tools/objtool/check.c

   1 /*
   2  * Copyright (C) 2015-2017 Josh Poimboeuf <[email protected]>
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include <string.h>
  19 #include <stdlib.h>
  20
  21 #include "check.h"
  22 #include "elf.h"
  23 #include "special.h"
  24 #include "arch.h"
  25 #include "warn.h"
  26
  27 #include <linux/hashtable.h>
  28 #include <linux/kernel.h>
  29
  30 struct alternative {
  31         struct list_head list;
  32         struct instruction *insn;
  33 };
  34
  35 const char *objname;
  36 static bool no_fp;
  37 struct cfi_state initial_func_cfi;
  38
  39 struct instruction *find_insn(struct objtool_file *file,
  40                               struct section *sec, unsigned long offset)
  41 {
  42         struct instruction *insn;
  43
  44         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  45                 if (insn->sec == sec && insn->offset == offset)
  46                         return insn;
  47
  48         return NULL;
  49 }
  50
  51 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  52                                               struct instruction *insn)
  53 {
  54         struct instruction *next = list_next_entry(insn, list);
  55
  56         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  57                 return NULL;
  58
  59         return next;
  60 }
  61
  62 #define func_for_each_insn(file, func, insn)                            \
  63         for (insn = find_insn(file, func->sec, func->offset);           \
  64              insn && &insn->list != &file->insn_list &&                 \
  65                 insn->sec == func->sec &&                               \
  66                 insn->offset < func->offset + func->len;                \
  67              insn = list_next_entry(insn, list))
  68
  69 #define func_for_each_insn_continue_reverse(file, func, insn)           \
  70         for (insn = list_prev_entry(insn, list);                        \
  71              &insn->list != &file->insn_list &&                         \
  72                 insn->sec == func->sec && insn->offset >= func->offset; \
  73              insn = list_prev_entry(insn, list))
  74
  75 #define sec_for_each_insn_from(file, insn)                              \
  76         for (; insn; insn = next_insn_same_sec(file, insn))
  77
  78 #define sec_for_each_insn_continue(file, insn)                          \
  79         for (insn = next_insn_same_sec(file, insn); insn;               \
  80              insn = next_insn_same_sec(file, insn))
  81
  82 /*
  83  * Check if the function has been manually whitelisted with the
  84  * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
  85  * due to its use of a context switching instruction.
  86  */
  87 static bool ignore_func(struct objtool_file *file, struct symbol *func)
  88 {
  89         struct rela *rela;
  90
  91         /* check for STACK_FRAME_NON_STANDARD */
  92         if (file->whitelist && file->whitelist->rela)
  93                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
  94                         if (rela->sym->type == STT_SECTION &&
  95                             rela->sym->sec == func->sec &&
  96                             rela->addend == func->offset)
  97                                 return true;
  98                         if (rela->sym->type == STT_FUNC && rela->sym == func)
  99                                 return true;
 100                 }
 101
 102         return false;
 103 }
 104
 105 /*
 106  * This checks to see if the given function is a "noreturn" function.
 107  *
 108  * For global functions which are outside the scope of this object file, we
 109  * have to keep a manual list of them.
 110  *
 111  * For local functions, we have to detect them manually by simply looking for
 112  * the lack of a return instruction.
 113  *
 114  * Returns:
 115  *  -1: error
 116  *   0: no dead end
 117  *   1: dead end
 118  */
 119 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 120                                int recursion)
 121 {
 122         int i;
 123         struct instruction *insn;
 124         bool empty = true;
 125
 126         /*
 127          * Unfortunately these have to be hard coded because the noreturn
 128          * attribute isn't provided in ELF data.
 129          */
 130         static const char * const global_noreturns[] = {
 131                 "__stack_chk_fail",
 132                 "panic",
 133                 "do_exit",
 134                 "do_task_dead",
 135                 "__module_put_and_exit",
 136                 "complete_and_exit",
 137                 "kvm_spurious_fault",
 138                 "__reiserfs_panic",
 139                 "lbug_with_loc",
 140                 "fortify_panic",
 141         };
 142
 143         if (func->bind == STB_WEAK)
 144                 return 0;
 145
 146         if (func->bind == STB_GLOBAL)
 147                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 148                         if (!strcmp(func->name, global_noreturns[i]))
 149                                 return 1;
 150
 151         if (!func->sec)
 152                 return 0;
 153
 154         func_for_each_insn(file, func, insn) {
 155                 empty = false;
 156
 157                 if (insn->type == INSN_RETURN)
 158                         return 0;
 159         }
 160
 161         if (empty)
 162                 return 0;
 163
 164         /*
 165          * A function can have a sibling call instead of a return.  In that
 166          * case, the function's dead-end status depends on whether the target
 167          * of the sibling call returns.
 168          */
 169         func_for_each_insn(file, func, insn) {
 170                 if (insn->sec != func->sec ||
 171                     insn->offset >= func->offset + func->len)
 172                         break;
 173
 174                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 175                         struct instruction *dest = insn->jump_dest;
 176                         struct symbol *dest_func;
 177
 178                         if (!dest)
 179                                 /* sibling call to another file */
 180                                 return 0;
 181
 182                         if (dest->sec != func->sec ||
 183                             dest->offset < func->offset ||
 184                             dest->offset >= func->offset + func->len) {
 185                                 /* local sibling call */
 186                                 dest_func = find_symbol_by_offset(dest->sec,
 187                                                                   dest->offset);
 188                                 if (!dest_func)
 189                                         continue;
 190
 191                                 if (recursion == 5) {
 192                                         WARN_FUNC("infinite recursion (objtool bug!)",
 193                                                   dest->sec, dest->offset);
 194                                         return -1;
 195                                 }
 196
 197                                 return __dead_end_function(file, dest_func,
 198                                                            recursion + 1);
 199                         }
 200                 }
 201
 202                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 203                         /* sibling call */
 204                         return 0;
 205         }
 206
 207         return 1;
 208 }
 209
 210 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 211 {
 212         return __dead_end_function(file, func, 0);
 213 }
 214
 215 static void clear_insn_state(struct insn_state *state)
 216 {
 217         int i;
 218
 219         memset(state, 0, sizeof(*state));
 220         state->cfa.base = CFI_UNDEFINED;
 221         for (i = 0; i < CFI_NUM_REGS; i++) {
 222                 state->regs[i].base = CFI_UNDEFINED;
 223                 state->vals[i].base = CFI_UNDEFINED;
 224         }
 225         state->drap_reg = CFI_UNDEFINED;
 226         state->drap_offset = -1;
 227 }
 228
 229 /*
 230  * Call the arch-specific instruction decoder for all the instructions and add
 231  * them to the global instruction list.
