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Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost
[cris-mirror.git] / tools / objtool / check.c
blob46c1d239cc1b8f3882451e63c278b9b634650f7b
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 "builtin.h"
22 #include "check.h"
23 #include "elf.h"
24 #include "special.h"
25 #include "arch.h"
26 #include "warn.h"
27
28 #include <linux/hashtable.h>
29 #include <linux/kernel.h>
30
31 struct alternative {
32 struct list_head list;
33 struct instruction *insn;
34 };
35
36 const char *objname;
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 insn->retpoline_safe = true;
501 continue;
502 } else {
503 /* sibling call */
504 insn->jump_dest = 0;
505 continue;
506 }
507
508 insn->jump_dest = find_insn(file, dest_sec, dest_off);
509 if (!insn->jump_dest) {
510
511 /*
512 * This is a special case where an alt instruction
513 * jumps past the end of the section. These are
514 * handled later in handle_group_alt().
515 */
516 if (!strcmp(insn->sec->name, ".altinstr_replacement"))
517 continue;
518
519 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
520 insn->sec, insn->offset, dest_sec->name,
521 dest_off);
522 return -1;
523 }
524 }
525
526 return 0;
527 }
528
529 /*
530 * Find the destination instructions for all calls.
531 */
532 static int add_call_destinations(struct objtool_file *file)
533 {
534 struct instruction *insn;
535 unsigned long dest_off;
536 struct rela *rela;
537
538 for_each_insn(file, insn) {
539 if (insn->type != INSN_CALL)
540 continue;
541
542 rela = find_rela_by_dest_range(insn->sec, insn->offset,
543 insn->len);
544 if (!rela) {
545 dest_off = insn->offset + insn->len + insn->immediate;
546 insn->call_dest = find_symbol_by_offset(insn->sec,
547 dest_off);
548
549 if (!insn->call_dest && !insn->ignore) {
550 WARN_FUNC("unsupported intra-function call",
551 insn->sec, insn->offset);
552 if (retpoline)
553 WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
554 return -1;
555 }
556
557 } else if (rela->sym->type == STT_SECTION) {
558 insn->call_dest = find_symbol_by_offset(rela->sym->sec,
559 rela->addend+4);
560 if (!insn->call_dest ||
561 insn->call_dest->type != STT_FUNC) {
562 WARN_FUNC("can't find call dest symbol at %s+0x%x",
563 insn->sec, insn->offset,
564 rela->sym->sec->name,
565 rela->addend + 4);
566 return -1;
567 }
568 } else
569 insn->call_dest = rela->sym;
570 }
571
572 return 0;
573 }
574
575 /*
576 * The .alternatives section requires some extra special care, over and above
577 * what other special sections require:
578 *
579 * 1. Because alternatives are patched in-place, we need to insert a fake jump
580 * instruction at the end so that validate_branch() skips all the original
581 * replaced instructions when validating the new instruction path.
582 *
583 * 2. An added wrinkle is that the new instruction length might be zero. In
584 * that case the old instructions are replaced with noops. We simulate that
585 * by creating a fake jump as the only new instruction.
586 *
587 * 3. In some cases, the alternative section includes an instruction which
588 * conditionally jumps to the _end_ of the entry. We have to modify these
589 * jumps' destinations to point back to .text rather than the end of the
590 * entry in .altinstr_replacement.
591 *
592 * 4. It has been requested that we don't validate the !POPCNT feature path
593 * which is a "very very small percentage of machines".
594 */
595 static int handle_group_alt(struct objtool_file *file,
596 struct special_alt *special_alt,
597 struct instruction *orig_insn,
598 struct instruction **new_insn)
599 {
600 struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
601 unsigned long dest_off;
602
603 last_orig_insn = NULL;
604 insn = orig_insn;
605 sec_for_each_insn_from(file, insn) {
606 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
607 break;
608
609 if (special_alt->skip_orig)
610 insn->type = INSN_NOP;
611
612 insn->alt_group = true;
613 last_orig_insn = insn;
614 }
615
616 if (next_insn_same_sec(file, last_orig_insn)) {
617 fake_jump = malloc(sizeof(*fake_jump));
618 if (!fake_jump) {
619 WARN("malloc failed");
620 return -1;
621 }
622 memset(fake_jump, 0, sizeof(*fake_jump));
623 INIT_LIST_HEAD(&fake_jump->alts);
624 clear_insn_state(&fake_jump->state);
625
626 fake_jump->sec = special_alt->new_sec;
627 fake_jump->offset = -1;
628 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
629 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
630 fake_jump->ignore = true;
631 }
632
633 if (!special_alt->new_len) {
634 if (!fake_jump) {
635 WARN("%s: empty alternative at end of section",
636 special_alt->orig_sec->name);
637 return -1;
638 }
639
640 *new_insn = fake_jump;
641 return 0;
642 }
643
644 last_new_insn = NULL;
645 insn = *new_insn;
646 sec_for_each_insn_from(file, insn) {
647 if (insn->offset >= special_alt->new_off + special_alt->new_len)
648 break;
649
650 last_new_insn = insn;
651
652 insn->ignore = orig_insn->ignore_alts;
653
654 if (insn->type != INSN_JUMP_CONDITIONAL &&
655 insn->type != INSN_JUMP_UNCONDITIONAL)
656 continue;
657
658 if (!insn->immediate)
659 continue;
660
661 dest_off = insn->offset + insn->len + insn->immediate;
662 if (dest_off == special_alt->new_off + special_alt->new_len) {
663 if (!fake_jump) {
664 WARN("%s: alternative jump to end of section",
665 special_alt->orig_sec->name);
666 return -1;
667 }
668 insn->jump_dest = fake_jump;
669 }
670
671 if (!insn->jump_dest) {
672 WARN_FUNC("can't find alternative jump destination",
673 insn->sec, insn->offset);
674 return -1;
675 }
676 }
677
678 if (!last_new_insn) {
679 WARN_FUNC("can't find last new alternative instruction",
680 special_alt->new_sec, special_alt->new_off);
681 return -1;
682 }
683
684 if (fake_jump)
685 list_add(&fake_jump->list, &last_new_insn->list);
686
687 return 0;
688 }
689
690 /*
691 * A jump table entry can either convert a nop to a jump or a jump to a nop.
