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                 "fortify_panic",
 197         };
 198
 199         if (func->bind == STB_WEAK)
 200                 return 0;
 201
 202         if (func->bind == STB_GLOBAL)
 203                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 204                         if (!strcmp(func->name, global_noreturns[i]))
 205                                 return 1;
 206
 207         if (!func->sec)
 208                 return 0;
 209
 210         func_for_each_insn(file, func, insn) {
 211                 empty = false;
 212
 213                 if (insn->type == INSN_RETURN)
 214                         return 0;
 215         }
 216
 217         if (empty)
 218                 return 0;
 219
 220         /*
 221          * A function can have a sibling call instead of a return.  In that
 222          * case, the function's dead-end status depends on whether the target
 223          * of the sibling call returns.
 224          */
 225         func_for_each_insn(file, func, insn) {
 226                 if (insn->sec != func->sec ||
 227                     insn->offset >= func->offset + func->len)
 228                         break;
 229
 230                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 231                         struct instruction *dest = insn->jump_dest;
 232                         struct symbol *dest_func;
 233
 234                         if (!dest)
 235                                 /* sibling call to another file */
 236                                 return 0;
 237
 238                         if (dest->sec != func->sec ||
 239                             dest->offset < func->offset ||
 240                             dest->offset >= func->offset + func->len) {
 241                                 /* local sibling call */
 242                                 dest_func = find_symbol_by_offset(dest->sec,
 243                                                                   dest->offset);
 244                                 if (!dest_func)
 245                                         continue;
 246
 247                                 if (recursion == 5) {
 248                                         WARN_FUNC("infinite recursion (objtool bug!)",
 249                                                   dest->sec, dest->offset);
 250                                         return -1;
 251                                 }
 252
 253                                 return __dead_end_function(file, dest_func,
 254                                                            recursion + 1);
 255                         }
 256                 }
 257
 258                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 259                         /* sibling call */
 260                         return 0;
 261         }
 262
 263         return 1;
 264 }
 265
 266 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 267 {
 268         return __dead_end_function(file, func, 0);
 269 }
 270
 271 /*
 272  * Call the arch-specific instruction decoder for all the instructions and add
 273  * them to the global instruction list.
 274  */
 275 static int decode_instructions(struct objtool_file *file)
 276 {
 277         struct section *sec;
 278         struct symbol *func;
 279         unsigned long offset;
 280         struct instruction *insn;
 281         int ret;
 282
 283         list_for_each_entry(sec, &file->elf->sections, list) {
 284
 285                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 286                         continue;
 287
 288                 for (offset = 0; offset < sec->len; offset += insn->len) {
 289                         insn = malloc(sizeof(*insn));
 290                         memset(insn, 0, sizeof(*insn));
 291
 292                         INIT_LIST_HEAD(&insn->alts);
 293                         insn->sec = sec;
 294                         insn->offset = offset;
 295
 296                         ret = arch_decode_instruction(file->elf, sec, offset,
 297                                                       sec->len - offset,
 298                                                       &insn->len, &insn->type,
 299                                                       &insn->immediate);
 300                         if (ret)
 301                                 return ret;
 302
 303                         if (!insn->type || insn->type > INSN_LAST) {
 304                                 WARN_FUNC("invalid instruction type %d",
 305                                           insn->sec, insn->offset, insn->type);
 306                                 return -1;
 307                         }
 308
 309                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 310                         list_add_tail(&insn->list, &file->insn_list);
 311                 }
 312
 313                 list_for_each_entry(func, &sec->symbol_list, list) {
 314                         if (func->type != STT_FUNC)
 315                                 continue;
 316
 317                         if (!find_insn(file, sec, func->offset)) {
 318                                 WARN("%s(): can't find starting instruction",
 319                                      func->name);
 320                                 return -1;
 321                         }
 322
 323                         func_for_each_insn(file, func, insn)
 324                                 if (!insn->func)
 325                                         insn->func = func;
 326                 }
 327         }
 328
 329         return 0;
 330 }
 331
 332 /*
 333  * Find all uses of the unreachable() macro, which are code path dead ends.
