Loading...
Note: File does not exist in v3.15.
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
31struct alternative {
32 struct list_head list;
33 struct instruction *insn;
34};
35
36const char *objname;
37struct cfi_state initial_func_cfi;
38
39struct 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
51static 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
62static struct instruction *next_insn_same_func(struct objtool_file *file,
63 struct instruction *insn)
64{
65 struct instruction *next = list_next_entry(insn, list);
66 struct symbol *func = insn->func;
67
68 if (!func)
69 return NULL;
70
71 if (&next->list != &file->insn_list && next->func == func)
72 return next;
73
74 /* Check if we're already in the subfunction: */
75 if (func == func->cfunc)
76 return NULL;
77
78 /* Move to the subfunction: */
79 return find_insn(file, func->cfunc->sec, func->cfunc->offset);
80}
81
82#define func_for_each_insn_all(file, func, insn) \
83 for (insn = find_insn(file, func->sec, func->offset); \
84 insn; \
85 insn = next_insn_same_func(file, insn))
86
87#define func_for_each_insn(file, func, insn) \
88 for (insn = find_insn(file, func->sec, func->offset); \
89 insn && &insn->list != &file->insn_list && \
90 insn->sec == func->sec && \
91 insn->offset < func->offset + func->len; \
92 insn = list_next_entry(insn, list))
93
94#define func_for_each_insn_continue_reverse(file, func, insn) \
95 for (insn = list_prev_entry(insn, list); \
96 &insn->list != &file->insn_list && \
97 insn->sec == func->sec && insn->offset >= func->offset; \
98 insn = list_prev_entry(insn, list))
99
100#define sec_for_each_insn_from(file, insn) \
101 for (; insn; insn = next_insn_same_sec(file, insn))
102
103#define sec_for_each_insn_continue(file, insn) \
104 for (insn = next_insn_same_sec(file, insn); insn; \
105 insn = next_insn_same_sec(file, insn))
106
107/*
108 * Check if the function has been manually whitelisted with the
109 * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
110 * due to its use of a context switching instruction.
111 */
112static bool ignore_func(struct objtool_file *file, struct symbol *func)
113{
114 struct rela *rela;
115
116 /* check for STACK_FRAME_NON_STANDARD */
117 if (file->whitelist && file->whitelist->rela)
118 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
119 if (rela->sym->type == STT_SECTION &&
120 rela->sym->sec == func->sec &&
121 rela->addend == func->offset)
122 return true;
123 if (rela->sym->type == STT_FUNC && rela->sym == func)
124 return true;
125 }
126
127 return false;
128}
129
130/*
131 * This checks to see if the given function is a "noreturn" function.
132 *
133 * For global functions which are outside the scope of this object file, we
134 * have to keep a manual list of them.
135 *
136 * For local functions, we have to detect them manually by simply looking for
137 * the lack of a return instruction.
138 *
139 * Returns:
140 * -1: error
141 * 0: no dead end
142 * 1: dead end
143 */
144static int __dead_end_function(struct objtool_file *file, struct symbol *func,
145 int recursion)
146{
147 int i;
148 struct instruction *insn;
149 bool empty = true;
150
151 /*
152 * Unfortunately these have to be hard coded because the noreturn
153 * attribute isn't provided in ELF data.
154 */
155 static const char * const global_noreturns[] = {
156 "__stack_chk_fail",
157 "panic",
158 "do_exit",
159 "do_task_dead",
160 "__module_put_and_exit",
161 "complete_and_exit",
162 "kvm_spurious_fault",
163 "__reiserfs_panic",
164 "lbug_with_loc",
165 "fortify_panic",
166 "usercopy_abort",
167 };
168
169 if (func->bind == STB_WEAK)
170 return 0;
171
172 if (func->bind == STB_GLOBAL)
173 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
174 if (!strcmp(func->name, global_noreturns[i]))
175 return 1;
176
177 if (!func->len)
178 return 0;
179
180 insn = find_insn(file, func->sec, func->offset);
181 if (!insn->func)
182 return 0;
183
184 func_for_each_insn_all(file, func, insn) {
185 empty = false;
186
187 if (insn->type == INSN_RETURN)
188 return 0;
189 }
190
191 if (empty)
192 return 0;
193
194 /*
195 * A function can have a sibling call instead of a return. In that
196 * case, the function's dead-end status depends on whether the target
197 * of the sibling call returns.
