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 #include <linux/kernel.h>
  40
  41 #define STATE_FP_SAVED          0x1
  42 #define STATE_FP_SETUP          0x2
  43 #define STATE_FENTRY            0x4
  44
  45 struct instruction {
  46         struct list_head list;
  47         struct hlist_node hash;
  48         struct section *sec;
  49         unsigned long offset;
  50         unsigned int len, state;
  51         unsigned char type;
  52         unsigned long immediate;
  53         bool alt_group, visited, dead_end;
  54         struct symbol *call_dest;
  55         struct instruction *jump_dest;
  56         struct list_head alts;
  57         struct symbol *func;
  58 };
  59
  60 struct alternative {
  61         struct list_head list;
  62         struct instruction *insn;
  63 };
  64
  65 struct objtool_file {
  66         struct elf *elf;
  67         struct list_head insn_list;
  68         DECLARE_HASHTABLE(insn_hash, 16);
  69         struct section *rodata, *whitelist;
  70         bool ignore_unreachables, c_file;
  71 };
  72
  73 const char *objname;
  74 static bool nofp;
  75
  76 static struct instruction *find_insn(struct objtool_file *file,
  77                                      struct section *sec, unsigned long offset)
  78 {
  79         struct instruction *insn;
  80
  81         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  82                 if (insn->sec == sec && insn->offset == offset)
  83                         return insn;
  84
  85         return NULL;
  86 }
  87
  88 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  89                                               struct instruction *insn)
  90 {
  91         struct instruction *next = list_next_entry(insn, list);
  92
  93         if (&next->list == &file->insn_list || next->sec != insn->sec)
  94                 return NULL;
  95
  96         return next;
  97 }
  98
  99 static bool gcov_enabled(struct objtool_file *file)
 100 {
 101         struct section *sec;
 102         struct symbol *sym;
 103
 104         list_for_each_entry(sec, &file->elf->sections, list)
 105                 list_for_each_entry(sym, &sec->symbol_list, list)
 106                         if (!strncmp(sym->name, "__gcov_.", 8))
 107                                 return true;
 108
 109         return false;
 110 }
 111
 112 #define for_each_insn(file, insn)                                       \
 113         list_for_each_entry(insn, &file->insn_list, list)
 114
 115 #define func_for_each_insn(file, func, insn)                            \
 116         for (insn = find_insn(file, func->sec, func->offset);           \
 117              insn && &insn->list != &file->insn_list &&                 \
 118                 insn->sec == func->sec &&                               \
 119                 insn->offset < func->offset + func->len;                \
 120              insn = list_next_entry(insn, list))
 121
 122 #define func_for_each_insn_continue_reverse(file, func, insn)           \
 123         for (insn = list_prev_entry(insn, list);                        \
 124              &insn->list != &file->insn_list &&                         \
 125                 insn->sec == func->sec && insn->offset >= func->offset; \
 126              insn = list_prev_entry(insn, list))
 127
 128 #define sec_for_each_insn_from(file, insn)                              \
 129         for (; insn; insn = next_insn_same_sec(file, insn))
 130
 131
 132 /*
 133  * Check if the function has been manually whitelisted with the
 134  * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
 135  * due to its use of a context switching instruction.
 136  */
 137 static bool ignore_func(struct objtool_file *file, struct symbol *func)
 138 {
 139         struct rela *rela;
 140         struct instruction *insn;
 141
 142         /* check for STACK_FRAME_NON_STANDARD */
 143         if (file->whitelist && file->whitelist->rela)
 144                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
 145                         if (rela->sym->type == STT_SECTION &&
 146                             rela->sym->sec == func->sec &&
 147                             rela->addend == func->offset)
 148                                 return true;
 149                         if (rela->sym->type == STT_FUNC && rela->sym == func)
 150                                 return true;
 151                 }
 152
 153         /* check if it has a context switching instruction */
 154         func_for_each_insn(file, func, insn)
 155                 if (insn->type == INSN_CONTEXT_SWITCH)
 156                         return true;
 157
 158         return false;
 159 }
 160
 161 /*
 162  * This checks to see if the given function is a "noreturn" function.
 163  *
 164  * For global functions which are outside the scope of this object file, we
 165  * have to keep a manual list of them.
 166  *
 167  * For local functions, we have to detect them manually by simply looking for
 168  * the lack of a return instruction.
 169  *
 170  * Returns:
 171  *  -1: error
 172  *   0: no dead end
 173  *   1: dead end
 174  */
 175 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 176                                int recursion)
 177 {
 178         int i;
 179         struct instruction *insn;
 180         bool empty = true;
 181
 182         /*
 183          * Unfortunately these have to be hard coded because the noreturn
 184          * attribute isn't provided in ELF data.