 334  */
 335 static int add_dead_ends(struct objtool_file *file)
 336 {
 337         struct section *sec;
 338         struct rela *rela;
 339         struct instruction *insn;
 340         bool found;
 341
 342         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 343         if (!sec)
 344                 return 0;
 345
 346         list_for_each_entry(rela, &sec->rela_list, list) {
 347                 if (rela->sym->type != STT_SECTION) {
 348                         WARN("unexpected relocation symbol type in %s", sec->name);
 349                         return -1;
 350                 }
 351                 insn = find_insn(file, rela->sym->sec, rela->addend);
 352                 if (insn)
 353                         insn = list_prev_entry(insn, list);
 354                 else if (rela->addend == rela->sym->sec->len) {
 355                         found = false;
 356                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 357                                 if (insn->sec == rela->sym->sec) {
 358                                         found = true;
 359                                         break;
 360                                 }
 361                         }
 362
 363                         if (!found) {
 364                                 WARN("can't find unreachable insn at %s+0x%x",
 365                                      rela->sym->sec->name, rela->addend);
 366                                 return -1;
 367                         }
 368                 } else {
 369                         WARN("can't find unreachable insn at %s+0x%x",
 370                              rela->sym->sec->name, rela->addend);
 371                         return -1;
 372                 }
 373
 374                 insn->dead_end = true;
 375         }
 376
 377         return 0;
 378 }
 379
 380 /*
 381  * Warnings shouldn't be reported for ignored functions.
 382  */
 383 static void add_ignores(struct objtool_file *file)
 384 {
 385         struct instruction *insn;
 386         struct section *sec;
 387         struct symbol *func;
 388
 389         list_for_each_entry(sec, &file->elf->sections, list) {
 390                 list_for_each_entry(func, &sec->symbol_list, list) {
 391                         if (func->type != STT_FUNC)
 392                                 continue;
 393
 394                         if (!ignore_func(file, func))
 395                                 continue;
 396
 397                         func_for_each_insn(file, func, insn)
 398                                 insn->visited = true;
 399                 }
 400         }
 401 }
 402
 403 /*
 404  * Find the destination instructions for all jumps.
 405  */
 406 static int add_jump_destinations(struct objtool_file *file)
 407 {
 408         struct instruction *insn;
 409         struct rela *rela;
 410         struct section *dest_sec;
 411         unsigned long dest_off;
 412
 413         for_each_insn(file, insn) {
 414                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 415                     insn->type != INSN_JUMP_UNCONDITIONAL)
 416                         continue;
 417
 418                 /* skip ignores */
 419                 if (insn->visited)
 420                         continue;
 421
 422                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 423                                                insn->len);
 424                 if (!rela) {
 425                         dest_sec = insn->sec;
 426                         dest_off = insn->offset + insn->len + insn->immediate;
 427                 } else if (rela->sym->type == STT_SECTION) {
 428                         dest_sec = rela->sym->sec;
 429                         dest_off = rela->addend + 4;
 430                 } else if (rela->sym->sec->idx) {
 431                         dest_sec = rela->sym->sec;
 432                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 433                 } else {
 434                         /* sibling call */
 435                         insn->jump_dest = 0;
 436                         continue;
 437                 }
 438
 439                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 440                 if (!insn->jump_dest) {
 441
 442                         /*
 443                          * This is a special case where an alt instruction
 444                          * jumps past the end of the section.  These are
 445                          * handled later in handle_group_alt().
 446                          */
 447                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 448                                 continue;
 449
 450                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 451                                   insn->sec, insn->offset, dest_sec->name,
 452                                   dest_off);
 453                         return -1;
 454                 }
 455         }
 456
 457         return 0;
 458 }
 459
 460 /*
 461  * Find the destination instructions for all calls.