198 */
199 func_for_each_insn_all(file, func, insn) {
200 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
201 struct instruction *dest = insn->jump_dest;
202
203 if (!dest)
204 /* sibling call to another file */
205 return 0;
206
207 if (dest->func && dest->func->pfunc != insn->func->pfunc) {
208
209 /* local sibling call */
210 if (recursion == 5) {
211 /*
212 * Infinite recursion: two functions
213 * have sibling calls to each other.
214 * This is a very rare case. It means
215 * they aren't dead ends.
216 */
217 return 0;
218 }
219
220 return __dead_end_function(file, dest->func,
221 recursion + 1);
222 }
223 }
224
225 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
226 /* sibling call */
227 return 0;
228 }
229
230 return 1;
231}
232
233static int dead_end_function(struct objtool_file *file, struct symbol *func)
234{
235 return __dead_end_function(file, func, 0);
236}
237
238static void clear_insn_state(struct insn_state *state)
239{
240 int i;
241
242 memset(state, 0, sizeof(*state));
243 state->cfa.base = CFI_UNDEFINED;
244 for (i = 0; i < CFI_NUM_REGS; i++) {
245 state->regs[i].base = CFI_UNDEFINED;
246 state->vals[i].base = CFI_UNDEFINED;
247 }
248 state->drap_reg = CFI_UNDEFINED;
249 state->drap_offset = -1;
250}
251
252/*
253 * Call the arch-specific instruction decoder for all the instructions and add
254 * them to the global instruction list.
255 */
256static int decode_instructions(struct objtool_file *file)
257{
258 struct section *sec;
259 struct symbol *func;
260 unsigned long offset;
261 struct instruction *insn;
262 int ret;
263
264 for_each_sec(file, sec) {
265
266 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
267 continue;
268
269 if (strcmp(sec->name, ".altinstr_replacement") &&
270 strcmp(sec->name, ".altinstr_aux") &&
271 strncmp(sec->name, ".discard.", 9))
272 sec->text = true;
273
274 for (offset = 0; offset < sec->len; offset += insn->len) {
275 insn = malloc(sizeof(*insn));
276 if (!insn) {
277 WARN("malloc failed");
278 return -1;
279 }
280 memset(insn, 0, sizeof(*insn));
281 INIT_LIST_HEAD(&insn->alts);
282 clear_insn_state(&insn->state);
283
284 insn->sec = sec;
285 insn->offset = offset;
286
287 ret = arch_decode_instruction(file->elf, sec, offset,
288 sec->len - offset,
289 &insn->len, &insn->type,
290 &insn->immediate,
291 &insn->stack_op);
292 if (ret)
293 goto err;
294
295 if (!insn->type || insn->type > INSN_LAST) {
296 WARN_FUNC("invalid instruction type %d",
297 insn->sec, insn->offset, insn->type);
298 ret = -1;
299 goto err;
300 }
301
302 hash_add(file->insn_hash, &insn->hash, insn->offset);
303 list_add_tail(&insn->list, &file->insn_list);
304 }
305
306 list_for_each_entry(func, &sec->symbol_list, list) {
307 if (func->type != STT_FUNC)
308 continue;
309
310 if (!find_insn(file, sec, func->offset)) {
311 WARN("%s(): can't find starting instruction",
312 func->name);
313 return -1;
314 }
315
316 func_for_each_insn(file, func, insn)
317 if (!insn->func)
318 insn->func = func;
319 }
320 }
321
322 return 0;
323
324err:
325 free(insn);
326 return ret;
327}
328
329/*
330 * Mark "ud2" instructions and manually annotated dead ends.
331 */
332static int add_dead_ends(struct objtool_file *file)
333{
334 struct section *sec;
335 struct rela *rela;
336 struct instruction *insn;
337 bool found;
338
339 /*
340 * By default, "ud2" is a dead end unless otherwise annotated, because
341 * GCC 7 inserts it for certain divide-by-zero cases.
