?  search:
summary | log | graphiclog1 | graphiclog2 | commit | commitdiff | tree | refs | edit | fork
blame | history | raw | HEAD
Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...
[cris-mirror.git] / tools / objtool / check.c
bloba8cb69a2657658ec41c5877f1b4a47526c8079b0
1 /*
2 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version 2
7 * of the License, or (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, see <http://www.gnu.org/licenses/>.
16 */
17
18 #include <string.h>
19 #include <stdlib.h>
20
21 #include "check.h"
22 #include "elf.h"
23 #include "special.h"
24 #include "arch.h"
25 #include "warn.h"
26
27 #include <linux/hashtable.h>
28 #include <linux/kernel.h>
29
30 struct alternative {
31 struct list_head list;
32 struct instruction *insn;
33 };
34
35 const char *objname;
36 static bool no_fp;
37 struct cfi_state initial_func_cfi;
38
39 struct instruction *find_insn(struct objtool_file *file,
40 struct section *sec, unsigned long offset)
41 {
42 struct instruction *insn;
43
44 hash_for_each_possible(file->insn_hash, insn, hash, offset)
45 if (insn->sec == sec && insn->offset == offset)
46 return insn;
47
48 return NULL;
49 }
50
51 static struct instruction *next_insn_same_sec(struct objtool_file *file,
52 struct instruction *insn)
53 {
54 struct instruction *next = list_next_entry(insn, list);
55
56 if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
57 return NULL;
58
59 return next;
60 }
61
62 #define func_for_each_insn(file, func, insn) \
63 for (insn = find_insn(file, func->sec, func->offset); \
64 insn && &insn->list != &file->insn_list && \
65 insn->sec == func->sec && \
66 insn->offset < func->offset + func->len; \
67 insn = list_next_entry(insn, list))
68
69 #define func_for_each_insn_continue_reverse(file, func, insn) \
70 for (insn = list_prev_entry(insn, list); \
71 &insn->list != &file->insn_list && \
72 insn->sec == func->sec && insn->offset >= func->offset; \
73 insn = list_prev_entry(insn, list))
74
75 #define sec_for_each_insn_from(file, insn) \
76 for (; insn; insn = next_insn_same_sec(file, insn))
77
78 #define sec_for_each_insn_continue(file, insn) \
79 for (insn = next_insn_same_sec(file, insn); insn; \
80 insn = next_insn_same_sec(file, insn))
81
82 /*
83 * Check if the function has been manually whitelisted with the
84 * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
85 * due to its use of a context switching instruction.
86 */
87 static bool ignore_func(struct objtool_file *file, struct symbol *func)
88 {
89 struct rela *rela;
90
91 /* check for STACK_FRAME_NON_STANDARD */
92 if (file->whitelist && file->whitelist->rela)
93 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
94 if (rela->sym->type == STT_SECTION &&
95 rela->sym->sec == func->sec &&
96 rela->addend == func->offset)
97 return true;
98 if (rela->sym->type == STT_FUNC && rela->sym == func)
99 return true;
100 }
101
102 return false;
103 }
104
105 /*
106 * This checks to see if the given function is a "noreturn" function.
107 *
108 * For global functions which are outside the scope of this object file, we
109 * have to keep a manual list of them.
110 *
111 * For local functions, we have to detect them manually by simply looking for
112 * the lack of a return instruction.
113 *
114 * Returns:
115 * -1: error
116 * 0: no dead end
117 * 1: dead end
118 */
119 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
120 int recursion)
121 {
122 int i;
123 struct instruction *insn;
124 bool empty = true;
125
126 /*
127 * Unfortunately these have to be hard coded because the noreturn
128 * attribute isn't provided in ELF data.
129 */
130 static const char * const global_noreturns[] = {
131 "__stack_chk_fail",
132 "panic",
133 "do_exit",
134 "do_task_dead",
135 "__module_put_and_exit",
136 "complete_and_exit",
137 "kvm_spurious_fault",
138 "__reiserfs_panic",
139 "lbug_with_loc",
140 "fortify_panic",
141 "usercopy_abort",
142 };
143
144 if (func->bind == STB_WEAK)
145 return 0;
146
147 if (func->bind == STB_GLOBAL)
148 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
149 if (!strcmp(func->name, global_noreturns[i]))
150 return 1;
151
152 if (!func->sec)
153 return 0;
154
155 func_for_each_insn(file, func, insn) {
156 empty = false;
157
158 if (insn->type == INSN_RETURN)
159 return 0;
160 }
161
162 if (empty)
163 return 0;
164
165 /*
166 * A function can have a sibling call instead of a return. In that
167 * case, the function's dead-end status depends on whether the target
168 * of the sibling call returns.
169 */
170 func_for_each_insn(file, func, insn) {
171 if (insn->sec != func->sec ||
172 insn->offset >= func->offset + func->len)
173 break;
174
175 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
176 struct instruction *dest = insn->jump_dest;
177 struct symbol *dest_func;
178
179 if (!dest)
180 /* sibling call to another file */
181 return 0;
182
183 if (dest->sec != func->sec ||
184 dest->offset < func->offset ||
185 dest->offset >= func->offset + func->len) {
186 /* local sibling call */
187 dest_func = find_symbol_by_offset(dest->sec,
188 dest->offset);
189 if (!dest_func)
190 continue;
191
192 if (recursion == 5) {
193 WARN_FUNC("infinite recursion (objtool bug!)",
194 dest->sec, dest->offset);
195 return -1;
196 }
197
198 return __dead_end_function(file, dest_func,
199 recursion + 1);
200 }
201 }
202
203 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
204 /* sibling call */
205 return 0;
206 }
207
208 return 1;
209 }
210
211 static int dead_end_function(struct objtool_file *file, struct symbol *func)
212 {
213 return __dead_end_function(file, func, 0);
214 }
215
216 static void clear_insn_state(struct insn_state *state)
217 {
218 int i;
219
220 memset(state, 0, sizeof(*state));
221 state->cfa.base = CFI_UNDEFINED;
222 for (i = 0; i < CFI_NUM_REGS; i++) {
223 state->regs[i].base = CFI_UNDEFINED;
224 state->vals[i].base = CFI_UNDEFINED;
225 }
226 state->drap_reg = CFI_UNDEFINED;
227 state->drap_offset = -1;
228 }
229
230 /*
231 * Call the arch-specific instruction decoder for all the instructions and add
232 * them to the global instruction list.
233 */
234 static int decode_instructions(struct objtool_file *file)
235 {
236 struct section *sec;
237 struct symbol *func;
238 unsigned long offset;
239 struct instruction *insn;
240 int ret;
241
242 for_each_sec(file, sec) {
243
244 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
245 continue;
246
247 if (strcmp(sec->name, ".altinstr_replacement") &&
248 strcmp(sec->name, ".altinstr_aux") &&
249 strncmp(sec->name, ".discard.", 9))
250 sec->text = true;
251
252 for (offset = 0; offset < sec->len; offset += insn->len) {
253 insn = malloc(sizeof(*insn));
254 if (!insn) {
255 WARN("malloc failed");
256 return -1;
257 }
258 memset(insn, 0, sizeof(*insn));
259 INIT_LIST_HEAD(&insn->alts);
260 clear_insn_state(&insn->state);
261
262 insn->sec = sec;
263 insn->offset = offset;
264
265 ret = arch_decode_instruction(file->elf, sec, offset,
266 sec->len - offset,
267 &insn->len, &insn->type,
268 &insn->immediate,
269 &insn->stack_op);
270 if (ret)
271 goto err;
272
273 if (!insn->type || insn->type > INSN_LAST) {
274 WARN_FUNC("invalid instruction type %d",
275 insn->sec, insn->offset, insn->type);
276 ret = -1;
277 goto err;
278 }
279
280 hash_add(file->insn_hash, &insn->hash, insn->offset);
281 list_add_tail(&insn->list, &file->insn_list);
282 }
283
284 list_for_each_entry(func, &sec->symbol_list, list) {
285 if (func->type != STT_FUNC)
286 continue;
287
288 if (!find_insn(file, sec, func->offset)) {
289 WARN("%s(): can't find starting instruction",
290 func->name);
291 return -1;
292 }
293
294 func_for_each_insn(file, func, insn)
295 if (!insn->func)
296 insn->func = func;
297 }
298 }
299
300 return 0;
301
302 err:
303 free(insn);
304 return ret;
305 }
306
307 /*
308 * Mark "ud2" instructions and manually annotated dead ends.