 462  */
 463 static int add_call_destinations(struct objtool_file *file)
 464 {
 465         struct instruction *insn;
 466         unsigned long dest_off;
 467         struct rela *rela;
 468
 469         for_each_insn(file, insn) {
 470                 if (insn->type != INSN_CALL)
 471                         continue;
 472
 473                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 474                                                insn->len);
 475                 if (!rela) {
 476                         dest_off = insn->offset + insn->len + insn->immediate;
 477                         insn->call_dest = find_symbol_by_offset(insn->sec,
 478                                                                 dest_off);
 479                         if (!insn->call_dest) {
 480                                 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 481                                           insn->sec, insn->offset, dest_off);
 482                                 return -1;
 483                         }
 484                 } else if (rela->sym->type == STT_SECTION) {
 485                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 486                                                                 rela->addend+4);
 487                         if (!insn->call_dest ||
 488                             insn->call_dest->type != STT_FUNC) {
 489                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 490                                           insn->sec, insn->offset,
 491                                           rela->sym->sec->name,
 492                                           rela->addend + 4);
 493                                 return -1;
 494                         }
 495                 } else
 496                         insn->call_dest = rela->sym;
 497         }
 498
 499         return 0;
 500 }
 501
 502 /*
 503  * The .alternatives section requires some extra special care, over and above
 504  * what other special sections require:
 505  *
 506  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 507  *    instruction at the end so that validate_branch() skips all the original
 508  *    replaced instructions when validating the new instruction path.
 509  *
 510  * 2. An added wrinkle is that the new instruction length might be zero.  In
 511  *    that case the old instructions are replaced with noops.  We simulate that
 512  *    by creating a fake jump as the only new instruction.
 513  *
 514  * 3. In some cases, the alternative section includes an instruction which
 515  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 516  *    jumps' destinations to point back to .text rather than the end of the
 517  *    entry in .altinstr_replacement.
 518  *
 519  * 4. It has been requested that we don't validate the !POPCNT feature path
 520  *    which is a "very very small percentage of machines".
 521  */
 522 static int handle_group_alt(struct objtool_file *file,
 523                             struct special_alt *special_alt,
 524                             struct instruction *orig_insn,
 525                             struct instruction **new_insn)
 526 {
 527         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
 528         unsigned long dest_off;
 529
 530         last_orig_insn = NULL;
 531         insn = orig_insn;
 532         sec_for_each_insn_from(file, insn) {
 533                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 534                         break;
 535
 536                 if (special_alt->skip_orig)
 537                         insn->type = INSN_NOP;
 538
 539                 insn->alt_group = true;
 540                 last_orig_insn = insn;
 541         }
 542
 543         if (!next_insn_same_sec(file, last_orig_insn)) {
 544                 WARN("%s: don't know how to handle alternatives at end of section",
 545                      special_alt->orig_sec->name);
 546                 return -1;
 547         }
 548
 549         fake_jump = malloc(sizeof(*fake_jump));
 550         if (!fake_jump) {
 551                 WARN("malloc failed");
 552                 return -1;
 553         }
 554         memset(fake_jump, 0, sizeof(*fake_jump));
 555         INIT_LIST_HEAD(&fake_jump->alts);
 556         fake_jump->sec = special_alt->new_sec;
 557         fake_jump->offset = -1;
 558         fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 559         fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 560
 561         if (!special_alt->new_len) {
 562                 *new_insn = fake_jump;
 563                 return 0;
 564         }
 565
 566         last_new_insn = NULL;
 567         insn = *new_insn;
 568         sec_for_each_insn_from(file, insn) {
 569                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 570                         break;
 571
 572                 last_new_insn = insn;
 573
 574                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 575                     insn->type != INSN_JUMP_UNCONDITIONAL)
 576                         continue;
 577
 578                 if (!insn->immediate)
 579                         continue;
 580
 581                 dest_off = insn->offset + insn->len + insn->immediate;
 582                 if (dest_off == special_alt->new_off + special_alt->new_len)
 583                         insn->jump_dest = fake_jump;
 584
 585                 if (!insn->jump_dest) {
 586                         WARN_FUNC("can't find alternative jump destination",
 587                                   insn->sec, insn->offset);
 588                         return -1;
 589                 }
 590         }
 591
 592         if (!last_new_insn) {
 593                 WARN_FUNC("can't find last new alternative instruction",
 594                           special_alt->new_sec, special_alt->new_off);
 595                 return -1;
 596         }
 597
 598         list_add(&fake_jump->list, &last_new_insn->list);
 599
 600         return 0;
 601 }
 602
 603 /*
 604  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 605  * If the original instruction is a jump, make the alt entry an effective nop
 606  * by just skipping the original instruction.
