tools/objtool/check.c

   1 /*
   2  * Copyright (C) 2015-2017 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 #include <string.h>
  19 #include <stdlib.h>
  20
  21 #include "check.h"
  22 #include "elf.h"
  23 #include "special.h"
  24 #include "arch.h"
  25 #include "warn.h"
  26
  27 #include <linux/hashtable.h>
  28 #include <linux/kernel.h>
  29
  30 struct alternative {
  31         struct list_head list;
  32         struct instruction *insn;
  33 };
  34
  35 const char *objname;
  36 static bool no_fp;
  37 struct cfi_state initial_func_cfi;
  38
  39 struct instruction *find_insn(struct objtool_file *file,
  40                               struct section *sec, unsigned long offset)
  41 {
  42         struct instruction *insn;
  43
  44         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  45                 if (insn->sec == sec && insn->offset == offset)
  46                         return insn;
  47
  48         return NULL;
  49 }
  50
  51 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  52                                               struct instruction *insn)
  53 {
  54         struct instruction *next = list_next_entry(insn, list);
  55
  56         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  57                 return NULL;
  58
  59         return next;
  60 }
  61
  62 #define func_for_each_insn(file, func, insn)                            \
  63         for (insn = find_insn(file, func->sec, func->offset);           \
  64              insn && &insn->list != &file->insn_list &&                 \
  65                 insn->sec == func->sec &&                               \
  66                 insn->offset < func->offset + func->len;                \
  67              insn = list_next_entry(insn, list))
  68
  69 #define func_for_each_insn_continue_reverse(file, func, insn)           \
  70         for (insn = list_prev_entry(insn, list);                        \
  71              &insn->list != &file->insn_list &&                         \
  72                 insn->sec == func->sec && insn->offset >= func->offset; \
  73              insn = list_prev_entry(insn, list))
  74
  75 #define sec_for_each_insn_from(file, insn)                              \
  76         for (; insn; insn = next_insn_same_sec(file, insn))
  77
  78 #define sec_for_each_insn_continue(file, insn)                          \
  79         for (insn = next_insn_same_sec(file, insn); insn;               \
  80              insn = next_insn_same_sec(file, insn))
  81
  82 /*
  83  * Check if the function has been manually whitelisted with the
  84  * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
  85  * due to its use of a context switching instruction.
  86  */
  87 static bool ignore_func(struct objtool_file *file, struct symbol *func)
  88 {
  89         struct rela *rela;
  90
  91         /* check for STACK_FRAME_NON_STANDARD */
  92         if (file->whitelist && file->whitelist->rela)
  93                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
  94                         if (rela->sym->type == STT_SECTION &&
  95                             rela->sym->sec == func->sec &&
  96                             rela->addend == func->offset)
  97                                 return true;
  98                         if (rela->sym->type == STT_FUNC && rela->sym == func)
  99                                 return true;
 100                 }
 101
 102         return false;
 103 }
 104
 105 /*
 106  * This checks to see if the given function is a "noreturn" function.
 107  *
 108  * For global functions which are outside the scope of this object file, we
 109  * have to keep a manual list of them.
 110  *
 111  * For local functions, we have to detect them manually by simply looking for
 112  * the lack of a return instruction.
 113  *
 114  * Returns:
 115  *  -1: error
 116  *   0: no dead end
 117  *   1: dead end
 118  */
 119 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 120                                int recursion)
 121 {
 122         int i;
 123         struct instruction *insn;
 124         bool empty = true;
 125
 126         /*
 127          * Unfortunately these have to be hard coded because the noreturn
 128          * attribute isn't provided in ELF data.
 129          */
 130         static const char * const global_noreturns[] = {
 131                 "__stack_chk_fail",
 132                 "panic",
 133                 "do_exit",
 134                 "do_task_dead",
 135                 "__module_put_and_exit",
 136                 "complete_and_exit",
 137                 "kvm_spurious_fault",
 138                 "__reiserfs_panic",
 139                 "lbug_with_loc",
 140                 "fortify_panic",
 141                 "usercopy_abort",
 142         };
 143
 144         if (func->bind == STB_WEAK)
 145                 return 0;
 146
 147         if (func->bind == STB_GLOBAL)
 148                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 149                         if (!strcmp(func->name, global_noreturns[i]))
 150                                 return 1;
 151
 152         if (!func->sec)
 153                 return 0;
 154
 155         func_for_each_insn(file, func, insn) {
 156                 empty = false;
 157
 158                 if (insn->type == INSN_RETURN)
 159                         return 0;
 160         }
 161
 162         if (empty)
 163                 return 0;
 164
 165         /*
 166          * A function can have a sibling call instead of a return.  In that
 167          * case, the function's dead-end status depends on whether the target
 168          * of the sibling call returns.
 169          */
 170         func_for_each_insn(file, func, insn) {
 171                 if (insn->sec != func->sec ||
 172                     insn->offset >= func->offset + func->len)
 173                         break;
 174
 175                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 176                         struct instruction *dest = insn->jump_dest;
 177                         struct symbol *dest_func;
 178
 179                         if (!dest)
 180                                 /* sibling call to another file */
 181                                 return 0;
 182
 183                         if (dest->sec != func->sec ||
 184                             dest->offset < func->offset ||
 185                             dest->offset >= func->offset + func->len) {
 186                                 /* local sibling call */
 187                                 dest_func = find_symbol_by_offset(dest->sec,
 188                                                                   dest->offset);
 189                                 if (!dest_func)
 190                                         continue;
 191
 192                                 if (recursion == 5) {
 193                                         WARN_FUNC("infinite recursion (objtool bug!)",
 194                                                   dest->sec, dest->offset);
 195                                         return -1;
 196                                 }
 197
 198                                 return __dead_end_function(file, dest_func,
 199                                                            recursion + 1);
 200                         }
 201                 }
 202
 203                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 204                         /* sibling call */
 205                         return 0;
 206         }
 207
 208         return 1;
 209 }
 210
 211 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 212 {
 213         return __dead_end_function(file, func, 0);
 214 }
 215
 216 static void clear_insn_state(struct insn_state *state)
 217 {
 218         int i;
 219
 220         memset(state, 0, sizeof(*state));
 221         state->cfa.base = CFI_UNDEFINED;
 222         for (i = 0; i < CFI_NUM_REGS; i++) {
 223                 state->regs[i].base = CFI_UNDEFINED;
 224                 state->vals[i].base = CFI_UNDEFINED;
 225         }
 226         state->drap_reg = CFI_UNDEFINED;
 227         state->drap_offset = -1;
 228 }
 229
 230 /*
 231  * Call the arch-specific instruction decoder for all the instructions and add
 232  * them to the global instruction list.