 232  */
 233 static int decode_instructions(struct objtool_file *file)
 234 {
 235         struct section *sec;
 236         struct symbol *func;
 237         unsigned long offset;
 238         struct instruction *insn;
 239         int ret;
 240
 241         for_each_sec(file, sec) {
 242
 243                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 244                         continue;
 245
 246                 if (strcmp(sec->name, ".altinstr_replacement") &&
 247                     strcmp(sec->name, ".altinstr_aux") &&
 248                     strncmp(sec->name, ".discard.", 9))
 249                         sec->text = true;
 250
 251                 for (offset = 0; offset < sec->len; offset += insn->len) {
 252                         insn = malloc(sizeof(*insn));
 253                         if (!insn) {
 254                                 WARN("malloc failed");
 255                                 return -1;
 256                         }
 257                         memset(insn, 0, sizeof(*insn));
 258                         INIT_LIST_HEAD(&insn->alts);
 259                         clear_insn_state(&insn->state);
 260
 261                         insn->sec = sec;
 262                         insn->offset = offset;
 263
 264                         ret = arch_decode_instruction(file->elf, sec, offset,
 265                                                       sec->len - offset,
 266                                                       &insn->len, &insn->type,
 267                                                       &insn->immediate,
 268                                                       &insn->stack_op);
 269                         if (ret)
 270                                 goto err;
 271
 272                         if (!insn->type || insn->type > INSN_LAST) {
 273                                 WARN_FUNC("invalid instruction type %d",
 274                                           insn->sec, insn->offset, insn->type);
 275                                 ret = -1;
 276                                 goto err;
 277                         }
 278
 279                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 280                         list_add_tail(&insn->list, &file->insn_list);
 281                 }
 282
 283                 list_for_each_entry(func, &sec->symbol_list, list) {
 284                         if (func->type != STT_FUNC)
 285                                 continue;
 286
 287                         if (!find_insn(file, sec, func->offset)) {
 288                                 WARN("%s(): can't find starting instruction",
 289                                      func->name);
 290                                 return -1;
 291                         }
 292
 293                         func_for_each_insn(file, func, insn)
 294                                 if (!insn->func)
 295                                         insn->func = func;
 296                 }
 297         }
 298
 299         return 0;
 300
 301 err:
 302         free(insn);
 303         return ret;
 304 }
 305
 306 /*
 307  * Mark "ud2" instructions and manually annotated dead ends.
 308  */
 309 static int add_dead_ends(struct objtool_file *file)
 310 {
 311         struct section *sec;
 312         struct rela *rela;
 313         struct instruction *insn;
 314         bool found;
 315
 316         /*
 317          * By default, "ud2" is a dead end unless otherwise annotated, because
 318          * GCC 7 inserts it for certain divide-by-zero cases.
 319          */
 320         for_each_insn(file, insn)
 321                 if (insn->type == INSN_BUG)
 322                         insn->dead_end = true;
 323
 324         /*
 325          * Check for manually annotated dead ends.
 326          */
 327         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 328         if (!sec)
 329                 goto reachable;
 330
 331         list_for_each_entry(rela, &sec->rela_list, list) {
 332                 if (rela->sym->type != STT_SECTION) {
 333                         WARN("unexpected relocation symbol type in %s", sec->name);
 334                         return -1;
 335                 }
 336                 insn = find_insn(file, rela->sym->sec, rela->addend);
 337                 if (insn)
 338                         insn = list_prev_entry(insn, list);
 339                 else if (rela->addend == rela->sym->sec->len) {
 340                         found = false;
 341                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 342                                 if (insn->sec == rela->sym->sec) {
 343                                         found = true;
 344                                         break;
 345                                 }
 346                         }
 347
 348                         if (!found) {
 349                                 WARN("can't find unreachable insn at %s+0x%x",
 350                                      rela->sym->sec->name, rela->addend);
 351                                 return -1;
 352                         }
 353                 } else {
 354                         WARN("can't find unreachable insn at %s+0x%x",
 355                              rela->sym->sec->name, rela->addend);
 356                         return -1;
 357                 }
 358
 359                 insn->dead_end = true;
 360         }
 361
 362 reachable:
 363         /*
 364          * These manually annotated reachable checks are needed for GCC 4.4,
 365          * where the Linux unreachable() macro isn't supported.  In that case
 366          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 367          * not a dead end.
 368          */
 369         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 370         if (!sec)
 371                 return 0;
 372
 373         list_for_each_entry(rela, &sec->rela_list, list) {
 374                 if (rela->sym->type != STT_SECTION) {
 375                         WARN("unexpected relocation symbol type in %s", sec->name);
 376                         return -1;
 377                 }
 378                 insn = find_insn(file, rela->sym->sec, rela->addend);
 379                 if (insn)
 380                         insn = list_prev_entry(insn, list);
 381                 else if (rela->addend == rela->sym->sec->len) {
 382                         found = false;
 383                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 384                                 if (insn->sec == rela->sym->sec) {
 385                                         found = true;
 386                                         break;
 387                                 }
 388                         }
 389
 390                         if (!found) {
 391                                 WARN("can't find reachable insn at %s+0x%x",
 392                                      rela->sym->sec->name, rela->addend);
 393                                 return -1;
 394                         }
 395                 } else {
 396                         WARN("can't find reachable insn at %s+0x%x",
 397                              rela->sym->sec->name, rela->addend);
 398                         return -1;
 399                 }
 400
 401                 insn->dead_end = false;
 402         }
 403
 404         return 0;
 405 }
 406
 407 /*
 408  * Warnings shouldn't be reported for ignored functions.
 409  */
 410 static void add_ignores(struct objtool_file *file)
 411 {
 412         struct instruction *insn;
 413         struct section *sec;
 414         struct symbol *func;
 415
 416         for_each_sec(file, sec) {
 417                 list_for_each_entry(func, &sec->symbol_list, list) {
 418                         if (func->type != STT_FUNC)
 419                                 continue;
 420
 421                         if (!ignore_func(file, func))
 422                                 continue;
 423
 424                         func_for_each_insn(file, func, insn)
 425                                 insn->ignore = true;
 426                 }
 427         }
 428 }
 429
 430 /*
 431  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 432  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 433  * But it at least allows objtool to understand the control flow *around* the
 434  * retpoline.
 435  */
 436 static int add_nospec_ignores(struct objtool_file *file)
 437 {
 438         struct section *sec;
 439         struct rela *rela;
 440         struct instruction *insn;
 441
 442         sec = find_section_by_name(file->elf, ".rela.discard.nospec");
 443         if (!sec)
 444                 return 0;
 445
 446         list_for_each_entry(rela, &sec->rela_list, list) {
 447                 if (rela->sym->type != STT_SECTION) {
 448                         WARN("unexpected relocation symbol type in %s", sec->name);
 449                         return -1;
 450                 }
 451
 452                 insn = find_insn(file, rela->sym->sec, rela->addend);
 453                 if (!insn) {
 454                         WARN("bad .discard.nospec entry");
 455                         return -1;
 456                 }
 457
 458                 insn->ignore_alts = true;
 459         }
 460
 461         return 0;
 462 }
 463
 464 /*
 465  * Find the destination instructions for all jumps.
 466  */
 467 static int add_jump_destinations(struct objtool_file *file)
 468 {
 469         struct instruction *insn;
 470         struct rela *rela;
 471         struct section *dest_sec;
 472         unsigned long dest_off;
 473
 474         for_each_insn(file, insn) {
 475                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 476                     insn->type != INSN_JUMP_UNCONDITIONAL)
 477                         continue;
 478
 479                 if (insn->ignore)
 480                         continue;
 481
 482                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 483                                                insn->len);
 484                 if (!rela) {
 485                         dest_sec = insn->sec;
 486                         dest_off = insn->offset + insn->len + insn->immediate;
 487                 } else if (rela->sym->type == STT_SECTION) {
 488                         dest_sec = rela->sym->sec;
 489                         dest_off = rela->addend + 4;
 490                 } else if (rela->sym->sec->idx) {
 491                         dest_sec = rela->sym->sec;
 492                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 493                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 494                         /*
 495                          * Retpoline jumps are really dynamic jumps in
 496                          * disguise, so convert them accordingly.
 497                          */
 498                         insn->type = INSN_JUMP_DYNAMIC;
 499                         continue;
 500                 } else {
 501                         /* sibling call */
 502                         insn->jump_dest = 0;
 503                         continue;
 504                 }
 505
 506                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 507                 if (!insn->jump_dest) {
 508
 509                         /*
 510                          * This is a special case where an alt instruction
 511                          * jumps past the end of the section.  These are
 512                          * handled later in handle_group_alt().
