644                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1645
1646                                 /* add imm, %rsp */
1647                                 state->stack_size -= op->src.offset;
1648                                 if (cfa->base == CFI_SP)
1649                                         cfa->offset -= op->src.offset;
1650                                 break;
1651                         }
1652
1653                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1654
1655                                 /* lea disp(%rbp), %rsp */
1656                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1657                                 break;
1658                         }
1659
1660                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1661
1662                                 /* drap: lea disp(%rsp), %drap */
1663                                 state->drap_reg = op->dest.reg;
1664
1665                                 /*
1666                                  * lea disp(%rsp), %reg
1667                                  *
1668                                  * This is needed for the rare case where GCC
1669                                  * does something dumb like:
1670                                  *
1671                                  *   lea    0x8(%rsp), %rcx
1672                                  *   ...
1673                                  *   mov    %rcx, %rsp
1674                                  */
1675                                 state->vals[op->dest.reg].base = CFI_CFA;
1676                                 state->vals[op->dest.reg].offset = \
1677                                         -state->stack_size + op->src.offset;
1678
1679                                 break;
1680                         }
1681
1682                         if (state->drap && op->dest.reg == CFI_SP &&
1683                             op->src.reg == state->drap_reg) {
1684
1685                                  /* drap: lea disp(%drap), %rsp */
1686                                 cfa->base = CFI_SP;
1687                                 cfa->offset = state->stack_size = -op->src.offset;
1688                                 state->drap_reg = CFI_UNDEFINED;
1689                                 state->drap = false;
1690                                 break;
1691                         }
1692
1693                         if (op->dest.reg == state->cfa.base) {
1694                                 WARN_FUNC("unsupported stack register modification",
1695                                           insn->sec, insn->offset);
1696                                 return -1;
1697                         }
1698
1699                         break;
1700
1701                 case OP_SRC_AND:
1702                         if (op->dest.reg != CFI_SP ||
1703                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1704                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1705                                 WARN_FUNC("unsupported stack pointer realignment",
1706                                           insn->sec, insn->offset);
1707                                 return -1;
1708                         }
1709
1710                         if (state->drap_reg != CFI_UNDEFINED) {
1711                                 /* drap: and imm, %rsp */
1712                                 cfa->base = state->drap_reg;
1713                                 cfa->offset = state->stack_size = 0;
1714                                 state->drap = true;
1715                         }
1716
1717                         /*
1718                          * Older versions of GCC (4.8ish) realign the stack
1719                          * without DRAP, with a frame pointer.
1720                          */
1721
1722                         break;
1723
1724                 case OP_SRC_POP:
1725                 case OP_SRC_POPF:
1726                         if (!state->drap && op->dest.reg == cfa->base) {
1727
1728                                 /* pop %rbp */
1729                                 cfa->base = CFI_SP;
1730                         }
1731
1732                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1733                             op->dest.reg == state->drap_reg &&
1734                             state->drap_offset == -state->stack_size) {
1735
1736                                 /* drap: pop %drap */
1737                                 cfa->base = state->drap_reg;
1738                                 cfa->offset = 0;
1739                                 state->drap_offset = -1;
1740
1741                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1742
1743                                 /* pop %reg */
1744                                 restore_reg(state, op->dest.reg);
1745                         }
1746
1747                         state->stack_size -= 8;
1748                         if (cfa->base == CFI_SP)
1749                                 cfa->offset -= 8;
1750
1751                         break;
1752
1753                 case OP_SRC_REG_INDIRECT:
1754                         if (state->drap && op->src.reg == CFI_BP &&
1755                             op->src.offset == state->drap_offset) {
1756
1757                                 /* drap: mov disp(%rbp), %drap */
1758                                 cfa->base = state->drap_reg;
1759                                 cfa->offset = 0;
1760                                 state->drap_offset = -1;
1761                         }
1762
1763                         if (state->drap && op->src.reg == CFI_BP &&
1764                             op->src.offset == regs[op->dest.reg].offset) {
1765
1766                                 /* drap: mov disp(%rbp), %reg */
1767                                 restore_reg(state, op->dest.reg);
1768
1769                         } else if (op->src.reg == cfa->base &&
1770                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1771
1772                                 /* mov disp(%rbp), %reg */
1773                                 /* mov disp(%rsp), %reg */
1774                                 restore_reg(state, op->dest.reg);
1775                         }
1776