 233  */
 234 static int decode_instructions(struct objtool_file *file)
 235 {
 236         struct section *sec;
 237         struct symbol *func;
 238         unsigned long offset;
 239         struct instruction *insn;
 240         int ret;
 241
 242         for_each_sec(file, sec) {
 243
 244                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 245                         continue;
 246
 247                 if (strcmp(sec->name, ".altinstr_replacement") &&
 248                     strcmp(sec->name, ".altinstr_aux") &&
 249                     strncmp(sec->name, ".discard.", 9))
 250                         sec->text = true;
 251
 252                 for (offset = 0; offset < sec->len; offset += insn->len) {
 253                         insn = malloc(sizeof(*insn));
 254                         if (!insn) {
 255                                 WARN("malloc failed");
 256                                 return -1;
 257                         }
 258                         memset(insn, 0, sizeof(*insn));
 259                         INIT_LIST_HEAD(&insn->alts);
 260                         clear_insn_state(&insn->state);
 261
 262                         insn->sec = sec;
 263                         insn->offset = offset;
 264
 265                         ret = arch_decode_instruction(file->elf, sec, offset,
 266                                                       sec->len - offset,
 267                                                       &insn->len, &insn->type,
 268                                                       &insn->immediate,
 269                                                       &insn->stack_op);
 270                         if (ret)
 271                                 goto err;
 272
 273                         if (!insn->type || insn->type > INSN_LAST) {
 274                                 WARN_FUNC("invalid instruction type %d",
 275                                           insn->sec, insn->offset, insn->type);
 276                                 ret = -1;
 277                                 goto err;
 278                         }
 279
 280                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 281                         list_add_tail(&insn->list, &file->insn_list);
 282                 }
 283
 284                 list_for_each_entry(func, &sec->symbol_list, list) {
 285                         if (func->type != STT_FUNC)
 286                                 continue;
 287
 288                         if (!find_insn(file, sec, func->offset)) {
 289                                 WARN("%s(): can't find starting instruction",
 290                                      func->name);
 291                                 return -1;
 292                         }
 293
 294                         func_for_each_insn(file, func, insn)
 295                                 if (!insn->func)
 296                                         insn->func = func;
 297                 }
 298         }
 299
 300         return 0;
 301
 302 err:
 303         free(insn);
 304         return ret;
 305 }
 306
 307 /*
 308  * Mark "ud2" instructions and manually annotated dead ends.
 309  */
 310 static int add_dead_ends(struct objtool_file *file)
 311 {
 312         struct section *sec;
 313         struct rela *rela;
 314         struct instruction *insn;
 315         bool found;
 316
 317         /*
 318          * By default, "ud2" is a dead end unless otherwise annotated, because
 319          * GCC 7 inserts it for certain divide-by-zero cases.
 320          */
 321         for_each_insn(file, insn)
 322                 if (insn->type == INSN_BUG)
 323                         insn->dead_end = true;
 324
 325         /*
 326          * Check for manually annotated dead ends.
 327          */
 328         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 329         if (!sec)
 330                 goto reachable;
 331
 332         list_for_each_entry(rela, &sec->rela_list, list) {
 333                 if (rela->sym->type != STT_SECTION) {
 334                         WARN("unexpected relocation symbol type in %s", sec->name);
 335                         return -1;
 336                 }
 337                 insn = find_insn(file, rela->sym->sec, rela->addend);
 338                 if (insn)
 339                         insn = list_prev_entry(insn, list);
 340                 else if (rela->addend == rela->sym->sec->len) {
 341                         found = false;
 342                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 343                                 if (insn->sec == rela->sym->sec) {
 344                                         found = true;
 345                                         break;
 346                                 }
 347                         }
 348
 349                         if (!found) {
 350                                 WARN("can't find unreachable insn at %s+0x%x",
 351                                      rela->sym->sec->name, rela->addend);
 352                                 return -1;
 353                         }
 354                 } else {
 355                         WARN("can't find unreachable insn at %s+0x%x",
 356                              rela->sym->sec->name, rela->addend);
 357                         return -1;
 358                 }
 359
 360                 insn->dead_end = true;
 361         }
 362
 363 reachable:
 364         /*
 365          * These manually annotated reachable checks are needed for GCC 4.4,
 366          * where the Linux unreachable() macro isn't supported.  In that case
 367          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 368          * not a dead end.
 369          */
 370         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 371         if (!sec)
 372                 return 0;
 373
 374         list_for_each_entry(rela, &sec->rela_list, list) {
 375                 if (rela->sym->type != STT_SECTION) {
 376                         WARN("unexpected relocation symbol type in %s", sec->name);
 377                         return -1;
 378                 }
 379                 insn = find_insn(file, rela->sym->sec, rela->addend);
 380                 if (insn)
 381                         insn = list_prev_entry(insn, list);
 382                 else if (rela->addend == rela->sym->sec->len) {
 383                         found = false;
 384                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 385                                 if (insn->sec == rela->sym->sec) {
 386                                         found = true;
 387                                         break;
 388                                 }
 389                         }
 390
 391                         if (!found) {
 392                                 WARN("can't find reachable insn at %s+0x%x",
 393                                      rela->sym->sec->name, rela->addend);
 394                                 return -1;
 395                         }
 396                 } else {
 397                         WARN("can't find reachable insn at %s+0x%x",
 398                              rela->sym->sec->name, rela->addend);
 399                         return -1;
 400                 }
 401
 402                 insn->dead_end = false;
 403         }
 404
 405         return 0;
 406 }
 407
 408 /*
 409  * Warnings shouldn't be reported for ignored functions.
 410  */
 411 static void add_ignores(struct objtool_file *file)
 412 {
 413         struct instruction *insn;
 414         struct section *sec;
 415         struct symbol *func;
 416
 417         for_each_sec(file, sec) {
 418                 list_for_each_entry(func, &sec->symbol_list, list) {
 419                         if (func->type != STT_FUNC)
 420                                 continue;
 421
 422                         if (!ignore_func(file, func))
 423                                 continue;
 424
 425                         func_for_each_insn(file, func, insn)
 426                                 insn->ignore = true;
 427                 }
 428         }
 429 }
 430
 431 /*
 432  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 433  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 434  * But it at least allows objtool to understand the control flow *around* the
 435  * retpoline.
 436  */
 437 static int add_nospec_ignores(struct objtool_file *file)
 438 {
 439         struct section *sec;
 440         struct rela *rela;
 441         struct instruction *insn;
 442
 443         sec = find_section_by_name(file->elf, ".rela.discard.nospec");
 444         if (!sec)
 445                 return 0;
 446
 447         list_for_each_entry(rela, &sec->rela_list, list) {
 448                 if (rela->sym->type != STT_SECTION) {
 449                         WARN("unexpected relocation symbol type in %s", sec->name);
 450                         return -1;
 451                 }
 452
 453                 insn = find_insn(file, rela->sym->sec, rela->addend);
 454                 if (!insn) {
 455                         WARN("bad .discard.nospec entry");
 456                         return -1;
 457                 }
 458
 459                 insn->ignore_alts = true;
 460         }
 461
 462         return 0;
 463 }
 464
 465 /*
 466  * Find the destination instructions for all jumps.
 467  */
 468 static int add_jump_destinations(struct objtool_file *file)
 469 {
 470         struct instruction *insn;
 471         struct rela *rela;
 472         struct section *dest_sec;
 473         unsigned long dest_off;
 474
 475         for_each_insn(file, insn) {
 476                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 477                     insn->type != INSN_JUMP_UNCONDITIONAL)
 478                         continue;
 479
 480                 if (insn->ignore)
 481                         continue;
 482
 483                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 484                                                insn->len);
 485                 if (!rela) {
 486                         dest_sec = insn->sec;
 487                         dest_off = insn->offset + insn->len + insn->immediate;
 488                 } else if (rela->sym->type == STT_SECTION) {
 489                         dest_sec = rela->sym->sec;
 490                         dest_off = rela->addend + 4;
 491                 } else if (rela->sym->sec->idx) {
 492                         dest_sec = rela->sym->sec;
 493                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 494                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 495                         /*
 496                          * Retpoline jumps are really dynamic jumps in
 497                          * disguise, so convert them accordingly.
 498                          */
 499                         insn->type = INSN_JUMP_DYNAMIC;
 500                         continue;
 501                 } else {
 502                         /* sibling call */
 503                         insn->jump_dest = 0;
 504                         continue;
 505                 }
 506
 507                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 508                 if (!insn->jump_dest) {
 509
 510                         /*
 511                          * This is a special case where an alt instruction
 512                          * jumps past the end of the section.  These are
 513                          * handled later in handle_group_alt().