 185          */
 186         static const char * const global_noreturns[] = {
 187                 "__stack_chk_fail",
 188                 "panic",
 189                 "do_exit",
 190                 "do_task_dead",
 191                 "__module_put_and_exit",
 192                 "complete_and_exit",
 193                 "kvm_spurious_fault",
 194                 "__reiserfs_panic",
 195                 "lbug_with_loc"
 196         };
 197
 198         if (func->bind == STB_WEAK)
 199                 return 0;
 200
 201         if (func->bind == STB_GLOBAL)
 202                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 203                         if (!strcmp(func->name, global_noreturns[i]))
 204                                 return 1;
 205
 206         if (!func->sec)
 207                 return 0;
 208
 209         func_for_each_insn(file, func, insn) {
 210                 empty = false;
 211
 212                 if (insn->type == INSN_RETURN)
 213                         return 0;
 214         }
 215
 216         if (empty)
 217                 return 0;
 218
 219         /*
 220          * A function can have a sibling call instead of a return.  In that
 221          * case, the function's dead-end status depends on whether the target
 222          * of the sibling call returns.
 223          */
 224         func_for_each_insn(file, func, insn) {
 225                 if (insn->sec != func->sec ||
 226                     insn->offset >= func->offset + func->len)
 227                         break;
 228
 229                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 230                         struct instruction *dest = insn->jump_dest;
 231                         struct symbol *dest_func;
 232
 233                         if (!dest)
 234                                 /* sibling call to another file */
 235                                 return 0;
 236
 237                         if (dest->sec != func->sec ||
 238                             dest->offset < func->offset ||
 239                             dest->offset >= func->offset + func->len) {
 240                                 /* local sibling call */
 241                                 dest_func = find_symbol_by_offset(dest->sec,
 242                                                                   dest->offset);
 243                                 if (!dest_func)
 244                                         continue;
 245
 246                                 if (recursion == 5) {
 247                                         WARN_FUNC("infinite recursion (objtool bug!)",
 248                                                   dest->sec, dest->offset);
 249                                         return -1;
 250                                 }
 251
 252                                 return __dead_end_function(file, dest_func,
 253                                                            recursion + 1);
 254                         }
 255                 }
 256
 257                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 258                         /* sibling call */
 259                         return 0;
 260         }
 261
 262         return 1;
 263 }
 264
 265 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 266 {
 267         return __dead_end_function(file, func, 0);
 268 }
 269
 270 /*
 271  * Call the arch-specific instruction decoder for all the instructions and add
 272  * them to the global instruction list.
 273  */
 274 static int decode_instructions(struct objtool_file *file)
 275 {
 276         struct section *sec;
 277         struct symbol *func;
 278         unsigned long offset;
 279         struct instruction *insn;
 280         int ret;
 281
 282         list_for_each_entry(sec, &file->elf->sections, list) {
 283
 284                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 285                         continue;
 286
 287                 for (offset = 0; offset < sec->len; offset += insn->len) {
 288                         insn = malloc(sizeof(*insn));
 289                         memset(insn, 0, sizeof(*insn));
 290
 291                         INIT_LIST_HEAD(&insn->alts);
 292                         insn->sec = sec;
 293                         insn->offset = offset;
 294
 295                         ret = arch_decode_instruction(file->elf, sec, offset,
 296                                                       sec->len - offset,
 297                                                       &insn->len, &insn->type,
 298                                                       &insn->immediate);
 299                         if (ret)
 300                                 return ret;
 301
 302                         if (!insn->type || insn->type > INSN_LAST) {
 303                                 WARN_FUNC("invalid instruction type %d",
 304                                           insn->sec, insn->offset, insn->type);
 305                                 return -1;
 306                         }
 307
 308                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 309                         list_add_tail(&insn->list, &file->insn_list);
 310                 }
 311
 312                 list_for_each_entry(func, &sec->symbol_list, list) {
 313                         if (func->type != STT_FUNC)
 314                                 continue;
 315
 316                         if (!find_insn(file, sec, func->offset)) {
 317                                 WARN("%s(): can't find starting instruction",
 318                                      func->name);
 319                                 return -1;
 320                         }
 321
 322                         func_for_each_insn(file, func, insn)
 323                                 if (!insn->func)
 324                                         insn->func = func;
 325                 }
 326         }
 327
 328         return 0;
 329 }
 330
 331 /*
 332  * Find all uses of the unreachable() macro, which are code path dead ends.
