tools/objtool/builtin-check.c

   1 /*
   2  * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
   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 /*
  19  * objtool check:
  20  *
  21  * This command analyzes every .o file and ensures the validity of its stack
  22  * trace metadata.  It enforces a set of rules on asm code and C inline
  23  * assembly code so that stack traces can be reliable.
  24  *
  25  * For more information, see tools/objtool/Documentation/stack-validation.txt.
  26  */
  27
  28 #include <string.h>
  29 #include <stdlib.h>
  30 #include <subcmd/parse-options.h>
  31
  32 #include "builtin.h"
  33 #include "elf.h"
  34 #include "special.h"
  35 #include "arch.h"
  36 #include "warn.h"
  37
  38 #include <linux/hashtable.h>
  39
  40 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
  41
  42 #define STATE_FP_SAVED          0x1
  43 #define STATE_FP_SETUP          0x2
  44 #define STATE_FENTRY            0x4
  45
  46 struct instruction {
  47         struct list_head list;
  48         struct hlist_node hash;
  49         struct section *sec;
  50         unsigned long offset;
  51         unsigned int len, state;
  52         unsigned char type;
  53         unsigned long immediate;
  54         bool alt_group, visited;
  55         struct symbol *call_dest;
  56         struct instruction *jump_dest;
  57         struct list_head alts;
  58         struct symbol *func;
  59 };
  60
  61 struct alternative {
  62         struct list_head list;
  63         struct instruction *insn;
  64 };
  65
  66 struct objtool_file {
  67         struct elf *elf;
  68         struct list_head insn_list;
  69         DECLARE_HASHTABLE(insn_hash, 16);
  70         struct section *rodata, *whitelist;
  71         bool ignore_unreachables, c_file;
  72 };
  73
  74 const char *objname;
  75 static bool nofp;
  76
  77 static struct instruction *find_insn(struct objtool_file *file,
  78                                      struct section *sec, unsigned long offset)
  79 {
  80         struct instruction *insn;
  81
  82         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  83                 if (insn->sec == sec && insn->offset == offset)
  84                         return insn;
  85
  86         return NULL;
  87 }
  88
  89 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  90                                               struct instruction *insn)
  91 {
  92         struct instruction *next = list_next_entry(insn, list);
  93
  94         if (&next->list == &file->insn_list || next->sec != insn->sec)
  95                 return NULL;
  96
  97         return next;
  98 }
  99
 100 #define for_each_insn(file, insn)                                       \
 101         list_for_each_entry(insn, &file->insn_list, list)
 102
 103 #define func_for_each_insn(file, func, insn)                            \
 104         for (insn = find_insn(file, func->sec, func->offset);           \
 105              insn && &insn->list != &file->insn_list &&                 \
 106                 insn->sec == func->sec &&                               \
 107                 insn->offset < func->offset + func->len;                \
 108              insn = list_next_entry(insn, list))
 109
 110 #define sec_for_each_insn_from(file, insn)                              \
 111         for (; insn; insn = next_insn_same_sec(file, insn))
 112
 113
 114 /*
 115  * Check if the function has been manually whitelisted with the
 116  * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
 117  * due to its use of a context switching instruction.
 118  */
 119 static bool ignore_func(struct objtool_file *file, struct symbol *func)
 120 {
 121         struct rela *rela;
 122         struct instruction *insn;
 123
 124         /* check for STACK_FRAME_NON_STANDARD */
 125         if (file->whitelist && file->whitelist->rela)
 126                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
 127                         if (rela->sym->type == STT_SECTION &&
 128                             rela->sym->sec == func->sec &&
 129                             rela->addend == func->offset)
 130                                 return true;
 131                         if (rela->sym->type == STT_FUNC && rela->sym == func)
 132                                 return true;
 133                 }
 134
 135         /* check if it has a context switching instruction */
 136         func_for_each_insn(file, func, insn)
 137                 if (insn->type == INSN_CONTEXT_SWITCH)
 138                         return true;
 139
 140         return false;
 141 }
 142
 143 /*
 144  * This checks to see if the given function is a "noreturn" function.
 145  *
 146  * For global functions which are outside the scope of this object file, we
 147  * have to keep a manual list of them.
 148  *
 149  * For local functions, we have to detect them manually by simply looking for
 150  * the lack of a return instruction.
 151  *
 152  * Returns:
 153  *  -1: error
 154  *   0: no dead end
 155  *   1: dead end
 156  */
 157 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 158                                int recursion)
 159 {
 160         int i;
 161         struct instruction *insn;
 162         bool empty = true;
 163
 164         /*
 165          * Unfortunately these have to be hard coded because the noreturn
 166          * attribute isn't provided in ELF data.