692 * If the original instruction is a jump, make the alt entry an effective nop
693 * by just skipping the original instruction.
694 */
695 static int handle_jump_alt(struct objtool_file *file,
696 struct special_alt *special_alt,
697 struct instruction *orig_insn,
698 struct instruction **new_insn)
699 {
700 if (orig_insn->type == INSN_NOP)
701 return 0;
702
703 if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
704 WARN_FUNC("unsupported instruction at jump label",
705 orig_insn->sec, orig_insn->offset);
706 return -1;
707 }
708
709 *new_insn = list_next_entry(orig_insn, list);
710 return 0;
711 }
712
713 /*
714 * Read all the special sections which have alternate instructions which can be
715 * patched in or redirected to at runtime. Each instruction having alternate
716 * instruction(s) has them added to its insn->alts list, which will be
717 * traversed in validate_branch().
718 */
719 static int add_special_section_alts(struct objtool_file *file)
720 {
721 struct list_head special_alts;
722 struct instruction *orig_insn, *new_insn;
723 struct special_alt *special_alt, *tmp;
724 struct alternative *alt;
725 int ret;
726
727 ret = special_get_alts(file->elf, &special_alts);
728 if (ret)
729 return ret;
730
731 list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
732
733 orig_insn = find_insn(file, special_alt->orig_sec,
734 special_alt->orig_off);
735 if (!orig_insn) {
736 WARN_FUNC("special: can't find orig instruction",
737 special_alt->orig_sec, special_alt->orig_off);
738 ret = -1;
739 goto out;
740 }
741
742 new_insn = NULL;
743 if (!special_alt->group || special_alt->new_len) {
744 new_insn = find_insn(file, special_alt->new_sec,
745 special_alt->new_off);
746 if (!new_insn) {
747 WARN_FUNC("special: can't find new instruction",
748 special_alt->new_sec,
749 special_alt->new_off);
750 ret = -1;
751 goto out;
752 }
753 }
754
755 if (special_alt->group) {
756 ret = handle_group_alt(file, special_alt, orig_insn,
757 &new_insn);
758 if (ret)
759 goto out;
760 } else if (special_alt->jump_or_nop) {
761 ret = handle_jump_alt(file, special_alt, orig_insn,
762 &new_insn);
763 if (ret)
764 goto out;
765 }
766
767 alt = malloc(sizeof(*alt));
768 if (!alt) {
769 WARN("malloc failed");
770 ret = -1;
771 goto out;
772 }
773
774 alt->insn = new_insn;
775 list_add_tail(&alt->list, &orig_insn->alts);
776
777 list_del(&special_alt->list);
778 free(special_alt);
779 }
780
781 out:
782 return ret;
783 }
784
785 static int add_switch_table(struct objtool_file *file, struct symbol *func,
786 struct instruction *insn, struct rela *table,
787 struct rela *next_table)
788 {
789 struct rela *rela = table;
790 struct instruction *alt_insn;
791 struct alternative *alt;
792
793 list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
794 if (rela == next_table)
795 break;
796
797 if (rela->sym->sec != insn->sec ||
798 rela->addend <= func->offset ||
799 rela->addend >= func->offset + func->len)
800 break;
801
802 alt_insn = find_insn(file, insn->sec, rela->addend);
803 if (!alt_insn) {
804 WARN("%s: can't find instruction at %s+0x%x",
805 file->rodata->rela->name, insn->sec->name,
806 rela->addend);
807 return -1;
808 }
809
810 alt = malloc(sizeof(*alt));
811 if (!alt) {
812 WARN("malloc failed");
813 return -1;
814 }
815
816 alt->insn = alt_insn;
817 list_add_tail(&alt->list, &insn->alts);
818 }
819
820 return 0;
821 }
822
823 /*
824 * find_switch_table() - Given a dynamic jump, find the switch jump table in
825 * .rodata associated with it.
826 *
827 * There are 3 basic patterns:
828 *
829 * 1. jmpq *[rodata addr](,%reg,8)
830 *
831 * This is the most common case by far. It jumps to an address in a simple
832 * jump table which is stored in .rodata.
833 *
834 * 2. jmpq *[rodata addr](%rip)
835 *
836 * This is caused by a rare GCC quirk, currently only seen in three driver
837 * functions in the kernel, only with certain obscure non-distro configs.
838 *
839 * As part of an optimization, GCC makes a copy of an existing switch jump
840 * table, modifies it, and then hard-codes the jump (albeit with an indirect
841 * jump) to use a single entry in the table. The rest of the jump table and
842 * some of its jump targets remain as dead code.
843 *
844 * In such a case we can just crudely ignore all unreachable instruction
845 * warnings for the entire object file. Ideally we would just ignore them
846 * for the function, but that would require redesigning the code quite a
847 * bit. And honestly that's just not worth doing: unreachable instruction
848 * warnings are of questionable value anyway, and this is such a rare issue.
849 *
850 * 3. mov [rodata addr],%reg1
851 * ... some instructions ...
852 * jmpq *(%reg1,%reg2,8)
853 *
854 * This is a fairly uncommon pattern which is new for GCC 6. As of this
855 * writing, there are 11 occurrences of it in the allmodconfig kernel.
856 *
857 * As of GCC 7 there are quite a few more of these and the 'in between' code
858 * is significant. Esp. with KASAN enabled some of the code between the mov
859 * and jmpq uses .rodata itself, which can confuse things.
860 *
861 * TODO: Once we have DWARF CFI and smarter instruction decoding logic,
862 * ensure the same register is used in the mov and jump instructions.
863 *
864 * NOTE: RETPOLINE made it harder still to decode dynamic jumps.
865 */
866 static struct rela *find_switch_table(struct objtool_file *file,
867 struct symbol *func,
868 struct instruction *insn)
869 {
870 struct rela *text_rela, *rodata_rela;
871 struct instruction *orig_insn = insn;
872
873 text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
874 if (text_rela && text_rela->sym == file->rodata->sym) {
875 /* case 1 */
876 rodata_rela = find_rela_by_dest(file->rodata,
877 text_rela->addend);
878 if (rodata_rela)
879 return rodata_rela;
880
881 /* case 2 */
882 rodata_rela = find_rela_by_dest(file->rodata,
883 text_rela->addend + 4);
884 if (!rodata_rela)
885 return NULL;
886
887 file->ignore_unreachables = true;
888 return rodata_rela;
889 }
890
891 /* case 3 */
892 /*
893 * Backward search using the @first_jump_src links, these help avoid
894 * much of the 'in between' code. Which avoids us getting confused by
895 * it.