 514                          */
 515                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 516                                 continue;
 517
 518                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 519                                   insn->sec, insn->offset, dest_sec->name,
 520                                   dest_off);
 521                         return -1;
 522                 }
 523         }
 524
 525         return 0;
 526 }
 527
 528 /*
 529  * Find the destination instructions for all calls.
 530  */
 531 static int add_call_destinations(struct objtool_file *file)
 532 {
 533         struct instruction *insn;
 534         unsigned long dest_off;
 535         struct rela *rela;
 536
 537         for_each_insn(file, insn) {
 538                 if (insn->type != INSN_CALL)
 539                         continue;
 540
 541                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 542                                                insn->len);
 543                 if (!rela) {
 544                         dest_off = insn->offset + insn->len + insn->immediate;
 545                         insn->call_dest = find_symbol_by_offset(insn->sec,
 546                                                                 dest_off);
 547
 548                         if (!insn->call_dest && !insn->ignore) {
 549                                 WARN_FUNC("unsupported intra-function call",
 550                                           insn->sec, insn->offset);
 551                                 WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 552                                 return -1;
 553                         }
 554
 555                 } else if (rela->sym->type == STT_SECTION) {
 556                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 557                                                                 rela->addend+4);
 558                         if (!insn->call_dest ||
 559                             insn->call_dest->type != STT_FUNC) {
 560                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 561                                           insn->sec, insn->offset,
 562                                           rela->sym->sec->name,
 563                                           rela->addend + 4);
 564                                 return -1;
 565                         }
 566                 } else
 567                         insn->call_dest = rela->sym;
 568         }
 569
 570         return 0;
 571 }
 572
 573 /*
 574  * The .alternatives section requires some extra special care, over and above
 575  * what other special sections require:
 576  *
 577  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 578  *    instruction at the end so that validate_branch() skips all the original
 579  *    replaced instructions when validating the new instruction path.
 580  *
 581  * 2. An added wrinkle is that the new instruction length might be zero.  In
 582  *    that case the old instructions are replaced with noops.  We simulate that
 583  *    by creating a fake jump as the only new instruction.
 584  *
 585  * 3. In some cases, the alternative section includes an instruction which
 586  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 587  *    jumps' destinations to point back to .text rather than the end of the
 588  *    entry in .altinstr_replacement.
 589  *
 590  * 4. It has been requested that we don't validate the !POPCNT feature path
 591  *    which is a "very very small percentage of machines".
 592  */
 593 static int handle_group_alt(struct objtool_file *file,
 594                             struct special_alt *special_alt,
 595                             struct instruction *orig_insn,
 596                             struct instruction **new_insn)
 597 {
 598         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 599         unsigned long dest_off;
 600
 601         last_orig_insn = NULL;
 602         insn = orig_insn;
 603         sec_for_each_insn_from(file, insn) {
 604                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 605                         break;
 606
 607                 if (special_alt->skip_orig)
 608                         insn->type = INSN_NOP;
 609
 610                 insn->alt_group = true;
 611                 last_orig_insn = insn;
 612         }
 613
 614         if (next_insn_same_sec(file, last_orig_insn)) {
 615                 fake_jump = malloc(sizeof(*fake_jump));
 616                 if (!fake_jump) {
 617                         WARN("malloc failed");
 618                         return -1;
 619                 }
 620                 memset(fake_jump, 0, sizeof(*fake_jump));
 621                 INIT_LIST_HEAD(&fake_jump->alts);
 622                 clear_insn_state(&fake_jump->state);
 623
 624                 fake_jump->sec = special_alt->new_sec;
 625                 fake_jump->offset = -1;
 626                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 627                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 628                 fake_jump->ignore = true;
 629         }
 630
 631         if (!special_alt->new_len) {
 632                 if (!fake_jump) {
 633                         WARN("%s: empty alternative at end of section",
 634                              special_alt->orig_sec->name);
 635                         return -1;
 636                 }
 637
 638                 *new_insn = fake_jump;
 639                 return 0;
 640         }
 641
 642         last_new_insn = NULL;
 643         insn = *new_insn;
 644         sec_for_each_insn_from(file, insn) {
 645                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 646                         break;
 647
 648                 last_new_insn = insn;
 649
 650                 insn->ignore = orig_insn->ignore_alts;
 651
 652                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 653                     insn->type != INSN_JUMP_UNCONDITIONAL)
 654                         continue;
 655
 656                 if (!insn->immediate)
 657                         continue;
 658
 659                 dest_off = insn->offset + insn->len + insn->immediate;
 660                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 661                         if (!fake_jump) {
 662                                 WARN("%s: alternative jump to end of section",
 663                                      special_alt->orig_sec->name);
 664                                 return -1;
 665                         }
 666                         insn->jump_dest = fake_jump;
 667                 }
 668
 669                 if (!insn->jump_dest) {
 670                         WARN_FUNC("can't find alternative jump destination",
 671                                   insn->sec, insn->offset);
 672                         return -1;
 673                 }
 674         }
 675
 676         if (!last_new_insn) {
 677                 WARN_FUNC("can't find last new alternative instruction",
 678                           special_alt->new_sec, special_alt->new_off);
 679                 return -1;
 680         }
 681
 682         if (fake_jump)
 683                 list_add(&fake_jump->list, &last_new_insn->list);
 684
 685         return 0;
 686 }
 687
 688 /*
 689  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 690  * If the original instruction is a jump, make the alt entry an effective nop
 691  * by just skipping the original instruction.
 692  */
 693 static int handle_jump_alt(struct objtool_file *file,
 694                            struct special_alt *special_alt,
 695                            struct instruction *orig_insn,
 696                            struct instruction **new_insn)
 697 {
 698         if (orig_insn->type == INSN_NOP)
 699                 return 0;
 700
 701         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 702                 WARN_FUNC("unsupported instruction at jump label",
 703                           orig_insn->sec, orig_insn->offset);
 704                 return -1;
 705         }
 706
 707         *new_insn = list_next_entry(orig_insn, list);
 708         return 0;
 709 }
 710
 711 /*
 712  * Read all the special sections which have alternate instructions which can be
 713  * patched in or redirected to at runtime.  Each instruction having alternate
 714  * instruction(s) has them added to its insn->alts list, which will be
 715  * traversed in validate_branch().