309 */
310 static int add_dead_ends(struct objtool_file *file)
311 {
312 struct section *sec;
313 struct rela *rela;
314 struct instruction *insn;
315 bool found;
316
317 /*
318 * By default, "ud2" is a dead end unless otherwise annotated, because
319 * GCC 7 inserts it for certain divide-by-zero cases.
320 */
321 for_each_insn(file, insn)
322 if (insn->type == INSN_BUG)
323 insn->dead_end = true;
324
325 /*
326 * Check for manually annotated dead ends.
327 */
328 sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
329 if (!sec)
330 goto reachable;
331
332 list_for_each_entry(rela, &sec->rela_list, list) {
333 if (rela->sym->type != STT_SECTION) {
334 WARN("unexpected relocation symbol type in %s", sec->name);
335 return -1;
336 }
337 insn = find_insn(file, rela->sym->sec, rela->addend);
338 if (insn)
339 insn = list_prev_entry(insn, list);
340 else if (rela->addend == rela->sym->sec->len) {
341 found = false;
342 list_for_each_entry_reverse(insn, &file->insn_list, list) {
343 if (insn->sec == rela->sym->sec) {
344 found = true;
345 break;
346 }
347 }
348
349 if (!found) {
350 WARN("can't find unreachable insn at %s+0x%x",
351 rela->sym->sec->name, rela->addend);
352 return -1;
353 }
354 } else {
355 WARN("can't find unreachable insn at %s+0x%x",
356 rela->sym->sec->name, rela->addend);
357 return -1;
358 }
359
360 insn->dead_end = true;
361 }
362
363 reachable:
364 /*
365 * These manually annotated reachable checks are needed for GCC 4.4,
366 * where the Linux unreachable() macro isn't supported. In that case
367 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
368 * not a dead end.
369 */
370 sec = find_section_by_name(file->elf, ".rela.discard.reachable");
371 if (!sec)
372 return 0;
373
374 list_for_each_entry(rela, &sec->rela_list, list) {
375 if (rela->sym->type != STT_SECTION) {
376 WARN("unexpected relocation symbol type in %s", sec->name);
377 return -1;
378 }
379 insn = find_insn(file, rela->sym->sec, rela->addend);
380 if (insn)
381 insn = list_prev_entry(insn, list);
382 else if (rela->addend == rela->sym->sec->len) {
383 found = false;
384 list_for_each_entry_reverse(insn, &file->insn_list, list) {
385 if (insn->sec == rela->sym->sec) {
386 found = true;
387 break;
388 }
389 }
390
391 if (!found) {
392 WARN("can't find reachable insn at %s+0x%x",
393 rela->sym->sec->name, rela->addend);
394 return -1;
395 }
396 } else {
397 WARN("can't find reachable insn at %s+0x%x",
398 rela->sym->sec->name, rela->addend);
399 return -1;
400 }
401
402 insn->dead_end = false;
403 }
404
405 return 0;
406 }
407
408 /*
409 * Warnings shouldn't be reported for ignored functions.
410 */
411 static void add_ignores(struct objtool_file *file)
412 {
413 struct instruction *insn;
414 struct section *sec;
415 struct symbol *func;
416
417 for_each_sec(file, sec) {
418 list_for_each_entry(func, &sec->symbol_list, list) {
419 if (func->type != STT_FUNC)
420 continue;
421
422 if (!ignore_func(file, func))
423 continue;
424
425 func_for_each_insn(file, func, insn)
426 insn->ignore = true;
427 }
428 }
429 }
430
431 /*
432 * FIXME: For now, just ignore any alternatives which add retpolines. This is
433 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
434 * But it at least allows objtool to understand the control flow *around* the
435 * retpoline.
436 */
437 static int add_nospec_ignores(struct objtool_file *file)
438 {
439 struct section *sec;
440 struct rela *rela;
441 struct instruction *insn;
442
443 sec = find_section_by_name(file->elf, ".rela.discard.nospec");
444 if (!sec)
445 return 0;
446
447 list_for_each_entry(rela, &sec->rela_list, list) {
448 if (rela->sym->type != STT_SECTION) {
449 WARN("unexpected relocation symbol type in %s", sec->name);
450 return -1;
451 }
452
453 insn = find_insn(file, rela->sym->sec, rela->addend);
454 if (!insn) {
455 WARN("bad .discard.nospec entry");
456 return -1;
457 }
458
459 insn->ignore_alts = true;
460 }
461
462 return 0;
463 }
464
465 /*
466 * Find the destination instructions for all jumps.
467 */
468 static int add_jump_destinations(struct objtool_file *file)
469 {
470 struct instruction *insn;
471 struct rela *rela;
472 struct section *dest_sec;
473 unsigned long dest_off;
474
475 for_each_insn(file, insn) {
476 if (insn->type != INSN_JUMP_CONDITIONAL &&
477 insn->type != INSN_JUMP_UNCONDITIONAL)
478 continue;
479
480 if (insn->ignore)
481 continue;
482
483 rela = find_rela_by_dest_range(insn->sec, insn->offset,
484 insn->len);
485 if (!rela) {
486 dest_sec = insn->sec;
487 dest_off = insn->offset + insn->len + insn->immediate;
488 } else if (rela->sym->type == STT_SECTION) {
489 dest_sec = rela->sym->sec;
490 dest_off = rela->addend + 4;
491 } else if (rela->sym->sec->idx) {
492 dest_sec = rela->sym->sec;
493 dest_off = rela->sym->sym.st_value + rela->addend + 4;
494 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
495 /*
496 * Retpoline jumps are really dynamic jumps in
497 * disguise, so convert them accordingly.
498 */
499 insn->type = INSN_JUMP_DYNAMIC;
500 continue;
501 } else {
502 /* sibling call */
503 insn->jump_dest = 0;
504 continue;
505 }
506
507 insn->jump_dest = find_insn(file, dest_sec, dest_off);
508 if (!insn->jump_dest) {
509
510 /*
511 * This is a special case where an alt instruction
512 * jumps past the end of the section. These are
513 * handled later in handle_group_alt().
514 */
515 if (!strcmp(insn->sec->name, ".altinstr_replacement"))
516 continue;
517
518 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
519 insn->sec, insn->offset, dest_sec->name,
520 dest_off);
521 return -1;
522 }
523 }
524
525 return 0;
526 }
527
528 /*
529 * Find the destination instructions for all calls.
