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