1777                         break;
1778
1779                 default:
1780                         WARN_FUNC("unknown stack-related instruction",
1781                                   insn->sec, insn->offset);
1782                         return -1;
1783                 }
1784
1785                 break;
1786
1787         case OP_DEST_PUSH:
1788         case OP_DEST_PUSHF:
1789                 state->stack_size += 8;
1790                 if (cfa->base == CFI_SP)
1791                         cfa->offset += 8;
1792
1793                 if (op->src.type != OP_SRC_REG)
1794                         break;
1795
1796                 if (state->drap) {
1797                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1798
1799                                 /* drap: push %drap */
1800                                 cfa->base = CFI_BP_INDIRECT;
1801                                 cfa->offset = -state->stack_size;
1802
1803                                 /* save drap so we know when to restore it */
1804                                 state->drap_offset = -state->stack_size;
1805
1806                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1807
1808                                 /* drap: push %rbp */
1809                                 state->stack_size = 0;
1810
1811                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1812
1813                                 /* drap: push %reg */
1814                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1815                         }
1816
1817                 } else {
1818
1819                         /* push %reg */
1820                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1821                 }
1822
1823                 /* detect when asm code uses rbp as a scratch register */
1824                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1825                     cfa->base != CFI_BP)
1826                         state->bp_scratch = true;
1827                 break;
1828
1829         case OP_DEST_REG_INDIRECT:
1830
1831                 if (state->drap) {
1832                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1833
1834                                 /* drap: mov %drap, disp(%rbp) */
1835                                 cfa->base = CFI_BP_INDIRECT;
1836                                 cfa->offset = op->dest.offset;
1837
1838                                 /* save drap offset so we know when to restore it */
1839                                 state->drap_offset = op->dest.offset;
1840                         }
1841
1842                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1843
1844                                 /* drap: mov reg, disp(%rbp) */
1845                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1846                         }
1847
1848                 } else if (op->dest.reg == cfa->base) {
1849
1850                         /* mov reg, disp(%rbp) */
1851                         /* mov reg, disp(%rsp) */
1852                         save_reg(state, op->src.reg, CFI_CFA,
1853                                  op->dest.offset - state->cfa.offset);
1854                 }
1855
1856                 break;
1857
1858         case OP_DEST_LEAVE:
1859                 if ((!state->drap && cfa->base != CFI_BP) ||
1860                     (state->drap && cfa->base != state->drap_reg)) {
1861                         WARN_FUNC("leave instruction with modified stack frame",
1862                                   insn->sec, insn->offset);
1863                         return -1;
1864                 }
1865
1866                 /* leave (mov %rbp, %rsp; pop %rbp) */
1867
1868                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1869                 restore_reg(state, CFI_BP);
1870
1871                 if (!state->drap) {
1872                         cfa->base = CFI_SP;
1873                         cfa->offset -= 8;
1874                 }
1875
1876                 break;
1877
1878         case OP_DEST_MEM:
1879                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1880                         WARN_FUNC("unknown stack-related memory operation",
1881                                   insn->sec, insn->offset);
1882                         return -1;
1883                 }
1884
1885                 /* pop mem */
1886                 state->stack_size -= 8;
1887                 if (cfa->base == CFI_SP)
1888                         cfa->offset -= 8;
1889
1890                 break;
1891
1892         default:
1893                 WARN_FUNC("unknown stack-related instruction",
1894                           insn->sec, insn->offset);
1895                 return -1;
1896         }
1897
1898         return 0;
1899 }
1900
1901 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1902 {
1903         struct insn_state *state1 = &insn->state, *state2 = state;
1904         int i;
1905
1906         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1907                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1908                           insn->sec, insn->offset,
1909                           state1->cfa.base, state1->cfa.offset,
1910                           state2->cfa.base, state2->cfa.offset);
1911
1912         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1913                 for (i = 0; i < CFI_NUM_REGS; i++) {
1914                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1915                                     sizeof(struct cfi_reg)))
1916                                 continue;
1917
1918                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1919                                   insn->sec, insn->offset,
1920                                   i, state1->regs[i].base, state1->regs[i].offset,
1921                                   i, state2->regs[i].base, state2->regs[i].offset);
1922                         break;
1923                 }
1924
1925         } else if (state1->type != state2->type) {
1926                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1927                           insn->sec, insn->offset, state1->type, state2->type);
1928
1929         } else if (state1->drap != state2->drap ||