530 */
531 static int add_call_destinations(struct objtool_file *file)
532 {
533 struct instruction *insn;
534 unsigned long dest_off;
535 struct rela *rela;
536
537 for_each_insn(file, insn) {
538 if (insn->type != INSN_CALL)
539 continue;
540
541 rela = find_rela_by_dest_range(insn->sec, insn->offset,
542 insn->len);
543 if (!rela) {
544 dest_off = insn->offset + insn->len + insn->immediate;
545 insn->call_dest = find_symbol_by_offset(insn->sec,
546 dest_off);
547
548 if (!insn->call_dest && !insn->ignore) {
549 WARN_FUNC("unsupported intra-function call",
550 insn->sec, insn->offset);
551 WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
552 return -1;
553 }
554
555 } else if (rela->sym->type == STT_SECTION) {
556 insn->call_dest = find_symbol_by_offset(rela->sym->sec,
557 rela->addend+4);
558 if (!insn->call_dest ||
559 insn->call_dest->type != STT_FUNC) {
560 WARN_FUNC("can't find call dest symbol at %s+0x%x",
561 insn->sec, insn->offset,
562 rela->sym->sec->name,
563 rela->addend + 4);
564 return -1;
565 }
566 } else
567 insn->call_dest = rela->sym;
568 }
569
570 return 0;
571 }
572
573 /*
574 * The .alternatives section requires some extra special care, over and above
575 * what other special sections require:
576 *
577 * 1. Because alternatives are patched in-place, we need to insert a fake jump
578 * instruction at the end so that validate_branch() skips all the original
579 * replaced instructions when validating the new instruction path.
580 *
581 * 2. An added wrinkle is that the new instruction length might be zero. In
582 * that case the old instructions are replaced with noops. We simulate that
583 * by creating a fake jump as the only new instruction.
584 *
585 * 3. In some cases, the alternative section includes an instruction which
586 * conditionally jumps to the _end_ of the entry. We have to modify these
587 * jumps' destinations to point back to .text rather than the end of the
588 * entry in .altinstr_replacement.
589 *
590 * 4. It has been requested that we don't validate the !POPCNT feature path
591 * which is a "very very small percentage of machines".
592 */
593 static int handle_group_alt(struct objtool_file *file,
594 struct special_alt *special_alt,
595 struct instruction *orig_insn,
596 struct instruction **new_insn)
597 {
598 struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
599 unsigned long dest_off;
600
601 last_orig_insn = NULL;
602 insn = orig_insn;
603 sec_for_each_insn_from(file, insn) {
604 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
605 break;
606
607 if (special_alt->skip_orig)
608 insn->type = INSN_NOP;
609
610 insn->alt_group = true;
611 last_orig_insn = insn;
612 }
613
614 if (next_insn_same_sec(file, last_orig_insn)) {
615 fake_jump = malloc(sizeof(*fake_jump));
616 if (!fake_jump) {
617 WARN("malloc failed");
618 return -1;
619 }
620 memset(fake_jump, 0, sizeof(*fake_jump));
621 INIT_LIST_HEAD(&fake_jump->alts);
622 clear_insn_state(&fake_jump->state);
623
624 fake_jump->sec = special_alt->new_sec;
625 fake_jump->offset = -1;
626 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
627 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
628 fake_jump->ignore = true;
629 }
630
631 if (!special_alt->new_len) {
632 if (!fake_jump) {
633 WARN("%s: empty alternative at end of section",
634 special_alt->orig_sec->name);
635 return -1;
636 }
637
638 *new_insn = fake_jump;
639 return 0;
640 }
641
642 last_new_insn = NULL;
643 insn = *new_insn;
644 sec_for_each_insn_from(file, insn) {
645 if (insn->offset >= special_alt->new_off + special_alt->new_len)
646 break;
647
648 last_new_insn = insn;
649
650 insn->ignore = orig_insn->ignore_alts;
651
652 if (insn->type != INSN_JUMP_CONDITIONAL &&
653 insn->type != INSN_JUMP_UNCONDITIONAL)
654 continue;
655
656 if (!insn->immediate)
657 continue;
658
659 dest_off = insn->offset + insn->len + insn->immediate;
660 if (dest_off == special_alt->new_off + special_alt->new_len) {
661 if (!fake_jump) {
662 WARN("%s: alternative jump to end of section",
663 special_alt->orig_sec->name);
664 return -1;
665 }
666 insn->jump_dest = fake_jump;
667 }
668
669 if (!insn->jump_dest) {
670 WARN_FUNC("can't find alternative jump destination",
671 insn->sec, insn->offset);
672 return -1;
673 }
674 }
675
676 if (!last_new_insn) {
677 WARN_FUNC("can't find last new alternative instruction",
678 special_alt->new_sec, special_alt->new_off);
679 return -1;
680 }
681
682 if (fake_jump)
683 list_add(&fake_jump->list, &last_new_insn->list);
684
685 return 0;
686 }
687
688 /*
689 * A jump table entry can either convert a nop to a jump or a jump to a nop.
690 * If the original instruction is a jump, make the alt entry an effective nop
691 * by just skipping the original instruction.
692 */
693 static int handle_jump_alt(struct objtool_file *file,
694 struct special_alt *special_alt,
695 struct instruction *orig_insn,
696 struct instruction **new_insn)
697 {
698 if (orig_insn->type == INSN_NOP)
699 return 0;
700
701 if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
702 WARN_FUNC("unsupported instruction at jump label",
703 orig_insn->sec, orig_insn->offset);
704 return -1;
705 }
706
707 *new_insn = list_next_entry(orig_insn, list);
708 return 0;
709 }
710
711 /*
712 * Read all the special sections which have alternate instructions which can be
713 * patched in or redirected to at runtime. Each instruction having alternate
714 * instruction(s) has them added to its insn->alts list, which will be
715 * traversed in validate_branch().
716 */
717 static int add_special_section_alts(struct objtool_file *file)
718 {
719 struct list_head special_alts;
720 struct instruction *orig_insn, *new_insn;
721 struct special_alt *special_alt, *tmp;
722 struct alternative *alt;
723 int ret;
724
725 ret = special_get_alts(file->elf, &special_alts);
726 if (ret)
727 return ret;
728
729 list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
730
731 orig_insn = find_insn(file, special_alt->orig_sec,
732 special_alt->orig_off);
733 if (!orig_insn) {
734 WARN_FUNC("special: can't find orig instruction",
735 special_alt->orig_sec, special_alt->orig_off);
736 ret = -1;
737 goto out;
738 }
739
740 new_insn = NULL;
741 if (!special_alt->group || special_alt->new_len) {
742 new_insn = find_insn(file, special_alt->new_sec,
743 special_alt->new_off);
744 if (!new_insn) {
745 WARN_FUNC("special: can't find new instruction",
746 special_alt->new_sec,
747 special_alt->new_off);
748 ret = -1;
749 goto out;
750 }
751 }
752
753 if (special_alt->group) {
754 ret = handle_group_alt(file, special_alt, orig_insn,
755 &new_insn);
756 if (ret)
757 goto out;
758 } else if (special_alt->jump_or_nop) {
759 ret = handle_jump_alt(file, special_alt, orig_insn,
760 &new_insn);
761 if (ret)
762 goto out;
763 }
764
765 alt = malloc(sizeof(*alt));
766 if (!alt) {
767 WARN("malloc failed");
768 ret = -1;
769 goto out;
770 }
771
772 alt->insn = new_insn;
773 list_add_tail(&alt->list, &orig_insn->alts);
774
775 list_del(&special_alt->list);
776 free(special_alt);
777 }
778
779 out:
780 return ret;
781 }
782
783 static int add_switch_table(struct objtool_file *file, struct symbol *func,
784 struct instruction *insn, struct rela *table,
785 struct rela *next_table)
786 {
787 struct rela *rela = table;
788 struct instruction *alt_insn;
789 struct alternative *alt;
790
791 list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
792 if (rela == next_table)
793 break;
794
795 if (rela->sym->sec != insn->sec ||
796 rela->addend <= func->offset ||
797 rela->addend >= func->offset + func->len)
798 break;
799
800 alt_insn = find_insn(file, insn->sec, rela->addend);
801 if (!alt_insn) {
802 WARN("%s: can't find instruction at %s+0x%x",
803 file->rodata->rela->name, insn->sec->name,
804 rela->addend);
805 return -1;
806 }
807
808 alt = malloc(sizeof(*alt));
809 if (!alt) {
810 WARN("malloc failed");
811 return -1;
812 }
813
814 alt->insn = alt_insn;
815 list_add_tail(&alt->list, &insn->alts);
816 }
817
818 return 0;
819 }
820
821 /*
822 * find_switch_table() - Given a dynamic jump, find the switch jump table in
823 * .rodata associated with it.