342 */
343 for_each_insn(file, insn)
344 if (insn->type == INSN_BUG)
345 insn->dead_end = true;
346
347 /*
348 * Check for manually annotated dead ends.
349 */
350 sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
351 if (!sec)
352 goto reachable;
353
354 list_for_each_entry(rela, &sec->rela_list, list) {
355 if (rela->sym->type != STT_SECTION) {
356 WARN("unexpected relocation symbol type in %s", sec->name);
357 return -1;
358 }
359 insn = find_insn(file, rela->sym->sec, rela->addend);
360 if (insn)
361 insn = list_prev_entry(insn, list);
362 else if (rela->addend == rela->sym->sec->len) {
363 found = false;
364 list_for_each_entry_reverse(insn, &file->insn_list, list) {
365 if (insn->sec == rela->sym->sec) {
366 found = true;
367 break;
368 }
369 }
370
371 if (!found) {
372 WARN("can't find unreachable insn at %s+0x%x",
373 rela->sym->sec->name, rela->addend);
374 return -1;
375 }
376 } else {
377 WARN("can't find unreachable insn at %s+0x%x",
378 rela->sym->sec->name, rela->addend);
379 return -1;
380 }
381
382 insn->dead_end = true;
383 }
384
385reachable:
386 /*
387 * These manually annotated reachable checks are needed for GCC 4.4,
388 * where the Linux unreachable() macro isn't supported. In that case
389 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
390 * not a dead end.
391 */
392 sec = find_section_by_name(file->elf, ".rela.discard.reachable");
393 if (!sec)
394 return 0;
395
396 list_for_each_entry(rela, &sec->rela_list, list) {
397 if (rela->sym->type != STT_SECTION) {
398 WARN("unexpected relocation symbol type in %s", sec->name);
399 return -1;
400 }
401 insn = find_insn(file, rela->sym->sec, rela->addend);
402 if (insn)
403 insn = list_prev_entry(insn, list);
404 else if (rela->addend == rela->sym->sec->len) {
405 found = false;
406 list_for_each_entry_reverse(insn, &file->insn_list, list) {
407 if (insn->sec == rela->sym->sec) {
408 found = true;
409 break;
410 }
411 }
412
413 if (!found) {
414 WARN("can't find reachable insn at %s+0x%x",
415 rela->sym->sec->name, rela->addend);
416 return -1;
417 }
418 } else {
419 WARN("can't find reachable insn at %s+0x%x",
420 rela->sym->sec->name, rela->addend);
421 return -1;
422 }
423
424 insn->dead_end = false;
425 }
426
427 return 0;
428}
429
430/*
431 * Warnings shouldn't be reported for ignored functions.
432 */
433static void add_ignores(struct objtool_file *file)
434{
435 struct instruction *insn;
436 struct section *sec;
437 struct symbol *func;
438
439 for_each_sec(file, sec) {
440 list_for_each_entry(func, &sec->symbol_list, list) {
441 if (func->type != STT_FUNC)
442 continue;
443
444 if (!ignore_func(file, func))
445 continue;
446
447 func_for_each_insn_all(file, func, insn)
448 insn->ignore = true;
449 }
450 }
451}
452
453/*
454 * FIXME: For now, just ignore any alternatives which add retpolines. This is
455 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
456 * But it at least allows objtool to understand the control flow *around* the
457 * retpoline.
458 */
459static int add_nospec_ignores(struct objtool_file *file)
460{
461 struct section *sec;
462 struct rela *rela;
463 struct instruction *insn;
464
465 sec = find_section_by_name(file->elf, ".rela.discard.nospec");
466 if (!sec)
467 return 0;
468
469 list_for_each_entry(rela, &sec->rela_list, list) {
470 if (rela->sym->type != STT_SECTION) {
471 WARN("unexpected relocation symbol type in %s", sec->name);
472 return -1;
473 }
474
475 insn = find_insn(file, rela->sym->sec, rela->addend);
476 if (!insn) {
477 WARN("bad .discard.nospec entry");
478 return -1;
479 }
480
481 insn->ignore_alts = true;
482 }
483
484 return 0;
485}
486
487/*
488 * Find the destination instructions for all jumps.