896 */
897 for (insn = list_prev_entry(insn, list);
898
899 &insn->list != &file->insn_list &&
900 insn->sec == func->sec &&
901 insn->offset >= func->offset;
902
903 insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
904
905 if (insn->type == INSN_JUMP_DYNAMIC)
906 break;
907
908 /* allow small jumps within the range */
909 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
910 insn->jump_dest &&
911 (insn->jump_dest->offset <= insn->offset ||
912 insn->jump_dest->offset > orig_insn->offset))
913 break;
914
915 /* look for a relocation which references .rodata */
916 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
917 insn->len);
918 if (!text_rela || text_rela->sym != file->rodata->sym)
919 continue;
920
921 /*
922 * Make sure the .rodata address isn't associated with a
923 * symbol. gcc jump tables are anonymous data.
924 */
925 if (find_symbol_containing(file->rodata, text_rela->addend))
926 continue;
927
928 rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend);
929 if (!rodata_rela)
930 continue;
931
932 return rodata_rela;
933 }
934
935 return NULL;
936 }
937
938
939 static int add_func_switch_tables(struct objtool_file *file,
940 struct symbol *func)
941 {
942 struct instruction *insn, *last = NULL, *prev_jump = NULL;
943 struct rela *rela, *prev_rela = NULL;
944 int ret;
945
946 func_for_each_insn(file, func, insn) {
947 if (!last)
948 last = insn;
949
950 /*
951 * Store back-pointers for unconditional forward jumps such
952 * that find_switch_table() can back-track using those and
953 * avoid some potentially confusing code.
954 */
955 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
956 insn->offset > last->offset &&
957 insn->jump_dest->offset > insn->offset &&
958 !insn->jump_dest->first_jump_src) {
959
960 insn->jump_dest->first_jump_src = insn;
961 last = insn->jump_dest;
962 }
963
964 if (insn->type != INSN_JUMP_DYNAMIC)
965 continue;
966
967 rela = find_switch_table(file, func, insn);
968 if (!rela)
969 continue;
970
971 /*
972 * We found a switch table, but we don't know yet how big it
973 * is. Don't add it until we reach the end of the function or
974 * the beginning of another switch table in the same function.
975 */
976 if (prev_jump) {
977 ret = add_switch_table(file, func, prev_jump, prev_rela,
978 rela);
979 if (ret)
980 return ret;
981 }
982
983 prev_jump = insn;
984 prev_rela = rela;
985 }
986
987 if (prev_jump) {
988 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
989 if (ret)
990 return ret;
991 }
992
993 return 0;
994 }
995
996 /*
997 * For some switch statements, gcc generates a jump table in the .rodata
998 * section which contains a list of addresses within the function to jump to.
999 * This finds these jump tables and adds them to the insn->alts lists.
1000 */
1001 static int add_switch_table_alts(struct objtool_file *file)
1002 {
1003 struct section *sec;
1004 struct symbol *func;
1005 int ret;
1006
1007 if (!file->rodata || !file->rodata->rela)
1008 return 0;
1009
1010 for_each_sec(file, sec) {
1011 list_for_each_entry(func, &sec->symbol_list, list) {
1012 if (func->type != STT_FUNC)
1013 continue;
1014
1015 ret = add_func_switch_tables(file, func);
1016 if (ret)
1017 return ret;
1018 }
1019 }
1020
1021 return 0;
1022 }
1023
1024 static int read_unwind_hints(struct objtool_file *file)
1025 {
1026 struct section *sec, *relasec;
1027 struct rela *rela;
1028 struct unwind_hint *hint;
1029 struct instruction *insn;
1030 struct cfi_reg *cfa;
1031 int i;
1032
1033 sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1034 if (!sec)
1035 return 0;
1036
1037 relasec = sec->rela;
1038 if (!relasec) {
1039 WARN("missing .rela.discard.unwind_hints section");
1040 return -1;
1041 }
1042
1043 if (sec->len % sizeof(struct unwind_hint)) {
1044 WARN("struct unwind_hint size mismatch");
1045 return -1;
1046 }
1047
1048 file->hints = true;
1049
1050 for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1051 hint = (struct unwind_hint *)sec->data->d_buf + i;
1052
1053 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1054 if (!rela) {
1055 WARN("can't find rela for unwind_hints[%d]", i);
1056 return -1;
1057 }
1058
1059 insn = find_insn(file, rela->sym->sec, rela->addend);
1060 if (!insn) {
1061 WARN("can't find insn for unwind_hints[%d]", i);
1062 return -1;
1063 }
1064
1065 cfa = &insn->state.cfa;
1066
1067 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1068 insn->save = true;
1069 continue;
1070
1071 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1072 insn->restore = true;
1073 insn->hint = true;
1074 continue;
1075 }
1076
1077 insn->hint = true;
1078
1079 switch (hint->sp_reg) {
1080 case ORC_REG_UNDEFINED:
1081 cfa->base = CFI_UNDEFINED;
1082 break;
1083 case ORC_REG_SP:
1084 cfa->base = CFI_SP;
1085 break;
1086 case ORC_REG_BP:
1087 cfa->base = CFI_BP;
1088 break;
1089 case ORC_REG_SP_INDIRECT:
1090 cfa->base = CFI_SP_INDIRECT;
1091 break;
1092 case ORC_REG_R10:
1093 cfa->base = CFI_R10;
1094 break;
1095 case ORC_REG_R13:
1096 cfa->base = CFI_R13;
1097 break;
1098 case ORC_REG_DI:
1099 cfa->base = CFI_DI;
1100 break;
1101 case ORC_REG_DX:
1102 cfa->base = CFI_DX;
1103 break;
1104 default:
1105 WARN_FUNC("unsupported unwind_hint sp base reg %d",
1106 insn->sec, insn->offset, hint->sp_reg);
1107 return -1;
1108 }
1109
1110 cfa->offset = hint->sp_offset;
1111 insn->state.type = hint->type;
1112 }
1113
1114 return 0;
1115 }
1116
1117 static int read_retpoline_hints(struct objtool_file *file)
1118 {