 513                          */
 514                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 515                                 continue;
 516
 517                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 518                                   insn->sec, insn->offset, dest_sec->name,
 519                                   dest_off);
 520                         return -1;
 521                 }
 522         }
 523
 524         return 0;
 525 }
 526
 527 /*
 528  * Find the destination instructions for all calls.
 529  */
 530 static int add_call_destinations(struct objtool_file *file)
 531 {
 532         struct instruction *insn;
 533         unsigned long dest_off;
 534         struct rela *rela;
 535
 536         for_each_insn(file, insn) {
 537                 if (insn->type != INSN_CALL)
 538                         continue;
 539
 540                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 541                                                insn->len);
 542                 if (!rela) {
 543                         dest_off = insn->offset + insn->len + insn->immediate;
 544                         insn->call_dest = find_symbol_by_offset(insn->sec,
 545                                                                 dest_off);
 546                         /*
 547                          * FIXME: Thanks to retpolines, it's now considered
 548                          * normal for a function to call within itself.  So
 549                          * disable this warning for now.
 550                          */
 551 #if 0
 552                         if (!insn->call_dest) {
 553                                 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 554                                           insn->sec, insn->offset, dest_off);
 555                                 return -1;
 556                         }
 557 #endif
 558                 } else if (rela->sym->type == STT_SECTION) {
 559                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 560                                                                 rela->addend+4);
 561                         if (!insn->call_dest ||
 562                             insn->call_dest->type != STT_FUNC) {
 563                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 564                                           insn->sec, insn->offset,
 565                                           rela->sym->sec->name,
 566                                           rela->addend + 4);
 567                                 return -1;
 568                         }
 569                 } else
 570                         insn->call_dest = rela->sym;
 571         }
 572
 573         return 0;
 574 }
 575
 576 /*
 577  * The .alternatives section requires some extra special care, over and above
 578  * what other special sections require:
 579  *
 580  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 581  *    instruction at the end so that validate_branch() skips all the original
 582  *    replaced instructions when validating the new instruction path.
 583  *
 584  * 2. An added wrinkle is that the new instruction length might be zero.  In
 585  *    that case the old instructions are replaced with noops.  We simulate that
 586  *    by creating a fake jump as the only new instruction.
 587  *
 588  * 3. In some cases, the alternative section includes an instruction which
 589  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 590  *    jumps' destinations to point back to .text rather than the end of the
 591  *    entry in .altinstr_replacement.
 592  *
 593  * 4. It has been requested that we don't validate the !POPCNT feature path
 594  *    which is a "very very small percentage of machines".
 595  */
 596 static int handle_group_alt(struct objtool_file *file,
 597                             struct special_alt *special_alt,
 598                             struct instruction *orig_insn,
 599                             struct instruction **new_insn)
 600 {
 601         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
 602         unsigned long dest_off;
 603
 604         last_orig_insn = NULL;
 605         insn = orig_insn;
 606         sec_for_each_insn_from(file, insn) {
 607                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 608                         break;
 609
 610                 if (special_alt->skip_orig)
 611                         insn->type = INSN_NOP;
 612
 613                 insn->alt_group = true;
 614                 last_orig_insn = insn;
 615         }
 616
 617         if (!next_insn_same_sec(file, last_orig_insn)) {
 618                 WARN("%s: don't know how to handle alternatives at end of section",
 619                      special_alt->orig_sec->name);
 620                 return -1;
 621         }
 622
 623         fake_jump = malloc(sizeof(*fake_jump));
 624         if (!fake_jump) {
 625                 WARN("malloc failed");
 626                 return -1;
 627         }
 628         memset(fake_jump, 0, sizeof(*fake_jump));
 629         INIT_LIST_HEAD(&fake_jump->alts);
 630         clear_insn_state(&fake_jump->state);
 631
 632         fake_jump->sec = special_alt->new_sec;
 633         fake_jump->offset = -1;
 634         fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 635         fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 636         fake_jump->ignore = true;
 637
 638         if (!special_alt->new_len) {
 639                 *new_insn = fake_jump;
 640                 return 0;
 641         }
 642
 643         last_new_insn = NULL;
 644         insn = *new_insn;
 645         sec_for_each_insn_from(file, insn) {
 646                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 647                         break;
 648
 649                 last_new_insn = insn;
 650
 651                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 652                     insn->type != INSN_JUMP_UNCONDITIONAL)
 653                         continue;
 654
 655                 if (!insn->immediate)
 656                         continue;
 657
 658                 dest_off = insn->offset + insn->len + insn->immediate;
 659                 if (dest_off == special_alt->new_off + special_alt->new_len)
 660                         insn->jump_dest = fake_jump;
 661
 662                 if (!insn->jump_dest) {
 663                         WARN_FUNC("can't find alternative jump destination",
 664                                   insn->sec, insn->offset);
 665                         return -1;
 666                 }
 667         }
 668
 669         if (!last_new_insn) {
 670                 WARN_FUNC("can't find last new alternative instruction",
 671                           special_alt->new_sec, special_alt->new_off);
 672                 return -1;
 673         }
 674
 675         list_add(&fake_jump->list, &last_new_insn->list);
 676
 677         return 0;
 678 }
 679
 680 /*
 681  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 682  * If the original instruction is a jump, make the alt entry an effective nop
 683  * by just skipping the original instruction.
 684  */
 685 static int handle_jump_alt(struct objtool_file *file,
 686                            struct special_alt *special_alt,
 687                            struct instruction *orig_insn,
 688                            struct instruction **new_insn)
 689 {
 690         if (orig_insn->type == INSN_NOP)
 691                 return 0;
 692
 693         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 694                 WARN_FUNC("unsupported instruction at jump label",
 695                           orig_insn->sec, orig_insn->offset);
 696                 return -1;
 697         }
 698
 699         *new_insn = list_next_entry(orig_insn, list);
 700         return 0;
 701 }
 702
 703 /*
 704  * Read all the special sections which have alternate instructions which can be
 705  * patched in or redirected to at runtime.  Each instruction having alternate
 706  * instruction(s) has them added to its insn->alts list, which will be
 707  * traversed in validate_branch().