 607  */
 608 static int handle_jump_alt(struct objtool_file *file,
 609                            struct special_alt *special_alt,
 610                            struct instruction *orig_insn,
 611                            struct instruction **new_insn)
 612 {
 613         if (orig_insn->type == INSN_NOP)
 614                 return 0;
 615
 616         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 617                 WARN_FUNC("unsupported instruction at jump label",
 618                           orig_insn->sec, orig_insn->offset);
 619                 return -1;
 620         }
 621
 622         *new_insn = list_next_entry(orig_insn, list);
 623         return 0;
 624 }
 625
 626 /*
 627  * Read all the special sections which have alternate instructions which can be
 628  * patched in or redirected to at runtime.  Each instruction having alternate
 629  * instruction(s) has them added to its insn->alts list, which will be
 630  * traversed in validate_branch().
 631  */
 632 static int add_special_section_alts(struct objtool_file *file)
 633 {
 634         struct list_head special_alts;
 635         struct instruction *orig_insn, *new_insn;
 636         struct special_alt *special_alt, *tmp;
 637         struct alternative *alt;
 638         int ret;
 639
 640         ret = special_get_alts(file->elf, &special_alts);
 641         if (ret)
 642                 return ret;
 643
 644         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 645                 alt = malloc(sizeof(*alt));
 646                 if (!alt) {
 647                         WARN("malloc failed");
 648                         ret = -1;
 649                         goto out;
 650                 }
 651
 652                 orig_insn = find_insn(file, special_alt->orig_sec,
 653                                       special_alt->orig_off);
 654                 if (!orig_insn) {
 655                         WARN_FUNC("special: can't find orig instruction",
 656                                   special_alt->orig_sec, special_alt->orig_off);
 657                         ret = -1;
 658                         goto out;
 659                 }
 660
 661                 new_insn = NULL;
 662                 if (!special_alt->group || special_alt->new_len) {
 663                         new_insn = find_insn(file, special_alt->new_sec,
 664                                              special_alt->new_off);
 665                         if (!new_insn) {
 666                                 WARN_FUNC("special: can't find new instruction",
 667                                           special_alt->new_sec,
 668                                           special_alt->new_off);
 669                                 ret = -1;
 670                                 goto out;
 671                         }
 672                 }
 673
 674                 if (special_alt->group) {
 675                         ret = handle_group_alt(file, special_alt, orig_insn,
 676                                                &new_insn);
 677                         if (ret)
 678                                 goto out;
 679                 } else if (special_alt->jump_or_nop) {
 680                         ret = handle_jump_alt(file, special_alt, orig_insn,
 681                                               &new_insn);
 682                         if (ret)
 683                                 goto out;
 684                 }
 685
 686                 alt->insn = new_insn;
 687                 list_add_tail(&alt->list, &orig_insn->alts);
 688
 689                 list_del(&special_alt->list);
 690                 free(special_alt);
 691         }
 692
 693 out:
 694         return ret;
 695 }
 696
 697 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 698                             struct instruction *insn, struct rela *table,
 699                             struct rela *next_table)
 700 {
 701         struct rela *rela = table;
 702         struct instruction *alt_insn;
 703         struct alternative *alt;
 704
 705         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 706                 if (rela == next_table)
 707                         break;
 708
 709                 if (rela->sym->sec != insn->sec ||
 710                     rela->addend <= func->offset ||
 711                     rela->addend >= func->offset + func->len)
 712                         break;
 713
 714                 alt_insn = find_insn(file, insn->sec, rela->addend);
 715                 if (!alt_insn) {
 716                         WARN("%s: can't find instruction at %s+0x%x",
 717                              file->rodata->rela->name, insn->sec->name,
 718                              rela->addend);
 719                         return -1;
 720                 }
 721
 722                 alt = malloc(sizeof(*alt));
 723                 if (!alt) {
 724                         WARN("malloc failed");
 725                         return -1;
 726                 }
 727
 728                 alt->insn = alt_insn;
 729                 list_add_tail(&alt->list, &insn->alts);
 730         }
 731
 732         return 0;
 733 }
 734
 735 /*
 736  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 737  * .rodata associated with it.
 738  *
 739  * There are 3 basic patterns:
 740  *
 741  * 1. jmpq *[rodata addr](,%reg,8)
 742  *
 743  *    This is the most common case by far.  It jumps to an address in a simple
 744  *    jump table which is stored in .rodata.
 745  *
 746  * 2. jmpq *[rodata addr](%rip)
 747  *
 748  *    This is caused by a rare GCC quirk, currently only seen in three driver
 749  *    functions in the kernel, only with certain obscure non-distro configs.