1930                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1931                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1932                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1933                           insn->sec, insn->offset,
1934                           state1->drap, state1->drap_reg, state1->drap_offset,
1935                           state2->drap, state2->drap_reg, state2->drap_offset);
1936
1937         } else
1938                 return true;
1939
1940         return false;
1941 }
1942
1943 static inline bool func_uaccess_safe(struct symbol *func)
1944 {
1945         if (func)
1946                 return func->uaccess_safe;
1947
1948         return false;
1949 }
1950
1951 static inline const char *call_dest_name(struct instruction *insn)
1952 {
1953         if (insn->call_dest)
1954                 return insn->call_dest->name;
1955
1956         return "{dynamic}";
1957 }
1958
1959 static int validate_call(struct instruction *insn, struct insn_state *state)
1960 {
1961         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1962                 WARN_FUNC("call to %s() with UACCESS enabled",
1963                                 insn->sec, insn->offset, call_dest_name(insn));
1964                 return 1;
1965         }
1966
1967         if (state->df) {
1968                 WARN_FUNC("call to %s() with DF set",
1969                                 insn->sec, insn->offset, call_dest_name(insn));
1970                 return 1;
1971         }
1972
1973         return 0;
1974 }
1975
1976 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1977 {
1978         if (has_modified_stack_frame(state)) {
1979                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1980                                 insn->sec, insn->offset);
1981                 return 1;
1982         }
1983
1984         return validate_call(insn, state);
1985 }
1986
1987 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
1988 {
1989         if (state->uaccess && !func_uaccess_safe(func)) {
1990                 WARN_FUNC("return with UACCESS enabled",
1991                           insn->sec, insn->offset);
1992                 return 1;
1993         }
1994
1995         if (!state->uaccess && func_uaccess_safe(func)) {
1996                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
1997                           insn->sec, insn->offset);
1998                 return 1;
1999         }
2000
2001         if (state->df) {
2002                 WARN_FUNC("return with DF set",
2003                           insn->sec, insn->offset);
2004                 return 1;
2005         }
2006
2007         if (func && has_modified_stack_frame(state)) {
2008                 WARN_FUNC("return with modified stack frame",
2009                           insn->sec, insn->offset);
2010                 return 1;
2011         }
2012
2013         if (state->bp_scratch) {
2014                 WARN_FUNC("BP used as a scratch register",
2015                           insn->sec, insn->offset);
2016                 return 1;
2017         }
2018
2019         return 0;
2020 }
2021
2022 /*
2023  * Follow the branch starting at the given instruction, and recursively follow
2024  * any other branches (jumps).  Meanwhile, track the frame pointer state at
2025  * each instruction and validate all the rules described in
2026  * tools/objtool/Documentation/stack-validation.txt.
2027  */
2028 static int validate_branch(struct objtool_file *file, struct symbol *func,
2029                            struct instruction *first, struct insn_state state)
2030 {
2031         struct alternative *alt;
2032         struct instruction *insn, *next_insn;
2033         struct section *sec;
2034         u8 visited;
2035         int ret;
2036
2037         insn = first;
2038         sec = insn->sec;
2039
2040         if (insn->alt_group && list_empty(&insn->alts)) {
2041                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
2042                           sec, insn->offset);
2043                 return 1;
2044         }
2045
2046         while (1) {
2047                 next_insn = next_insn_same_sec(file, insn);
2048
2049                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2050                         WARN("%s() falls through to next function %s()",
2051                              func->name, insn->func->name);
2052                         return 1;
2053                 }
2054
2055                 if (func && insn->ignore) {
2056                         WARN_FUNC("BUG: why am I validating an ignored function?",
2057                                   sec, insn->offset);
2058                         return 1;
2059                 }
2060
2061                 visited = 1 << state.uaccess;
2062                 if (insn->visited) {
2063                         if (!insn->hint && !insn_state_match(insn, &state))
2064                                 return 1;
2065
2066                         if (insn->visited & visited)
2067                                 return 0;
2068                 }
2069
2070                 if (insn->hint) {
2071                         if (insn->restore) {
2072                                 struct instruction *save_insn, *i;
2073
2074                                 i = insn;
2075                                 save_insn = NULL;
2076                                 sym_for_each_insn_continue_reverse(file, func, i) {
2077                                         if (i->save) {
2078                                                 save_insn = i;
2079                                                 break;
2080                                         }
2081                                 }
2082
2083                                 if (!save_insn) {
2084                                         WARN_FUNC("no corresponding CFI save for CFI restore",
2085                                                   sec, insn->offset);
2086                                         return 1;
2087                                 }
2088
2089                                 if (!save_insn->visited) {
2090                                         /*
2091                                          * Oops, no state to copy yet.