 333  */
 334 static int add_dead_ends(struct objtool_file *file)
 335 {
 336         struct section *sec;
 337         struct rela *rela;
 338         struct instruction *insn;
 339         bool found;
 340
 341         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 342         if (!sec)
 343                 return 0;
 344
 345         list_for_each_entry(rela, &sec->rela_list, list) {
 346                 if (rela->sym->type != STT_SECTION) {
 347                         WARN("unexpected relocation symbol type in %s", sec->name);
 348                         return -1;
 349                 }
 350                 insn = find_insn(file, rela->sym->sec, rela->addend);
 351                 if (insn)
 352                         insn = list_prev_entry(insn, list);
 353                 else if (rela->addend == rela->sym->sec->len) {
 354                         found = false;
 355                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 356                                 if (insn->sec == rela->sym->sec) {
 357                                         found = true;
 358                                         break;
 359                                 }
 360                         }
 361
 362                         if (!found) {
 363                                 WARN("can't find unreachable insn at %s+0x%x",
 364                                      rela->sym->sec->name, rela->addend);
 365                                 return -1;
 366                         }
 367                 } else {
 368                         WARN("can't find unreachable insn at %s+0x%x",
 369                              rela->sym->sec->name, rela->addend);
 370                         return -1;
 371                 }
 372
 373                 insn->dead_end = true;
 374         }
 375
 376         return 0;
 377 }
 378
 379 /*
 380  * Warnings shouldn't be reported for ignored functions.
 381  */
 382 static void add_ignores(struct objtool_file *file)
 383 {
 384         struct instruction *insn;
 385         struct section *sec;
 386         struct symbol *func;
 387
 388         list_for_each_entry(sec, &file->elf->sections, list) {
 389                 list_for_each_entry(func, &sec->symbol_list, list) {
 390                         if (func->type != STT_FUNC)
 391                                 continue;
 392
 393                         if (!ignore_func(file, func))
 394                                 continue;
 395
 396                         func_for_each_insn(file, func, insn)
 397                                 insn->visited = true;
 398                 }
 399         }
 400 }
 401
 402 /*
 403  * Find the destination instructions for all jumps.
 404  */
 405 static int add_jump_destinations(struct objtool_file *file)
 406 {
 407         struct instruction *insn;
 408         struct rela *rela;
 409         struct section *dest_sec;
 410         unsigned long dest_off;
 411
 412         for_each_insn(file, insn) {
 413                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 414                     insn->type != INSN_JUMP_UNCONDITIONAL)
 415                         continue;
 416
 417                 /* skip ignores */
 418                 if (insn->visited)
 419                         continue;
 420
 421                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 422                                                insn->len);
 423                 if (!rela) {
 424                         dest_sec = insn->sec;
 425                         dest_off = insn->offset + insn->len + insn->immediate;
 426                 } else if (rela->sym->type == STT_SECTION) {
 427                         dest_sec = rela->sym->sec;
 428                         dest_off = rela->addend + 4;
 429                 } else if (rela->sym->sec->idx) {
 430                         dest_sec = rela->sym->sec;
 431                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 432                 } else {
 433                         /* sibling call */
 434                         insn->jump_dest = 0;
 435                         continue;
 436                 }
 437
 438                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 439                 if (!insn->jump_dest) {
 440
 441                         /*
 442                          * This is a special case where an alt instruction
 443                          * jumps past the end of the section.  These are
 444                          * handled later in handle_group_alt().
 445                          */
 446                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 447                                 continue;
 448
 449                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 450                                   insn->sec, insn->offset, dest_sec->name,
 451                                   dest_off);
 452                         return -1;
 453                 }
 454         }
 455
 456         return 0;
 457 }
 458
 459 /*
 460  * Find the destination instructions for all calls.
 461  */
 462 static int add_call_destinations(struct objtool_file *file)
 463 {
 464         struct instruction *insn;
 465         unsigned long dest_off;
 466         struct rela *rela;
 467
 468         for_each_insn(file, insn) {
 469                 if (insn->type != INSN_CALL)
 470                         continue;
 471
 472                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 473                                                insn->len);
 474                 if (!rela) {
 475                         dest_off = insn->offset + insn->len + insn->immediate;
 476                         insn->call_dest = find_symbol_by_offset(insn->sec,
 477                                                                 dest_off);
 478                         if (!insn->call_dest) {
 479                                 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 480                                           insn->sec, insn->offset, dest_off);
 481                                 return -1;
 482                         }
 483                 } else if (rela->sym->type == STT_SECTION) {
 484                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 485                                                                 rela->addend+4);
 486                         if (!insn->call_dest ||
 487                             insn->call_dest->type != STT_FUNC) {
 488                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 489                                           insn->sec, insn->offset,
 490                                           rela->sym->sec->name,
 491                                           rela->addend + 4);
 492                                 return -1;
 493                         }
 494                 } else
 495                         insn->call_dest = rela->sym;
 496         }
 497
 498         return 0;
 499 }
 500
 501 /*
 502  * The .alternatives section requires some extra special care, over and above
 503  * what other special sections require:
 504  *
 505  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 506  *    instruction at the end so that validate_branch() skips all the original
 507  *    replaced instructions when validating the new instruction path.
 508  *
 509  * 2. An added wrinkle is that the new instruction length might be zero.  In
 510  *    that case the old instructions are replaced with noops.  We simulate that
 511  *    by creating a fake jump as the only new instruction.
 512  *
 513  * 3. In some cases, the alternative section includes an instruction which
 514  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 515  *    jumps' destinations to point back to .text rather than the end of the
 516  *    entry in .altinstr_replacement.