 708  */
 709 static int add_special_section_alts(struct objtool_file *file)
 710 {
 711         struct list_head special_alts;
 712         struct instruction *orig_insn, *new_insn;
 713         struct special_alt *special_alt, *tmp;
 714         struct alternative *alt;
 715         int ret;
 716
 717         ret = special_get_alts(file->elf, &special_alts);
 718         if (ret)
 719                 return ret;
 720
 721         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 722
 723                 orig_insn = find_insn(file, special_alt->orig_sec,
 724                                       special_alt->orig_off);
 725                 if (!orig_insn) {
 726                         WARN_FUNC("special: can't find orig instruction",
 727                                   special_alt->orig_sec, special_alt->orig_off);
 728                         ret = -1;
 729                         goto out;
 730                 }
 731
 732                 /* Ignore retpoline alternatives. */
 733                 if (orig_insn->ignore_alts)
 734                         continue;
 735
 736                 new_insn = NULL;
 737                 if (!special_alt->group || special_alt->new_len) {
 738                         new_insn = find_insn(file, special_alt->new_sec,
 739                                              special_alt->new_off);
 740                         if (!new_insn) {
 741                                 WARN_FUNC("special: can't find new instruction",
 742                                           special_alt->new_sec,
 743                                           special_alt->new_off);
 744                                 ret = -1;
 745                                 goto out;
 746                         }
 747                 }
 748
 749                 if (special_alt->group) {
 750                         ret = handle_group_alt(file, special_alt, orig_insn,
 751                                                &new_insn);
 752                         if (ret)
 753                                 goto out;
 754                 } else if (special_alt->jump_or_nop) {
 755                         ret = handle_jump_alt(file, special_alt, orig_insn,
 756                                               &new_insn);
 757                         if (ret)
 758                                 goto out;
 759                 }
 760
 761                 alt = malloc(sizeof(*alt));
 762                 if (!alt) {
 763                         WARN("malloc failed");
 764                         ret = -1;
 765                         goto out;
 766                 }
 767
 768                 alt->insn = new_insn;
 769                 list_add_tail(&alt->list, &orig_insn->alts);
 770
 771                 list_del(&special_alt->list);
 772                 free(special_alt);
 773         }
 774
 775 out:
 776         return ret;
 777 }
 778
 779 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 780                             struct instruction *insn, struct rela *table,
 781                             struct rela *next_table)
 782 {
 783         struct rela *rela = table;
 784         struct instruction *alt_insn;
 785         struct alternative *alt;
 786
 787         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 788                 if (rela == next_table)
 789                         break;
 790
 791                 if (rela->sym->sec != insn->sec ||
 792                     rela->addend <= func->offset ||
 793                     rela->addend >= func->offset + func->len)
 794                         break;
 795
 796                 alt_insn = find_insn(file, insn->sec, rela->addend);
 797                 if (!alt_insn) {
 798                         WARN("%s: can't find instruction at %s+0x%x",
 799                              file->rodata->rela->name, insn->sec->name,
 800                              rela->addend);
 801                         return -1;
 802                 }
 803
 804                 alt = malloc(sizeof(*alt));
 805                 if (!alt) {
 806                         WARN("malloc failed");
 807                         return -1;
 808                 }
 809
 810                 alt->insn = alt_insn;
 811                 list_add_tail(&alt->list, &insn->alts);
 812         }
 813
 814         return 0;
 815 }
 816
 817 /*
 818  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 819  * .rodata associated with it.
 820  *
 821  * There are 3 basic patterns:
 822  *
 823  * 1. jmpq *[rodata addr](,%reg,8)
 824  *
 825  *    This is the most common case by far.  It jumps to an address in a simple
 826  *    jump table which is stored in .rodata.
 827  *
 828  * 2. jmpq *[rodata addr](%rip)
 829  *
 830  *    This is caused by a rare GCC quirk, currently only seen in three driver
 831  *    functions in the kernel, only with certain obscure non-distro configs.
 832  *
 833  *    As part of an optimization, GCC makes a copy of an existing switch jump
 834  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 835  *    jump) to use a single entry in the table.  The rest of the jump table and
 836  *    some of its jump targets remain as dead code.
 837  *
 838  *    In such a case we can just crudely ignore all unreachable instruction
 839  *    warnings for the entire object file.  Ideally we would just ignore them
 840  *    for the function, but that would require redesigning the code quite a
 841  *    bit.  And honestly that's just not worth doing: unreachable instruction
 842  *    warnings are of questionable value anyway, and this is such a rare issue.
 843  *
 844  * 3. mov [rodata addr],%reg1
 845  *    ... some instructions ...
 846  *    jmpq *(%reg1,%reg2,8)
 847  *
 848  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 849  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 850  *
 851  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 852  *    ensure the same register is used in the mov and jump instructions.
 853  */
 854 static struct rela *find_switch_table(struct objtool_file *file,
 855                                       struct symbol *func,
 856                                       struct instruction *insn)
 857 {
 858         struct rela *text_rela, *rodata_rela;
 859         struct instruction *orig_insn = insn;
 860
 861         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 862         if (text_rela && text_rela->sym == file->rodata->sym) {
 863                 /* case 1 */
 864                 rodata_rela = find_rela_by_dest(file->rodata,
 865                                                 text_rela->addend);
 866                 if (rodata_rela)
 867                         return rodata_rela;
 868
 869                 /* case 2 */
 870                 rodata_rela = find_rela_by_dest(file->rodata,
 871                                                 text_rela->addend + 4);
 872                 if (!rodata_rela)
 873                         return NULL;
 874                 file->ignore_unreachables = true;
 875                 return rodata_rela;
 876         }
 877
 878         /* case 3 */
 879         func_for_each_insn_continue_reverse(file, func, insn) {
 880                 if (insn->type == INSN_JUMP_DYNAMIC)
 881                         break;
 882
 883                 /* allow small jumps within the range */
 884                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
 885                     insn->jump_dest &&
 886                     (insn->jump_dest->offset <= insn->offset ||
 887                      insn->jump_dest->offset > orig_insn->offset))
 888                     break;
 889
 890                 /* look for a relocation which references .rodata */
 891                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 892                                                     insn->len);
 893                 if (!text_rela || text_rela->sym != file->rodata->sym)
 894                         continue;
 895
 896                 /*
 897                  * Make sure the .rodata address isn't associated with a
 898                  * symbol.  gcc jump tables are anonymous data.
 899                  */
 900                 if (find_symbol_containing(file->rodata, text_rela->addend))
 901                         continue;
 902
 903                 return find_rela_by_dest(file->rodata, text_rela->addend);
 904         }
 905
 906         return NULL;
 907 }
 908
 909 static int add_func_switch_tables(struct objtool_file *file,
 910                                   struct symbol *func)
 911 {
 912         struct instruction *insn, *prev_jump = NULL;
 913         struct rela *rela, *prev_rela = NULL;
 914         int ret;
 915
 916         func_for_each_insn(file, func, insn) {
 917                 if (insn->type != INSN_JUMP_DYNAMIC)
 918                         continue;
 919
 920                 rela = find_switch_table(file, func, insn);
 921                 if (!rela)
 922                         continue;
 923
 924                 /*
 925                  * We found a switch table, but we don't know yet how big it
 926                  * is.  Don't add it until we reach the end of the function or
 927                  * the beginning of another switch table in the same function.
 928                  */
 929                 if (prev_jump) {
 930                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 931                                                rela);
 932                         if (ret)
 933                                 return ret;
 934                 }
 935
 936                 prev_jump = insn;
 937                 prev_rela = rela;
 938         }
 939
 940         if (prev_jump) {
 941                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 942                 if (ret)
 943                         return ret;
 944         }
 945
 946         return 0;
 947 }
 948
 949 /*
 950  * For some switch statements, gcc generates a jump table in the .rodata
 951  * section which contains a list of addresses within the function to jump to.
 952  * This finds these jump tables and adds them to the insn->alts lists.
