tools/objtool/check.c

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