 517  *
 518  * 4. It has been requested that we don't validate the !POPCNT feature path
 519  *    which is a "very very small percentage of machines".
 520  */
 521 static int handle_group_alt(struct objtool_file *file,
 522                             struct special_alt *special_alt,
 523                             struct instruction *orig_insn,
 524                             struct instruction **new_insn)
 525 {
 526         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
 527         unsigned long dest_off;
 528
 529         last_orig_insn = NULL;
 530         insn = orig_insn;
 531         sec_for_each_insn_from(file, insn) {
 532                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 533                         break;
 534
 535                 if (special_alt->skip_orig)
 536                         insn->type = INSN_NOP;
 537
 538                 insn->alt_group = true;
 539                 last_orig_insn = insn;
 540         }
 541
 542         if (!next_insn_same_sec(file, last_orig_insn)) {
 543                 WARN("%s: don't know how to handle alternatives at end of section",
 544                      special_alt->orig_sec->name);
 545                 return -1;
 546         }
 547
 548         fake_jump = malloc(sizeof(*fake_jump));
 549         if (!fake_jump) {
 550                 WARN("malloc failed");
 551                 return -1;
 552         }
 553         memset(fake_jump, 0, sizeof(*fake_jump));
 554         INIT_LIST_HEAD(&fake_jump->alts);
 555         fake_jump->sec = special_alt->new_sec;
 556         fake_jump->offset = -1;
 557         fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 558         fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 559
 560         if (!special_alt->new_len) {
 561                 *new_insn = fake_jump;
 562                 return 0;
 563         }
 564
 565         last_new_insn = NULL;
 566         insn = *new_insn;
 567         sec_for_each_insn_from(file, insn) {
 568                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 569                         break;
 570
 571                 last_new_insn = insn;
 572
 573                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 574                     insn->type != INSN_JUMP_UNCONDITIONAL)
 575                         continue;
 576
 577                 if (!insn->immediate)
 578                         continue;
 579
 580                 dest_off = insn->offset + insn->len + insn->immediate;
 581                 if (dest_off == special_alt->new_off + special_alt->new_len)
 582                         insn->jump_dest = fake_jump;
 583
 584                 if (!insn->jump_dest) {
 585                         WARN_FUNC("can't find alternative jump destination",
 586                                   insn->sec, insn->offset);
 587                         return -1;
 588                 }
 589         }
 590
 591         if (!last_new_insn) {
 592                 WARN_FUNC("can't find last new alternative instruction",
 593                           special_alt->new_sec, special_alt->new_off);
 594                 return -1;
 595         }
 596
 597         list_add(&fake_jump->list, &last_new_insn->list);
 598
 599         return 0;
 600 }
 601
 602 /*
 603  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 604  * If the original instruction is a jump, make the alt entry an effective nop
 605  * by just skipping the original instruction.
 606  */
 607 static int handle_jump_alt(struct objtool_file *file,
 608                            struct special_alt *special_alt,
 609                            struct instruction *orig_insn,
 610                            struct instruction **new_insn)
 611 {
 612         if (orig_insn->type == INSN_NOP)
 613                 return 0;
 614
 615         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 616                 WARN_FUNC("unsupported instruction at jump label",
 617                           orig_insn->sec, orig_insn->offset);
 618                 return -1;
 619         }
 620
 621         *new_insn = list_next_entry(orig_insn, list);
 622         return 0;
 623 }
 624
 625 /*
 626  * Read all the special sections which have alternate instructions which can be
 627  * patched in or redirected to at runtime.  Each instruction having alternate
 628  * instruction(s) has them added to its insn->alts list, which will be
 629  * traversed in validate_branch().