824 *
825 * There are 3 basic patterns:
826 *
827 * 1. jmpq *[rodata addr](,%reg,8)
828 *
829 * This is the most common case by far. It jumps to an address in a simple
830 * jump table which is stored in .rodata.
831 *
832 * 2. jmpq *[rodata addr](%rip)
833 *
834 * This is caused by a rare GCC quirk, currently only seen in three driver
835 * functions in the kernel, only with certain obscure non-distro configs.
836 *
837 * As part of an optimization, GCC makes a copy of an existing switch jump
838 * table, modifies it, and then hard-codes the jump (albeit with an indirect
839 * jump) to use a single entry in the table. The rest of the jump table and
840 * some of its jump targets remain as dead code.
841 *
842 * In such a case we can just crudely ignore all unreachable instruction
843 * warnings for the entire object file. Ideally we would just ignore them
844 * for the function, but that would require redesigning the code quite a
845 * bit. And honestly that's just not worth doing: unreachable instruction
846 * warnings are of questionable value anyway, and this is such a rare issue.
847 *
848 * 3. mov [rodata addr],%reg1
849 * ... some instructions ...
850 * jmpq *(%reg1,%reg2,8)
851 *
852 * This is a fairly uncommon pattern which is new for GCC 6. As of this
853 * writing, there are 11 occurrences of it in the allmodconfig kernel.
854 *
855 * As of GCC 7 there are quite a few more of these and the 'in between' code
856 * is significant. Esp. with KASAN enabled some of the code between the mov
857 * and jmpq uses .rodata itself, which can confuse things.
858 *
859 * TODO: Once we have DWARF CFI and smarter instruction decoding logic,
860 * ensure the same register is used in the mov and jump instructions.
861 *
862 * NOTE: RETPOLINE made it harder still to decode dynamic jumps.
863 */
864 static struct rela *find_switch_table(struct objtool_file *file,
865 struct symbol *func,
866 struct instruction *insn)
867 {
868 struct rela *text_rela, *rodata_rela;
869 struct instruction *orig_insn = insn;
870
871 text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
872 if (text_rela && text_rela->sym == file->rodata->sym) {
873 /* case 1 */
874 rodata_rela = find_rela_by_dest(file->rodata,
875 text_rela->addend);
876 if (rodata_rela)
877 return rodata_rela;
878
879 /* case 2 */
880 rodata_rela = find_rela_by_dest(file->rodata,
881 text_rela->addend + 4);
882 if (!rodata_rela)
883 return NULL;
884
885 file->ignore_unreachables = true;
886 return rodata_rela;
887 }
888
889 /* case 3 */
890 /*
891 * Backward search using the @first_jump_src links, these help avoid
892 * much of the 'in between' code. Which avoids us getting confused by
893 * it.
894 */
895 for (insn = list_prev_entry(insn, list);
896
897 &insn->list != &file->insn_list &&
898 insn->sec == func->sec &&
899 insn->offset >= func->offset;
900
901 insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
902
903 if (insn->type == INSN_JUMP_DYNAMIC)
904 break;
905
906 /* allow small jumps within the range */
907 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
908 insn->jump_dest &&
909 (insn->jump_dest->offset <= insn->offset ||
910 insn->jump_dest->offset > orig_insn->offset))
911 break;
912
913 /* look for a relocation which references .rodata */
914 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
915 insn->len);
916 if (!text_rela || text_rela->sym != file->rodata->sym)
917 continue;
918
919 /*
920 * Make sure the .rodata address isn't associated with a
921 * symbol. gcc jump tables are anonymous data.
922 */
923 if (find_symbol_containing(file->rodata, text_rela->addend))
924 continue;
925
926 return find_rela_by_dest(file->rodata, text_rela->addend);
927 }
928
929 return NULL;
930 }
931
932
933 static int add_func_switch_tables(struct objtool_file *file,
934 struct symbol *func)
935 {
936 struct instruction *insn, *last = NULL, *prev_jump = NULL;
937 struct rela *rela, *prev_rela = NULL;
938 int ret;
939
940 func_for_each_insn(file, func, insn) {
941 if (!last)
942 last = insn;
943
944 /*
945 * Store back-pointers for unconditional forward jumps such
946 * that find_switch_table() can back-track using those and
947 * avoid some potentially confusing code.
948 */
949 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
950 insn->offset > last->offset &&
951 insn->jump_dest->offset > insn->offset &&
952 !insn->jump_dest->first_jump_src) {
953
954 insn->jump_dest->first_jump_src = insn;
955 last = insn->jump_dest;
956 }
957
958 if (insn->type != INSN_JUMP_DYNAMIC)
959 continue;
960
961 rela = find_switch_table(file, func, insn);
962 if (!rela)
963 continue;
964
965 /*
966 * We found a switch table, but we don't know yet how big it
967 * is. Don't add it until we reach the end of the function or
968 * the beginning of another switch table in the same function.
969 */
970 if (prev_jump) {
971 ret = add_switch_table(file, func, prev_jump, prev_rela,
972 rela);
973 if (ret)
974 return ret;
975 }
976
977 prev_jump = insn;
978 prev_rela = rela;
979 }
980
981 if (prev_jump) {
982 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
983 if (ret)
984 return ret;
985 }
986
987 return 0;
988 }
989
990 /*
991 * For some switch statements, gcc generates a jump table in the .rodata
992 * section which contains a list of addresses within the function to jump to.
993 * This finds these jump tables and adds them to the insn->alts lists.