 167          */
 168         static const char * const global_noreturns[] = {
 169                 "__stack_chk_fail",
 170                 "panic",
 171                 "do_exit",
 172                 "__module_put_and_exit",
 173                 "complete_and_exit",
 174                 "kvm_spurious_fault",
 175                 "__reiserfs_panic",
 176                 "lbug_with_loc"
 177         };
 178
 179         if (func->bind == STB_WEAK)
 180                 return 0;
 181
 182         if (func->bind == STB_GLOBAL)
 183                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 184                         if (!strcmp(func->name, global_noreturns[i]))
 185                                 return 1;
 186
 187         if (!func->sec)
 188                 return 0;
 189
 190         func_for_each_insn(file, func, insn) {
 191                 empty = false;
 192
 193                 if (insn->type == INSN_RETURN)
 194                         return 0;
 195         }
 196
 197         if (empty)
 198                 return 0;
 199
 200         /*
 201          * A function can have a sibling call instead of a return.  In that
 202          * case, the function's dead-end status depends on whether the target
 203          * of the sibling call returns.
 204          */
 205         func_for_each_insn(file, func, insn) {
 206                 if (insn->sec != func->sec ||
 207                     insn->offset >= func->offset + func->len)
 208                         break;
 209
 210                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 211                         struct instruction *dest = insn->jump_dest;
 212                         struct symbol *dest_func;
 213
 214                         if (!dest)
 215                                 /* sibling call to another file */
 216                                 return 0;
 217
 218                         if (dest->sec != func->sec ||
 219                             dest->offset < func->offset ||
 220                             dest->offset >= func->offset + func->len) {
 221                                 /* local sibling call */
 222                                 dest_func = find_symbol_by_offset(dest->sec,
 223                                                                   dest->offset);
 224                                 if (!dest_func)
 225                                         continue;
 226
 227                                 if (recursion == 5) {
 228                                         WARN_FUNC("infinite recursion (objtool bug!)",
 229                                                   dest->sec, dest->offset);
 230                                         return -1;
 231                                 }
 232
 233                                 return __dead_end_function(file, dest_func,
 234                                                            recursion + 1);
 235                         }
 236                 }
 237
 238                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 239                         /* sibling call */
 240                         return 0;
 241         }
 242
 243         return 1;
 244 }
 245
 246 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 247 {
 248         return __dead_end_function(file, func, 0);
 249 }
 250
 251 /*
 252  * Call the arch-specific instruction decoder for all the instructions and add
 253  * them to the global instruction list.
 254  */
 255 static int decode_instructions(struct objtool_file *file)
 256 {
 257         struct section *sec;
 258         struct symbol *func;
 259         unsigned long offset;
 260         struct instruction *insn;
 261         int ret;
 262
 263         list_for_each_entry(sec, &file->elf->sections, list) {
 264
 265                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 266                         continue;
 267
 268                 for (offset = 0; offset < sec->len; offset += insn->len) {
 269                         insn = malloc(sizeof(*insn));
 270                         memset(insn, 0, sizeof(*insn));
 271
 272                         INIT_LIST_HEAD(&insn->alts);
 273                         insn->sec = sec;
 274                         insn->offset = offset;
 275
 276                         ret = arch_decode_instruction(file->elf, sec, offset,
 277                                                       sec->len - offset,
 278                                                       &insn->len, &insn->type,
 279                                                       &insn->immediate);
 280                         if (ret)
 281                                 return ret;
 282
 283                         if (!insn->type || insn->type > INSN_LAST) {
 284                                 WARN_FUNC("invalid instruction type %d",
 285                                           insn->sec, insn->offset, insn->type);
 286                                 return -1;
 287                         }
 288
 289                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 290                         list_add_tail(&insn->list, &file->insn_list);
 291                 }
 292
 293                 list_for_each_entry(func, &sec->symbol_list, list) {
 294                         if (func->type != STT_FUNC)
 295                                 continue;
 296
 297                         if (!find_insn(file, sec, func->offset)) {
 298                                 WARN("%s(): can't find starting instruction",
 299                                      func->name);
 300                                 return -1;
 301                         }
 302
 303                         func_for_each_insn(file, func, insn)
 304                                 if (!insn->func)
 305                                         insn->func = func;
 306                 }
 307         }
 308
 309         return 0;
 310 }
 311
 312 /*
 313  * Warnings shouldn't be reported for ignored functions.