 953  */
 954 static int add_switch_table_alts(struct objtool_file *file)
 955 {
 956         struct section *sec;
 957         struct symbol *func;
 958         int ret;
 959
 960         if (!file->rodata || !file->rodata->rela)
 961                 return 0;
 962
 963         for_each_sec(file, sec) {
 964                 list_for_each_entry(func, &sec->symbol_list, list) {
 965                         if (func->type != STT_FUNC)
 966                                 continue;
 967
 968                         ret = add_func_switch_tables(file, func);
 969                         if (ret)
 970                                 return ret;
 971                 }
 972         }
 973
 974         return 0;
 975 }
 976
 977 static int read_unwind_hints(struct objtool_file *file)
 978 {
 979         struct section *sec, *relasec;
 980         struct rela *rela;
 981         struct unwind_hint *hint;
 982         struct instruction *insn;
 983         struct cfi_reg *cfa;
 984         int i;
 985
 986         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
 987         if (!sec)
 988                 return 0;
 989
 990         relasec = sec->rela;
 991         if (!relasec) {
 992                 WARN("missing .rela.discard.unwind_hints section");
 993                 return -1;
 994         }
 995
 996         if (sec->len % sizeof(struct unwind_hint)) {
 997                 WARN("struct unwind_hint size mismatch");
 998                 return -1;
 999         }
1000
1001         file->hints = true;
1002
1003         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1004                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1005
1006                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1007                 if (!rela) {
1008                         WARN("can't find rela for unwind_hints[%d]", i);
1009                         return -1;
1010                 }
1011
1012                 insn = find_insn(file, rela->sym->sec, rela->addend);
1013                 if (!insn) {
1014                         WARN("can't find insn for unwind_hints[%d]", i);
1015                         return -1;
1016                 }
1017
1018                 cfa = &insn->state.cfa;
1019
1020                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1021                         insn->save = true;
1022                         continue;
1023
1024                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1025                         insn->restore = true;
1026                         insn->hint = true;
1027                         continue;
1028                 }
1029
1030                 insn->hint = true;
1031
1032                 switch (hint->sp_reg) {
1033                 case ORC_REG_UNDEFINED:
1034                         cfa->base = CFI_UNDEFINED;
1035                         break;
1036                 case ORC_REG_SP:
1037                         cfa->base = CFI_SP;
1038                         break;
1039                 case ORC_REG_BP:
1040                         cfa->base = CFI_BP;
1041                         break;
1042                 case ORC_REG_SP_INDIRECT:
1043                         cfa->base = CFI_SP_INDIRECT;
1044                         break;
1045                 case ORC_REG_R10:
1046                         cfa->base = CFI_R10;
1047                         break;
1048                 case ORC_REG_R13:
1049                         cfa->base = CFI_R13;
1050                         break;
1051                 case ORC_REG_DI:
1052                         cfa->base = CFI_DI;
1053                         break;
1054                 case ORC_REG_DX:
1055                         cfa->base = CFI_DX;
1056                         break;
1057                 default:
1058                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1059                                   insn->sec, insn->offset, hint->sp_reg);
1060                         return -1;
1061                 }
1062
1063                 cfa->offset = hint->sp_offset;
1064                 insn->state.type = hint->type;
1065         }
1066
1067         return 0;
1068 }
1069
1070 static int decode_sections(struct objtool_file *file)
1071 {
1072         int ret;
1073
1074         ret = decode_instructions(file);
1075         if (ret)
1076                 return ret;
1077
1078         ret = add_dead_ends(file);
1079         if (ret)
1080                 return ret;
1081
1082         add_ignores(file);
1083
1084         ret = add_nospec_ignores(file);
1085         if (ret)
1086                 return ret;
1087
1088         ret = add_jump_destinations(file);
1089         if (ret)
1090                 return ret;
1091
1092         ret = add_call_destinations(file);
1093         if (ret)
1094                 return ret;
1095
1096         ret = add_special_section_alts(file);
1097         if (ret)
1098                 return ret;
1099
1100         ret = add_switch_table_alts(file);
1101         if (ret)
1102                 return ret;
1103
1104         ret = read_unwind_hints(file);
1105         if (ret)
1106                 return ret;
1107
1108         return 0;
1109 }
1110
1111 static bool is_fentry_call(struct instruction *insn)
1112 {
1113         if (insn->type == INSN_CALL &&
1114             insn->call_dest->type == STT_NOTYPE &&
1115             !strcmp(insn->call_dest->name, "__fentry__"))
1116                 return true;
1117
1118         return false;
1119 }
1120
1121 static bool has_modified_stack_frame(struct insn_state *state)
1122 {
1123         int i;
1124
1125         if (state->cfa.base != initial_func_cfi.cfa.base ||
1126             state->cfa.offset != initial_func_cfi.cfa.offset ||
1127             state->stack_size != initial_func_cfi.cfa.offset ||
1128             state->drap)
1129                 return true;
1130
1131         for (i = 0; i < CFI_NUM_REGS; i++)
1132                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1133                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1134                         return true;
1135
1136         return false;
1137 }
1138
1139 static bool has_valid_stack_frame(struct insn_state *state)
1140 {
1141         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1142             state->regs[CFI_BP].offset == -16)
1143                 return true;
1144
1145         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1146                 return true;
1147
1148         return false;
1149 }
1150
1151 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1152 {
1153         struct cfi_reg *cfa = &state->cfa;
1154         struct stack_op *op = &insn->stack_op;
1155
1156         if (cfa->base != CFI_SP)
1157                 return 0;
1158
1159         /* push */
1160         if (op->dest.type == OP_DEST_PUSH)
1161                 cfa->offset += 8;
1162
1163         /* pop */
1164         if (op->src.type == OP_SRC_POP)
1165                 cfa->offset -= 8;
1166
1167         /* add immediate to sp */
1168         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1169             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1170                 cfa->offset -= op->src.offset;
1171
1172         return 0;
1173 }
1174
1175 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1176                      int offset)
1177 {
1178         if (arch_callee_saved_reg(reg) &&
1179             state->regs[reg].base == CFI_UNDEFINED) {
1180                 state->regs[reg].base = base;
1181                 state->regs[reg].offset = offset;
1182         }
1183 }
1184
1185 static void restore_reg(struct insn_state *state, unsigned char reg)
1186 {
1187         state->regs[reg].base = CFI_UNDEFINED;
1188         state->regs[reg].offset = 0;
1189 }
1190
1191 /*
1192  * A note about DRAP stack alignment:
1193  *
1194  * GCC has the concept of a DRAP register, which is used to help keep track of
1195  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1196  * register.  The typical DRAP pattern is:
1197  *
1198  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1199  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1200  *   41 ff 72 f8                pushq  -0x8(%r10)
1201  *   55                         push   %rbp
1202  *   48 89 e5                   mov    %rsp,%rbp
1203  *                              (more pushes)
1204  *   41 52                      push   %r10
1205  *                              ...
1206  *   41 5a                      pop    %r10
1207  *                              (more pops)
1208  *   5d                         pop    %rbp
1209  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1210  *   c3                         retq
1211  *
1212  * There are some variations in the epilogues, like:
1213  *
1214  *   5b                         pop    %rbx
1215  *   41 5a                      pop    %r10
1216  *   41 5c                      pop    %r12
1217  *   41 5d                      pop    %r13
1218  *   41 5e                      pop    %r14
1219  *   c9                         leaveq
1220  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1221  *   c3                         retq
1222  *
1223  * and:
1224  *
1225  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1226  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1227  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1228  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1229  *   c9                         leaveq
1230  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1231  *   c3                         retq
1232  *
1233  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1234  * restored beforehand:
1235  *
1236  *   41 55                      push   %r13
1237  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1238  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1239  *                              ...
1240  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1241  *   41 5d                      pop    %r13
1242  *   c3                         retq
1243  */
1244 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1245 {
1246         struct stack_op *op = &insn->stack_op;
1247         struct cfi_reg *cfa = &state->cfa;
1248         struct cfi_reg *regs = state->regs;
1249
1250         /* stack operations don't make sense with an undefined CFA */
1251         if (cfa->base == CFI_UNDEFINED) {
1252                 if (insn->func) {
1253                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1254                         return -1;
1255                 }
1256                 return 0;
1257         }
1258
1259         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1260                 return update_insn_state_regs(insn, state);
1261
1262         switch (op->dest.type) {
1263
1264         case OP_DEST_REG:
1265                 switch (op->src.type) {
1266
1267                 case OP_SRC_REG:
1268                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1269                             cfa->base == CFI_SP &&
1270                             regs[CFI_BP].base == CFI_CFA &&
1271                             regs[CFI_BP].offset == -cfa->offset) {
1272
1273                                 /* mov %rsp, %rbp */
1274                                 cfa->base = op->dest.reg;
1275                                 state->bp_scratch = false;
1276                         }
1277
1278                         else if (op->src.reg == CFI_SP &&
1279                                  op->dest.reg == CFI_BP && state->drap) {
1280
1281                                 /* drap: mov %rsp, %rbp */
1282                                 regs[CFI_BP].base = CFI_BP;
1283                                 regs[CFI_BP].offset = -state->stack_size;
1284                                 state->bp_scratch = false;
1285                         }
1286
1287                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1288
1289                                 /*
1290                                  * mov %rsp, %reg
1291                                  *
1292                                  * This is needed for the rare case where GCC
1293                                  * does:
1294                                  *
1295                                  *   mov    %rsp, %rax
1296                                  *   ...