2092                                          * Hopefully we can reach this
2093                                          * instruction from another branch
2094                                          * after the save insn has been
2095                                          * visited.
2096                                          */
2097                                         if (insn == first)
2098                                                 return 0;
2099
2100                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2101                                                   sec, insn->offset);
2102                                         return 1;
2103                                 }
2104
2105                                 insn->state = save_insn->state;
2106                         }
2107
2108                         state = insn->state;
2109
2110                 } else
2111                         insn->state = state;
2112
2113                 insn->visited |= visited;
2114
2115                 if (!insn->ignore_alts) {
2116                         bool skip_orig = false;
2117
2118                         list_for_each_entry(alt, &insn->alts, list) {
2119                                 if (alt->skip_orig)
2120                                         skip_orig = true;
2121
2122                                 ret = validate_branch(file, func, alt->insn, state);
2123                                 if (ret) {
2124                                         if (backtrace)
2125                                                 BT_FUNC("(alt)", insn);
2126                                         return ret;
2127                                 }
2128                         }
2129
2130                         if (skip_orig)
2131                                 return 0;
2132                 }
2133
2134                 switch (insn->type) {
2135
2136                 case INSN_RETURN:
2137                         return validate_return(func, insn, &state);
2138
2139                 case INSN_CALL:
2140                 case INSN_CALL_DYNAMIC:
2141                         ret = validate_call(insn, &state);
2142                         if (ret)
2143                                 return ret;
2144
2145                         if (!no_fp && func && !is_fentry_call(insn) &&
2146                             !has_valid_stack_frame(&state)) {
2147                                 WARN_FUNC("call without frame pointer save/setup",
2148                                           sec, insn->offset);
2149                                 return 1;
2150                         }
2151
2152                         if (dead_end_function(file, insn->call_dest))
2153                                 return 0;
2154
2155                         break;
2156
2157                 case INSN_JUMP_CONDITIONAL:
2158                 case INSN_JUMP_UNCONDITIONAL:
2159                         if (func && is_sibling_call(insn)) {
2160                                 ret = validate_sibling_call(insn, &state);
2161                                 if (ret)
2162                                         return ret;
2163
2164                         } else if (insn->jump_dest) {
2165                                 ret = validate_branch(file, func,
2166                                                       insn->jump_dest, state);
2167                                 if (ret) {
2168                                         if (backtrace)
2169                                                 BT_FUNC("(branch)", insn);
2170                                         return ret;
2171                                 }
2172                         }
2173
2174                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2175                                 return 0;
2176
2177                         break;
2178
2179                 case INSN_JUMP_DYNAMIC:
2180                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2181                         if (func && is_sibling_call(insn)) {
2182                                 ret = validate_sibling_call(insn, &state);
2183                                 if (ret)
2184                                         return ret;
2185                         }
2186
2187                         if (insn->type == INSN_JUMP_DYNAMIC)
2188                                 return 0;
2189
2190                         break;
2191
2192                 case INSN_CONTEXT_SWITCH:
2193                         if (func && (!next_insn || !next_insn->hint)) {
2194                                 WARN_FUNC("unsupported instruction in callable function",
2195                                           sec, insn->offset);
2196                                 return 1;
2197                         }
2198                         return 0;
2199
2200                 case INSN_STACK:
2201                         if (update_insn_state(insn, &state))
2202                                 return 1;
2203
2204                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2205                                 if (!state.uaccess_stack) {
2206                                         state.uaccess_stack = 1;
2207                                 } else if (state.uaccess_stack >> 31) {
2208                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2209                                         return 1;
2210                                 }
2211                                 state.uaccess_stack <<= 1;
2212                                 state.uaccess_stack  |= state.uaccess;
2213                         }
2214
2215                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2216                                 if (state.uaccess_stack) {
2217                                         state.uaccess = state.uaccess_stack & 1;
2218                                         state.uaccess_stack >>= 1;
2219                                         if (state.uaccess_stack == 1)
2220                                                 state.uaccess_stack = 0;
2221                                 }