489 */
490static int add_jump_destinations(struct objtool_file *file)
491{
492 struct instruction *insn;
493 struct rela *rela;
494 struct section *dest_sec;
495 unsigned long dest_off;
496
497 for_each_insn(file, insn) {
498 if (insn->type != INSN_JUMP_CONDITIONAL &&
499 insn->type != INSN_JUMP_UNCONDITIONAL)
500 continue;
501
502 if (insn->ignore)
503 continue;
504
505 rela = find_rela_by_dest_range(insn->sec, insn->offset,
506 insn->len);
507 if (!rela) {
508 dest_sec = insn->sec;
509 dest_off = insn->offset + insn->len + insn->immediate;
510 } else if (rela->sym->type == STT_SECTION) {
511 dest_sec = rela->sym->sec;
512 dest_off = rela->addend + 4;
513 } else if (rela->sym->sec->idx) {
514 dest_sec = rela->sym->sec;
515 dest_off = rela->sym->sym.st_value + rela->addend + 4;
516 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
517 /*
518 * Retpoline jumps are really dynamic jumps in
519 * disguise, so convert them accordingly.
520 */
521 insn->type = INSN_JUMP_DYNAMIC;
522 insn->retpoline_safe = true;
523 continue;
524 } else {
525 /* sibling call */
526 insn->jump_dest = 0;
527 continue;
528 }
529
530 insn->jump_dest = find_insn(file, dest_sec, dest_off);
531 if (!insn->jump_dest) {
532
533 /*
534 * This is a special case where an alt instruction
535 * jumps past the end of the section. These are
536 * handled later in handle_group_alt().
537 */
538 if (!strcmp(insn->sec->name, ".altinstr_replacement"))
539 continue;
540
541 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
542 insn->sec, insn->offset, dest_sec->name,
543 dest_off);
544 return -1;
545 }
546 }
547
548 return 0;
549}
550
551/*
552 * Find the destination instructions for all calls.
553 */
554static int add_call_destinations(struct objtool_file *file)
555{
556 struct instruction *insn;
557 unsigned long dest_off;
558 struct rela *rela;
559
560 for_each_insn(file, insn) {
561 if (insn->type != INSN_CALL)
562 continue;
563
564 rela = find_rela_by_dest_range(insn->sec, insn->offset,
565 insn->len);
566 if (!rela) {
567 dest_off = insn->offset + insn->len + insn->immediate;
568 insn->call_dest = find_symbol_by_offset(insn->sec,
569 dest_off);
570
571 if (!insn->call_dest && !insn->ignore) {
572 WARN_FUNC("unsupported intra-function call",
573 insn->sec, insn->offset);
574 if (retpoline)
575 WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
576 return -1;
577 }
578
579 } else if (rela->sym->type == STT_SECTION) {
580 insn->call_dest = find_symbol_by_offset(rela->sym->sec,
581 rela->addend+4);
582 if (!insn->call_dest ||
583 insn->call_dest->type != STT_FUNC) {
584 WARN_FUNC("can't find call dest symbol at %s+0x%x",
585 insn->sec, insn->offset,
586 rela->sym->sec->name,
587 rela->addend + 4);
588 return -1;
589 }
590 } else
591 insn->call_dest = rela->sym;
592 }
593
594 return 0;
595}
596
597/*
598 * The .alternatives section requires some extra special care, over and above
599 * what other special sections require:
600 *
601 * 1. Because alternatives are patched in-place, we need to insert a fake jump
602 * instruction at the end so that validate_branch() skips all the original
603 * replaced instructions when validating the new instruction path.
604 *
605 * 2. An added wrinkle is that the new instruction length might be zero. In
606 * that case the old instructions are replaced with noops. We simulate that
607 * by creating a fake jump as the only new instruction.
608 *
609 * 3. In some cases, the alternative section includes an instruction which
610 * conditionally jumps to the _end_ of the entry. We have to modify these
611 * jumps' destinations to point back to .text rather than the end of the
612 * entry in .altinstr_replacement.
613 *
614 * 4. It has been requested that we don't validate the !POPCNT feature path
615 * which is a "very very small percentage of machines".