1297                                  *   mov    %rax, %rsp
1298                                  */
1299                                 state->vals[op->dest.reg].base = CFI_CFA;
1300                                 state->vals[op->dest.reg].offset = -state->stack_size;
1301                         }
1302
1303                         else if (op->dest.reg == cfa->base) {
1304
1305                                 /* mov %reg, %rsp */
1306                                 if (cfa->base == CFI_SP &&
1307                                     state->vals[op->src.reg].base == CFI_CFA) {
1308
1309                                         /*
1310                                          * This is needed for the rare case
1311                                          * where GCC does something dumb like:
1312                                          *
1313                                          *   lea    0x8(%rsp), %rcx
1314                                          *   ...
1315                                          *   mov    %rcx, %rsp
1316                                          */
1317                                         cfa->offset = -state->vals[op->src.reg].offset;
1318                                         state->stack_size = cfa->offset;
1319
1320                                 } else {
1321                                         cfa->base = CFI_UNDEFINED;
1322                                         cfa->offset = 0;
1323                                 }
1324                         }
1325
1326                         break;
1327
1328                 case OP_SRC_ADD:
1329                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1330
1331                                 /* add imm, %rsp */
1332                                 state->stack_size -= op->src.offset;
1333                                 if (cfa->base == CFI_SP)
1334                                         cfa->offset -= op->src.offset;
1335                                 break;
1336                         }
1337
1338                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1339
1340                                 /* lea disp(%rbp), %rsp */
1341                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1342                                 break;
1343                         }
1344
1345                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1346
1347                                 /* drap: lea disp(%rsp), %drap */
1348                                 state->drap_reg = op->dest.reg;
1349
1350                                 /*
1351                                  * lea disp(%rsp), %reg
1352                                  *
1353                                  * This is needed for the rare case where GCC
1354                                  * does something dumb like:
1355                                  *
1356                                  *   lea    0x8(%rsp), %rcx
1357                                  *   ...
1358                                  *   mov    %rcx, %rsp
1359                                  */
1360                                 state->vals[op->dest.reg].base = CFI_CFA;
1361                                 state->vals[op->dest.reg].offset = \
1362                                         -state->stack_size + op->src.offset;
1363
1364                                 break;
1365                         }
1366
1367                         if (state->drap && op->dest.reg == CFI_SP &&
1368                             op->src.reg == state->drap_reg) {
1369
1370                                  /* drap: lea disp(%drap), %rsp */
1371                                 cfa->base = CFI_SP;
1372                                 cfa->offset = state->stack_size = -op->src.offset;
1373                                 state->drap_reg = CFI_UNDEFINED;
1374                                 state->drap = false;
1375                                 break;
1376                         }
1377
1378                         if (op->dest.reg == state->cfa.base) {
1379                                 WARN_FUNC("unsupported stack register modification",
1380                                           insn->sec, insn->offset);
1381                                 return -1;
1382                         }
1383
1384                         break;
1385
1386                 case OP_SRC_AND:
1387                         if (op->dest.reg != CFI_SP ||
1388                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1389                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1390                                 WARN_FUNC("unsupported stack pointer realignment",
1391                                           insn->sec, insn->offset);
1392                                 return -1;
1393                         }
1394
1395                         if (state->drap_reg != CFI_UNDEFINED) {
1396                                 /* drap: and imm, %rsp */
1397                                 cfa->base = state->drap_reg;
1398                                 cfa->offset = state->stack_size = 0;
1399                                 state->drap = true;
1400                         }
1401
1402                         /*
1403                          * Older versions of GCC (4.8ish) realign the stack
1404                          * without DRAP, with a frame pointer.
1405                          */
1406
1407                         break;
1408
1409                 case OP_SRC_POP:
1410                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1411                             op->dest.reg == cfa->base) {
1412
1413                                 /* pop %rbp */
1414                                 cfa->base = CFI_SP;
1415                         }
1416
1417                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1418                             op->dest.type == OP_DEST_REG &&
1419                             op->dest.reg == state->drap_reg &&
1420                             state->drap_offset == -state->stack_size) {
1421
1422                                 /* drap: pop %drap */
1423                                 cfa->base = state->drap_reg;
1424                                 cfa->offset = 0;
1425                                 state->drap_offset = -1;
1426
1427                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1428
1429                                 /* pop %reg */
1430                                 restore_reg(state, op->dest.reg);
1431                         }
1432
1433                         state->stack_size -= 8;
1434                         if (cfa->base == CFI_SP)
1435                                 cfa->offset -= 8;
1436
1437                         break;
1438
1439                 case OP_SRC_REG_INDIRECT:
1440                         if (state->drap && op->src.reg == CFI_BP &&
1441                             op->src.offset == state->drap_offset) {
1442
1443                                 /* drap: mov disp(%rbp), %drap */
1444                                 cfa->base = state->drap_reg;
1445                                 cfa->offset = 0;
1446                                 state->drap_offset = -1;
1447                         }
1448
1449                         if (state->drap && op->src.reg == CFI_BP &&
1450                             op->src.offset == regs[op->dest.reg].offset) {
1451
1452                                 /* drap: mov disp(%rbp), %reg */
1453                                 restore_reg(state, op->dest.reg);
1454
1455                         } else if (op->src.reg == cfa->base &&
1456                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1457
1458                                 /* mov disp(%rbp), %reg */
1459                                 /* mov disp(%rsp), %reg */
1460                                 restore_reg(state, op->dest.reg);
1461                         }
1462
1463                         break;
1464
1465                 default:
1466                         WARN_FUNC("unknown stack-related instruction",
1467                                   insn->sec, insn->offset);
1468                         return -1;
1469                 }
1470
1471                 break;
1472
1473         case OP_DEST_PUSH:
1474                 state->stack_size += 8;
1475                 if (cfa->base == CFI_SP)
1476                         cfa->offset += 8;
1477
1478                 if (op->src.type != OP_SRC_REG)
1479                         break;
1480
1481                 if (state->drap) {
1482                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1483
1484                                 /* drap: push %drap */
1485                                 cfa->base = CFI_BP_INDIRECT;
1486                                 cfa->offset = -state->stack_size;
1487
1488                                 /* save drap so we know when to restore it */
1489                                 state->drap_offset = -state->stack_size;
1490