1119 struct section *sec, *relasec;
1120 struct instruction *insn;
1121 struct rela *rela;
1122 int i;
1123
1124 sec = find_section_by_name(file->elf, ".discard.retpoline_safe");
1125 if (!sec)
1126 return 0;
1127
1128 relasec = sec->rela;
1129 if (!relasec) {
1130 WARN("missing .rela.discard.retpoline_safe section");
1131 return -1;
1132 }
1133
1134 if (sec->len % sizeof(unsigned long)) {
1135 WARN("retpoline_safe size mismatch: %d %ld", sec->len, sizeof(unsigned long));
1136 return -1;
1137 }
1138
1139 for (i = 0; i < sec->len / sizeof(unsigned long); i++) {
1140 rela = find_rela_by_dest(sec, i * sizeof(unsigned long));
1141 if (!rela) {
1142 WARN("can't find rela for retpoline_safe[%d]", i);
1143 return -1;
1144 }
1145
1146 insn = find_insn(file, rela->sym->sec, rela->addend);
1147 if (!insn) {
1148 WARN("can't find insn for retpoline_safe[%d]", i);
1149 return -1;
1150 }
1151
1152 if (insn->type != INSN_JUMP_DYNAMIC &&
1153 insn->type != INSN_CALL_DYNAMIC) {
1154 WARN_FUNC("retpoline_safe hint not a indirect jump/call",
1155 insn->sec, insn->offset);
1156 return -1;
1157 }
1158
1159 insn->retpoline_safe = true;
1160 }
1161
1162 return 0;
1163 }
1164
1165 static int decode_sections(struct objtool_file *file)
1166 {
1167 int ret;
1168
1169 ret = decode_instructions(file);
1170 if (ret)
1171 return ret;
1172
1173 ret = add_dead_ends(file);
1174 if (ret)
1175 return ret;
1176
1177 add_ignores(file);
1178
1179 ret = add_nospec_ignores(file);
1180 if (ret)
1181 return ret;
1182
1183 ret = add_jump_destinations(file);
1184 if (ret)
1185 return ret;
1186
1187 ret = add_special_section_alts(file);
1188 if (ret)
1189 return ret;
1190
1191 ret = add_call_destinations(file);
1192 if (ret)
1193 return ret;
1194
1195 ret = add_switch_table_alts(file);
1196 if (ret)
1197 return ret;
1198
1199 ret = read_unwind_hints(file);
1200 if (ret)
1201 return ret;
1202
1203 ret = read_retpoline_hints(file);
1204 if (ret)
1205 return ret;
1206
1207 return 0;
1208 }
1209
1210 static bool is_fentry_call(struct instruction *insn)
1211 {
1212 if (insn->type == INSN_CALL &&
1213 insn->call_dest->type == STT_NOTYPE &&
1214 !strcmp(insn->call_dest->name, "__fentry__"))
1215 return true;
1216
1217 return false;
1218 }
1219
1220 static bool has_modified_stack_frame(struct insn_state *state)
1221 {
1222 int i;
1223
1224 if (state->cfa.base != initial_func_cfi.cfa.base ||
1225 state->cfa.offset != initial_func_cfi.cfa.offset ||
1226 state->stack_size != initial_func_cfi.cfa.offset ||
1227 state->drap)
1228 return true;
1229
1230 for (i = 0; i < CFI_NUM_REGS; i++)
1231 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1232 state->regs[i].offset != initial_func_cfi.regs[i].offset)
1233 return true;
1234
1235 return false;
1236 }
1237
1238 static bool has_valid_stack_frame(struct insn_state *state)
1239 {
1240 if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1241 state->regs[CFI_BP].offset == -16)
1242 return true;
1243
1244 if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1245 return true;
1246
1247 return false;
1248 }
1249
1250 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1251 {
1252 struct cfi_reg *cfa = &state->cfa;
1253 struct stack_op *op = &insn->stack_op;
1254
1255 if (cfa->base != CFI_SP)
1256 return 0;
1257
1258 /* push */
1259 if (op->dest.type == OP_DEST_PUSH)
1260 cfa->offset += 8;
1261
1262 /* pop */
1263 if (op->src.type == OP_SRC_POP)
1264 cfa->offset -= 8;
1265
1266 /* add immediate to sp */
1267 if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1268 op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1269 cfa->offset -= op->src.offset;
1270
1271 return 0;
1272 }
1273
1274 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1275 int offset)
1276 {
1277 if (arch_callee_saved_reg(reg) &&
1278 state->regs[reg].base == CFI_UNDEFINED) {
1279 state->regs[reg].base = base;
1280 state->regs[reg].offset = offset;
1281 }
1282 }
1283
1284 static void restore_reg(struct insn_state *state, unsigned char reg)
1285 {
1286 state->regs[reg].base = CFI_UNDEFINED;
1287 state->regs[reg].offset = 0;
1288 }
1289
1290 /*
1291 * A note about DRAP stack alignment:
1292 *
1293 * GCC has the concept of a DRAP register, which is used to help keep track of
1294 * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
1295 * register. The typical DRAP pattern is:
1296 *
1297 * 4c 8d 54 24 08 lea 0x8(%rsp),%r10
1298 * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
1299 * 41 ff 72 f8 pushq -0x8(%r10)
1300 * 55 push %rbp
1301 * 48 89 e5 mov %rsp,%rbp
1302 * (more pushes)
1303 * 41 52 push %r10
1304 * ...
1305 * 41 5a pop %r10
1306 * (more pops)
1307 * 5d pop %rbp
1308 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1309 * c3 retq
1310 *
1311 * There are some variations in the epilogues, like:
1312 *
1313 * 5b pop %rbx
1314 * 41 5a pop %r10
1315 * 41 5c pop %r12
1316 * 41 5d pop %r13
1317 * 41 5e pop %r14
1318 * c9 leaveq
1319 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1320 * c3 retq
1321 *
1322 * and:
1323 *
1324 * 4c 8b 55 e8 mov -0x18(%rbp),%r10
1325 * 48 8b 5d e0 mov -0x20(%rbp),%rbx
1326 * 4c 8b 65 f0 mov -0x10(%rbp),%r12
1327 * 4c 8b 6d f8 mov -0x8(%rbp),%r13
1328 * c9 leaveq
1329 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1330 * c3 retq
1331 *
1332 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1333 * restored beforehand:
1334 *
1335 * 41 55 push %r13
1336 * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
1337 * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
1338 * ...