 630  */
 631 static int add_special_section_alts(struct objtool_file *file)
 632 {
 633         struct list_head special_alts;
 634         struct instruction *orig_insn, *new_insn;
 635         struct special_alt *special_alt, *tmp;
 636         struct alternative *alt;
 637         int ret;
 638
 639         ret = special_get_alts(file->elf, &special_alts);
 640         if (ret)
 641                 return ret;
 642
 643         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 644                 alt = malloc(sizeof(*alt));
 645                 if (!alt) {
 646                         WARN("malloc failed");
 647                         ret = -1;
 648                         goto out;
 649                 }
 650
 651                 orig_insn = find_insn(file, special_alt->orig_sec,
 652                                       special_alt->orig_off);
 653                 if (!orig_insn) {
 654                         WARN_FUNC("special: can't find orig instruction",
 655                                   special_alt->orig_sec, special_alt->orig_off);
 656                         ret = -1;
 657                         goto out;
 658                 }
 659
 660                 new_insn = NULL;
 661                 if (!special_alt->group || special_alt->new_len) {
 662                         new_insn = find_insn(file, special_alt->new_sec,
 663                                              special_alt->new_off);
 664                         if (!new_insn) {
 665                                 WARN_FUNC("special: can't find new instruction",
 666                                           special_alt->new_sec,
 667                                           special_alt->new_off);
 668                                 ret = -1;
 669                                 goto out;
 670                         }
 671                 }
 672
 673                 if (special_alt->group) {
 674                         ret = handle_group_alt(file, special_alt, orig_insn,
 675                                                &new_insn);
 676                         if (ret)
 677                                 goto out;
 678                 } else if (special_alt->jump_or_nop) {
 679                         ret = handle_jump_alt(file, special_alt, orig_insn,
 680                                               &new_insn);
 681                         if (ret)
 682                                 goto out;
 683                 }
 684
 685                 alt->insn = new_insn;
 686                 list_add_tail(&alt->list, &orig_insn->alts);
 687
 688                 list_del(&special_alt->list);
 689                 free(special_alt);
 690         }
 691
 692 out:
 693         return ret;
 694 }
 695
 696 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 697                             struct instruction *insn, struct rela *table,
 698                             struct rela *next_table)
 699 {
 700         struct rela *rela = table;
 701         struct instruction *alt_insn;
 702         struct alternative *alt;
 703
 704         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 705                 if (rela == next_table)
 706                         break;
 707
 708                 if (rela->sym->sec != insn->sec ||
 709                     rela->addend <= func->offset ||
 710                     rela->addend >= func->offset + func->len)
 711                         break;
 712
 713                 alt_insn = find_insn(file, insn->sec, rela->addend);
 714                 if (!alt_insn) {
 715                         WARN("%s: can't find instruction at %s+0x%x",
 716                              file->rodata->rela->name, insn->sec->name,
 717                              rela->addend);
 718                         return -1;
 719                 }
 720
 721                 alt = malloc(sizeof(*alt));
 722                 if (!alt) {
 723                         WARN("malloc failed");
 724                         return -1;
 725                 }
 726
 727                 alt->insn = alt_insn;
 728                 list_add_tail(&alt->list, &insn->alts);
 729         }
 730
 731         return 0;
 732 }
 733
 734 /*
 735  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 736  * .rodata associated with it.
 737  *
 738  * There are 3 basic patterns:
 739  *
 740  * 1. jmpq *[rodata addr](,%reg,8)
 741  *
 742  *    This is the most common case by far.  It jumps to an address in a simple
 743  *    jump table which is stored in .rodata.
 744  *
 745  * 2. jmpq *[rodata addr](%rip)
 746  *
 747  *    This is caused by a rare GCC quirk, currently only seen in three driver
 748  *    functions in the kernel, only with certain obscure non-distro configs.
 749  *
 750  *    As part of an optimization, GCC makes a copy of an existing switch jump
 751  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 752  *    jump) to use a single entry in the table.  The rest of the jump table and
 753  *    some of its jump targets remain as dead code.
 754  *
 755  *    In such a case we can just crudely ignore all unreachable instruction
 756  *    warnings for the entire object file.  Ideally we would just ignore them
 757  *    for the function, but that would require redesigning the code quite a
 758  *    bit.  And honestly that's just not worth doing: unreachable instruction
 759  *    warnings are of questionable value anyway, and this is such a rare issue.
 760  *
 761  * 3. mov [rodata addr],%reg1
 762  *    ... some instructions ...
 763  *    jmpq *(%reg1,%reg2,8)
 764  *
 765  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 766  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 767  *
 768  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 769  *    ensure the same register is used in the mov and jump instructions.
 770  */
 771 static struct rela *find_switch_table(struct objtool_file *file,
 772                                       struct symbol *func,
 773                                       struct instruction *insn)
 774 {
 775         struct rela *text_rela, *rodata_rela;
 776         struct instruction *orig_insn = insn;
 777
 778         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 779         if (text_rela && text_rela->sym == file->rodata->sym) {
 780                 /* case 1 */
 781                 rodata_rela = find_rela_by_dest(file->rodata,
 782                                                 text_rela->addend);
 783                 if (rodata_rela)
 784                         return rodata_rela;
 785
 786                 /* case 2 */
 787                 rodata_rela = find_rela_by_dest(file->rodata,
 788                                                 text_rela->addend + 4);
 789                 if (!rodata_rela)
 790                         return NULL;
 791                 file->ignore_unreachables = true;
 792                 return rodata_rela;
 793         }
 794
 795         /* case 3 */
 796         func_for_each_insn_continue_reverse(file, func, insn) {
 797                 if (insn->type == INSN_JUMP_DYNAMIC)
 798                         break;
 799
 800                 /* allow small jumps within the range */
 801                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
 802                     insn->jump_dest &&
 803                     (insn->jump_dest->offset <= insn->offset ||
 804                      insn->jump_dest->offset > orig_insn->offset))
 805                     break;
 806
 807                 /* look for a relocation which references .rodata */
 808                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 809                                                     insn->len);
 810                 if (!text_rela || text_rela->sym != file->rodata->sym)
 811                         continue;
 812
 813                 /*
 814                  * Make sure the .rodata address isn't associated with a
 815                  * symbol.  gcc jump tables are anonymous data.