994 */
995 static int add_switch_table_alts(struct objtool_file *file)
996 {
997 struct section *sec;
998 struct symbol *func;
999 int ret;
1000
1001 if (!file->rodata || !file->rodata->rela)
1002 return 0;
1003
1004 for_each_sec(file, sec) {
1005 list_for_each_entry(func, &sec->symbol_list, list) {
1006 if (func->type != STT_FUNC)
1007 continue;
1008
1009 ret = add_func_switch_tables(file, func);
1010 if (ret)
1011 return ret;
1012 }
1013 }
1014
1015 return 0;
1016 }
1017
1018 static int read_unwind_hints(struct objtool_file *file)
1019 {
1020 struct section *sec, *relasec;
1021 struct rela *rela;
1022 struct unwind_hint *hint;
1023 struct instruction *insn;
1024 struct cfi_reg *cfa;
1025 int i;
1026
1027 sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1028 if (!sec)
1029 return 0;
1030
1031 relasec = sec->rela;
1032 if (!relasec) {
1033 WARN("missing .rela.discard.unwind_hints section");
1034 return -1;
1035 }
1036
1037 if (sec->len % sizeof(struct unwind_hint)) {
1038 WARN("struct unwind_hint size mismatch");
1039 return -1;
1040 }
1041
1042 file->hints = true;
1043
1044 for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1045 hint = (struct unwind_hint *)sec->data->d_buf + i;
1046
1047 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1048 if (!rela) {
1049 WARN("can't find rela for unwind_hints[%d]", i);
1050 return -1;
1051 }
1052
1053 insn = find_insn(file, rela->sym->sec, rela->addend);
1054 if (!insn) {
1055 WARN("can't find insn for unwind_hints[%d]", i);
1056 return -1;
1057 }
1058
1059 cfa = &insn->state.cfa;
1060
1061 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1062 insn->save = true;
1063 continue;
1064
1065 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1066 insn->restore = true;
1067 insn->hint = true;
1068 continue;
1069 }
1070
1071 insn->hint = true;
1072
1073 switch (hint->sp_reg) {
1074 case ORC_REG_UNDEFINED:
1075 cfa->base = CFI_UNDEFINED;
1076 break;
1077 case ORC_REG_SP:
1078 cfa->base = CFI_SP;
1079 break;
1080 case ORC_REG_BP:
1081 cfa->base = CFI_BP;
1082 break;
1083 case ORC_REG_SP_INDIRECT:
1084 cfa->base = CFI_SP_INDIRECT;
1085 break;
1086 case ORC_REG_R10:
1087 cfa->base = CFI_R10;
1088 break;
1089 case ORC_REG_R13:
1090 cfa->base = CFI_R13;
1091 break;
1092 case ORC_REG_DI:
1093 cfa->base = CFI_DI;
1094 break;
1095 case ORC_REG_DX:
1096 cfa->base = CFI_DX;
1097 break;
1098 default:
1099 WARN_FUNC("unsupported unwind_hint sp base reg %d",
1100 insn->sec, insn->offset, hint->sp_reg);
1101 return -1;
1102 }
1103
1104 cfa->offset = hint->sp_offset;
1105 insn->state.type = hint->type;
1106 }
1107
1108 return 0;
1109 }
1110
1111 static int decode_sections(struct objtool_file *file)
1112 {
1113 int ret;
1114
1115 ret = decode_instructions(file);
1116 if (ret)
1117 return ret;
1118
1119 ret = add_dead_ends(file);
1120 if (ret)
1121 return ret;
1122
1123 add_ignores(file);
1124
1125 ret = add_nospec_ignores(file);
1126 if (ret)
1127 return ret;
1128
1129 ret = add_jump_destinations(file);
1130 if (ret)
1131 return ret;
1132
1133 ret = add_special_section_alts(file);
1134 if (ret)
1135 return ret;
1136
1137 ret = add_call_destinations(file);
1138 if (ret)
1139 return ret;
1140
1141 ret = add_switch_table_alts(file);
1142 if (ret)
1143 return ret;
1144
1145 ret = read_unwind_hints(file);
1146 if (ret)
1147 return ret;
1148
1149 return 0;
1150 }
1151
1152 static bool is_fentry_call(struct instruction *insn)
1153 {
1154 if (insn->type == INSN_CALL &&
1155 insn->call_dest->type == STT_NOTYPE &&
1156 !strcmp(insn->call_dest->name, "__fentry__"))
1157 return true;
1158
1159 return false;
1160 }
1161
1162 static bool has_modified_stack_frame(struct insn_state *state)
1163 {
1164 int i;
1165
1166 if (state->cfa.base != initial_func_cfi.cfa.base ||
1167 state->cfa.offset != initial_func_cfi.cfa.offset ||
1168 state->stack_size != initial_func_cfi.cfa.offset ||
1169 state->drap)
1170 return true;
1171
1172 for (i = 0; i < CFI_NUM_REGS; i++)
1173 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1174 state->regs[i].offset != initial_func_cfi.regs[i].offset)
1175 return true;
1176
1177 return false;
1178 }
1179
1180 static bool has_valid_stack_frame(struct insn_state *state)
1181 {
1182 if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1183 state->regs[CFI_BP].offset == -16)
1184 return true;
1185
1186 if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1187 return true;
1188
1189 return false;
1190 }
1191
1192 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1193 {
1194 struct cfi_reg *cfa = &state->cfa;
1195 struct stack_op *op = &insn->stack_op;
1196
1197 if (cfa->base != CFI_SP)
1198 return 0;
1199
1200 /* push */
1201 if (op->dest.type == OP_DEST_PUSH)
1202 cfa->offset += 8;
1203
1204 /* pop */
1205 if (op->src.type == OP_SRC_POP)
1206 cfa->offset -= 8;
1207
1208 /* add immediate to sp */
1209 if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1210 op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1211 cfa->offset -= op->src.offset;
1212
1213 return 0;
1214 }
1215
1216 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1217 int offset)
1218 {
1219 if (arch_callee_saved_reg(reg) &&
1220 state->regs[reg].base == CFI_UNDEFINED) {
1221 state->regs[reg].base = base;
1222 state->regs[reg].offset = offset;
1223 }
1224 }
1225
1226 static void restore_reg(struct insn_state *state, unsigned char reg)
1227 {
1228 state->regs[reg].base = CFI_UNDEFINED;
1229 state->regs[reg].offset = 0;
1230 }
1231
1232 /*
1233 * A note about DRAP stack alignment:
1234 *
1235 * GCC has the concept of a DRAP register, which is used to help keep track of
1236 * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
1237 * register. The typical DRAP pattern is:
1238 *
1239 * 4c 8d 54 24 08 lea 0x8(%rsp),%r10
1240 * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
1241 * 41 ff 72 f8 pushq -0x8(%r10)
1242 * 55 push %rbp
1243 * 48 89 e5 mov %rsp,%rbp
1244 * (more pushes)
1245 * 41 52 push %r10
1246 * ...
1247 * 41 5a pop %r10
1248 * (more pops)
1249 * 5d pop %rbp
1250 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1251 * c3 retq
1252 *
1253 * There are some variations in the epilogues, like:
1254 *
1255 * 5b pop %rbx
1256 * 41 5a pop %r10
1257 * 41 5c pop %r12
1258 * 41 5d pop %r13
1259 * 41 5e pop %r14
1260 * c9 leaveq
1261 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1262 * c3 retq
1263 *
1264 * and:
1265 *
1266 * 4c 8b 55 e8 mov -0x18(%rbp),%r10
1267 * 48 8b 5d e0 mov -0x20(%rbp),%rbx
1268 * 4c 8b 65 f0 mov -0x10(%rbp),%r12
1269 * 4c 8b 6d f8 mov -0x8(%rbp),%r13
1270 * c9 leaveq
1271 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1272 * c3 retq
1273 *
1274 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1275 * restored beforehand:
1276 *
1277 * 41 55 push %r13
1278 * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
1279 * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
1280 * ...