1339 * 49 8d 65 f0 lea -0x10(%r13),%rsp
1340 * 41 5d pop %r13
1341 * c3 retq
1342 */
1343 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1344 {
1345 struct stack_op *op = &insn->stack_op;
1346 struct cfi_reg *cfa = &state->cfa;
1347 struct cfi_reg *regs = state->regs;
1348
1349 /* stack operations don't make sense with an undefined CFA */
1350 if (cfa->base == CFI_UNDEFINED) {
1351 if (insn->func) {
1352 WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1353 return -1;
1354 }
1355 return 0;
1356 }
1357
1358 if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1359 return update_insn_state_regs(insn, state);
1360
1361 switch (op->dest.type) {
1362
1363 case OP_DEST_REG:
1364 switch (op->src.type) {
1365
1366 case OP_SRC_REG:
1367 if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1368 cfa->base == CFI_SP &&
1369 regs[CFI_BP].base == CFI_CFA &&
1370 regs[CFI_BP].offset == -cfa->offset) {
1371
1372 /* mov %rsp, %rbp */
1373 cfa->base = op->dest.reg;
1374 state->bp_scratch = false;
1375 }
1376
1377 else if (op->src.reg == CFI_SP &&
1378 op->dest.reg == CFI_BP && state->drap) {
1379
1380 /* drap: mov %rsp, %rbp */
1381 regs[CFI_BP].base = CFI_BP;
1382 regs[CFI_BP].offset = -state->stack_size;
1383 state->bp_scratch = false;
1384 }
1385
1386 else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1387
1388 /*
1389 * mov %rsp, %reg
1390 *
1391 * This is needed for the rare case where GCC
1392 * does:
1393 *
1394 * mov %rsp, %rax
1395 * ...
1396 * mov %rax, %rsp
1397 */
1398 state->vals[op->dest.reg].base = CFI_CFA;
1399 state->vals[op->dest.reg].offset = -state->stack_size;
1400 }
1401
1402 else if (op->dest.reg == cfa->base) {
1403
1404 /* mov %reg, %rsp */
1405 if (cfa->base == CFI_SP &&
1406 state->vals[op->src.reg].base == CFI_CFA) {
1407
1408 /*
1409 * This is needed for the rare case
1410 * where GCC does something dumb like:
1411 *
1412 * lea 0x8(%rsp), %rcx
1413 * ...
1414 * mov %rcx, %rsp
1415 */
1416 cfa->offset = -state->vals[op->src.reg].offset;
1417 state->stack_size = cfa->offset;
1418
1419 } else {
1420 cfa->base = CFI_UNDEFINED;
1421 cfa->offset = 0;
1422 }
1423 }
1424
1425 break;
1426
1427 case OP_SRC_ADD:
1428 if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1429
1430 /* add imm, %rsp */
1431 state->stack_size -= op->src.offset;
1432 if (cfa->base == CFI_SP)
1433 cfa->offset -= op->src.offset;
1434 break;
1435 }
1436
1437 if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1438
1439 /* lea disp(%rbp), %rsp */
1440 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1441 break;
1442 }
1443
1444 if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1445
1446 /* drap: lea disp(%rsp), %drap */
1447 state->drap_reg = op->dest.reg;
1448
1449 /*
1450 * lea disp(%rsp), %reg
1451 *
1452 * This is needed for the rare case where GCC
1453 * does something dumb like:
1454 *
1455 * lea 0x8(%rsp), %rcx
1456 * ...
1457 * mov %rcx, %rsp
1458 */
1459 state->vals[op->dest.reg].base = CFI_CFA;
1460 state->vals[op->dest.reg].offset = \
1461 -state->stack_size + op->src.offset;
1462
1463 break;
1464 }
1465
1466 if (state->drap && op->dest.reg == CFI_SP &&
1467 op->src.reg == state->drap_reg) {
1468
1469 /* drap: lea disp(%drap), %rsp */
1470 cfa->base = CFI_SP;
1471 cfa->offset = state->stack_size = -op->src.offset;
1472 state->drap_reg = CFI_UNDEFINED;
1473 state->drap = false;
1474 break;
1475 }
1476
1477 if (op->dest.reg == state->cfa.base) {
1478 WARN_FUNC("unsupported stack register modification",
1479 insn->sec, insn->offset);
1480 return -1;
1481 }
1482
1483 break;
1484
1485 case OP_SRC_AND:
1486 if (op->dest.reg != CFI_SP ||
1487 (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1488 (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1489 WARN_FUNC("unsupported stack pointer realignment",
1490 insn->sec, insn->offset);
1491 return -1;
1492 }
1493
1494 if (state->drap_reg != CFI_UNDEFINED) {
1495 /* drap: and imm, %rsp */
1496 cfa->base = state->drap_reg;
1497 cfa->offset = state->stack_size = 0;
1498 state->drap = true;
1499 }
1500
1501 /*
1502 * Older versions of GCC (4.8ish) realign the stack
1503 * without DRAP, with a frame pointer.