616 */
617static int handle_group_alt(struct objtool_file *file,
618 struct special_alt *special_alt,
619 struct instruction *orig_insn,
620 struct instruction **new_insn)
621{
622 struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
623 unsigned long dest_off;
624
625 last_orig_insn = NULL;
626 insn = orig_insn;
627 sec_for_each_insn_from(file, insn) {
628 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
629 break;
630
631 if (special_alt->skip_orig)
632 insn->type = INSN_NOP;
633
634 insn->alt_group = true;
635 last_orig_insn = insn;
636 }
637
638 if (next_insn_same_sec(file, last_orig_insn)) {
639 fake_jump = malloc(sizeof(*fake_jump));
640 if (!fake_jump) {
641 WARN("malloc failed");
642 return -1;
643 }
644 memset(fake_jump, 0, sizeof(*fake_jump));
645 INIT_LIST_HEAD(&fake_jump->alts);
646 clear_insn_state(&fake_jump->state);
647
648 fake_jump->sec = special_alt->new_sec;
649 fake_jump->offset = -1;
650 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
651 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
652 fake_jump->ignore = true;
653 }
654
655 if (!special_alt->new_len) {
656 if (!fake_jump) {
657 WARN("%s: empty alternative at end of section",
658 special_alt->orig_sec->name);
659 return -1;
660 }
661
662 *new_insn = fake_jump;
663 return 0;
664 }
665
666 last_new_insn = NULL;
667 insn = *new_insn;
668 sec_for_each_insn_from(file, insn) {
669 if (insn->offset >= special_alt->new_off + special_alt->new_len)
670 break;
671
672 last_new_insn = insn;
673
674 insn->ignore = orig_insn->ignore_alts;
675
676 if (insn->type != INSN_JUMP_CONDITIONAL &&
677 insn->type != INSN_JUMP_UNCONDITIONAL)
678 continue;
679
680 if (!insn->immediate)
681 continue;
682
683 dest_off = insn->offset + insn->len + insn->immediate;
684 if (dest_off == special_alt->new_off + special_alt->new_len) {
685 if (!fake_jump) {
686 WARN("%s: alternative jump to end of section",
687 special_alt->orig_sec->name);
688 return -1;
689 }
690 insn->jump_dest = fake_jump;
691 }
692
693 if (!insn->jump_dest) {
694 WARN_FUNC("can't find alternative jump destination",
695 insn->sec, insn->offset);
696 return -1;
697 }
698 }
699
700 if (!last_new_insn) {
701 WARN_FUNC("can't find last new alternative instruction",
702 special_alt->new_sec, special_alt->new_off);
703 return -1;
704 }
705
706 if (fake_jump)
707 list_add(&fake_jump->list, &last_new_insn->list);
708
709 return 0;
710}
711
712/*
713 * A jump table entry can either convert a nop to a jump or a jump to a nop.
714 * If the original instruction is a jump, make the alt entry an effective nop
715 * by just skipping the original instruction.
716 */
717static int handle_jump_alt(struct objtool_file *file,
718 struct special_alt *special_alt,
719 struct instruction *orig_insn,
720 struct instruction **new_insn)
721{
722 if (orig_insn->type == INSN_NOP)
723 return 0;
724
725 if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
726 WARN_FUNC("unsupported instruction at jump label",
727 orig_insn->sec, orig_insn->offset);
728 return -1;
729 }
730
731 *new_insn = list_next_entry(orig_insn, list);
732 return 0;
733}
734
735/*
736 * Read all the special sections which have alternate instructions which can be
737 * patched in or redirected to at runtime. Each instruction having alternate
738 * instruction(s) has them added to its insn->alts list, which will be
739 * traversed in validate_branch().