1281 * 49 8d 65 f0 lea -0x10(%r13),%rsp
1282 * 41 5d pop %r13
1283 * c3 retq
1284 */
1285 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1286 {
1287 struct stack_op *op = &insn->stack_op;
1288 struct cfi_reg *cfa = &state->cfa;
1289 struct cfi_reg *regs = state->regs;
1290
1291 /* stack operations don't make sense with an undefined CFA */
1292 if (cfa->base == CFI_UNDEFINED) {
1293 if (insn->func) {
1294 WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1295 return -1;
1296 }
1297 return 0;
1298 }
1299
1300 if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1301 return update_insn_state_regs(insn, state);
1302
1303 switch (op->dest.type) {
1304
1305 case OP_DEST_REG:
1306 switch (op->src.type) {
1307
1308 case OP_SRC_REG:
1309 if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1310 cfa->base == CFI_SP &&
1311 regs[CFI_BP].base == CFI_CFA &&
1312 regs[CFI_BP].offset == -cfa->offset) {
1313
1314 /* mov %rsp, %rbp */
1315 cfa->base = op->dest.reg;
1316 state->bp_scratch = false;
1317 }
1318
1319 else if (op->src.reg == CFI_SP &&
1320 op->dest.reg == CFI_BP && state->drap) {
1321
1322 /* drap: mov %rsp, %rbp */
1323 regs[CFI_BP].base = CFI_BP;
1324 regs[CFI_BP].offset = -state->stack_size;
1325 state->bp_scratch = false;
1326 }
1327
1328 else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1329
1330 /*
1331 * mov %rsp, %reg
1332 *
1333 * This is needed for the rare case where GCC
1334 * does:
1335 *
1336 * mov %rsp, %rax
1337 * ...
1338 * mov %rax, %rsp
1339 */
1340 state->vals[op->dest.reg].base = CFI_CFA;
1341 state->vals[op->dest.reg].offset = -state->stack_size;
1342 }
1343
1344 else if (op->dest.reg == cfa->base) {
1345
1346 /* mov %reg, %rsp */
1347 if (cfa->base == CFI_SP &&
1348 state->vals[op->src.reg].base == CFI_CFA) {
1349
1350 /*
1351 * This is needed for the rare case
1352 * where GCC does something dumb like:
1353 *
1354 * lea 0x8(%rsp), %rcx
1355 * ...
1356 * mov %rcx, %rsp
1357 */
1358 cfa->offset = -state->vals[op->src.reg].offset;
1359 state->stack_size = cfa->offset;
1360
1361 } else {
1362 cfa->base = CFI_UNDEFINED;
1363 cfa->offset = 0;
1364 }
1365 }
1366
1367 break;
1368
1369 case OP_SRC_ADD:
1370 if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1371
1372 /* add imm, %rsp */
1373 state->stack_size -= op->src.offset;
1374 if (cfa->base == CFI_SP)
1375 cfa->offset -= op->src.offset;
1376 break;
1377 }
1378
1379 if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1380
1381 /* lea disp(%rbp), %rsp */
1382 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1383 break;
1384 }
1385
1386 if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1387
1388 /* drap: lea disp(%rsp), %drap */
1389 state->drap_reg = op->dest.reg;
1390
1391 /*
1392 * lea disp(%rsp), %reg
1393 *
1394 * This is needed for the rare case where GCC
1395 * does something dumb like:
1396 *
1397 * lea 0x8(%rsp), %rcx
1398 * ...
1399 * mov %rcx, %rsp
1400 */
1401 state->vals[op->dest.reg].base = CFI_CFA;
1402 state->vals[op->dest.reg].offset = \
1403 -state->stack_size + op->src.offset;
1404
1405 break;
1406 }
1407
1408 if (state->drap && op->dest.reg == CFI_SP &&
1409 op->src.reg == state->drap_reg) {
1410
1411 /* drap: lea disp(%drap), %rsp */
1412 cfa->base = CFI_SP;
1413 cfa->offset = state->stack_size = -op->src.offset;
1414 state->drap_reg = CFI_UNDEFINED;
1415 state->drap = false;
1416 break;
1417 }
1418
1419 if (op->dest.reg == state->cfa.base) {
1420 WARN_FUNC("unsupported stack register modification",
1421 insn->sec, insn->offset);
1422 return -1;
1423 }
1424
1425 break;
1426
1427 case OP_SRC_AND:
1428 if (op->dest.reg != CFI_SP ||
1429 (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1430 (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1431 WARN_FUNC("unsupported stack pointer realignment",
1432 insn->sec, insn->offset);
1433 return -1;
1434 }
1435
1436 if (state->drap_reg != CFI_UNDEFINED) {
1437 /* drap: and imm, %rsp */
1438 cfa->base = state->drap_reg;
1439 cfa->offset = state->stack_size = 0;
1440 state->drap = true;
1441 }
1442
1443 /*
1444 * Older versions of GCC (4.8ish) realign the stack
1445 * without DRAP, with a frame pointer.
1446 */
1447
1448 break;
1449
1450 case OP_SRC_POP:
1451 if (!state->drap && op->dest.type == OP_DEST_REG &&
1452 op->dest.reg == cfa->base) {
1453
1454 /* pop %rbp */
1455 cfa->base = CFI_SP;
1456 }
1457
1458 if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1459 op->dest.type == OP_DEST_REG &&
1460 op->dest.reg == state->drap_reg &&
1461 state->drap_offset == -state->stack_size) {
1462
1463 /* drap: pop %drap */
1464 cfa->base = state->drap_reg;
1465 cfa->offset = 0;
1466 state->drap_offset = -1;
1467
1468 } else if (regs[op->dest.reg].offset == -state->stack_size) {
1469
1470 /* pop %reg */
1471 restore_reg(state, op->dest.reg);
1472 }
1473
1474 state->stack_size -= 8;
1475 if (cfa->base == CFI_SP)
1476 cfa->offset -= 8;
1477
1478 break;
1479
1480 case OP_SRC_REG_INDIRECT:
1481 if (state->drap && op->src.reg == CFI_BP &&
1482 op->src.offset == state->drap_offset) {
1483
1484 /* drap: mov disp(%rbp), %drap */
1485 cfa->base = state->drap_reg;
1486 cfa->offset = 0;
1487 state->drap_offset = -1;
1488 }
1489
1490 if (state->drap && op->src.reg == CFI_BP &&
1491 op->src.offset == regs[op->dest.reg].offset) {
1492
1493 /* drap: mov disp(%rbp), %reg */
1494 restore_reg(state, op->dest.reg);
1495
1496 } else if (op->src.reg == cfa->base &&
1497 op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1498
1499 /* mov disp(%rbp), %reg */
1500 /* mov disp(%rsp), %reg */
1501 restore_reg(state, op->dest.reg);
1502 }
1503
1504 break;
1505
1506 default:
1507 WARN_FUNC("unknown stack-related instruction",
1508 insn->sec, insn->offset);
1509 return -1;
1510 }
1511
1512 break;
1513
1514 case OP_DEST_PUSH:
1515 state->stack_size += 8;
1516 if (cfa->base == CFI_SP)
1517 cfa->offset += 8;
1518
1519 if (op->src.type != OP_SRC_REG)
1520 break;
1521
1522 if (state->drap) {