 816                  */
 817                 if (find_symbol_containing(file->rodata, text_rela->addend))
 818                         continue;
 819
 820                 return find_rela_by_dest(file->rodata, text_rela->addend);
 821         }
 822
 823         return NULL;
 824 }
 825
 826 static int add_func_switch_tables(struct objtool_file *file,
 827                                   struct symbol *func)
 828 {
 829         struct instruction *insn, *prev_jump = NULL;
 830         struct rela *rela, *prev_rela = NULL;
 831         int ret;
 832
 833         func_for_each_insn(file, func, insn) {
 834                 if (insn->type != INSN_JUMP_DYNAMIC)
 835                         continue;
 836
 837                 rela = find_switch_table(file, func, insn);
 838                 if (!rela)
 839                         continue;
 840
 841                 /*
 842                  * We found a switch table, but we don't know yet how big it
 843                  * is.  Don't add it until we reach the end of the function or
 844                  * the beginning of another switch table in the same function.
 845                  */
 846                 if (prev_jump) {
 847                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 848                                                rela);
 849                         if (ret)
 850                                 return ret;
 851                 }
 852
 853                 prev_jump = insn;
 854                 prev_rela = rela;
 855         }
 856
 857         if (prev_jump) {
 858                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 859                 if (ret)
 860                         return ret;
 861         }
 862
 863         return 0;
 864 }
 865
 866 /*
 867  * For some switch statements, gcc generates a jump table in the .rodata
 868  * section which contains a list of addresses within the function to jump to.
 869  * This finds these jump tables and adds them to the insn->alts lists.
 870  */
 871 static int add_switch_table_alts(struct objtool_file *file)
 872 {
 873         struct section *sec;
 874         struct symbol *func;
 875         int ret;
 876
 877         if (!file->rodata || !file->rodata->rela)
 878                 return 0;
 879
 880         list_for_each_entry(sec, &file->elf->sections, list) {
 881                 list_for_each_entry(func, &sec->symbol_list, list) {
 882                         if (func->type != STT_FUNC)
 883                                 continue;
 884
 885                         ret = add_func_switch_tables(file, func);
 886                         if (ret)
 887                                 return ret;
 888                 }
 889         }
 890
 891         return 0;
 892 }
 893
 894 static int decode_sections(struct objtool_file *file)
 895 {
 896         int ret;
 897
 898         ret = decode_instructions(file);
 899         if (ret)
 900                 return ret;
 901
 902         ret = add_dead_ends(file);
 903         if (ret)
 904                 return ret;
 905
 906         add_ignores(file);
 907
 908         ret = add_jump_destinations(file);
 909         if (ret)
 910                 return ret;
 911
 912         ret = add_call_destinations(file);
 913         if (ret)
 914                 return ret;
 915
 916         ret = add_special_section_alts(file);
 917         if (ret)
 918                 return ret;
 919
 920         ret = add_switch_table_alts(file);
 921         if (ret)
 922                 return ret;
 923
 924         return 0;
 925 }
 926
 927 static bool is_fentry_call(struct instruction *insn)
 928 {
 929         if (insn->type == INSN_CALL &&
 930             insn->call_dest->type == STT_NOTYPE &&
 931             !strcmp(insn->call_dest->name, "__fentry__"))
 932                 return true;
 933
 934         return false;
 935 }
 936
 937 static bool has_modified_stack_frame(struct instruction *insn)
 938 {
 939         return (insn->state & STATE_FP_SAVED) ||
 940                (insn->state & STATE_FP_SETUP);
 941 }
 942
 943 static bool has_valid_stack_frame(struct instruction *insn)
 944 {
 945         return (insn->state & STATE_FP_SAVED) &&
 946                (insn->state & STATE_FP_SETUP);
 947 }
 948
 949 static unsigned int frame_state(unsigned long state)
 950 {
 951         return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
 952 }
 953
 954 /*
 955  * Follow the branch starting at the given instruction, and recursively follow
 956  * any other branches (jumps).  Meanwhile, track the frame pointer state at
 957  * each instruction and validate all the rules described in
 958  * tools/objtool/Documentation/stack-validation.txt.