 750  *
 751  *    As part of an optimization, GCC makes a copy of an existing switch jump
 752  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 753  *    jump) to use a single entry in the table.  The rest of the jump table and
 754  *    some of its jump targets remain as dead code.
 755  *
 756  *    In such a case we can just crudely ignore all unreachable instruction
 757  *    warnings for the entire object file.  Ideally we would just ignore them
 758  *    for the function, but that would require redesigning the code quite a
 759  *    bit.  And honestly that's just not worth doing: unreachable instruction
 760  *    warnings are of questionable value anyway, and this is such a rare issue.
 761  *
 762  * 3. mov [rodata addr],%reg1
 763  *    ... some instructions ...
 764  *    jmpq *(%reg1,%reg2,8)
 765  *
 766  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 767  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 768  *
 769  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 770  *    ensure the same register is used in the mov and jump instructions.
 771  */
 772 static struct rela *find_switch_table(struct objtool_file *file,
 773                                       struct symbol *func,
 774                                       struct instruction *insn)
 775 {
 776         struct rela *text_rela, *rodata_rela;
 777         struct instruction *orig_insn = insn;
 778
 779         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 780         if (text_rela && text_rela->sym == file->rodata->sym) {
 781                 /* case 1 */
 782                 rodata_rela = find_rela_by_dest(file->rodata,
 783                                                 text_rela->addend);
 784                 if (rodata_rela)
 785                         return rodata_rela;
 786
 787                 /* case 2 */
 788                 rodata_rela = find_rela_by_dest(file->rodata,
 789                                                 text_rela->addend + 4);
 790                 if (!rodata_rela)
 791                         return NULL;
 792                 file->ignore_unreachables = true;
 793                 return rodata_rela;
 794         }
 795
 796         /* case 3 */
 797         func_for_each_insn_continue_reverse(file, func, insn) {
 798                 if (insn->type == INSN_JUMP_DYNAMIC)
 799                         break;
 800
 801                 /* allow small jumps within the range */
 802                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
 803                     insn->jump_dest &&
 804                     (insn->jump_dest->offset <= insn->offset ||
 805                      insn->jump_dest->offset > orig_insn->offset))
 806                     break;
 807
 808                 /* look for a relocation which references .rodata */
 809                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 810                                                     insn->len);
 811                 if (!text_rela || text_rela->sym != file->rodata->sym)
 812                         continue;
 813
 814                 /*
 815                  * Make sure the .rodata address isn't associated with a
 816                  * symbol.  gcc jump tables are anonymous data.
 817                  */
 818                 if (find_symbol_containing(file->rodata, text_rela->addend))
 819                         continue;
 820
 821                 return find_rela_by_dest(file->rodata, text_rela->addend);
 822         }
 823
 824         return NULL;
 825 }
 826
 827 static int add_func_switch_tables(struct objtool_file *file,
 828                                   struct symbol *func)
 829 {
 830         struct instruction *insn, *prev_jump = NULL;
 831         struct rela *rela, *prev_rela = NULL;
 832         int ret;
 833
 834         func_for_each_insn(file, func, insn) {
 835                 if (insn->type != INSN_JUMP_DYNAMIC)
 836                         continue;
 837
 838                 rela = find_switch_table(file, func, insn);
 839                 if (!rela)
 840                         continue;
 841
 842                 /*
 843                  * We found a switch table, but we don't know yet how big it
 844                  * is.  Don't add it until we reach the end of the function or
 845                  * the beginning of another switch table in the same function.
 846                  */
 847                 if (prev_jump) {
 848                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 849                                                rela);
 850                         if (ret)
 851                                 return ret;
 852                 }
 853
 854                 prev_jump = insn;
 855                 prev_rela = rela;
 856         }
 857
 858         if (prev_jump) {
 859                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 860                 if (ret)
 861                         return ret;
 862         }
 863
 864         return 0;
 865 }
 866
 867 /*
 868  * For some switch statements, gcc generates a jump table in the .rodata
 869  * section which contains a list of addresses within the function to jump to.
 870  * This finds these jump tables and adds them to the insn->alts lists.