 716  */
 717 static int add_special_section_alts(struct objtool_file *file)
 718 {
 719         struct list_head special_alts;
 720         struct instruction *orig_insn, *new_insn;
 721         struct special_alt *special_alt, *tmp;
 722         struct alternative *alt;
 723         int ret;
 724
 725         ret = special_get_alts(file->elf, &special_alts);
 726         if (ret)
 727                 return ret;
 728
 729         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 730
 731                 orig_insn = find_insn(file, special_alt->orig_sec,
 732                                       special_alt->orig_off);
 733                 if (!orig_insn) {
 734                         WARN_FUNC("special: can't find orig instruction",
 735                                   special_alt->orig_sec, special_alt->orig_off);
 736                         ret = -1;
 737                         goto out;
 738                 }
 739
 740                 new_insn = NULL;
 741                 if (!special_alt->group || special_alt->new_len) {
 742                         new_insn = find_insn(file, special_alt->new_sec,
 743                                              special_alt->new_off);
 744                         if (!new_insn) {
 745                                 WARN_FUNC("special: can't find new instruction",
 746                                           special_alt->new_sec,
 747                                           special_alt->new_off);
 748                                 ret = -1;
 749                                 goto out;
 750                         }
 751                 }
 752
 753                 if (special_alt->group) {
 754                         ret = handle_group_alt(file, special_alt, orig_insn,
 755                                                &new_insn);
 756                         if (ret)
 757                                 goto out;
 758                 } else if (special_alt->jump_or_nop) {
 759                         ret = handle_jump_alt(file, special_alt, orig_insn,
 760                                               &new_insn);
 761                         if (ret)
 762                                 goto out;
 763                 }
 764
 765                 alt = malloc(sizeof(*alt));
 766                 if (!alt) {
 767                         WARN("malloc failed");
 768                         ret = -1;
 769                         goto out;
 770                 }
 771
 772                 alt->insn = new_insn;
 773                 list_add_tail(&alt->list, &orig_insn->alts);
 774
 775                 list_del(&special_alt->list);
 776                 free(special_alt);
 777         }
 778
 779 out:
 780         return ret;
 781 }
 782
 783 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 784                             struct instruction *insn, struct rela *table,
 785                             struct rela *next_table)
 786 {
 787         struct rela *rela = table;
 788         struct instruction *alt_insn;
 789         struct alternative *alt;
 790
 791         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 792                 if (rela == next_table)
 793                         break;
 794
 795                 if (rela->sym->sec != insn->sec ||
 796                     rela->addend <= func->offset ||
 797                     rela->addend >= func->offset + func->len)
 798                         break;
 799
 800                 alt_insn = find_insn(file, insn->sec, rela->addend);
 801                 if (!alt_insn) {
 802                         WARN("%s: can't find instruction at %s+0x%x",
 803                              file->rodata->rela->name, insn->sec->name,
 804                              rela->addend);
 805                         return -1;
 806                 }
 807
 808                 alt = malloc(sizeof(*alt));
 809                 if (!alt) {
 810                         WARN("malloc failed");
 811                         return -1;
 812                 }
 813
 814                 alt->insn = alt_insn;
 815                 list_add_tail(&alt->list, &insn->alts);
 816         }
 817
 818         return 0;
 819 }
 820
 821 /*
 822  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 823  * .rodata associated with it.
 824  *
 825  * There are 3 basic patterns:
 826  *
 827  * 1. jmpq *[rodata addr](,%reg,8)
 828  *
 829  *    This is the most common case by far.  It jumps to an address in a simple
 830  *    jump table which is stored in .rodata.
 831  *
 832  * 2. jmpq *[rodata addr](%rip)
 833  *
 834  *    This is caused by a rare GCC quirk, currently only seen in three driver
 835  *    functions in the kernel, only with certain obscure non-distro configs.
 836  *
 837  *    As part of an optimization, GCC makes a copy of an existing switch jump
 838  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 839  *    jump) to use a single entry in the table.  The rest of the jump table and
 840  *    some of its jump targets remain as dead code.
 841  *
 842  *    In such a case we can just crudely ignore all unreachable instruction
 843  *    warnings for the entire object file.  Ideally we would just ignore them
 844  *    for the function, but that would require redesigning the code quite a
 845  *    bit.  And honestly that's just not worth doing: unreachable instruction
 846  *    warnings are of questionable value anyway, and this is such a rare issue.
 847  *
 848  * 3. mov [rodata addr],%reg1
 849  *    ... some instructions ...
 850  *    jmpq *(%reg1,%reg2,8)
 851  *
 852  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 853  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 854  *
 855  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 856  *    ensure the same register is used in the mov and jump instructions.
 857  */
 858 static struct rela *find_switch_table(struct objtool_file *file,
 859                                       struct symbol *func,
 860                                       struct instruction *insn)
 861 {
 862         struct rela *text_rela, *rodata_rela;
 863         struct instruction *orig_insn = insn;
 864
 865         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 866         if (text_rela && text_rela->sym == file->rodata->sym) {
 867                 /* case 1 */
 868                 rodata_rela = find_rela_by_dest(file->rodata,
 869                                                 text_rela->addend);
 870                 if (rodata_rela)
 871                         return rodata_rela;
 872
 873                 /* case 2 */
 874                 rodata_rela = find_rela_by_dest(file->rodata,
 875                                                 text_rela->addend + 4);
 876                 if (!rodata_rela)
 877                         return NULL;
 878                 file->ignore_unreachables = true;
 879                 return rodata_rela;
 880         }
 881
 882         /* case 3 */
 883         func_for_each_insn_continue_reverse(file, func, insn) {
 884                 if (insn->type == INSN_JUMP_DYNAMIC)
 885                         break;
 886
 887                 /* allow small jumps within the range */
 888                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
 889                     insn->jump_dest &&
 890                     (insn->jump_dest->offset <= insn->offset ||
 891                      insn->jump_dest->offset > orig_insn->offset))
 892                     break;
 893
 894                 /* look for a relocation which references .rodata */
 895                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 896                                                     insn->len);
 897                 if (!text_rela || text_rela->sym != file->rodata->sym)
 898                         continue;
 899
 900                 /*
 901                  * Make sure the .rodata address isn't associated with a
 902                  * symbol.  gcc jump tables are anonymous data.
 903                  */
 904                 if (find_symbol_containing(file->rodata, text_rela->addend))
 905                         continue;
 906
 907                 return find_rela_by_dest(file->rodata, text_rela->addend);
 908         }
 909
 910         return NULL;
 911 }
 912
 913 static int add_func_switch_tables(struct objtool_file *file,
 914                                   struct symbol *func)
 915 {
 916         struct instruction *insn, *prev_jump = NULL;
 917         struct rela *rela, *prev_rela = NULL;
 918         int ret;
 919
 920         func_for_each_insn(file, func, insn) {
 921                 if (insn->type != INSN_JUMP_DYNAMIC)
 922                         continue;
 923
 924                 rela = find_switch_table(file, func, insn);
 925                 if (!rela)
 926                         continue;
 927
 928                 /*
 929                  * We found a switch table, but we don't know yet how big it
 930                  * is.  Don't add it until we reach the end of the function or
 931                  * the beginning of another switch table in the same function.
 932                  */
 933                 if (prev_jump) {
 934                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 935                                                rela);
 936                         if (ret)
 937                                 return ret;
 938                 }
 939
 940                 prev_jump = insn;
 941                 prev_rela = rela;
 942         }
 943
 944         if (prev_jump) {
 945                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 946                 if (ret)
 947                         return ret;
 948         }
 949
 950         return 0;
 951 }
 952
 953 /*
 954  * For some switch statements, gcc generates a jump table in the .rodata
 955  * section which contains a list of addresses within the function to jump to.
 956  * This finds these jump tables and adds them to the insn->alts lists.