 314  */
 315 static void add_ignores(struct objtool_file *file)
 316 {
 317         struct instruction *insn;
 318         struct section *sec;
 319         struct symbol *func;
 320
 321         list_for_each_entry(sec, &file->elf->sections, list) {
 322                 list_for_each_entry(func, &sec->symbol_list, list) {
 323                         if (func->type != STT_FUNC)
 324                                 continue;
 325
 326                         if (!ignore_func(file, func))
 327                                 continue;
 328
 329                         func_for_each_insn(file, func, insn)
 330                                 insn->visited = true;
 331                 }
 332         }
 333 }
 334
 335 /*
 336  * Find the destination instructions for all jumps.
 337  */
 338 static int add_jump_destinations(struct objtool_file *file)
 339 {
 340         struct instruction *insn;
 341         struct rela *rela;
 342         struct section *dest_sec;
 343         unsigned long dest_off;
 344
 345         for_each_insn(file, insn) {
 346                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 347                     insn->type != INSN_JUMP_UNCONDITIONAL)
 348                         continue;
 349
 350                 /* skip ignores */
 351                 if (insn->visited)
 352                         continue;
 353
 354                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 355                                                insn->len);
 356                 if (!rela) {
 357                         dest_sec = insn->sec;
 358                         dest_off = insn->offset + insn->len + insn->immediate;
 359                 } else if (rela->sym->type == STT_SECTION) {
 360                         dest_sec = rela->sym->sec;
 361                         dest_off = rela->addend + 4;
 362                 } else if (rela->sym->sec->idx) {
 363                         dest_sec = rela->sym->sec;
 364                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 365                 } else {
 366                         /* sibling call */
 367                         insn->jump_dest = 0;
 368                         continue;
 369                 }
 370
 371                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 372                 if (!insn->jump_dest) {
 373
 374                         /*
 375                          * This is a special case where an alt instruction
 376                          * jumps past the end of the section.  These are
 377                          * handled later in handle_group_alt().
 378                          */
 379                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 380                                 continue;
 381
 382                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 383                                   insn->sec, insn->offset, dest_sec->name,
 384                                   dest_off);
 385                         return -1;
 386                 }
 387         }
 388
 389         return 0;
 390 }
 391
 392 /*
 393  * Find the destination instructions for all calls.
 394  */
 395 static int add_call_destinations(struct objtool_file *file)
 396 {
 397         struct instruction *insn;
 398         unsigned long dest_off;
 399         struct rela *rela;
 400
 401         for_each_insn(file, insn) {
 402                 if (insn->type != INSN_CALL)
 403                         continue;
 404
 405                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 406                                                insn->len);
 407                 if (!rela) {
 408                         dest_off = insn->offset + insn->len + insn->immediate;
 409                         insn->call_dest = find_symbol_by_offset(insn->sec,
 410                                                                 dest_off);
 411                         if (!insn->call_dest) {
 412                                 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 413                                           insn->sec, insn->offset, dest_off);
 414                                 return -1;
 415                         }
 416                 } else if (rela->sym->type == STT_SECTION) {
 417                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 418                                                                 rela->addend+4);
 419                         if (!insn->call_dest ||
 420                             insn->call_dest->type != STT_FUNC) {
 421                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 422                                           insn->sec, insn->offset,
 423                                           rela->sym->sec->name,
 424                                           rela->addend + 4);
 425                                 return -1;
 426                         }
 427                 } else
 428                         insn->call_dest = rela->sym;
 429         }
 430
 431         return 0;
 432 }
 433
 434 /*
 435  * The .alternatives section requires some extra special care, over and above
 436  * what other special sections require:
 437  *
 438  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 439  *    instruction at the end so that validate_branch() skips all the original
 440  *    replaced instructions when validating the new instruction path.
 441  *
 442  * 2. An added wrinkle is that the new instruction length might be zero.  In
 443  *    that case the old instructions are replaced with noops.  We simulate that
 444  *    by creating a fake jump as the only new instruction.
 445  *
 446  * 3. In some cases, the alternative section includes an instruction which
 447  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 448  *    jumps' destinations to point back to .text rather than the end of the
 449  *    entry in .altinstr_replacement.
 450  *
 451  * 4. It has been requested that we don't validate the !POPCNT feature path
 452  *    which is a "very very small percentage of machines".