1491                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1492
1493                                 /* drap: push %rbp */
1494                                 state->stack_size = 0;
1495
1496                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1497
1498                                 /* drap: push %reg */
1499                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1500                         }
1501
1502                 } else {
1503
1504                         /* push %reg */
1505                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1506                 }
1507
1508                 /* detect when asm code uses rbp as a scratch register */
1509                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1510                     cfa->base != CFI_BP)
1511                         state->bp_scratch = true;
1512                 break;
1513
1514         case OP_DEST_REG_INDIRECT:
1515
1516                 if (state->drap) {
1517                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1518
1519                                 /* drap: mov %drap, disp(%rbp) */
1520                                 cfa->base = CFI_BP_INDIRECT;
1521                                 cfa->offset = op->dest.offset;
1522
1523                                 /* save drap offset so we know when to restore it */
1524                                 state->drap_offset = op->dest.offset;
1525                         }
1526
1527                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1528
1529                                 /* drap: mov reg, disp(%rbp) */
1530                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1531                         }
1532
1533                 } else if (op->dest.reg == cfa->base) {
1534
1535                         /* mov reg, disp(%rbp) */
1536                         /* mov reg, disp(%rsp) */
1537                         save_reg(state, op->src.reg, CFI_CFA,
1538                                  op->dest.offset - state->cfa.offset);
1539                 }
1540
1541                 break;
1542
1543         case OP_DEST_LEAVE:
1544                 if ((!state->drap && cfa->base != CFI_BP) ||
1545                     (state->drap && cfa->base != state->drap_reg)) {
1546                         WARN_FUNC("leave instruction with modified stack frame",
1547                                   insn->sec, insn->offset);
1548                         return -1;
1549                 }
1550
1551                 /* leave (mov %rbp, %rsp; pop %rbp) */
1552
1553                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1554                 restore_reg(state, CFI_BP);
1555
1556                 if (!state->drap) {
1557                         cfa->base = CFI_SP;
1558                         cfa->offset -= 8;
1559                 }
1560
1561                 break;
1562
1563         case OP_DEST_MEM:
1564                 if (op->src.type != OP_SRC_POP) {
1565                         WARN_FUNC("unknown stack-related memory operation",
1566                                   insn->sec, insn->offset);
1567                         return -1;
1568                 }
1569
1570                 /* pop mem */
1571                 state->stack_size -= 8;
1572                 if (cfa->base == CFI_SP)
1573                         cfa->offset -= 8;
1574
1575                 break;
1576
1577         default:
1578                 WARN_FUNC("unknown stack-related instruction",
1579                           insn->sec, insn->offset);
1580                 return -1;
1581         }
1582
1583         return 0;
1584 }
1585
1586 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1587 {
1588         struct insn_state *state1 = &insn->state, *state2 = state;
1589         int i;
1590
1591         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1592                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1593                           insn->sec, insn->offset,
1594                           state1->cfa.base, state1->cfa.offset,
1595                           state2->cfa.base, state2->cfa.offset);
1596
1597         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1598                 for (i = 0; i < CFI_NUM_REGS; i++) {
1599                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1600                                     sizeof(struct cfi_reg)))
1601                                 continue;
1602
1603                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1604                                   insn->sec, insn->offset,
1605                                   i, state1->regs[i].base, state1->regs[i].offset,
1606                                   i, state2->regs[i].base, state2->regs[i].offset);
1607                         break;
1608                 }
1609
1610         } else if (state1->type != state2->type) {
1611                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1612                           insn->sec, insn->offset, state1->type, state2->type);
1613
1614         } else if (state1->drap != state2->drap ||
1615                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1616                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1617                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1618                           insn->sec, insn->offset,
1619                           state1->drap, state1->drap_reg, state1->drap_offset,
1620                           state2->drap, state2->drap_reg, state2->drap_offset);
1621
1622         } else
1623                 return true;
1624
1625         return false;
1626 }
1627
1628 /*
1629  * Follow the branch starting at the given instruction, and recursively follow
1630  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1631  * each instruction and validate all the rules described in
1632  * tools/objtool/Documentation/stack-validation.txt.
1633  */
1634 static int validate_branch(struct objtool_file *file, struct instruction *first,
1635                            struct insn_state state)
1636 {
1637         struct alternative *alt;
1638         struct instruction *insn, *next_insn;
1639         struct section *sec;
1640         struct symbol *func = NULL;
1641         int ret;
1642
1643         insn = first;
1644         sec = insn->sec;
1645
1646         if (insn->alt_group && list_empty(&insn->alts)) {
1647                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1648                           sec, insn->offset);
1649                 return 1;
1650         }
1651
1652         while (1) {
1653                 next_insn = next_insn_same_sec(file, insn);
1654
1655
1656                 if (file->c_file && func && insn->func && func != insn->func) {
1657                         WARN("%s() falls through to next function %s()",
1658                              func->name, insn->func->name);
1659                         return 1;
1660                 }
1661
1662                 if (insn->func)
1663                         func = insn->func;
1664
1665                 if (func && insn->ignore) {
1666                         WARN_FUNC("BUG: why am I validating an ignored function?",
1667                                   sec, insn->offset);
1668                         return 1;
1669                 }
1670
1671                 if (insn->visited) {
1672                         if (!insn->hint && !insn_state_match(insn, &state))
1673                                 return 1;
1674
1675                         return 0;
1676                 }
1677
1678                 if (insn->hint) {
1679                         if (insn->restore) {
1680                                 struct instruction *save_insn, *i;
1681
1682                                 i = insn;
1683                                 save_insn = NULL;
1684                                 func_for_each_insn_continue_reverse(file, func, i) {
1685                                         if (i->save) {
1686                                                 save_insn = i;
1687                                                 break;
1688                                         }
1689                                 }
1690
1691                                 if (!save_insn) {
1692                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1693                                                   sec, insn->offset);
1694                                         return 1;
1695                                 }
1696
1697                                 if (!save_insn->visited) {
1698                                         /*
1699                                          * Oops, no state to copy yet.
1700                                          * Hopefully we can reach this
1701                                          * instruction from another branch
1702                                          * after the save insn has been
1703                                          * visited.