2222                         }
2223
2224                         break;
2225
2226                 case INSN_STAC:
2227                         if (state.uaccess) {
2228                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2229                                 return 1;
2230                         }
2231
2232                         state.uaccess = true;
2233                         break;
2234
2235                 case INSN_CLAC:
2236                         if (!state.uaccess && func) {
2237                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2238                                 return 1;
2239                         }
2240
2241                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2242                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2243                                 return 1;
2244                         }
2245
2246                         state.uaccess = false;
2247                         break;
2248
2249                 case INSN_STD:
2250                         if (state.df)
2251                                 WARN_FUNC("recursive STD", sec, insn->offset);
2252
2253                         state.df = true;
2254                         break;
2255
2256                 case INSN_CLD:
2257                         if (!state.df && func)
2258                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2259
2260                         state.df = false;
2261                         break;
2262
2263                 default:
2264                         break;
2265                 }
2266
2267                 if (insn->dead_end)
2268                         return 0;
2269
2270                 if (!next_insn) {
2271                         if (state.cfa.base == CFI_UNDEFINED)
2272                                 return 0;
2273                         WARN("%s: unexpected end of section", sec->name);
2274                         return 1;
2275                 }
2276
2277                 insn = next_insn;
2278         }
2279
2280         return 0;
2281 }
2282
2283 static int validate_unwind_hints(struct objtool_file *file)
2284 {
2285         struct instruction *insn;
2286         int ret, warnings = 0;
2287         struct insn_state state;
2288
2289         if (!file->hints)
2290                 return 0;
2291
2292         clear_insn_state(&state);
2293
2294         for_each_insn(file, insn) {
2295                 if (insn->hint && !insn->visited) {
2296                         ret = validate_branch(file, insn->func, insn, state);
2297                         if (ret && backtrace)
2298                                 BT_FUNC("<=== (hint)", insn);
2299                         warnings += ret;
2300                 }
2301         }
2302
2303         return warnings;
2304 }
2305
2306 static int validate_retpoline(struct objtool_file *file)
2307 {
2308         struct instruction *insn;
2309         int warnings = 0;
2310
2311         for_each_insn(file, insn) {
2312                 if (insn->type != INSN_JUMP_DYNAMIC &&
2313                     insn->type != INSN_CALL_DYNAMIC)
2314                         continue;
2315
2316                 if (insn->retpoline_safe)
2317                         continue;
2318
2319                 /*
2320                  * .init.text code is ran before userspace and thus doesn't
2321                  * strictly need retpolines, except for modules which are
2322                  * loaded late, they very much do need retpoline in their
2323                  * .init.text
2324                  */
2325                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2326                         continue;
2327
2328                 WARN_FUNC("indirect %s found in RETPOLINE build",
2329                           insn->sec, insn->offset,
2330                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2331
2332                 warnings++;
2333         }
2334
2335         return warnings;
2336 }
2337
2338 static bool is_kasan_insn(struct instruction *insn)
2339 {
2340         return (insn->type == INSN_CALL &&
2341                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2342 }
2343
2344 static bool is_ubsan_insn(struct instruction *insn)
2345 {
2346         return (insn->type == INSN_CALL &&
2347                 !strcmp(insn->call_dest->name,
2348                         "__ubsan_handle_builtin_unreachable"));
2349 }
2350
2351 static bool ignore_unreachable_insn(struct instruction *insn)
2352 {
2353         int i;
2354
2355         if (insn->ignore || insn->type == INSN_NOP)
2356                 return true;
2357
2358         /*
2359          * Ignore any unused exceptions.  This can happen when a whitelisted
2360          * function has an exception table entry.
2361          *
2362          * Also ignore alternative replacement instructions.  This can happen
2363          * when a whitelisted function uses one of the ALTERNATIVE macros.
2364          */
2365         if (!strcmp(insn->sec->name, ".fixup") ||
2366             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2367             !strcmp(insn->sec->name, ".altinstr_aux"))
2368                 return true;
2369
2370         if (!insn->func)
2371                 return false;
2372
2373         /*
2374          * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2375          * __builtin_unreachable().  The BUG() macro has an unreachable() after
2376          * the UD2, which causes GCC's undefined trap logic to emit another UD2
2377          * (or occasionally a JMP to UD2).
2378          */
2379         if (list_prev_entry(insn, list)->dead_end &&
2380             (insn->type == INSN_BUG ||
2381              (insn->type == INSN_JUMP_UNCONDITIONAL &&
2382               insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2383                 return true;
2384
2385         /*
2386          * Check if this (or a subsequent) instruction is related to
2387          * CONFIG_UBSAN or CONFIG_KASAN.
2388          *
2389          * End the search at 5 instructions to avoid going into the weeds.