 957  */
 958 static int add_switch_table_alts(struct objtool_file *file)
 959 {
 960         struct section *sec;
 961         struct symbol *func;
 962         int ret;
 963
 964         if (!file->rodata || !file->rodata->rela)
 965                 return 0;
 966
 967         for_each_sec(file, sec) {
 968                 list_for_each_entry(func, &sec->symbol_list, list) {
 969                         if (func->type != STT_FUNC)
 970                                 continue;
 971
 972                         ret = add_func_switch_tables(file, func);
 973                         if (ret)
 974                                 return ret;
 975                 }
 976         }
 977
 978         return 0;
 979 }
 980
 981 static int read_unwind_hints(struct objtool_file *file)
 982 {
 983         struct section *sec, *relasec;
 984         struct rela *rela;
 985         struct unwind_hint *hint;
 986         struct instruction *insn;
 987         struct cfi_reg *cfa;
 988         int i;
 989
 990         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
 991         if (!sec)
 992                 return 0;
 993
 994         relasec = sec->rela;
 995         if (!relasec) {
 996                 WARN("missing .rela.discard.unwind_hints section");
 997                 return -1;
 998         }
 999
1000         if (sec->len % sizeof(struct unwind_hint)) {
1001                 WARN("struct unwind_hint size mismatch");
1002                 return -1;
1003         }
1004
1005         file->hints = true;
1006
1007         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1008                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1009
1010                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1011                 if (!rela) {
1012                         WARN("can't find rela for unwind_hints[%d]", i);
1013                         return -1;
1014                 }
1015
1016                 insn = find_insn(file, rela->sym->sec, rela->addend);
1017                 if (!insn) {
1018                         WARN("can't find insn for unwind_hints[%d]", i);
1019                         return -1;
1020                 }
1021
1022                 cfa = &insn->state.cfa;
1023
1024                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1025                         insn->save = true;
1026                         continue;
1027
1028                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1029                         insn->restore = true;
1030                         insn->hint = true;
1031                         continue;
1032                 }
1033
1034                 insn->hint = true;
1035
1036                 switch (hint->sp_reg) {
1037                 case ORC_REG_UNDEFINED:
1038                         cfa->base = CFI_UNDEFINED;
1039                         break;
1040                 case ORC_REG_SP:
1041                         cfa->base = CFI_SP;
1042                         break;
1043                 case ORC_REG_BP:
1044                         cfa->base = CFI_BP;
1045                         break;
1046                 case ORC_REG_SP_INDIRECT:
1047                         cfa->base = CFI_SP_INDIRECT;
1048                         break;
1049                 case ORC_REG_R10:
1050                         cfa->base = CFI_R10;
1051                         break;
1052                 case ORC_REG_R13:
1053                         cfa->base = CFI_R13;
1054                         break;
1055                 case ORC_REG_DI:
1056                         cfa->base = CFI_DI;
1057                         break;
1058                 case ORC_REG_DX:
1059                         cfa->base = CFI_DX;
1060                         break;
1061                 default:
1062                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1063                                   insn->sec, insn->offset, hint->sp_reg);
1064                         return -1;
1065                 }
1066
1067                 cfa->offset = hint->sp_offset;
1068                 insn->state.type = hint->type;
1069         }
1070
1071         return 0;
1072 }
1073
1074 static int decode_sections(struct objtool_file *file)
1075 {
1076         int ret;
1077
1078         ret = decode_instructions(file);
1079         if (ret)
1080                 return ret;
1081
1082         ret = add_dead_ends(file);
1083         if (ret)
1084                 return ret;
1085
1086         add_ignores(file);
1087
1088         ret = add_nospec_ignores(file);
1089         if (ret)
1090                 return ret;
1091
1092         ret = add_jump_destinations(file);
1093         if (ret)
1094                 return ret;
1095
1096         ret = add_special_section_alts(file);
1097         if (ret)
1098                 return ret;
1099
1100         ret = add_call_destinations(file);
1101         if (ret)
1102                 return ret;
1103
1104         ret = add_switch_table_alts(file);
1105         if (ret)
1106                 return ret;
1107
1108         ret = read_unwind_hints(file);
1109         if (ret)
1110                 return ret;
1111
1112         return 0;
1113 }
1114
1115 static bool is_fentry_call(struct instruction *insn)
1116 {
1117         if (insn->type == INSN_CALL &&
1118             insn->call_dest->type == STT_NOTYPE &&
1119             !strcmp(insn->call_dest->name, "__fentry__"))
1120                 return true;
1121
1122         return false;
1123 }
1124
1125 static bool has_modified_stack_frame(struct insn_state *state)
1126 {
1127         int i;
1128
1129         if (state->cfa.base != initial_func_cfi.cfa.base ||
1130             state->cfa.offset != initial_func_cfi.cfa.offset ||
1131             state->stack_size != initial_func_cfi.cfa.offset ||
1132             state->drap)
1133                 return true;
1134
1135         for (i = 0; i < CFI_NUM_REGS; i++)
1136                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1137                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1138                         return true;
1139
1140         return false;
1141 }
1142
1143 static bool has_valid_stack_frame(struct insn_state *state)
1144 {
1145         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1146             state->regs[CFI_BP].offset == -16)
1147                 return true;
1148
1149         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1150                 return true;
1151
1152         return false;
1153 }
1154
1155 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1156 {
1157         struct cfi_reg *cfa = &state->cfa;
1158         struct stack_op *op = &insn->stack_op;
1159
1160         if (cfa->base != CFI_SP)
1161                 return 0;
1162
1163         /* push */
1164         if (op->dest.type == OP_DEST_PUSH)
1165                 cfa->offset += 8;
1166
1167         /* pop */
1168         if (op->src.type == OP_SRC_POP)
1169                 cfa->offset -= 8;
1170
1171         /* add immediate to sp */
1172         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1173             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1174                 cfa->offset -= op->src.offset;
1175
1176         return 0;
1177 }
1178
1179 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1180                      int offset)
1181 {
1182         if (arch_callee_saved_reg(reg) &&
1183             state->regs[reg].base == CFI_UNDEFINED) {
1184                 state->regs[reg].base = base;
1185                 state->regs[reg].offset = offset;
1186         }
1187 }
1188
1189 static void restore_reg(struct insn_state *state, unsigned char reg)
1190 {
1191         state->regs[reg].base = CFI_UNDEFINED;
1192         state->regs[reg].offset = 0;
1193 }
1194
1195 /*
1196  * A note about DRAP stack alignment:
1197  *
1198  * GCC has the concept of a DRAP register, which is used to help keep track of
1199  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1200  * register.  The typical DRAP pattern is:
1201  *
1202  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1203  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1204  *   41 ff 72 f8                pushq  -0x8(%r10)
1205  *   55                         push   %rbp
1206  *   48 89 e5                   mov    %rsp,%rbp
1207  *                              (more pushes)
1208  *   41 52                      push   %r10
1209  *                              ...
1210  *   41 5a                      pop    %r10
1211  *                              (more pops)
1212  *   5d                         pop    %rbp
1213  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1214  *   c3                         retq
1215  *
1216  * There are some variations in the epilogues, like:
1217  *
1218  *   5b                         pop    %rbx
1219  *   41 5a                      pop    %r10
1220  *   41 5c                      pop    %r12
1221  *   41 5d                      pop    %r13
1222  *   41 5e                      pop    %r14
1223  *   c9                         leaveq
1224  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1225  *   c3                         retq
1226  *
1227  * and:
1228  *
1229  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1230  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1231  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1232  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1233  *   c9                         leaveq
1234  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1235  *   c3                         retq
1236  *
1237  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1238  * restored beforehand:
1239  *
1240  *   41 55                      push   %r13
1241  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1242  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1243  *                              ...
1244  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1245  *   41 5d                      pop    %r13
1246  *   c3                         retq
1247  */
1248 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1249 {
1250         struct stack_op *op = &insn->stack_op;
1251         struct cfi_reg *cfa = &state->cfa;
1252         struct cfi_reg *regs = state->regs;
1253
1254         /* stack operations don't make sense with an undefined CFA */
1255         if (cfa->base == CFI_UNDEFINED) {
1256                 if (insn->func) {
1257                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1258                         return -1;
1259                 }
1260                 return 0;
1261         }
1262
1263         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1264                 return update_insn_state_regs(insn, state);
1265
1266         switch (op->dest.type) {
1267
1268         case OP_DEST_REG:
1269                 switch (op->src.type) {
1270
1271                 case OP_SRC_REG:
1272                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1273                             cfa->base == CFI_SP &&
1274                             regs[CFI_BP].base == CFI_CFA &&
1275                             regs[CFI_BP].offset == -cfa->offset) {
1276
1277                                 /* mov %rsp, %rbp */
1278                                 cfa->base = op->dest.reg;
1279                                 state->bp_scratch = false;
1280                         }
1281
1282                         else if (op->src.reg == CFI_SP &&
1283                                  op->dest.reg == CFI_BP && state->drap) {
1284
1285                                 /* drap: mov %rsp, %rbp */
1286                                 regs[CFI_BP].base = CFI_BP;
1287                                 regs[CFI_BP].offset = -state->stack_size;
1288                                 state->bp_scratch = false;
1289                         }
1290
1291                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1292
1293                                 /*
1294                                  * mov %rsp, %reg
1295                                  *
1296                                  * This is needed for the rare case where GCC
1297                                  * does:
1298                                  *
1299                                  *   mov    %rsp, %rax
1300                                  *   ...