1704                                          */
1705                                         if (insn == first)
1706                                                 return 0;
1707
1708                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1709                                                   sec, insn->offset);
1710                                         return 1;
1711                                 }
1712
1713                                 insn->state = save_insn->state;
1714                         }
1715
1716                         state = insn->state;
1717
1718                 } else
1719                         insn->state = state;
1720
1721                 insn->visited = true;
1722
1723                 list_for_each_entry(alt, &insn->alts, list) {
1724                         ret = validate_branch(file, alt->insn, state);
1725                         if (ret)
1726                                 return 1;
1727                 }
1728
1729                 switch (insn->type) {
1730
1731                 case INSN_RETURN:
1732                         if (func && has_modified_stack_frame(&state)) {
1733                                 WARN_FUNC("return with modified stack frame",
1734                                           sec, insn->offset);
1735                                 return 1;
1736                         }
1737
1738                         if (state.bp_scratch) {
1739                                 WARN("%s uses BP as a scratch register",
1740                                      insn->func->name);
1741                                 return 1;
1742                         }
1743
1744                         return 0;
1745
1746                 case INSN_CALL:
1747                         if (is_fentry_call(insn))
1748                                 break;
1749
1750                         ret = dead_end_function(file, insn->call_dest);
1751                         if (ret == 1)
1752                                 return 0;
1753                         if (ret == -1)
1754                                 return 1;
1755
1756                         /* fallthrough */
1757                 case INSN_CALL_DYNAMIC:
1758                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
1759                                 WARN_FUNC("call without frame pointer save/setup",
1760                                           sec, insn->offset);
1761                                 return 1;
1762                         }
1763                         break;
1764
1765                 case INSN_JUMP_CONDITIONAL:
1766                 case INSN_JUMP_UNCONDITIONAL:
1767                         if (insn->jump_dest &&
1768                             (!func || !insn->jump_dest->func ||
1769                              func == insn->jump_dest->func)) {
1770                                 ret = validate_branch(file, insn->jump_dest,
1771                                                       state);
1772                                 if (ret)
1773                                         return 1;
1774
1775                         } else if (func && has_modified_stack_frame(&state)) {
1776                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1777                                           sec, insn->offset);
1778                                 return 1;
1779                         }
1780
1781                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1782                                 return 0;
1783
1784                         break;
1785
1786                 case INSN_JUMP_DYNAMIC:
1787                         if (func && list_empty(&insn->alts) &&
1788                             has_modified_stack_frame(&state)) {
1789                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1790                                           sec, insn->offset);
1791                                 return 1;
1792                         }
1793
1794                         return 0;
1795
1796                 case INSN_CONTEXT_SWITCH:
1797                         if (func && (!next_insn || !next_insn->hint)) {
1798                                 WARN_FUNC("unsupported instruction in callable function",
1799                                           sec, insn->offset);
1800                                 return 1;
1801                         }
1802                         return 0;
1803
1804                 case INSN_STACK:
1805                         if (update_insn_state(insn, &state))
1806                                 return 1;
1807
1808                         break;
1809
1810                 default:
1811                         break;
1812                 }
1813
1814                 if (insn->dead_end)
1815                         return 0;
1816
1817                 if (!next_insn) {
1818                         if (state.cfa.base == CFI_UNDEFINED)
1819                                 return 0;
1820                         WARN("%s: unexpected end of section", sec->name);
1821                         return 1;
1822                 }
1823
1824                 insn = next_insn;
1825         }
1826
1827         return 0;
1828 }
1829
1830 static int validate_unwind_hints(struct objtool_file *file)
1831 {
1832         struct instruction *insn;
1833         int ret, warnings = 0;
1834         struct insn_state state;
1835
1836         if (!file->hints)
1837                 return 0;
1838
1839         clear_insn_state(&state);
1840
1841         for_each_insn(file, insn) {
1842                 if (insn->hint && !insn->visited) {
1843                         ret = validate_branch(file, insn, state);
1844                         warnings += ret;
1845                 }
1846         }
1847
1848         return warnings;
1849 }
1850
1851 static bool is_kasan_insn(struct instruction *insn)
1852 {
1853         return (insn->type == INSN_CALL &&
1854                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1855 }
1856
1857 static bool is_ubsan_insn(struct instruction *insn)
1858 {
1859         return (insn->type == INSN_CALL &&
1860                 !strcmp(insn->call_dest->name,
1861                         "__ubsan_handle_builtin_unreachable"));
1862 }
1863
1864 static bool ignore_unreachable_insn(struct instruction *insn)
1865 {
1866         int i;
1867
1868         if (insn->ignore || insn->type == INSN_NOP)
1869                 return true;
1870
1871         /*
1872          * Ignore any unused exceptions.  This can happen when a whitelisted
1873          * function has an exception table entry.
1874          *
1875          * Also ignore alternative replacement instructions.  This can happen
1876          * when a whitelisted function uses one of the ALTERNATIVE macros.
1877          */
1878         if (!strcmp(insn->sec->name, ".fixup") ||
1879             !strcmp(insn->sec->name, ".altinstr_replacement") ||
1880             !strcmp(insn->sec->name, ".altinstr_aux"))
1881                 return true;
1882
1883         /*
1884          * Check if this (or a subsequent) instruction is related to
1885          * CONFIG_UBSAN or CONFIG_KASAN.
1886          *
1887          * End the search at 5 instructions to avoid going into the weeds.
1888          */
1889         if (!insn->func)
1890                 return false;
1891         for (i = 0; i < 5; i++) {
1892
1893                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1894                         return true;
1895
1896                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1897                         insn = insn->jump_dest;
1898                         continue;
1899                 }
1900
1901                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
1902                         break;
1903                 insn = list_next_entry(insn, list);
1904         }
1905
1906         return false;
1907 }
1908
1909 static int validate_functions(struct objtool_file *file)
1910 {
1911         struct section *sec;
1912         struct symbol *func;
1913         struct instruction *insn;
1914         struct insn_state state;
1915         int ret, warnings = 0;
1916
1917         clear_insn_state(&state);
1918
1919         state.cfa = initial_func_cfi.cfa;
1920         memcpy(&state.regs, &initial_func_cfi.regs,
1921                CFI_NUM_REGS * sizeof(struct cfi_reg));
1922         state.stack_size = initial_func_cfi.cfa.offset;
1923
1924         for_each_sec(file, sec) {
1925                 list_for_each_entry(func, &sec->symbol_list, list) {
1926                         if (func->type != STT_FUNC)
1927                                 continue;
1928
1929                         insn = find_insn(file, sec, func->offset);
1930                         if (!insn || insn->ignore)
1931                                 continue;
1932
1933                         ret = validate_branch(file, insn, state);
1934                         warnings += ret;
1935                 }
1936         }
1937
1938         return warnings;
1939 }
1940
1941 static int validate_reachable_instructions(struct objtool_file *file)
1942 {
1943         struct instruction *insn;
1944
1945         if (file->ignore_unreachables)
1946                 return 0;
1947
1948         for_each_insn(file, insn) {
1949                 if (insn->visited || ignore_unreachable_insn(insn))
1950                         continue;
1951
1952                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
1953                 return 1;
1954         }
1955
1956         return 0;
1957 }
1958
1959 static void cleanup(struct objtool_file *file)
1960 {
1961         struct instruction *insn, *tmpinsn;
1962         struct alternative *alt, *tmpalt;
1963
1964         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1965                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1966                         list_del(&alt->list);
1967                         free(alt);
1968                 }
1969                 list_del(&insn->list);
1970                 hash_del(&insn->hash);
1971                 free(insn);
1972         }
1973         elf_close(file->elf);
1974 }
1975
1976 int check(const char *_objname, bool _no_fp, bool no_unreachable, bool orc)
1977 {
1978         struct objtool_file file;
1979         int ret, warnings = 0;
1980
1981         objname = _objname;
1982         no_fp = _no_fp;
1983
1984         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
1985         if (!file.elf)
1986                 return 1;
1987
1988         INIT_LIST_HEAD(&file.insn_list);
1989         hash_init(file.insn_hash);
1990         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
1991         file.rodata = find_section_by_name(file.elf, ".rodata");
1992         file.c_file = find_section_by_name(file.elf, ".comment");
1993         file.ignore_unreachables = no_unreachable;
1994         file.hints = false;
1995
1996         arch_initial_func_cfi_state(&initial_func_cfi);
1997
1998         ret = decode_sections(&file);
1999         if (ret < 0)
2000                 goto out;
2001         warnings += ret;
2002
2003         if (list_empty(&file.insn_list))
2004                 goto out;
2005
2006         ret = validate_functions(&file);
2007         if (ret < 0)
2008                 goto out;
2009         warnings += ret;
2010
2011         ret = validate_unwind_hints(&file);
2012         if (ret < 0)
2013                 goto out;
2014         warnings += ret;
2015
2016         if (!warnings) {
2017                 ret = validate_reachable_instructions(&file);
2018                 if (ret < 0)
2019                         goto out;
2020                 warnings += ret;
2021         }
2022
2023         if (orc) {
2024                 ret = create_orc(&file);
2025                 if (ret < 0)
2026                         goto out;
2027
2028                 ret = create_orc_sections(&file);
2029                 if (ret < 0)
2030                         goto out;
2031
2032                 ret = elf_write(file.elf);
2033                 if (ret < 0)
2034                         goto out;
2035         }
2036
2037 out:
2038         cleanup(&file);
2039
2040         /* ignore warnings for now until we get all the code cleaned up */
2041         if (ret || warnings)
2042                 return 0;
2043         return 0;
2044 }