 871  */
 872 static int add_switch_table_alts(struct objtool_file *file)
 873 {
 874         struct section *sec;
 875         struct symbol *func;
 876         int ret;
 877
 878         if (!file->rodata || !file->rodata->rela)
 879                 return 0;
 880
 881         list_for_each_entry(sec, &file->elf->sections, list) {
 882                 list_for_each_entry(func, &sec->symbol_list, list) {
 883                         if (func->type != STT_FUNC)
 884                                 continue;
 885
 886                         ret = add_func_switch_tables(file, func);
 887                         if (ret)
 888                                 return ret;
 889                 }
 890         }
 891
 892         return 0;
 893 }
 894
 895 static int decode_sections(struct objtool_file *file)
 896 {
 897         int ret;
 898
 899         ret = decode_instructions(file);
 900         if (ret)
 901                 return ret;
 902
 903         ret = add_dead_ends(file);
 904         if (ret)
 905                 return ret;
 906
 907         add_ignores(file);
 908
 909         ret = add_jump_destinations(file);
 910         if (ret)
 911                 return ret;
 912
 913         ret = add_call_destinations(file);
 914         if (ret)
 915                 return ret;
 916
 917         ret = add_special_section_alts(file);
 918         if (ret)
 919                 return ret;
 920
 921         ret = add_switch_table_alts(file);
 922         if (ret)
 923                 return ret;
 924
 925         return 0;
 926 }
 927
 928 static bool is_fentry_call(struct instruction *insn)
 929 {
 930         if (insn->type == INSN_CALL &&
 931             insn->call_dest->type == STT_NOTYPE &&
 932             !strcmp(insn->call_dest->name, "__fentry__"))
 933                 return true;
 934
 935         return false;
 936 }
 937
 938 static bool has_modified_stack_frame(struct instruction *insn)
 939 {
 940         return (insn->state & STATE_FP_SAVED) ||
 941                (insn->state & STATE_FP_SETUP);
 942 }
 943
 944 static bool has_valid_stack_frame(struct instruction *insn)
 945 {
 946         return (insn->state & STATE_FP_SAVED) &&
 947                (insn->state & STATE_FP_SETUP);
 948 }
 949
 950 static unsigned int frame_state(unsigned long state)
 951 {
 952         return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
 953 }
 954
 955 /*
 956  * Follow the branch starting at the given instruction, and recursively follow
 957  * any other branches (jumps).  Meanwhile, track the frame pointer state at
 958  * each instruction and validate all the rules described in
 959  * tools/objtool/Documentation/stack-validation.txt.
 960  */
 961 static int validate_branch(struct objtool_file *file,
 962                            struct instruction *first, unsigned char first_state)
 963 {
 964         struct alternative *alt;
 965         struct instruction *insn;
 966         struct section *sec;
 967         struct symbol *func = NULL;
 968         unsigned char state;
 969         int ret;
 970
 971         insn = first;
 972         sec = insn->sec;
 973         state = first_state;
 974
 975         if (insn->alt_group && list_empty(&insn->alts)) {
 976                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
 977                           sec, insn->offset);
 978                 return 1;
 979         }
 980
 981         while (1) {
 982                 if (file->c_file && insn->func) {
 983                         if (func && func != insn->func) {
 984                                 WARN("%s() falls through to next function %s()",
 985                                      func->name, insn->func->name);
 986                                 return 1;
 987                         }
 988
 989                         func = insn->func;
 990                 }
 991
 992                 if (insn->visited) {
 993                         if (frame_state(insn->state) != frame_state(state)) {
 994                                 WARN_FUNC("frame pointer state mismatch",
 995                                           sec, insn->offset);
 996                                 return 1;
 997                         }
 998
 999                         return 0;
1000                 }
1001
1002                 insn->visited = true;
1003                 insn->state = state;
1004
1005                 list_for_each_entry(alt, &insn->alts, list) {
1006                         ret = validate_branch(file, alt->insn, state);
1007                         if (ret)
1008                                 return 1;
1009                 }
1010
1011                 switch (insn->type) {
1012
1013                 case INSN_FP_SAVE:
1014                         if (!nofp) {
1015                                 if (state & STATE_FP_SAVED) {
1016                                         WARN_FUNC("duplicate frame pointer save",
1017                                                   sec, insn->offset);
1018                                         return 1;
1019                                 }