740 */
741static int add_special_section_alts(struct objtool_file *file)
742{
743 struct list_head special_alts;
744 struct instruction *orig_insn, *new_insn;
745 struct special_alt *special_alt, *tmp;
746 struct alternative *alt;
747 int ret;
748
749 ret = special_get_alts(file->elf, &special_alts);
750 if (ret)
751 return ret;
752
753 list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
754
755 orig_insn = find_insn(file, special_alt->orig_sec,
756 special_alt->orig_off);
757 if (!orig_insn) {
758 WARN_FUNC("special: can't find orig instruction",
759 special_alt->orig_sec, special_alt->orig_off);
760 ret = -1;
761 goto out;
762 }
763
764 new_insn = NULL;
765 if (!special_alt->group || special_alt->new_len) {
766 new_insn = find_insn(file, special_alt->new_sec,
767 special_alt->new_off);
768 if (!new_insn) {
769 WARN_FUNC("special: can't find new instruction",
770 special_alt->new_sec,
771 special_alt->new_off);
772 ret = -1;
773 goto out;
774 }
775 }
776
777 if (special_alt->group) {
778 ret = handle_group_alt(file, special_alt, orig_insn,
779 &new_insn);
780 if (ret)
781 goto out;
782 } else if (special_alt->jump_or_nop) {
783 ret = handle_jump_alt(file, special_alt, orig_insn,
784 &new_insn);
785 if (ret)
786 goto out;
787 }
788
789 alt = malloc(sizeof(*alt));
790 if (!alt) {
791 WARN("malloc failed");
792 ret = -1;
793 goto out;
794 }
795
796 alt->insn = new_insn;
797 list_add_tail(&alt->list, &orig_insn->alts);
798
799 list_del(&special_alt->list);
800 free(special_alt);
801 }
802
803out:
804 return ret;
805}
806
807static int add_switch_table(struct objtool_file *file, struct instruction *insn,
808 struct rela *table, struct rela *next_table)
809{
810 struct rela *rela = table;
811 struct instruction *alt_insn;
812 struct alternative *alt;
813 struct symbol *pfunc = insn->func->pfunc;
814 unsigned int prev_offset = 0;
815
816 list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
817 if (rela == next_table)
818 break;
819
820 /* Make sure the switch table entries are consecutive: */
821 if (prev_offset && rela->offset != prev_offset + 8)
822 break;
823
824 /* Detect function pointers from contiguous objects: */
825 if (rela->sym->sec == pfunc->sec &&
826 rela->addend == pfunc->offset)
827 break;
828
829 alt_insn = find_insn(file, rela->sym->sec, rela->addend);
830 if (!alt_insn)
831 break;
832
833 /* Make sure the jmp dest is in the function or subfunction: */
834 if (alt_insn->func->pfunc != pfunc)
835 break;
836
837 alt = malloc(sizeof(*alt));
838 if (!alt) {
839 WARN("malloc failed");
840 return -1;
841 }
842
843 alt->insn = alt_insn;
844 list_add_tail(&alt->list, &insn->alts);
845 prev_offset = rela->offset;
846 }
847
848 if (!prev_offset) {
849 WARN_FUNC("can't find switch jump table",
850 insn->sec, insn->offset);
851 return -1;
852 }
853
854 return 0;
855}
856
857/*
858 * find_switch_table() - Given a dynamic jump, find the switch jump table in
859 * .rodata associated with it.
860 *
861 * There are 3 basic patterns:
862 *
863 * 1. jmpq *[rodata addr](,%reg,8)
864 *
865 * This is the most common case by far. It jumps to an address in a simple
866 * jump table which is stored in .rodata.
867 *
868 * 2. jmpq *[rodata addr](%rip)
869 *
870 * This is caused by a rare GCC quirk, currently only seen in three driver
871 * functions in the kernel, only with certain obscure non-distro configs.
872 *
873 * As part of an optimization, GCC makes a copy of an existing switch jump
874 * table, modifies it, and then hard-codes the jump (albeit with an indirect
875 * jump) to use a single entry in the table. The rest of the jump table and
876 * some of its jump targets remain as dead code.
877 *
878 * In such a case we can just crudely ignore all unreachable instruction
879 * warnings for the entire object file. Ideally we would just ignore them
880 * for the function, but that would require redesigning the code quite a
881 * bit. And honestly that's just not worth doing: unreachable instruction
882 * warnings are of questionable value anyway, and this is such a rare issue.
883 *
884 * 3. mov [rodata addr],%reg1
885 * ... some instructions ...
886 * jmpq *(%reg1,%reg2,8)
887 *
888 * This is a fairly uncommon pattern which is new for GCC 6. As of this
889 * writing, there are 11 occurrences of it in the allmodconfig kernel.
890 *
891 * As of GCC 7 there are quite a few more of these and the 'in between' code
892 * is significant. Esp. with KASAN enabled some of the code between the mov
893 * and jmpq uses .rodata itself, which can confuse things.