1301                                  *   mov    %rax, %rsp
1302                                  */
1303                                 state->vals[op->dest.reg].base = CFI_CFA;
1304                                 state->vals[op->dest.reg].offset = -state->stack_size;
1305                         }
1306
1307                         else if (op->dest.reg == cfa->base) {
1308
1309                                 /* mov %reg, %rsp */
1310                                 if (cfa->base == CFI_SP &&
1311                                     state->vals[op->src.reg].base == CFI_CFA) {
1312
1313                                         /*
1314                                          * This is needed for the rare case
1315                                          * where GCC does something dumb like:
1316                                          *
1317                                          *   lea    0x8(%rsp), %rcx
1318                                          *   ...
1319                                          *   mov    %rcx, %rsp
1320                                          */
1321                                         cfa->offset = -state->vals[op->src.reg].offset;
1322                                         state->stack_size = cfa->offset;
1323
1324                                 } else {
1325                                         cfa->base = CFI_UNDEFINED;
1326                                         cfa->offset = 0;
1327                                 }
1328                         }
1329
1330                         break;
1331
1332                 case OP_SRC_ADD:
1333                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1334
1335                                 /* add imm, %rsp */
1336                                 state->stack_size -= op->src.offset;
1337                                 if (cfa->base == CFI_SP)
1338                                         cfa->offset -= op->src.offset;
1339                                 break;
1340                         }
1341
1342                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1343
1344                                 /* lea disp(%rbp), %rsp */
1345                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1346                                 break;
1347                         }
1348
1349                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1350
1351                                 /* drap: lea disp(%rsp), %drap */
1352                                 state->drap_reg = op->dest.reg;
1353
1354                                 /*
1355                                  * lea disp(%rsp), %reg
1356                                  *
1357                                  * This is needed for the rare case where GCC
1358                                  * does something dumb like:
1359                                  *
1360                                  *   lea    0x8(%rsp), %rcx
1361                                  *   ...
1362                                  *   mov    %rcx, %rsp
1363                                  */
1364                                 state->vals[op->dest.reg].base = CFI_CFA;
1365                                 state->vals[op->dest.reg].offset = \
1366                                         -state->stack_size + op->src.offset;
1367
1368                                 break;
1369                         }
1370
1371                         if (state->drap && op->dest.reg == CFI_SP &&
1372                             op->src.reg == state->drap_reg) {
1373
1374                                  /* drap: lea disp(%drap), %rsp */
1375                                 cfa->base = CFI_SP;
1376                                 cfa->offset = state->stack_size = -op->src.offset;
1377                                 state->drap_reg = CFI_UNDEFINED;
1378                                 state->drap = false;
1379                                 break;
1380                         }
1381
1382                         if (op->dest.reg == state->cfa.base) {
1383                                 WARN_FUNC("unsupported stack register modification",
1384                                           insn->sec, insn->offset);
1385                                 return -1;
1386                         }
1387
1388                         break;
1389
1390                 case OP_SRC_AND:
1391                         if (op->dest.reg != CFI_SP ||
1392                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1393                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1394                                 WARN_FUNC("unsupported stack pointer realignment",
1395                                           insn->sec, insn->offset);
1396                                 return -1;
1397                         }
1398
1399                         if (state->drap_reg != CFI_UNDEFINED) {
1400                                 /* drap: and imm, %rsp */
1401                                 cfa->base = state->drap_reg;
1402                                 cfa->offset = state->stack_size = 0;
1403                                 state->drap = true;
1404                         }
1405
1406                         /*
1407                          * Older versions of GCC (4.8ish) realign the stack
1408                          * without DRAP, with a frame pointer.
1409                          */
1410
1411                         break;
1412
1413                 case OP_SRC_POP:
1414                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1415                             op->dest.reg == cfa->base) {
1416
1417                                 /* pop %rbp */
1418                                 cfa->base = CFI_SP;
1419                         }
1420
1421                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1422                             op->dest.type == OP_DEST_REG &&
1423                             op->dest.reg == state->drap_reg &&
1424                             state->drap_offset == -state->stack_size) {
1425
1426                                 /* drap: pop %drap */
1427                                 cfa->base = state->drap_reg;
1428                                 cfa->offset = 0;
1429                                 state->drap_offset = -1;
1430
1431                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1432
1433                                 /* pop %reg */
1434                                 restore_reg(state, op->dest.reg);
1435                         }
1436
1437                         state->stack_size -= 8;
1438                         if (cfa->base == CFI_SP)
1439                                 cfa->offset -= 8;
1440
1441                         break;
1442
1443                 case OP_SRC_REG_INDIRECT:
1444                         if (state->drap && op->src.reg == CFI_BP &&
1445                             op->src.offset == state->drap_offset) {
1446
1447                                 /* drap: mov disp(%rbp), %drap */
1448                                 cfa->base = state->drap_reg;
1449                                 cfa->offset = 0;
1450                                 state->drap_offset = -1;
1451                         }
1452
1453                         if (state->drap && op->src.reg == CFI_BP &&
1454                             op->src.offset == regs[op->dest.reg].offset) {
1455
1456                                 /* drap: mov disp(%rbp), %reg */
1457                                 restore_reg(state, op->dest.reg);
1458
1459                         } else if (op->src.reg == cfa->base &&
1460                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1461
1462                                 /* mov disp(%rbp), %reg */
1463                                 /* mov disp(%rsp), %reg */
1464                                 restore_reg(state, op->dest.reg);
1465                         }
1466
1467                         break;
1468
1469                 default:
1470                         WARN_FUNC("unknown stack-related instruction",
1471                                   insn->sec, insn->offset);
1472                         return -1;
1473                 }
1474
1475                 break;
1476
1477         case OP_DEST_PUSH:
1478                 state->stack_size += 8;
1479                 if (cfa->base == CFI_SP)
1480                         cfa->offset += 8;
1481
1482                 if (op->src.type != OP_SRC_REG)
1483                         break;
1484
1485                 if (state->drap) {
1486                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1487
1488                                 /* drap: push %drap */
1489                                 cfa->base = CFI_BP_INDIRECT;
1490                                 cfa->offset = -state->stack_size;
1491
1492                                 /* save drap so we know when to restore it */
1493                                 state->drap_offset = -state->stack_size;
1494