2390          */
2391         for (i = 0; i < 5; i++) {
2392
2393                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2394                         return true;
2395
2396                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2397                         if (insn->jump_dest &&
2398                             insn->jump_dest->func == insn->func) {
2399                                 insn = insn->jump_dest;
2400                                 continue;
2401                         }
2402
2403                         break;
2404                 }
2405
2406                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2407                         break;
2408
2409                 insn = list_next_entry(insn, list);
2410         }
2411
2412         return false;
2413 }
2414
2415 static int validate_section(struct objtool_file *file, struct section *sec)
2416 {
2417         struct symbol *func;
2418         struct instruction *insn;
2419         struct insn_state state;
2420         int ret, warnings = 0;
2421
2422         list_for_each_entry(func, &sec->symbol_list, list) {
2423                 if (func->type != STT_FUNC)
2424                         continue;
2425
2426                 if (!func->len) {
2427                         WARN("%s() is missing an ELF size annotation",
2428                              func->name);
2429                         warnings++;
2430                 }
2431
2432                 if (func->pfunc != func || func->alias != func)
2433                         continue;
2434
2435                 insn = find_insn(file, sec, func->offset);
2436                 if (!insn || insn->ignore || insn->visited)
2437                         continue;
2438
2439                 clear_insn_state(&state);
2440                 state.cfa = initial_func_cfi.cfa;
2441                 memcpy(&state.regs, &initial_func_cfi.regs,
2442                        CFI_NUM_REGS * sizeof(struct cfi_reg));
2443                 state.stack_size = initial_func_cfi.cfa.offset;
2444
2445                 state.uaccess = func->uaccess_safe;
2446
2447                 ret = validate_branch(file, func, insn, state);
2448                 if (ret && backtrace)
2449                         BT_FUNC("<=== (func)", insn);
2450                 warnings += ret;
2451         }
2452
2453         return warnings;
2454 }
2455
2456 static int validate_functions(struct objtool_file *file)
2457 {
2458         struct section *sec;
2459         int warnings = 0;
2460
2461         for_each_sec(file, sec)
2462                 warnings += validate_section(file, sec);
2463
2464         return warnings;
2465 }
2466
2467 static int validate_reachable_instructions(struct objtool_file *file)
2468 {
2469         struct instruction *insn;
2470
2471         if (file->ignore_unreachables)
2472                 return 0;
2473
2474         for_each_insn(file, insn) {
2475                 if (insn->visited || ignore_unreachable_insn(insn))
2476                         continue;
2477
2478                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2479                 return 1;
2480         }
2481
2482         return 0;
2483 }
2484
2485 static struct objtool_file file;
2486
2487 int check(const char *_objname, bool orc)
2488 {
2489         int ret, warnings = 0;
2490
2491         objname = _objname;
2492
2493         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2494         if (!file.elf)
2495                 return 1;
2496
2497         INIT_LIST_HEAD(&file.insn_list);
2498         hash_init(file.insn_hash);
2499         file.c_file = find_section_by_name(file.elf, ".comment");
2500         file.ignore_unreachables = no_unreachable;
2501         file.hints = false;
2502
2503         arch_initial_func_cfi_state(&initial_func_cfi);
2504
2505         ret = decode_sections(&file);
2506         if (ret < 0)
2507                 goto out;
2508         warnings += ret;
2509
2510         if (list_empty(&file.insn_list))
2511                 goto out;
2512
2513         if (retpoline) {
2514                 ret = validate_retpoline(&file);
2515                 if (ret < 0)
2516                         return ret;
2517                 warnings += ret;
2518         }
2519
2520         ret = validate_functions(&file);
2521         if (ret < 0)
2522                 goto out;
2523         warnings += ret;
2524
2525         ret = validate_unwind_hints(&file);
2526         if (ret < 0)
2527                 goto out;
2528         warnings += ret;
2529
2530         if (!warnings) {
2531                 ret = validate_reachable_instructions(&file);
2532                 if (ret < 0)
2533                         goto out;
2534                 warnings += ret;
2535         }
2536
2537         if (orc) {
2538                 ret = create_orc(&file);
2539                 if (ret < 0)
2540                         goto out;
2541
2542                 ret = create_orc_sections(&file);
2543                 if (ret < 0)
2544                         goto out;
2545
2546                 ret = elf_write(file.elf);
2547                 if (ret < 0)
2548                         goto out;
2549         }
2550
2551 out:
2552         if (ret < 0) {
2553                 /*
2554                  *  Fatal error.  The binary is corrupt or otherwise broken in
2555                  *  some way, or objtool itself is broken.  Fail the kernel
2556                  *  build.
2557                  */
2558                 return ret;
2559         }
2560
2561         return 0;
2562 }