1523 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1524
1525 /* drap: push %drap */
1526 cfa->base = CFI_BP_INDIRECT;
1527 cfa->offset = -state->stack_size;
1528
1529 /* save drap so we know when to restore it */
1530 state->drap_offset = -state->stack_size;
1531
1532 } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1533
1534 /* drap: push %rbp */
1535 state->stack_size = 0;
1536
1537 } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1538
1539 /* drap: push %reg */
1540 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1541 }
1542
1543 } else {
1544
1545 /* push %reg */
1546 save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1547 }
1548
1549 /* detect when asm code uses rbp as a scratch register */
1550 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1551 cfa->base != CFI_BP)
1552 state->bp_scratch = true;
1553 break;
1554
1555 case OP_DEST_REG_INDIRECT:
1556
1557 if (state->drap) {
1558 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1559
1560 /* drap: mov %drap, disp(%rbp) */
1561 cfa->base = CFI_BP_INDIRECT;
1562 cfa->offset = op->dest.offset;
1563
1564 /* save drap offset so we know when to restore it */
1565 state->drap_offset = op->dest.offset;
1566 }
1567
1568 else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1569
1570 /* drap: mov reg, disp(%rbp) */
1571 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1572 }
1573
1574 } else if (op->dest.reg == cfa->base) {
1575
1576 /* mov reg, disp(%rbp) */
1577 /* mov reg, disp(%rsp) */
1578 save_reg(state, op->src.reg, CFI_CFA,
1579 op->dest.offset - state->cfa.offset);
1580 }
1581
1582 break;
1583
1584 case OP_DEST_LEAVE:
1585 if ((!state->drap && cfa->base != CFI_BP) ||
1586 (state->drap && cfa->base != state->drap_reg)) {
1587 WARN_FUNC("leave instruction with modified stack frame",
1588 insn->sec, insn->offset);
1589 return -1;
1590 }
1591
1592 /* leave (mov %rbp, %rsp; pop %rbp) */
1593
1594 state->stack_size = -state->regs[CFI_BP].offset - 8;
1595 restore_reg(state, CFI_BP);
1596
1597 if (!state->drap) {
1598 cfa->base = CFI_SP;
1599 cfa->offset -= 8;
1600 }
1601
1602 break;
1603
1604 case OP_DEST_MEM:
1605 if (op->src.type != OP_SRC_POP) {
1606 WARN_FUNC("unknown stack-related memory operation",
1607 insn->sec, insn->offset);
1608 return -1;
1609 }
1610
1611 /* pop mem */
1612 state->stack_size -= 8;
1613 if (cfa->base == CFI_SP)
1614 cfa->offset -= 8;
1615
1616 break;
1617
1618 default:
1619 WARN_FUNC("unknown stack-related instruction",
1620 insn->sec, insn->offset);
1621 return -1;
1622 }
1623
1624 return 0;
1625 }
1626
1627 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1628 {
1629 struct insn_state *state1 = &insn->state, *state2 = state;
1630 int i;
1631
1632 if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1633 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1634 insn->sec, insn->offset,
1635 state1->cfa.base, state1->cfa.offset,
1636 state2->cfa.base, state2->cfa.offset);
1637
1638 } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1639 for (i = 0; i < CFI_NUM_REGS; i++) {
1640 if (!memcmp(&state1->regs[i], &state2->regs[i],
1641 sizeof(struct cfi_reg)))
1642 continue;
1643
1644 WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1645 insn->sec, insn->offset,
1646 i, state1->regs[i].base, state1->regs[i].offset,
1647 i, state2->regs[i].base, state2->regs[i].offset);
1648 break;
1649 }
1650
1651 } else if (state1->type != state2->type) {
1652 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1653 insn->sec, insn->offset, state1->type, state2->type);
1654
1655 } else if (state1->drap != state2->drap ||
1656 (state1->drap && state1->drap_reg != state2->drap_reg) ||
1657 (state1->drap && state1->drap_offset != state2->drap_offset)) {
1658 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1659 insn->sec, insn->offset,
1660 state1->drap, state1->drap_reg, state1->drap_offset,
1661 state2->drap, state2->drap_reg, state2->drap_offset);
1662
1663 } else
1664 return true;
1665
1666 return false;
1667 }
1668
1669 /*
1670 * Follow the branch starting at the given instruction, and recursively follow
1671 * any other branches (jumps). Meanwhile, track the frame pointer state at
1672 * each instruction and validate all the rules described in
1673 * tools/objtool/Documentation/stack-validation.txt.
1674 */
1675 static int validate_branch(struct objtool_file *file, struct instruction *first,
1676 struct insn_state state)
1677 {
1678 struct alternative *alt;
1679 struct instruction *insn, *next_insn;
1680 struct section *sec;
1681 struct symbol *func = NULL;
1682 int ret;
1683
1684 insn = first;
1685 sec = insn->sec;
1686
1687 if (insn->alt_group && list_empty(&insn->alts)) {
1688 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1689 sec, insn->offset);
1690 return 1;
1691 }
1692
1693 while (1) {
1694 next_insn = next_insn_same_sec(file, insn);
1695
1696
1697 if (file->c_file && func && insn->func && func != insn->func) {
1698 WARN("%s() falls through to next function %s()",
1699 func->name, insn->func->name);
1700 return 1;
1701 }
1702
1703 if (insn->func)
1704 func = insn->func;
1705
1706 if (func && insn->ignore) {
1707 WARN_FUNC("BUG: why am I validating an ignored function?",
1708 sec, insn->offset);
1709 return 1;
1710 }
1711
1712 if (insn->visited) {
1713 if (!insn->hint && !insn_state_match(insn, &state))
1714 return 1;
1715
1716 return 0;
1717 }
1718
1719 if (insn->hint) {
1720 if (insn->restore) {
1721 struct instruction *save_insn, *i;
1722
1723 i = insn;
1724 save_insn = NULL;
1725 func_for_each_insn_continue_reverse(file, func, i) {
1726 if (i->save) {
1727 save_insn = i;
1728 break;
1729 }
1730 }
1731
1732 if (!save_insn) {
1733 WARN_FUNC("no corresponding CFI save for CFI restore",
1734 sec, insn->offset);
1735 return 1;
1736 }
1737
1738 if (!save_insn->visited) {
1739 /*
1740 * Oops, no state to copy yet.
1741 * Hopefully we can reach this
1742 * instruction from another branch
1743 * after the save insn has been
1744 * visited.