1504 */
1505
1506 break;
1507
1508 case OP_SRC_POP:
1509 if (!state->drap && op->dest.type == OP_DEST_REG &&
1510 op->dest.reg == cfa->base) {
1511
1512 /* pop %rbp */
1513 cfa->base = CFI_SP;
1514 }
1515
1516 if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1517 op->dest.type == OP_DEST_REG &&
1518 op->dest.reg == state->drap_reg &&
1519 state->drap_offset == -state->stack_size) {
1520
1521 /* drap: pop %drap */
1522 cfa->base = state->drap_reg;
1523 cfa->offset = 0;
1524 state->drap_offset = -1;
1525
1526 } else if (regs[op->dest.reg].offset == -state->stack_size) {
1527
1528 /* pop %reg */
1529 restore_reg(state, op->dest.reg);
1530 }
1531
1532 state->stack_size -= 8;
1533 if (cfa->base == CFI_SP)
1534 cfa->offset -= 8;
1535
1536 break;
1537
1538 case OP_SRC_REG_INDIRECT:
1539 if (state->drap && op->src.reg == CFI_BP &&
1540 op->src.offset == state->drap_offset) {
1541
1542 /* drap: mov disp(%rbp), %drap */
1543 cfa->base = state->drap_reg;
1544 cfa->offset = 0;
1545 state->drap_offset = -1;
1546 }
1547
1548 if (state->drap && op->src.reg == CFI_BP &&
1549 op->src.offset == regs[op->dest.reg].offset) {
1550
1551 /* drap: mov disp(%rbp), %reg */
1552 restore_reg(state, op->dest.reg);
1553
1554 } else if (op->src.reg == cfa->base &&
1555 op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1556
1557 /* mov disp(%rbp), %reg */
1558 /* mov disp(%rsp), %reg */
1559 restore_reg(state, op->dest.reg);
1560 }
1561
1562 break;
1563
1564 default:
1565 WARN_FUNC("unknown stack-related instruction",
1566 insn->sec, insn->offset);
1567 return -1;
1568 }
1569
1570 break;
1571
1572 case OP_DEST_PUSH:
1573 state->stack_size += 8;
1574 if (cfa->base == CFI_SP)
1575 cfa->offset += 8;
1576
1577 if (op->src.type != OP_SRC_REG)
1578 break;
1579
1580 if (state->drap) {
1581 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1582
1583 /* drap: push %drap */
1584 cfa->base = CFI_BP_INDIRECT;
1585 cfa->offset = -state->stack_size;
1586
1587 /* save drap so we know when to restore it */
1588 state->drap_offset = -state->stack_size;
1589
1590 } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1591
1592 /* drap: push %rbp */
1593 state->stack_size = 0;
1594
1595 } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1596
1597 /* drap: push %reg */
1598 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1599 }
1600
1601 } else {
1602
1603 /* push %reg */
1604 save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1605 }
1606
1607 /* detect when asm code uses rbp as a scratch register */
1608 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1609 cfa->base != CFI_BP)
1610 state->bp_scratch = true;
1611 break;
1612
1613 case OP_DEST_REG_INDIRECT:
1614
1615 if (state->drap) {
1616 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1617
1618 /* drap: mov %drap, disp(%rbp) */
1619 cfa->base = CFI_BP_INDIRECT;
1620 cfa->offset = op->dest.offset;
1621
1622 /* save drap offset so we know when to restore it */
1623 state->drap_offset = op->dest.offset;
1624 }
1625
1626 else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1627
1628 /* drap: mov reg, disp(%rbp) */
1629 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1630 }
1631
1632 } else if (op->dest.reg == cfa->base) {
1633
1634 /* mov reg, disp(%rbp) */
1635 /* mov reg, disp(%rsp) */
1636 save_reg(state, op->src.reg, CFI_CFA,
1637 op->dest.offset - state->cfa.offset);
1638 }
1639
1640 break;
1641
1642 case OP_DEST_LEAVE:
1643 if ((!state->drap && cfa->base != CFI_BP) ||
1644 (state->drap && cfa->base != state->drap_reg)) {
1645 WARN_FUNC("leave instruction with modified stack frame",
1646 insn->sec, insn->offset);
1647 return -1;
1648 }
1649
1650 /* leave (mov %rbp, %rsp; pop %rbp) */
1651
1652 state->stack_size = -state->regs[CFI_BP].offset - 8;
1653 restore_reg(state, CFI_BP);
1654
1655 if (!state->drap) {
1656 cfa->base = CFI_SP;
1657 cfa->offset -= 8;
1658 }
1659
1660 break;
1661
1662 case OP_DEST_MEM:
1663 if (op->src.type != OP_SRC_POP) {
1664 WARN_FUNC("unknown stack-related memory operation",
1665 insn->sec, insn->offset);
1666 return -1;
1667 }
1668
1669 /* pop mem */
1670 state->stack_size -= 8;
1671 if (cfa->base == CFI_SP)
1672 cfa->offset -= 8;
1673
1674 break;
1675
1676 default:
1677 WARN_FUNC("unknown stack-related instruction",
1678 insn->sec, insn->offset);
1679 return -1;
1680 }
1681
1682 return 0;
1683 }
1684
1685 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1686 {
1687 struct insn_state *state1 = &insn->state, *state2 = state;
1688 int i;
1689
1690 if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1691 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1692 insn->sec, insn->offset,
1693 state1->cfa.base, state1->cfa.offset,
1694 state2->cfa.base, state2->cfa.offset);
1695
1696 } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1697 for (i = 0; i < CFI_NUM_REGS; i++) {
1698 if (!memcmp(&state1->regs[i], &state2->regs[i],
1699 sizeof(struct cfi_reg)))
1700 continue;
1701
1702 WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1703 insn->sec, insn->offset,
1704 i, state1->regs[i].base, state1->regs[i].offset,
1705 i, state2->regs[i].base, state2->regs[i].offset);
1706 break;
1707 }
1708
1709 } else if (state1->type != state2->type) {
1710 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1711 insn->sec, insn->offset, state1->type, state2->type);
1712
1713 } else if (state1->drap != state2->drap ||
1714 (state1->drap && state1->drap_reg != state2->drap_reg) ||
1715 (state1->drap && state1->drap_offset != state2->drap_offset)) {
1716 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1717 insn->sec, insn->offset,
1718 state1->drap, state1->drap_reg, state1->drap_offset,
1719 state2->drap, state2->drap_reg, state2->drap_offset);
1720
1721 } else
1722 return true;
1723
1724 return false;
1725 }
1726
1727 /*
1728 * Follow the branch starting at the given instruction, and recursively follow
1729 * any other branches (jumps). Meanwhile, track the frame pointer state at
1730 * each instruction and validate all the rules described in
1731 * tools/objtool/Documentation/stack-validation.txt.