 453  */
 454 static int handle_group_alt(struct objtool_file *file,
 455                             struct special_alt *special_alt,
 456                             struct instruction *orig_insn,
 457                             struct instruction **new_insn)
 458 {
 459         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
 460         unsigned long dest_off;
 461
 462         last_orig_insn = NULL;
 463         insn = orig_insn;
 464         sec_for_each_insn_from(file, insn) {
 465                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 466                         break;
 467
 468                 if (special_alt->skip_orig)
 469                         insn->type = INSN_NOP;
 470
 471                 insn->alt_group = true;
 472                 last_orig_insn = insn;
 473         }
 474
 475         if (!next_insn_same_sec(file, last_orig_insn)) {
 476                 WARN("%s: don't know how to handle alternatives at end of section",
 477                      special_alt->orig_sec->name);
 478                 return -1;
 479         }
 480
 481         fake_jump = malloc(sizeof(*fake_jump));
 482         if (!fake_jump) {
 483                 WARN("malloc failed");
 484                 return -1;
 485         }
 486         memset(fake_jump, 0, sizeof(*fake_jump));
 487         INIT_LIST_HEAD(&fake_jump->alts);
 488         fake_jump->sec = special_alt->new_sec;
 489         fake_jump->offset = -1;
 490         fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 491         fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 492
 493         if (!special_alt->new_len) {
 494                 *new_insn = fake_jump;
 495                 return 0;
 496         }
 497
 498         last_new_insn = NULL;
 499         insn = *new_insn;
 500         sec_for_each_insn_from(file, insn) {
 501                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 502                         break;
 503
 504                 last_new_insn = insn;
 505
 506                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 507                     insn->type != INSN_JUMP_UNCONDITIONAL)
 508                         continue;
 509
 510                 if (!insn->immediate)
 511                         continue;
 512
 513                 dest_off = insn->offset + insn->len + insn->immediate;
 514                 if (dest_off == special_alt->new_off + special_alt->new_len)
 515                         insn->jump_dest = fake_jump;
 516
 517                 if (!insn->jump_dest) {
 518                         WARN_FUNC("can't find alternative jump destination",
 519                                   insn->sec, insn->offset);
 520                         return -1;
 521                 }
 522         }
 523
 524         if (!last_new_insn) {
 525                 WARN_FUNC("can't find last new alternative instruction",
 526                           special_alt->new_sec, special_alt->new_off);
 527                 return -1;
 528         }
 529
 530         list_add(&fake_jump->list, &last_new_insn->list);
 531
 532         return 0;
 533 }
 534
 535 /*
 536  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 537  * If the original instruction is a jump, make the alt entry an effective nop
 538  * by just skipping the original instruction.
 539  */
 540 static int handle_jump_alt(struct objtool_file *file,
 541                            struct special_alt *special_alt,
 542                            struct instruction *orig_insn,
 543                            struct instruction **new_insn)
 544 {
 545         if (orig_insn->type == INSN_NOP)
 546                 return 0;
 547
 548         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 549                 WARN_FUNC("unsupported instruction at jump label",
 550                           orig_insn->sec, orig_insn->offset);
 551                 return -1;
 552         }
 553
 554         *new_insn = list_next_entry(orig_insn, list);
 555         return 0;
 556 }
 557
 558 /*
 559  * Read all the special sections which have alternate instructions which can be
 560  * patched in or redirected to at runtime.  Each instruction having alternate
 561  * instruction(s) has them added to its insn->alts list, which will be
 562  * traversed in validate_branch().
 563  */
 564 static int add_special_section_alts(struct objtool_file *file)
 565 {
 566         struct list_head special_alts;
 567         struct instruction *orig_insn, *new_insn;
 568         struct special_alt *special_alt, *tmp;
 569         struct alternative *alt;
 570         int ret;
 571
 572         ret = special_get_alts(file->elf, &special_alts);
 573         if (ret)
 574                 return ret;
 575
 576         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 577                 alt = malloc(sizeof(*alt));
 578                 if (!alt) {
 579                         WARN("malloc failed");
 580                         ret = -1;
 581                         goto out;
 582                 }
 583
 584                 orig_insn = find_insn(file, special_alt->orig_sec,
 585                                       special_alt->orig_off);
 586                 if (!orig_insn) {
 587                         WARN_FUNC("special: can't find orig instruction",
 588                                   special_alt->orig_sec, special_alt->orig_off);
 589                         ret = -1;
 590                         goto out;
 591                 }
 592
 593                 new_insn = NULL;
 594                 if (!special_alt->group || special_alt->new_len) {
 595                         new_insn = find_insn(file, special_alt->new_sec,
 596                                              special_alt->new_off);
 597                         if (!new_insn) {
 598                                 WARN_FUNC("special: can't find new instruction",
 599                                           special_alt->new_sec,