1745 */
1746 if (insn == first)
1747 return 0;
1748
1749 WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1750 sec, insn->offset);
1751 return 1;
1752 }
1753
1754 insn->state = save_insn->state;
1755 }
1756
1757 state = insn->state;
1758
1759 } else
1760 insn->state = state;
1761
1762 insn->visited = true;
1763
1764 if (!insn->ignore_alts) {
1765 list_for_each_entry(alt, &insn->alts, list) {
1766 ret = validate_branch(file, alt->insn, state);
1767 if (ret)
1768 return 1;
1769 }
1770 }
1771
1772 switch (insn->type) {
1773
1774 case INSN_RETURN:
1775 if (func && has_modified_stack_frame(&state)) {
1776 WARN_FUNC("return with modified stack frame",
1777 sec, insn->offset);
1778 return 1;
1779 }
1780
1781 if (state.bp_scratch) {
1782 WARN("%s uses BP as a scratch register",
1783 insn->func->name);
1784 return 1;
1785 }
1786
1787 return 0;
1788
1789 case INSN_CALL:
1790 if (is_fentry_call(insn))
1791 break;
1792
1793 ret = dead_end_function(file, insn->call_dest);
1794 if (ret == 1)
1795 return 0;
1796 if (ret == -1)
1797 return 1;
1798
1799 /* fallthrough */
1800 case INSN_CALL_DYNAMIC:
1801 if (!no_fp && func && !has_valid_stack_frame(&state)) {
1802 WARN_FUNC("call without frame pointer save/setup",
1803 sec, insn->offset);
1804 return 1;
1805 }
1806 break;
1807
1808 case INSN_JUMP_CONDITIONAL:
1809 case INSN_JUMP_UNCONDITIONAL:
1810 if (insn->jump_dest &&
1811 (!func || !insn->jump_dest->func ||
1812 func == insn->jump_dest->func)) {
1813 ret = validate_branch(file, insn->jump_dest,
1814 state);
1815 if (ret)
1816 return 1;
1817
1818 } else if (func && has_modified_stack_frame(&state)) {
1819 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1820 sec, insn->offset);
1821 return 1;
1822 }
1823
1824 if (insn->type == INSN_JUMP_UNCONDITIONAL)
1825 return 0;
1826
1827 break;
1828
1829 case INSN_JUMP_DYNAMIC:
1830 if (func && list_empty(&insn->alts) &&
1831 has_modified_stack_frame(&state)) {
1832 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1833 sec, insn->offset);
1834 return 1;
1835 }
1836
1837 return 0;
1838
1839 case INSN_CONTEXT_SWITCH:
1840 if (func && (!next_insn || !next_insn->hint)) {
1841 WARN_FUNC("unsupported instruction in callable function",
1842 sec, insn->offset);
1843 return 1;
1844 }
1845 return 0;
1846
1847 case INSN_STACK:
1848 if (update_insn_state(insn, &state))
1849 return 1;
1850
1851 break;
1852
1853 default:
1854 break;
1855 }
1856
1857 if (insn->dead_end)
1858 return 0;
1859
1860 if (!next_insn) {
1861 if (state.cfa.base == CFI_UNDEFINED)
1862 return 0;
1863 WARN("%s: unexpected end of section", sec->name);
1864 return 1;
1865 }
1866
1867 insn = next_insn;
1868 }
1869
1870 return 0;
1871 }
1872
1873 static int validate_unwind_hints(struct objtool_file *file)
1874 {
1875 struct instruction *insn;
1876 int ret, warnings = 0;
1877 struct insn_state state;
1878
1879 if (!file->hints)
1880 return 0;
1881
1882 clear_insn_state(&state);
1883
1884 for_each_insn(file, insn) {
1885 if (insn->hint && !insn->visited) {
1886 ret = validate_branch(file, insn, state);
1887 warnings += ret;
1888 }
1889 }
1890
1891 return warnings;
1892 }
1893
1894 static bool is_kasan_insn(struct instruction *insn)
1895 {
1896 return (insn->type == INSN_CALL &&
1897 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1898 }
1899
1900 static bool is_ubsan_insn(struct instruction *insn)
1901 {
1902 return (insn->type == INSN_CALL &&
1903 !strcmp(insn->call_dest->name,
1904 "__ubsan_handle_builtin_unreachable"));
1905 }
1906
1907 static bool ignore_unreachable_insn(struct instruction *insn)
1908 {
1909 int i;
1910
1911 if (insn->ignore || insn->type == INSN_NOP)
1912 return true;
1913
1914 /*
1915 * Ignore any unused exceptions. This can happen when a whitelisted
1916 * function has an exception table entry.
1917 *
1918 * Also ignore alternative replacement instructions. This can happen
1919 * when a whitelisted function uses one of the ALTERNATIVE macros.
1920 */
1921 if (!strcmp(insn->sec->name, ".fixup") ||
1922 !strcmp(insn->sec->name, ".altinstr_replacement") ||
1923 !strcmp(insn->sec->name, ".altinstr_aux"))
1924 return true;
1925
1926 /*
1927 * Check if this (or a subsequent) instruction is related to
1928 * CONFIG_UBSAN or CONFIG_KASAN.
1929 *
1930 * End the search at 5 instructions to avoid going into the weeds.
1931 */
1932 if (!insn->func)
1933 return false;
1934 for (i = 0; i < 5; i++) {
1935
1936 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1937 return true;
1938
1939 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
1940 if (insn->jump_dest &&
1941 insn->jump_dest->func == insn->func) {
1942 insn = insn->jump_dest;
1943 continue;
1944 }
1945
1946 break;
1947 }
1948
1949 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
1950 break;
1951
1952 insn = list_next_entry(insn, list);
1953 }
1954
1955 return false;
1956 }
1957
1958 static int validate_functions(struct objtool_file *file)
1959 {
1960 struct section *sec;
1961 struct symbol *func;
1962 struct instruction *insn;
1963 struct insn_state state;
1964 int ret, warnings = 0;
1965
1966 clear_insn_state(&state);
1967
1968 state.cfa = initial_func_cfi.cfa;
1969 memcpy(&state.regs, &initial_func_cfi.regs,
1970 CFI_NUM_REGS * sizeof(struct cfi_reg));
1971 state.stack_size = initial_func_cfi.cfa.offset;
1972
1973 for_each_sec(file, sec) {
1974 list_for_each_entry(func, &sec->symbol_list, list) {
1975 if (func->type != STT_FUNC)
1976 continue;
1977
1978 insn = find_insn(file, sec, func->offset);
1979 if (!insn || insn->ignore)
1980 continue;
1981
1982 ret = validate_branch(file, insn, state);
1983 warnings += ret;
1984 }
1985 }
1986
1987 return warnings;
1988 }
1989
1990 static int validate_reachable_instructions(struct objtool_file *file)
1991 {
1992 struct instruction *insn;
1993
1994 if (file->ignore_unreachables)
1995 return 0;
1996
1997 for_each_insn(file, insn) {
1998 if (insn->visited || ignore_unreachable_insn(insn))
1999 continue;
2000
2001 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2002 return 1;
2003 }
2004
2005 return 0;
2006 }
2007
2008 static void cleanup(struct objtool_file *file)
2009 {
2010 struct instruction *insn, *tmpinsn;
2011 struct alternative *alt, *tmpalt;
2012
2013 list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2014 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2015 list_del(&alt->list);
2016 free(alt);
2017 }
2018 list_del(&insn->list);
2019 hash_del(&insn->hash);
2020 free(insn);
2021 }
2022 elf_close(file->elf);
2023 }
2024
2025 int check(const char *_objname, bool _no_fp, bool no_unreachable, bool orc)
2026 {
2027 struct objtool_file file;
2028 int ret, warnings = 0;
2029
2030 objname = _objname;
2031 no_fp = _no_fp;
2032
2033 file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2034 if (!file.elf)
2035 return 1;
2036
2037 INIT_LIST_HEAD(&file.insn_list);
2038 hash_init(file.insn_hash);
2039 file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
2040 file.rodata = find_section_by_name(file.elf, ".rodata");
2041 file.c_file = find_section_by_name(file.elf, ".comment");
2042 file.ignore_unreachables = no_unreachable;
2043 file.hints = false;
2044
2045 arch_initial_func_cfi_state(&initial_func_cfi);
2046
2047 ret = decode_sections(&file);
2048 if (ret < 0)
2049 goto out;
2050 warnings += ret;
2051
2052 if (list_empty(&file.insn_list))
2053 goto out;
2054
2055 ret = validate_functions(&file);
2056 if (ret < 0)
2057 goto out;
2058 warnings += ret;
2059
2060 ret = validate_unwind_hints(&file);
2061 if (ret < 0)
2062 goto out;
2063 warnings += ret;
2064
2065 if (!warnings) {
2066 ret = validate_reachable_instructions(&file);
2067 if (ret < 0)
2068 goto out;
2069 warnings += ret;
2070 }
2071
2072 if (orc) {
2073 ret = create_orc(&file);
2074 if (ret < 0)
2075 goto out;
2076
2077 ret = create_orc_sections(&file);
2078 if (ret < 0)
2079 goto out;
2080
2081 ret = elf_write(file.elf);
2082 if (ret < 0)
2083 goto out;
2084 }
2085
2086 out:
2087 cleanup(&file);
2088
2089 /* ignore warnings for now until we get all the code cleaned up */
2090 if (ret || warnings)
2091 return 0;
2092 return 0;
2093 }
CRIS linux kernel tree