1732 */
1733 static int validate_branch(struct objtool_file *file, struct instruction *first,
1734 struct insn_state state)
1735 {
1736 struct alternative *alt;
1737 struct instruction *insn, *next_insn;
1738 struct section *sec;
1739 struct symbol *func = NULL;
1740 int ret;
1741
1742 insn = first;
1743 sec = insn->sec;
1744
1745 if (insn->alt_group && list_empty(&insn->alts)) {
1746 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1747 sec, insn->offset);
1748 return 1;
1749 }
1750
1751 while (1) {
1752 next_insn = next_insn_same_sec(file, insn);
1753
1754
1755 if (file->c_file && func && insn->func && func != insn->func) {
1756 WARN("%s() falls through to next function %s()",
1757 func->name, insn->func->name);
1758 return 1;
1759 }
1760
1761 if (insn->func)
1762 func = insn->func;
1763
1764 if (func && insn->ignore) {
1765 WARN_FUNC("BUG: why am I validating an ignored function?",
1766 sec, insn->offset);
1767 return 1;
1768 }
1769
1770 if (insn->visited) {
1771 if (!insn->hint && !insn_state_match(insn, &state))
1772 return 1;
1773
1774 return 0;
1775 }
1776
1777 if (insn->hint) {
1778 if (insn->restore) {
1779 struct instruction *save_insn, *i;
1780
1781 i = insn;
1782 save_insn = NULL;
1783 func_for_each_insn_continue_reverse(file, func, i) {
1784 if (i->save) {
1785 save_insn = i;
1786 break;
1787 }
1788 }
1789
1790 if (!save_insn) {
1791 WARN_FUNC("no corresponding CFI save for CFI restore",
1792 sec, insn->offset);
1793 return 1;
1794 }
1795
1796 if (!save_insn->visited) {
1797 /*
1798 * Oops, no state to copy yet.
1799 * Hopefully we can reach this
1800 * instruction from another branch
1801 * after the save insn has been
1802 * visited.
1803 */
1804 if (insn == first)
1805 return 0;
1806
1807 WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1808 sec, insn->offset);
1809 return 1;
1810 }
1811
1812 insn->state = save_insn->state;
1813 }
1814
1815 state = insn->state;
1816
1817 } else
1818 insn->state = state;
1819
1820 insn->visited = true;
1821
1822 if (!insn->ignore_alts) {
1823 list_for_each_entry(alt, &insn->alts, list) {
1824 ret = validate_branch(file, alt->insn, state);
1825 if (ret)
1826 return 1;
1827 }
1828 }
1829
1830 switch (insn->type) {
1831
1832 case INSN_RETURN:
1833 if (func && has_modified_stack_frame(&state)) {
1834 WARN_FUNC("return with modified stack frame",
1835 sec, insn->offset);
1836 return 1;
1837 }
1838
1839 if (state.bp_scratch) {
1840 WARN("%s uses BP as a scratch register",
1841 insn->func->name);
1842 return 1;
1843 }
1844
1845 return 0;
1846
1847 case INSN_CALL:
1848 if (is_fentry_call(insn))
1849 break;
1850
1851 ret = dead_end_function(file, insn->call_dest);
1852 if (ret == 1)
1853 return 0;
1854 if (ret == -1)
1855 return 1;
1856
1857 /* fallthrough */
1858 case INSN_CALL_DYNAMIC:
1859 if (!no_fp && func && !has_valid_stack_frame(&state)) {
1860 WARN_FUNC("call without frame pointer save/setup",
1861 sec, insn->offset);
1862 return 1;
1863 }
1864 break;
1865
1866 case INSN_JUMP_CONDITIONAL:
1867 case INSN_JUMP_UNCONDITIONAL:
1868 if (insn->jump_dest &&
1869 (!func || !insn->jump_dest->func ||
1870 func == insn->jump_dest->func)) {
1871 ret = validate_branch(file, insn->jump_dest,
1872 state);
1873 if (ret)
1874 return 1;
1875
1876 } else if (func && has_modified_stack_frame(&state)) {
1877 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1878 sec, insn->offset);
1879 return 1;
1880 }
1881
1882 if (insn->type == INSN_JUMP_UNCONDITIONAL)
1883 return 0;
1884
1885 break;
1886
1887 case INSN_JUMP_DYNAMIC:
1888 if (func && list_empty(&insn->alts) &&
1889 has_modified_stack_frame(&state)) {
1890 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1891 sec, insn->offset);
1892 return 1;
1893 }
1894
1895 return 0;
1896
1897 case INSN_CONTEXT_SWITCH:
1898 if (func && (!next_insn || !next_insn->hint)) {
1899 WARN_FUNC("unsupported instruction in callable function",
1900 sec, insn->offset);
1901 return 1;
1902 }
1903 return 0;
1904
1905 case INSN_STACK:
1906 if (update_insn_state(insn, &state))
1907 return 1;
1908
1909 break;
1910
1911 default:
1912 break;
1913 }
1914
1915 if (insn->dead_end)
1916 return 0;
1917
1918 if (!next_insn) {
1919 if (state.cfa.base == CFI_UNDEFINED)
1920 return 0;
1921 WARN("%s: unexpected end of section", sec->name);
1922 return 1;
1923 }
1924
1925 insn = next_insn;
1926 }
1927
1928 return 0;
1929 }
1930
1931 static int validate_unwind_hints(struct objtool_file *file)
1932 {
1933 struct instruction *insn;
1934 int ret, warnings = 0;
1935 struct insn_state state;
1936
1937 if (!file->hints)
1938 return 0;
1939
1940 clear_insn_state(&state);
1941
1942 for_each_insn(file, insn) {
1943 if (insn->hint && !insn->visited) {
1944 ret = validate_branch(file, insn, state);
1945 warnings += ret;
1946 }
1947 }
1948
1949 return warnings;
1950 }
1951
1952 static int validate_retpoline(struct objtool_file *file)
1953 {
1954 struct instruction *insn;
1955 int warnings = 0;
1956
1957 for_each_insn(file, insn) {
1958 if (insn->type != INSN_JUMP_DYNAMIC &&
1959 insn->type != INSN_CALL_DYNAMIC)
1960 continue;
1961
1962 if (insn->retpoline_safe)
1963 continue;
1964
1965 /*
1966 * .init.text code is ran before userspace and thus doesn't
1967 * strictly need retpolines, except for modules which are
1968 * loaded late, they very much do need retpoline in their
1969 * .init.text
1970 */
1971 if (!strcmp(insn->sec->name, ".init.text") && !module)
1972 continue;
1973
1974 WARN_FUNC("indirect %s found in RETPOLINE build",
1975 insn->sec, insn->offset,
1976 insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
1977
1978 warnings++;
1979 }
1980
1981 return warnings;
1982 }
1983
1984 static bool is_kasan_insn(struct instruction *insn)
1985 {
1986 return (insn->type == INSN_CALL &&
1987 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1988 }
1989
1990 static bool is_ubsan_insn(struct instruction *insn)
1991 {
1992 return (insn->type == INSN_CALL &&
1993 !strcmp(insn->call_dest->name,
1994 "__ubsan_handle_builtin_unreachable"));
1995 }
1996
1997 static bool ignore_unreachable_insn(struct instruction *insn)
1998 {
1999 int i;
2000
2001 if (insn->ignore || insn->type == INSN_NOP)
2002 return true;
2003
2004 /*
2005 * Ignore any unused exceptions. This can happen when a whitelisted
2006 * function has an exception table entry.