1495                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1496
1497                                 /* drap: push %rbp */
1498                                 state->stack_size = 0;
1499
1500                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1501
1502                                 /* drap: push %reg */
1503                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1504                         }
1505
1506                 } else {
1507
1508                         /* push %reg */
1509                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1510                 }
1511
1512                 /* detect when asm code uses rbp as a scratch register */
1513                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1514                     cfa->base != CFI_BP)
1515                         state->bp_scratch = true;
1516                 break;
1517
1518         case OP_DEST_REG_INDIRECT:
1519
1520                 if (state->drap) {
1521                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1522
1523                                 /* drap: mov %drap, disp(%rbp) */
1524                                 cfa->base = CFI_BP_INDIRECT;
1525                                 cfa->offset = op->dest.offset;
1526
1527                                 /* save drap offset so we know when to restore it */
1528                                 state->drap_offset = op->dest.offset;
1529                         }
1530
1531                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1532
1533                                 /* drap: mov reg, disp(%rbp) */
1534                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1535                         }
1536
1537                 } else if (op->dest.reg == cfa->base) {
1538
1539                         /* mov reg, disp(%rbp) */
1540                         /* mov reg, disp(%rsp) */
1541                         save_reg(state, op->src.reg, CFI_CFA,
1542                                  op->dest.offset - state->cfa.offset);
1543                 }
1544
1545                 break;
1546
1547         case OP_DEST_LEAVE:
1548                 if ((!state->drap && cfa->base != CFI_BP) ||
1549                     (state->drap && cfa->base != state->drap_reg)) {
1550                         WARN_FUNC("leave instruction with modified stack frame",
1551                                   insn->sec, insn->offset);
1552                         return -1;
1553                 }
1554
1555                 /* leave (mov %rbp, %rsp; pop %rbp) */
1556
1557                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1558                 restore_reg(state, CFI_BP);
1559
1560                 if (!state->drap) {
1561                         cfa->base = CFI_SP;
1562                         cfa->offset -= 8;
1563                 }
1564
1565                 break;
1566
1567         case OP_DEST_MEM:
1568                 if (op->src.type != OP_SRC_POP) {
1569                         WARN_FUNC("unknown stack-related memory operation",
1570                                   insn->sec, insn->offset);
1571                         return -1;
1572                 }
1573
1574                 /* pop mem */
1575                 state->stack_size -= 8;
1576                 if (cfa->base == CFI_SP)
1577                         cfa->offset -= 8;
1578
1579                 break;
1580
1581         default:
1582                 WARN_FUNC("unknown stack-related instruction",
1583                           insn->sec, insn->offset);
1584                 return -1;
1585         }
1586
1587         return 0;
1588 }
1589
1590 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1591 {
1592         struct insn_state *state1 = &insn->state, *state2 = state;
1593         int i;
1594
1595         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1596                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1597                           insn->sec, insn->offset,
1598                           state1->cfa.base, state1->cfa.offset,
1599                           state2->cfa.base, state2->cfa.offset);
1600
1601         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1602                 for (i = 0; i < CFI_NUM_REGS; i++) {
1603                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1604                                     sizeof(struct cfi_reg)))
1605                                 continue;
1606
1607                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1608                                   insn->sec, insn->offset,
1609                                   i, state1->regs[i].base, state1->regs[i].offset,
1610                                   i, state2->regs[i].base, state2->regs[i].offset);
1611                         break;
1612                 }
1613
1614         } else if (state1->type != state2->type) {
1615                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1616                           insn->sec, insn->offset, state1->type, state2->type);
1617
1618         } else if (state1->drap != state2->drap ||
1619                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1620                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1621                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1622                           insn->sec, insn->offset,
1623                           state1->drap, state1->drap_reg, state1->drap_offset,
1624                           state2->drap, state2->drap_reg, state2->drap_offset);
1625
1626         } else
1627                 return true;
1628
1629         return false;
1630 }
1631
1632 /*
1633  * Follow the branch starting at the given instruction, and recursively follow
1634  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1635  * each instruction and validate all the rules described in
1636  * tools/objtool/Documentation/stack-validation.txt.
1637  */
1638 static int validate_branch(struct objtool_file *file, struct instruction *first,
1639                            struct insn_state state)
1640 {
1641         struct alternative *alt;
1642         struct instruction *insn, *next_insn;
1643         struct section *sec;
1644         struct symbol *func = NULL;
1645         int ret;
1646
1647         insn = first;
1648         sec = insn->sec;
1649
1650         if (insn->alt_group && list_empty(&insn->alts)) {
1651                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1652                           sec, insn->offset);
1653                 return 1;
1654         }
1655
1656         while (1) {
1657                 next_insn = next_insn_same_sec(file, insn);
1658
1659
1660                 if (file->c_file && func && insn->func && func != insn->func) {
1661                         WARN("%s() falls through to next function %s()",
1662                              func->name, insn->func->name);
1663                         return 1;
1664                 }
1665
1666                 if (insn->func)
1667                         func = insn->func;
1668
1669                 if (func && insn->ignore) {
1670                         WARN_FUNC("BUG: why am I validating an ignored function?",
1671                                   sec, insn->offset);
1672                         return 1;
1673                 }
1674
1675                 if (insn->visited) {
1676                         if (!insn->hint && !insn_state_match(insn, &state))
1677                                 return 1;
1678
1679                         return 0;
1680                 }
1681
1682                 if (insn->hint) {
1683                         if (insn->restore) {
1684                                 struct instruction *save_insn, *i;
1685
1686                                 i = insn;
1687                                 save_insn = NULL;
1688                                 func_for_each_insn_continue_reverse(file, func, i) {
1689                                         if (i->save) {
1690                                                 save_insn = i;
1691                                                 break;
1692                                         }
1693                                 }
1694
1695                                 if (!save_insn) {
1696                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1697                                                   sec, insn->offset);
1698                                         return 1;
1699                                 }
1700
1701                                 if (!save_insn->visited) {
1702                                         /*
1703                                          * Oops, no state to copy yet.
1704                                          * Hopefully we can reach this
1705                                          * instruction from another branch
1706                                          * after the save insn has been
1707                                          * visited.