 600                                           special_alt->new_off);
 601                                 ret = -1;
 602                                 goto out;
 603                         }
 604                 }
 605
 606                 if (special_alt->group) {
 607                         ret = handle_group_alt(file, special_alt, orig_insn,
 608                                                &new_insn);
 609                         if (ret)
 610                                 goto out;
 611                 } else if (special_alt->jump_or_nop) {
 612                         ret = handle_jump_alt(file, special_alt, orig_insn,
 613                                               &new_insn);
 614                         if (ret)
 615                                 goto out;
 616                 }
 617
 618                 alt->insn = new_insn;
 619                 list_add_tail(&alt->list, &orig_insn->alts);
 620
 621                 list_del(&special_alt->list);
 622                 free(special_alt);
 623         }
 624
 625 out:
 626         return ret;
 627 }
 628
 629 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 630                             struct instruction *insn, struct rela *table,
 631                             struct rela *next_table)
 632 {
 633         struct rela *rela = table;
 634         struct instruction *alt_insn;
 635         struct alternative *alt;
 636
 637         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 638                 if (rela == next_table)
 639                         break;
 640
 641                 if (rela->sym->sec != insn->sec ||
 642                     rela->addend <= func->offset ||
 643                     rela->addend >= func->offset + func->len)
 644                         break;
 645
 646                 alt_insn = find_insn(file, insn->sec, rela->addend);
 647                 if (!alt_insn) {
 648                         WARN("%s: can't find instruction at %s+0x%x",
 649                              file->rodata->rela->name, insn->sec->name,
 650                              rela->addend);
 651                         return -1;
 652                 }
 653
 654                 alt = malloc(sizeof(*alt));
 655                 if (!alt) {
 656                         WARN("malloc failed");
 657                         return -1;
 658                 }
 659
 660                 alt->insn = alt_insn;
 661                 list_add_tail(&alt->list, &insn->alts);
 662         }
 663
 664         return 0;
 665 }
 666
 667 static int add_func_switch_tables(struct objtool_file *file,
 668                                   struct symbol *func)
 669 {
 670         struct instruction *insn, *prev_jump;
 671         struct rela *text_rela, *rodata_rela, *prev_rela = NULL;
 672         int ret;
 673
 674         prev_jump = NULL;
 675
 676         func_for_each_insn(file, func, insn) {
 677                 if (insn->type != INSN_JUMP_DYNAMIC)
 678                         continue;
 679
 680                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 681                                                     insn->len);
 682                 if (!text_rela || text_rela->sym != file->rodata->sym)
 683                         continue;
 684
 685                 /* common case: jmpq *[addr](,%rax,8) */
 686                 rodata_rela = find_rela_by_dest(file->rodata,
 687                                                 text_rela->addend);
 688
 689                 /*
 690                  * rare case:   jmpq *[addr](%rip)
 691                  *
 692                  * This check is for a rare gcc quirk, currently only seen in
 693                  * three driver functions in the kernel, only with certain
 694                  * obscure non-distro configs.
 695                  *
 696                  * As part of an optimization, gcc makes a copy of an existing
 697                  * switch jump table, modifies it, and then hard-codes the jump
 698                  * (albeit with an indirect jump) to use a single entry in the
 699                  * table.  The rest of the jump table and some of its jump
 700                  * targets remain as dead code.
 701                  *
 702                  * In such a case we can just crudely ignore all unreachable
 703                  * instruction warnings for the entire object file.  Ideally we
 704                  * would just ignore them for the function, but that would
 705                  * require redesigning the code quite a bit.  And honestly
 706                  * that's just not worth doing: unreachable instruction
 707                  * warnings are of questionable value anyway, and this is such
 708                  * a rare issue.
 709                  *
 710                  * kbuild reports:
 711                  * - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com
 712                  * - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com
 713                  * - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com
 714                  *
 715                  * gcc bug:
 716                  * - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604
 717                  */
 718                 if (!rodata_rela) {
 719                         rodata_rela = find_rela_by_dest(file->rodata,
 720                                                         text_rela->addend + 4);
 721                         if (rodata_rela)
 722                                 file->ignore_unreachables = true;
 723                 }
 724
 725                 if (!rodata_rela)
 726                         continue;
 727
 728                 /*
 729                  * We found a switch table, but we don't know yet how big it
 730                  * is.  Don't add it until we reach the end of the function or
 731                  * the beginning of another switch table in the same function.