2007 *
2008 * Also ignore alternative replacement instructions. This can happen
2009 * when a whitelisted function uses one of the ALTERNATIVE macros.
2010 */
2011 if (!strcmp(insn->sec->name, ".fixup") ||
2012 !strcmp(insn->sec->name, ".altinstr_replacement") ||
2013 !strcmp(insn->sec->name, ".altinstr_aux"))
2014 return true;
2015
2016 /*
2017 * Check if this (or a subsequent) instruction is related to
2018 * CONFIG_UBSAN or CONFIG_KASAN.
2019 *
2020 * End the search at 5 instructions to avoid going into the weeds.
2021 */
2022 if (!insn->func)
2023 return false;
2024 for (i = 0; i < 5; i++) {
2025
2026 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2027 return true;
2028
2029 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2030 if (insn->jump_dest &&
2031 insn->jump_dest->func == insn->func) {
2032 insn = insn->jump_dest;
2033 continue;
2034 }
2035
2036 break;
2037 }
2038
2039 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2040 break;
2041
2042 insn = list_next_entry(insn, list);
2043 }
2044
2045 return false;
2046 }
2047
2048 static int validate_functions(struct objtool_file *file)
2049 {
2050 struct section *sec;
2051 struct symbol *func;
2052 struct instruction *insn;
2053 struct insn_state state;
2054 int ret, warnings = 0;
2055
2056 clear_insn_state(&state);
2057
2058 state.cfa = initial_func_cfi.cfa;
2059 memcpy(&state.regs, &initial_func_cfi.regs,
2060 CFI_NUM_REGS * sizeof(struct cfi_reg));
2061 state.stack_size = initial_func_cfi.cfa.offset;
2062
2063 for_each_sec(file, sec) {
2064 list_for_each_entry(func, &sec->symbol_list, list) {
2065 if (func->type != STT_FUNC)
2066 continue;
2067
2068 insn = find_insn(file, sec, func->offset);
2069 if (!insn || insn->ignore)
2070 continue;
2071
2072 ret = validate_branch(file, insn, state);
2073 warnings += ret;
2074 }
2075 }
2076
2077 return warnings;
2078 }
2079
2080 static int validate_reachable_instructions(struct objtool_file *file)
2081 {
2082 struct instruction *insn;
2083
2084 if (file->ignore_unreachables)
2085 return 0;
2086
2087 for_each_insn(file, insn) {
2088 if (insn->visited || ignore_unreachable_insn(insn))
2089 continue;
2090
2091 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2092 return 1;
2093 }
2094
2095 return 0;
2096 }
2097
2098 static void cleanup(struct objtool_file *file)
2099 {
2100 struct instruction *insn, *tmpinsn;
2101 struct alternative *alt, *tmpalt;
2102
2103 list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2104 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2105 list_del(&alt->list);
2106 free(alt);
2107 }
2108 list_del(&insn->list);
2109 hash_del(&insn->hash);
2110 free(insn);
2111 }
2112 elf_close(file->elf);
2113 }
2114
2115 int check(const char *_objname, bool orc)
2116 {
2117 struct objtool_file file;
2118 int ret, warnings = 0;
2119
2120 objname = _objname;
2121
2122 file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2123 if (!file.elf)
2124 return 1;
2125
2126 INIT_LIST_HEAD(&file.insn_list);
2127 hash_init(file.insn_hash);
2128 file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
2129 file.rodata = find_section_by_name(file.elf, ".rodata");
2130 file.c_file = find_section_by_name(file.elf, ".comment");
2131 file.ignore_unreachables = no_unreachable;
2132 file.hints = false;
2133
2134 arch_initial_func_cfi_state(&initial_func_cfi);
2135
2136 ret = decode_sections(&file);
2137 if (ret < 0)
2138 goto out;
2139 warnings += ret;
2140
2141 if (list_empty(&file.insn_list))
2142 goto out;
2143
2144 if (retpoline) {
2145 ret = validate_retpoline(&file);
2146 if (ret < 0)
2147 return ret;
2148 warnings += ret;
2149 }
2150
2151 ret = validate_functions(&file);
2152 if (ret < 0)
2153 goto out;
2154 warnings += ret;
2155
2156 ret = validate_unwind_hints(&file);
2157 if (ret < 0)
2158 goto out;
2159 warnings += ret;
2160
2161 if (!warnings) {
2162 ret = validate_reachable_instructions(&file);
2163 if (ret < 0)
2164 goto out;
2165 warnings += ret;
2166 }
2167
2168 if (orc) {
2169 ret = create_orc(&file);
2170 if (ret < 0)
2171 goto out;
2172
2173 ret = create_orc_sections(&file);
2174 if (ret < 0)
2175 goto out;
2176
2177 ret = elf_write(file.elf);
2178 if (ret < 0)
2179 goto out;
2180 }
2181
2182 out:
2183 cleanup(&file);
2184
2185 /* ignore warnings for now until we get all the code cleaned up */
2186 if (ret || warnings)
2187 return 0;
2188 return 0;
2189 }
CRIS linux kernel tree