1020                                 state |= STATE_FP_SAVED;
1021                         }
1022                         break;
1023
1024                 case INSN_FP_SETUP:
1025                         if (!nofp) {
1026                                 if (state & STATE_FP_SETUP) {
1027                                         WARN_FUNC("duplicate frame pointer setup",
1028                                                   sec, insn->offset);
1029                                         return 1;
1030                                 }
1031                                 state |= STATE_FP_SETUP;
1032                         }
1033                         break;
1034
1035                 case INSN_FP_RESTORE:
1036                         if (!nofp) {
1037                                 if (has_valid_stack_frame(insn))
1038                                         state &= ~STATE_FP_SETUP;
1039
1040                                 state &= ~STATE_FP_SAVED;
1041                         }
1042                         break;
1043
1044                 case INSN_RETURN:
1045                         if (!nofp && has_modified_stack_frame(insn)) {
1046                                 WARN_FUNC("return without frame pointer restore",
1047                                           sec, insn->offset);
1048                                 return 1;
1049                         }
1050                         return 0;
1051
1052                 case INSN_CALL:
1053                         if (is_fentry_call(insn)) {
1054                                 state |= STATE_FENTRY;
1055                                 break;
1056                         }
1057
1058                         ret = dead_end_function(file, insn->call_dest);
1059                         if (ret == 1)
1060                                 return 0;
1061                         if (ret == -1)
1062                                 return 1;
1063
1064                         /* fallthrough */
1065                 case INSN_CALL_DYNAMIC:
1066                         if (!nofp && !has_valid_stack_frame(insn)) {
1067                                 WARN_FUNC("call without frame pointer save/setup",
1068                                           sec, insn->offset);
1069                                 return 1;
1070                         }
1071                         break;
1072
1073                 case INSN_JUMP_CONDITIONAL:
1074                 case INSN_JUMP_UNCONDITIONAL:
1075                         if (insn->jump_dest) {
1076                                 ret = validate_branch(file, insn->jump_dest,
1077                                                       state);
1078                                 if (ret)
1079                                         return 1;
1080                         } else if (has_modified_stack_frame(insn)) {
1081                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1082                                           sec, insn->offset);
1083                                 return 1;
1084                         } /* else it's a sibling call */
1085
1086                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1087                                 return 0;
1088
1089                         break;
1090
1091                 case INSN_JUMP_DYNAMIC:
1092                         if (list_empty(&insn->alts) &&
1093                             has_modified_stack_frame(insn)) {
1094                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1095                                           sec, insn->offset);
1096                                 return 1;
1097                         }
1098
1099                         return 0;
1100
1101                 default:
1102                         break;
1103                 }
1104
1105                 if (insn->dead_end)
1106                         return 0;
1107
1108                 insn = next_insn_same_sec(file, insn);
1109                 if (!insn) {
1110                         WARN("%s: unexpected end of section", sec->name);
1111                         return 1;
1112                 }
1113         }
1114
1115         return 0;
1116 }
1117
1118 static bool is_kasan_insn(struct instruction *insn)
1119 {
1120         return (insn->type == INSN_CALL &&
1121                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1122 }
1123
1124 static bool is_ubsan_insn(struct instruction *insn)
1125 {
1126         return (insn->type == INSN_CALL &&
1127                 !strcmp(insn->call_dest->name,
1128                         "__ubsan_handle_builtin_unreachable"));
1129 }
1130
1131 static bool ignore_unreachable_insn(struct symbol *func,
1132                                     struct instruction *insn)
1133 {
1134         int i;
1135
1136         if (insn->type == INSN_NOP)
1137                 return true;
1138
1139         /*
1140          * Check if this (or a subsequent) instruction is related to
1141          * CONFIG_UBSAN or CONFIG_KASAN.
1142          *
1143          * End the search at 5 instructions to avoid going into the weeds.