 959  */
 960 static int validate_branch(struct objtool_file *file,
 961                            struct instruction *first, unsigned char first_state)
 962 {
 963         struct alternative *alt;
 964         struct instruction *insn;
 965         struct section *sec;
 966         struct symbol *func = NULL;
 967         unsigned char state;
 968         int ret;
 969
 970         insn = first;
 971         sec = insn->sec;
 972         state = first_state;
 973
 974         if (insn->alt_group && list_empty(&insn->alts)) {
 975                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
 976                           sec, insn->offset);
 977                 return 1;
 978         }
 979
 980         while (1) {
 981                 if (file->c_file && insn->func) {
 982                         if (func && func != insn->func) {
 983                                 WARN("%s() falls through to next function %s()",
 984                                      func->name, insn->func->name);
 985                                 return 1;
 986                         }
 987
 988                         func = insn->func;
 989                 }
 990
 991                 if (insn->visited) {
 992                         if (frame_state(insn->state) != frame_state(state)) {
 993                                 WARN_FUNC("frame pointer state mismatch",
 994                                           sec, insn->offset);
 995                                 return 1;
 996                         }
 997
 998                         return 0;
 999                 }
1000
1001                 insn->visited = true;
1002                 insn->state = state;
1003
1004                 list_for_each_entry(alt, &insn->alts, list) {
1005                         ret = validate_branch(file, alt->insn, state);
1006                         if (ret)
1007                                 return 1;
1008                 }
1009
1010                 switch (insn->type) {
1011
1012                 case INSN_FP_SAVE:
1013                         if (!nofp) {
1014                                 if (state & STATE_FP_SAVED) {
1015                                         WARN_FUNC("duplicate frame pointer save",
1016                                                   sec, insn->offset);
1017                                         return 1;
1018                                 }
1019                                 state |= STATE_FP_SAVED;
1020                         }
1021                         break;
1022
1023                 case INSN_FP_SETUP:
1024                         if (!nofp) {
1025                                 if (state & STATE_FP_SETUP) {
1026                                         WARN_FUNC("duplicate frame pointer setup",
1027                                                   sec, insn->offset);
1028                                         return 1;
1029                                 }
1030                                 state |= STATE_FP_SETUP;
1031                         }
1032                         break;
1033
1034                 case INSN_FP_RESTORE:
1035                         if (!nofp) {
1036                                 if (has_valid_stack_frame(insn))
1037                                         state &= ~STATE_FP_SETUP;
1038
1039                                 state &= ~STATE_FP_SAVED;
1040                         }
1041                         break;
1042
1043                 case INSN_RETURN:
1044                         if (!nofp && has_modified_stack_frame(insn)) {
1045                                 WARN_FUNC("return without frame pointer restore",
1046                                           sec, insn->offset);
1047                                 return 1;
1048                         }
1049                         return 0;
1050
1051                 case INSN_CALL:
1052                         if (is_fentry_call(insn)) {
1053                                 state |= STATE_FENTRY;
1054                                 break;
1055                         }
1056
1057                         ret = dead_end_function(file, insn->call_dest);
1058                         if (ret == 1)
1059                                 return 0;
1060                         if (ret == -1)
1061                                 return 1;
1062
1063                         /* fallthrough */
1064                 case INSN_CALL_DYNAMIC:
1065                         if (!nofp && !has_valid_stack_frame(insn)) {
1066                                 WARN_FUNC("call without frame pointer save/setup",
1067                                           sec, insn->offset);
1068                                 return 1;
1069                         }
1070                         break;
1071
1072                 case INSN_JUMP_CONDITIONAL:
1073                 case INSN_JUMP_UNCONDITIONAL:
1074                         if (insn->jump_dest) {
1075                                 ret = validate_branch(file, insn->jump_dest,
1076                                                       state);
1077                                 if (ret)
1078                                         return 1;
1079                         } else if (has_modified_stack_frame(insn)) {
1080                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1081                                           sec, insn->offset);
1082                                 return 1;
1083                         } /* else it's a sibling call */
1084
1085                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1086                                 return 0;
1087
1088                         break;
1089
1090                 case INSN_JUMP_DYNAMIC:
1091                         if (list_empty(&insn->alts) &&
1092                             has_modified_stack_frame(insn)) {
1093                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1094                                           sec, insn->offset);
1095                                 return 1;
1096                         }
1097
1098                         return 0;
1099
1100                 default:
1101                         break;
1102                 }
1103
1104                 if (insn->dead_end)
1105                         return 0;
1106
1107                 insn = next_insn_same_sec(file, insn);
1108                 if (!insn) {
1109                         WARN("%s: unexpected end of section", sec->name);
1110                         return 1;
1111                 }
1112         }
1113
1114         return 0;
1115 }
1116
1117 static bool is_kasan_insn(struct instruction *insn)
1118 {
1119         return (insn->type == INSN_CALL &&
1120                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1121 }
1122
1123 static bool is_ubsan_insn(struct instruction *insn)
1124 {
1125         return (insn->type == INSN_CALL &&
1126                 !strcmp(insn->call_dest->name,
1127                         "__ubsan_handle_builtin_unreachable"));
1128 }
1129
1130 static bool ignore_unreachable_insn(struct symbol *func,
1131                                     struct instruction *insn)
1132 {
1133         int i;
1134
1135         if (insn->type == INSN_NOP)
1136                 return true;
1137
1138         /*
1139          * Check if this (or a subsequent) instruction is related to
1140          * CONFIG_UBSAN or CONFIG_KASAN.