 732                  */
 733                 if (prev_jump) {
 734                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 735                                                rodata_rela);
 736                         if (ret)
 737                                 return ret;
 738                 }
 739
 740                 prev_jump = insn;
 741                 prev_rela = rodata_rela;
 742         }
 743
 744         if (prev_jump) {
 745                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 746                 if (ret)
 747                         return ret;
 748         }
 749
 750         return 0;
 751 }
 752
 753 /*
 754  * For some switch statements, gcc generates a jump table in the .rodata
 755  * section which contains a list of addresses within the function to jump to.
 756  * This finds these jump tables and adds them to the insn->alts lists.
 757  */
 758 static int add_switch_table_alts(struct objtool_file *file)
 759 {
 760         struct section *sec;
 761         struct symbol *func;
 762         int ret;
 763
 764         if (!file->rodata || !file->rodata->rela)
 765                 return 0;
 766
 767         list_for_each_entry(sec, &file->elf->sections, list) {
 768                 list_for_each_entry(func, &sec->symbol_list, list) {
 769                         if (func->type != STT_FUNC)
 770                                 continue;
 771
 772                         ret = add_func_switch_tables(file, func);
 773                         if (ret)
 774                                 return ret;
 775                 }
 776         }
 777
 778         return 0;
 779 }
 780
 781 static int decode_sections(struct objtool_file *file)
 782 {
 783         int ret;
 784
 785         ret = decode_instructions(file);
 786         if (ret)
 787                 return ret;
 788
 789         add_ignores(file);
 790
 791         ret = add_jump_destinations(file);
 792         if (ret)
 793                 return ret;
 794
 795         ret = add_call_destinations(file);
 796         if (ret)
 797                 return ret;
 798
 799         ret = add_special_section_alts(file);
 800         if (ret)
 801                 return ret;
 802
 803         ret = add_switch_table_alts(file);
 804         if (ret)
 805                 return ret;
 806
 807         return 0;
 808 }
 809
 810 static bool is_fentry_call(struct instruction *insn)
 811 {
 812         if (insn->type == INSN_CALL &&
 813             insn->call_dest->type == STT_NOTYPE &&
 814             !strcmp(insn->call_dest->name, "__fentry__"))
 815                 return true;
 816
 817         return false;
 818 }
 819
 820 static bool has_modified_stack_frame(struct instruction *insn)
 821 {
 822         return (insn->state & STATE_FP_SAVED) ||
 823                (insn->state & STATE_FP_SETUP);
 824 }
 825
 826 static bool has_valid_stack_frame(struct instruction *insn)
 827 {
 828         return (insn->state & STATE_FP_SAVED) &&
 829                (insn->state & STATE_FP_SETUP);
 830 }
 831
 832 static unsigned int frame_state(unsigned long state)
 833 {
 834         return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
 835 }
 836
 837 /*
 838  * Follow the branch starting at the given instruction, and recursively follow
 839  * any other branches (jumps).  Meanwhile, track the frame pointer state at
 840  * each instruction and validate all the rules described in
 841  * tools/objtool/Documentation/stack-validation.txt.
 842  */
 843 static int validate_branch(struct objtool_file *file,
 844                            struct instruction *first, unsigned char first_state)
 845 {
 846         struct alternative *alt;
 847         struct instruction *insn;
 848         struct section *sec;
 849         struct symbol *func = NULL;
 850         unsigned char state;
 851         int ret;
 852
 853         insn = first;
 854         sec = insn->sec;
 855         state = first_state;
 856
 857         if (insn->alt_group && list_empty(&insn->alts)) {
 858                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
 859                           sec, insn->offset);
 860                 return 1;
 861         }
 862
 863         while (1) {
 864                 if (file->c_file && insn->func) {
 865                         if (func && func != insn->func) {
 866                                 WARN("%s() falls through to next function %s()",
 867                                      func->name, insn->func->name);
 868                                 return 1;
 869                         }
 870
 871                         func = insn->func;
 872                 }
 873
 874                 if (insn->visited) {
 875                         if (frame_state(insn->state) != frame_state(state)) {
 876                                 WARN_FUNC("frame pointer state mismatch",
 877                                           sec, insn->offset);
 878                                 return 1;
 879                         }
 880
 881                         return 0;
 882                 }
 883
 884                 insn->visited = true;
 885                 insn->state = state;
 886
 887                 list_for_each_entry(alt, &insn->alts, list) {
 888                         ret = validate_branch(file, alt->insn, state);
 889                         if (ret)
 890                                 return 1;
 891                 }
 892
 893                 switch (insn->type) {
 894
 895                 case INSN_FP_SAVE:
 896                         if (!nofp) {
 897                                 if (state & STATE_FP_SAVED) {
 898                                         WARN_FUNC("duplicate frame pointer save",
 899                                                   sec, insn->offset);
 900                                         return 1;
 901                                 }
 902                                 state |= STATE_FP_SAVED;