1144          */
1145         for (i = 0; i < 5; i++) {
1146
1147                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1148                         return true;
1149
1150                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1151                         insn = insn->jump_dest;
1152                         continue;
1153                 }
1154
1155                 if (insn->offset + insn->len >= func->offset + func->len)
1156                         break;
1157                 insn = list_next_entry(insn, list);
1158         }
1159
1160         return false;
1161 }
1162
1163 static int validate_functions(struct objtool_file *file)
1164 {
1165         struct section *sec;
1166         struct symbol *func;
1167         struct instruction *insn;
1168         int ret, warnings = 0;
1169
1170         list_for_each_entry(sec, &file->elf->sections, list) {
1171                 list_for_each_entry(func, &sec->symbol_list, list) {
1172                         if (func->type != STT_FUNC)
1173                                 continue;
1174
1175                         insn = find_insn(file, sec, func->offset);
1176                         if (!insn)
1177                                 continue;
1178
1179                         ret = validate_branch(file, insn, 0);
1180                         warnings += ret;
1181                 }
1182         }
1183
1184         list_for_each_entry(sec, &file->elf->sections, list) {
1185                 list_for_each_entry(func, &sec->symbol_list, list) {
1186                         if (func->type != STT_FUNC)
1187                                 continue;
1188
1189                         func_for_each_insn(file, func, insn) {
1190                                 if (insn->visited)
1191                                         continue;
1192
1193                                 insn->visited = true;
1194
1195                                 if (file->ignore_unreachables || warnings ||
1196                                     ignore_unreachable_insn(func, insn))
1197                                         continue;
1198
1199                                 /*
1200                                  * gcov produces a lot of unreachable
1201                                  * instructions.  If we get an unreachable
1202                                  * warning and the file has gcov enabled, just
1203                                  * ignore it, and all other such warnings for
1204                                  * the file.
1205                                  */
1206                                 if (!file->ignore_unreachables &&
1207                                     gcov_enabled(file)) {
1208                                         file->ignore_unreachables = true;
1209                                         continue;
1210                                 }
1211
1212                                 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1213                                 warnings++;
1214                         }
1215                 }
1216         }
1217
1218         return warnings;
1219 }
1220
1221 static int validate_uncallable_instructions(struct objtool_file *file)
1222 {
1223         struct instruction *insn;
1224         int warnings = 0;
1225
1226         for_each_insn(file, insn) {
1227                 if (!insn->visited && insn->type == INSN_RETURN) {
1228                         WARN_FUNC("return instruction outside of a callable function",
1229                                   insn->sec, insn->offset);
1230                         warnings++;
1231                 }
1232         }
1233
1234         return warnings;
1235 }
1236
1237 static void cleanup(struct objtool_file *file)
1238 {
1239         struct instruction *insn, *tmpinsn;
1240         struct alternative *alt, *tmpalt;
1241
1242         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1243                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1244                         list_del(&alt->list);
1245                         free(alt);
1246                 }
1247                 list_del(&insn->list);
1248                 hash_del(&insn->hash);
1249                 free(insn);
1250         }
1251         elf_close(file->elf);
1252 }
1253
1254 const char * const check_usage[] = {
1255         "objtool check [<options>] file.o",
1256         NULL,
1257 };
1258
1259 int cmd_check(int argc, const char **argv)
1260 {
1261         struct objtool_file file;
1262         int ret, warnings = 0;
1263
1264         const struct option options[] = {
1265                 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1266                 OPT_END(),
1267         };
1268
1269         argc = parse_options(argc, argv, options, check_usage, 0);
1270
1271         if (argc != 1)
1272                 usage_with_options(check_usage, options);
1273
1274         objname = argv[0];
1275
1276         file.elf = elf_open(objname);
1277         if (!file.elf) {
1278                 fprintf(stderr, "error reading elf file %s\n", objname);
1279                 return 1;
1280         }
1281
1282         INIT_LIST_HEAD(&file.insn_list);
1283         hash_init(file.insn_hash);
1284         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
1285         file.rodata = find_section_by_name(file.elf, ".rodata");
1286         file.ignore_unreachables = false;
1287         file.c_file = find_section_by_name(file.elf, ".comment");
1288
1289         ret = decode_sections(&file);
1290         if (ret < 0)
1291                 goto out;
1292         warnings += ret;
1293
1294         ret = validate_functions(&file);
1295         if (ret < 0)
1296                 goto out;
1297         warnings += ret;
1298
1299         ret = validate_uncallable_instructions(&file);
1300         if (ret < 0)
1301                 goto out;
1302         warnings += ret;
1303
1304 out:
1305         cleanup(&file);
1306
1307         /* ignore warnings for now until we get all the code cleaned up */
1308         if (ret || warnings)
1309                 return 0;
1310         return 0;
1311 }