1141          *
1142          * End the search at 5 instructions to avoid going into the weeds.
1143          */
1144         for (i = 0; i < 5; i++) {
1145
1146                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1147                         return true;
1148
1149                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1150                         insn = insn->jump_dest;
1151                         continue;
1152                 }
1153
1154                 if (insn->offset + insn->len >= func->offset + func->len)
1155                         break;
1156                 insn = list_next_entry(insn, list);
1157         }
1158
1159         return false;
1160 }
1161
1162 static int validate_functions(struct objtool_file *file)
1163 {
1164         struct section *sec;
1165         struct symbol *func;
1166         struct instruction *insn;
1167         int ret, warnings = 0;
1168
1169         list_for_each_entry(sec, &file->elf->sections, list) {
1170                 list_for_each_entry(func, &sec->symbol_list, list) {
1171                         if (func->type != STT_FUNC)
1172                                 continue;
1173
1174                         insn = find_insn(file, sec, func->offset);
1175                         if (!insn)
1176                                 continue;
1177
1178                         ret = validate_branch(file, insn, 0);
1179                         warnings += ret;
1180                 }
1181         }
1182
1183         list_for_each_entry(sec, &file->elf->sections, list) {
1184                 list_for_each_entry(func, &sec->symbol_list, list) {
1185                         if (func->type != STT_FUNC)
1186                                 continue;
1187
1188                         func_for_each_insn(file, func, insn) {
1189                                 if (insn->visited)
1190                                         continue;
1191
1192                                 insn->visited = true;
1193
1194                                 if (file->ignore_unreachables || warnings ||
1195                                     ignore_unreachable_insn(func, insn))
1196                                         continue;
1197
1198                                 /*
1199                                  * gcov produces a lot of unreachable
1200                                  * instructions.  If we get an unreachable
1201                                  * warning and the file has gcov enabled, just
1202                                  * ignore it, and all other such warnings for
1203                                  * the file.
1204                                  */
1205                                 if (!file->ignore_unreachables &&
1206                                     gcov_enabled(file)) {
1207                                         file->ignore_unreachables = true;
1208                                         continue;
1209                                 }
1210
1211                                 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1212                                 warnings++;
1213                         }
1214                 }
1215         }
1216
1217         return warnings;
1218 }
1219
1220 static int validate_uncallable_instructions(struct objtool_file *file)
1221 {
1222         struct instruction *insn;
1223         int warnings = 0;
1224
1225         for_each_insn(file, insn) {
1226                 if (!insn->visited && insn->type == INSN_RETURN) {
1227                         WARN_FUNC("return instruction outside of a callable function",
1228                                   insn->sec, insn->offset);
1229                         warnings++;
1230                 }
1231         }
1232
1233         return warnings;
1234 }
1235
1236 static void cleanup(struct objtool_file *file)
1237 {
1238         struct instruction *insn, *tmpinsn;
1239         struct alternative *alt, *tmpalt;
1240
1241         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1242                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1243                         list_del(&alt->list);
1244                         free(alt);
1245                 }
1246                 list_del(&insn->list);
1247                 hash_del(&insn->hash);
1248                 free(insn);
1249         }
1250         elf_close(file->elf);
1251 }
1252
1253 const char * const check_usage[] = {
1254         "objtool check [<options>] file.o",
1255         NULL,
1256 };
1257
1258 int cmd_check(int argc, const char **argv)
1259 {
1260         struct objtool_file file;
1261         int ret, warnings = 0;
1262
1263         const struct option options[] = {
1264                 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1265                 OPT_END(),
1266         };
1267
1268         argc = parse_options(argc, argv, options, check_usage, 0);
1269
1270         if (argc != 1)
1271                 usage_with_options(check_usage, options);
1272
1273         objname = argv[0];
1274
1275         file.elf = elf_open(objname);
1276         if (!file.elf) {
1277                 fprintf(stderr, "error reading elf file %s\n", objname);
1278                 return 1;
1279         }
1280
1281         INIT_LIST_HEAD(&file.insn_list);
1282         hash_init(file.insn_hash);
1283         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
1284         file.rodata = find_section_by_name(file.elf, ".rodata");
1285         file.ignore_unreachables = false;
1286         file.c_file = find_section_by_name(file.elf, ".comment");
1287
1288         ret = decode_sections(&file);
1289         if (ret < 0)
1290                 goto out;
1291         warnings += ret;
1292
1293         ret = validate_functions(&file);
1294         if (ret < 0)
1295                 goto out;
1296         warnings += ret;
1297
1298         ret = validate_uncallable_instructions(&file);
1299         if (ret < 0)
1300                 goto out;
1301         warnings += ret;
1302
1303 out:
1304         cleanup(&file);
1305
1306         /* ignore warnings for now until we get all the code cleaned up */
1307         if (ret || warnings)
1308                 return 0;
1309         return 0;
1310 }