 903                         }
 904                         break;
 905
 906                 case INSN_FP_SETUP:
 907                         if (!nofp) {
 908                                 if (state & STATE_FP_SETUP) {
 909                                         WARN_FUNC("duplicate frame pointer setup",
 910                                                   sec, insn->offset);
 911                                         return 1;
 912                                 }
 913                                 state |= STATE_FP_SETUP;
 914                         }
 915                         break;
 916
 917                 case INSN_FP_RESTORE:
 918                         if (!nofp) {
 919                                 if (has_valid_stack_frame(insn))
 920                                         state &= ~STATE_FP_SETUP;
 921
 922                                 state &= ~STATE_FP_SAVED;
 923                         }
 924                         break;
 925
 926                 case INSN_RETURN:
 927                         if (!nofp && has_modified_stack_frame(insn)) {
 928                                 WARN_FUNC("return without frame pointer restore",
 929                                           sec, insn->offset);
 930                                 return 1;
 931                         }
 932                         return 0;
 933
 934                 case INSN_CALL:
 935                         if (is_fentry_call(insn)) {
 936                                 state |= STATE_FENTRY;
 937                                 break;
 938                         }
 939
 940                         ret = dead_end_function(file, insn->call_dest);
 941                         if (ret == 1)
 942                                 return 0;
 943                         if (ret == -1)
 944                                 return 1;
 945
 946                         /* fallthrough */
 947                 case INSN_CALL_DYNAMIC:
 948                         if (!nofp && !has_valid_stack_frame(insn)) {
 949                                 WARN_FUNC("call without frame pointer save/setup",
 950                                           sec, insn->offset);
 951                                 return 1;
 952                         }
 953                         break;
 954
 955                 case INSN_JUMP_CONDITIONAL:
 956                 case INSN_JUMP_UNCONDITIONAL:
 957                         if (insn->jump_dest) {
 958                                 ret = validate_branch(file, insn->jump_dest,
 959                                                       state);
 960                                 if (ret)
 961                                         return 1;
 962                         } else if (has_modified_stack_frame(insn)) {
 963                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
 964                                           sec, insn->offset);
 965                                 return 1;
 966                         } /* else it's a sibling call */
 967
 968                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 969                                 return 0;
 970
 971                         break;
 972
 973                 case INSN_JUMP_DYNAMIC:
 974                         if (list_empty(&insn->alts) &&
 975                             has_modified_stack_frame(insn)) {
 976                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
 977                                           sec, insn->offset);
 978                                 return 1;
 979                         }
 980
 981                         return 0;
 982
 983                 case INSN_BUG:
 984                         return 0;
 985
 986                 default:
 987                         break;
 988                 }
 989
 990                 insn = next_insn_same_sec(file, insn);
 991                 if (!insn) {
 992                         WARN("%s: unexpected end of section", sec->name);
 993                         return 1;
 994                 }
 995         }
 996
 997         return 0;
 998 }
 999
1000 static bool is_gcov_insn(struct instruction *insn)
1001 {
1002         struct rela *rela;
1003         struct section *sec;
1004         struct symbol *sym;
1005         unsigned long offset;
1006
1007         rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
1008         if (!rela)
1009                 return false;
1010
1011         if (rela->sym->type != STT_SECTION)
1012                 return false;
1013
1014         sec = rela->sym->sec;
1015         offset = rela->addend + insn->offset + insn->len - rela->offset;
1016
1017         list_for_each_entry(sym, &sec->symbol_list, list) {
1018                 if (sym->type != STT_OBJECT)
1019                         continue;
1020
1021                 if (offset >= sym->offset && offset < sym->offset + sym->len)
1022                         return (!memcmp(sym->name, "__gcov0.", 8));
1023         }
1024
1025         return false;
1026 }
1027
1028 static bool is_kasan_insn(struct instruction *insn)
1029 {
1030         return (insn->type == INSN_CALL &&
1031                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1032 }
1033
1034 static bool is_ubsan_insn(struct instruction *insn)
1035 {
1036         return (insn->type == INSN_CALL &&
1037                 !strcmp(insn->call_dest->name,
1038                         "__ubsan_handle_builtin_unreachable"));
1039 }
1040
1041 static bool ignore_unreachable_insn(struct symbol *func,
1042                                     struct instruction *insn)
1043 {
1044         int i;
1045
1046         if (insn->type == INSN_NOP)
1047                 return true;
1048
1049         if (is_gcov_insn(insn))
1050                 return true;
1051
1052         /*
1053          * Check if this (or a subsequent) instruction is related to
1054          * CONFIG_UBSAN or CONFIG_KASAN.