1708                                          */
1709                                         if (insn == first)
1710                                                 return 0;
1711
1712                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1713                                                   sec, insn->offset);
1714                                         return 1;
1715                                 }
1716
1717                                 insn->state = save_insn->state;
1718                         }
1719
1720                         state = insn->state;
1721
1722                 } else
1723                         insn->state = state;
1724
1725                 insn->visited = true;
1726
1727                 if (!insn->ignore_alts) {
1728                         list_for_each_entry(alt, &insn->alts, list) {
1729                                 ret = validate_branch(file, alt->insn, state);
1730                                 if (ret)
1731                                         return 1;
1732                         }
1733                 }
1734
1735                 switch (insn->type) {
1736
1737                 case INSN_RETURN:
1738                         if (func && has_modified_stack_frame(&state)) {
1739                                 WARN_FUNC("return with modified stack frame",
1740                                           sec, insn->offset);
1741                                 return 1;
1742                         }
1743
1744                         if (state.bp_scratch) {
1745                                 WARN("%s uses BP as a scratch register",
1746                                      insn->func->name);
1747                                 return 1;
1748                         }
1749
1750                         return 0;
1751
1752                 case INSN_CALL:
1753                         if (is_fentry_call(insn))
1754                                 break;
1755
1756                         ret = dead_end_function(file, insn->call_dest);
1757                         if (ret == 1)
1758                                 return 0;
1759                         if (ret == -1)
1760                                 return 1;
1761
1762                         /* fallthrough */
1763                 case INSN_CALL_DYNAMIC:
1764                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
1765                                 WARN_FUNC("call without frame pointer save/setup",
1766                                           sec, insn->offset);
1767                                 return 1;
1768                         }
1769                         break;
1770
1771                 case INSN_JUMP_CONDITIONAL:
1772                 case INSN_JUMP_UNCONDITIONAL:
1773                         if (insn->jump_dest &&
1774                             (!func || !insn->jump_dest->func ||
1775                              func == insn->jump_dest->func)) {
1776                                 ret = validate_branch(file, insn->jump_dest,
1777                                                       state);
1778                                 if (ret)
1779                                         return 1;
1780
1781                         } else if (func && has_modified_stack_frame(&state)) {
1782                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1783                                           sec, insn->offset);
1784                                 return 1;
1785                         }
1786
1787                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1788                                 return 0;
1789
1790                         break;
1791
1792                 case INSN_JUMP_DYNAMIC:
1793                         if (func && list_empty(&insn->alts) &&
1794                             has_modified_stack_frame(&state)) {
1795                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1796                                           sec, insn->offset);
1797                                 return 1;
1798                         }
1799
1800                         return 0;
1801
1802                 case INSN_CONTEXT_SWITCH:
1803                         if (func && (!next_insn || !next_insn->hint)) {
1804                                 WARN_FUNC("unsupported instruction in callable function",
1805                                           sec, insn->offset);
1806                                 return 1;
1807                         }
1808                         return 0;
1809
1810                 case INSN_STACK:
1811                         if (update_insn_state(insn, &state))
1812                                 return 1;
1813
1814                         break;
1815
1816                 default:
1817                         break;
1818                 }
1819
1820                 if (insn->dead_end)
1821                         return 0;
1822
1823                 if (!next_insn) {
1824                         if (state.cfa.base == CFI_UNDEFINED)
1825                                 return 0;
1826                         WARN("%s: unexpected end of section", sec->name);
1827                         return 1;
1828                 }
1829
1830                 insn = next_insn;
1831         }
1832
1833         return 0;
1834 }
1835
1836 static int validate_unwind_hints(struct objtool_file *file)
1837 {
1838         struct instruction *insn;
1839         int ret, warnings = 0;
1840         struct insn_state state;
1841
1842         if (!file->hints)
1843                 return 0;
1844
1845         clear_insn_state(&state);
1846
1847         for_each_insn(file, insn) {
1848                 if (insn->hint && !insn->visited) {
1849                         ret = validate_branch(file, insn, state);
1850                         warnings += ret;
1851                 }
1852         }
1853
1854         return warnings;
1855 }
1856
1857 static bool is_kasan_insn(struct instruction *insn)
1858 {
1859         return (insn->type == INSN_CALL &&
1860                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1861 }
1862
1863 static bool is_ubsan_insn(struct instruction *insn)
1864 {
1865         return (insn->type == INSN_CALL &&
1866                 !strcmp(insn->call_dest->name,
1867                         "__ubsan_handle_builtin_unreachable"));
1868 }
1869
1870 static bool ignore_unreachable_insn(struct instruction *insn)
1871 {
1872         int i;
1873
1874         if (insn->ignore || insn->type == INSN_NOP)
1875                 return true;
1876
1877         /*
1878          * Ignore any unused exceptions.  This can happen when a whitelisted
1879          * function has an exception table entry.
1880          *
1881          * Also ignore alternative replacement instructions.  This can happen
1882          * when a whitelisted function uses one of the ALTERNATIVE macros.
1883          */
1884         if (!strcmp(insn->sec->name, ".fixup") ||
1885             !strcmp(insn->sec->name, ".altinstr_replacement") ||
1886             !strcmp(insn->sec->name, ".altinstr_aux"))
1887                 return true;
1888
1889         /*
1890          * Check if this (or a subsequent) instruction is related to
1891          * CONFIG_UBSAN or CONFIG_KASAN.
1892          *
1893          * End the search at 5 instructions to avoid going into the weeds.
1894          */
1895         if (!insn->func)
1896                 return false;
1897         for (i = 0; i < 5; i++) {
1898
1899                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1900                         return true;
1901
1902                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1903                         insn = insn->jump_dest;
1904                         continue;
1905                 }
1906
1907                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
1908                         break;
1909                 insn = list_next_entry(insn, list);
1910         }
1911
1912         return false;
1913 }
1914
1915 static int validate_functions(struct objtool_file *file)
1916 {
1917         struct section *sec;
1918         struct symbol *func;
1919         struct instruction *insn;
1920         struct insn_state state;
1921         int ret, warnings = 0;
1922
1923         clear_insn_state(&state);
1924
1925         state.cfa = initial_func_cfi.cfa;
1926         memcpy(&state.regs, &initial_func_cfi.regs,
1927                CFI_NUM_REGS * sizeof(struct cfi_reg));
1928         state.stack_size = initial_func_cfi.cfa.offset;
1929
1930         for_each_sec(file, sec) {
1931                 list_for_each_entry(func, &sec->symbol_list, list) {
1932                         if (func->type != STT_FUNC)
1933                                 continue;
1934
1935                         insn = find_insn(file, sec, func->offset);
1936                         if (!insn || insn->ignore)
1937                                 continue;
1938
1939                         ret = validate_branch(file, insn, state);
1940                         warnings += ret;
1941                 }
1942         }
1943
1944         return warnings;
1945 }
1946
1947 static int validate_reachable_instructions(struct objtool_file *file)
1948 {
1949         struct instruction *insn;
1950
1951         if (file->ignore_unreachables)
1952                 return 0;
1953
1954         for_each_insn(file, insn) {
1955                 if (insn->visited || ignore_unreachable_insn(insn))
1956                         continue;
1957
1958                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
1959                 return 1;
1960         }
1961
1962         return 0;
1963 }
1964
1965 static void cleanup(struct objtool_file *file)
1966 {
1967         struct instruction *insn, *tmpinsn;
1968         struct alternative *alt, *tmpalt;
1969
1970         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1971                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1972                         list_del(&alt->list);
1973                         free(alt);
1974                 }
1975                 list_del(&insn->list);
1976                 hash_del(&insn->hash);
1977                 free(insn);
1978         }
1979         elf_close(file->elf);
1980 }
1981
1982 int check(const char *_objname, bool _no_fp, bool no_unreachable, bool orc)
1983 {
1984         struct objtool_file file;
1985         int ret, warnings = 0;
1986
1987         objname = _objname;
1988         no_fp = _no_fp;
1989
1990         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
1991         if (!file.elf)
1992                 return 1;
1993
1994         INIT_LIST_HEAD(&file.insn_list);
1995         hash_init(file.insn_hash);
1996         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
1997         file.rodata = find_section_by_name(file.elf, ".rodata");
1998         file.c_file = find_section_by_name(file.elf, ".comment");
1999         file.ignore_unreachables = no_unreachable;
2000         file.hints = false;
2001
2002         arch_initial_func_cfi_state(&initial_func_cfi);
2003
2004         ret = decode_sections(&file);
2005         if (ret < 0)
2006                 goto out;
2007         warnings += ret;
2008
2009         if (list_empty(&file.insn_list))
2010                 goto out;
2011
2012         ret = validate_functions(&file);
2013         if (ret < 0)
2014                 goto out;
2015         warnings += ret;
2016
2017         ret = validate_unwind_hints(&file);
2018         if (ret < 0)
2019                 goto out;
2020         warnings += ret;
2021
2022         if (!warnings) {
2023                 ret = validate_reachable_instructions(&file);
2024                 if (ret < 0)
2025                         goto out;
2026                 warnings += ret;
2027         }
2028
2029         if (orc) {
2030                 ret = create_orc(&file);
2031                 if (ret < 0)
2032                         goto out;
2033
2034                 ret = create_orc_sections(&file);
2035                 if (ret < 0)
2036                         goto out;
2037
2038                 ret = elf_write(file.elf);
2039                 if (ret < 0)
2040                         goto out;
2041         }
2042
2043 out:
2044         cleanup(&file);
2045
2046         /* ignore warnings for now until we get all the code cleaned up */
2047         if (ret || warnings)
2048                 return 0;
2049         return 0;
2050 }