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