1055          *
1056          * End the search at 5 instructions to avoid going into the weeds.
1057          */
1058         for (i = 0; i < 5; i++) {
1059
1060                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1061                         return true;
1062
1063                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1064                         insn = insn->jump_dest;
1065                         continue;
1066                 }
1067
1068                 if (insn->offset + insn->len >= func->offset + func->len)
1069                         break;
1070                 insn = list_next_entry(insn, list);
1071         }
1072
1073         return false;
1074 }
1075
1076 static int validate_functions(struct objtool_file *file)
1077 {
1078         struct section *sec;
1079         struct symbol *func;
1080         struct instruction *insn;
1081         int ret, warnings = 0;
1082
1083         list_for_each_entry(sec, &file->elf->sections, list) {
1084                 list_for_each_entry(func, &sec->symbol_list, list) {
1085                         if (func->type != STT_FUNC)
1086                                 continue;
1087
1088                         insn = find_insn(file, sec, func->offset);
1089                         if (!insn)
1090                                 continue;
1091
1092                         ret = validate_branch(file, insn, 0);
1093                         warnings += ret;
1094                 }
1095         }
1096
1097         list_for_each_entry(sec, &file->elf->sections, list) {
1098                 list_for_each_entry(func, &sec->symbol_list, list) {
1099                         if (func->type != STT_FUNC)
1100                                 continue;
1101
1102                         func_for_each_insn(file, func, insn) {
1103                                 if (insn->visited)
1104                                         continue;
1105
1106                                 insn->visited = true;
1107
1108                                 if (file->ignore_unreachables || warnings ||
1109                                     ignore_unreachable_insn(func, insn))
1110                                         continue;
1111
1112                                 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1113                                 warnings++;
1114                         }
1115                 }
1116         }
1117
1118         return warnings;
1119 }
1120
1121 static int validate_uncallable_instructions(struct objtool_file *file)
1122 {
1123         struct instruction *insn;
1124         int warnings = 0;
1125
1126         for_each_insn(file, insn) {
1127                 if (!insn->visited && insn->type == INSN_RETURN) {
1128                         WARN_FUNC("return instruction outside of a callable function",
1129                                   insn->sec, insn->offset);
1130                         warnings++;
1131                 }
1132         }
1133
1134         return warnings;
1135 }
1136
1137 static void cleanup(struct objtool_file *file)
1138 {
1139         struct instruction *insn, *tmpinsn;
1140         struct alternative *alt, *tmpalt;
1141
1142         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1143                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1144                         list_del(&alt->list);
1145                         free(alt);
1146                 }
1147                 list_del(&insn->list);
1148                 hash_del(&insn->hash);
1149                 free(insn);
1150         }
1151         elf_close(file->elf);
1152 }
1153
1154 const char * const check_usage[] = {
1155         "objtool check [<options>] file.o",
1156         NULL,
1157 };
1158
1159 int cmd_check(int argc, const char **argv)
1160 {
1161         struct objtool_file file;
1162         int ret, warnings = 0;
1163
1164         const struct option options[] = {
1165                 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1166                 OPT_END(),
1167         };
1168
1169         argc = parse_options(argc, argv, options, check_usage, 0);
1170
1171         if (argc != 1)
1172                 usage_with_options(check_usage, options);
1173
1174         objname = argv[0];
1175
1176         file.elf = elf_open(objname);
1177         if (!file.elf) {
1178                 fprintf(stderr, "error reading elf file %s\n", objname);
1179                 return 1;
1180         }
1181
1182         INIT_LIST_HEAD(&file.insn_list);
1183         hash_init(file.insn_hash);
1184         file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
1185         file.rodata = find_section_by_name(file.elf, ".rodata");
1186         file.ignore_unreachables = false;
1187         file.c_file = find_section_by_name(file.elf, ".comment");
1188
1189         ret = decode_sections(&file);
1190         if (ret < 0)
1191                 goto out;
1192         warnings += ret;
1193
1194         ret = validate_functions(&file);
1195         if (ret < 0)
1196                 goto out;
1197         warnings += ret;
1198
1199         ret = validate_uncallable_instructions(&file);
1200         if (ret < 0)
1201                 goto out;
1202         warnings += ret;
1203
1204 out:
1205         cleanup(&file);
1206
1207         /* ignore warnings for now until we get all the code cleaned up */
1208         if (ret || warnings)
1209                 return 0;
1210         return 0;
1211 }