894 *
895 * TODO: Once we have DWARF CFI and smarter instruction decoding logic,
896 * ensure the same register is used in the mov and jump instructions.
897 *
898 * NOTE: RETPOLINE made it harder still to decode dynamic jumps.
899 */
900static struct rela *find_switch_table(struct objtool_file *file,
901 struct symbol *func,
902 struct instruction *insn)
903{
904 struct rela *text_rela, *rodata_rela;
905 struct instruction *orig_insn = insn;
906 unsigned long table_offset;
907
908 /*
909 * Backward search using the @first_jump_src links, these help avoid
910 * much of the 'in between' code. Which avoids us getting confused by
911 * it.
912 */
913 for (;
914 &insn->list != &file->insn_list &&
915 insn->sec == func->sec &&
916 insn->offset >= func->offset;
917
918 insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
919
920 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
921 break;
922
923 /* allow small jumps within the range */
924 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
925 insn->jump_dest &&
926 (insn->jump_dest->offset <= insn->offset ||
927 insn->jump_dest->offset > orig_insn->offset))
928 break;
929
930 /* look for a relocation which references .rodata */
931 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
932 insn->len);
933 if (!text_rela || text_rela->sym != file->rodata->sym)
934 continue;
935
936 table_offset = text_rela->addend;
937 if (text_rela->type == R_X86_64_PC32)
938 table_offset += 4;
939
940 /*
941 * Make sure the .rodata address isn't associated with a
942 * symbol. gcc jump tables are anonymous data.
943 */
944 if (find_symbol_containing(file->rodata, table_offset))
945 continue;
946
947 rodata_rela = find_rela_by_dest(file->rodata, table_offset);
948 if (rodata_rela) {
949 /*
950 * Use of RIP-relative switch jumps is quite rare, and
951 * indicates a rare GCC quirk/bug which can leave dead
952 * code behind.
953 */
954 if (text_rela->type == R_X86_64_PC32)
955 file->ignore_unreachables = true;
956
957 return rodata_rela;
958 }
959 }
960
961 return NULL;
962}
963
964
965static int add_func_switch_tables(struct objtool_file *file,
966 struct symbol *func)
967{
968 struct instruction *insn, *last = NULL, *prev_jump = NULL;
969 struct rela *rela, *prev_rela = NULL;
970 int ret;
971
972 func_for_each_insn_all(file, func, insn) {
973 if (!last)
974 last = insn;
975
976 /*
977 * Store back-pointers for unconditional forward jumps such
978 * that find_switch_table() can back-track using those and
979 * avoid some potentially confusing code.
980 */
981 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
982 insn->offset > last->offset &&
983 insn->jump_dest->offset > insn->offset &&
984 !insn->jump_dest->first_jump_src) {
985
986 insn->jump_dest->first_jump_src = insn;
987 last = insn->jump_dest;
988 }
989
990 if (insn->type != INSN_JUMP_DYNAMIC)
991 continue;
992
993 rela = find_switch_table(file, func, insn);
994 if (!rela)
995 continue;
996
997 /*
998 * We found a switch table, but we don't know yet how big it
999 * is. Don't add it until we reach the end of the function or
1000 * the beginning of another switch table in the same function.
1001 */
1002 if (prev_jump) {
1003 ret = add_switch_table(file, prev_jump, prev_rela, rela);
1004 if (ret)
1005 return ret;
1006 }
1007
1008 prev_jump = insn;
1009 prev_rela = rela;
1010 }
1011
1012 if (prev_jump) {
1013 ret = add_switch_table(file, prev_jump, prev_rela, NULL);
1014 if (ret)
1015 return ret;
1016 }
1017
1018 return 0;
1019}
1020
1021/*
1022 * For some switch statements, gcc generates a jump table in the .rodata
1023 * section which contains a list of addresses within the function to jump to.
1024 * This finds these jump tables and adds them to the insn->alts lists.
1025 */
1026static int add_switch_table_alts(struct objtool_file *file)
1027{
1028 struct section *sec;
1029 struct symbol *func;
1030 int ret;
1031
1032 if (!file->rodata || !file->rodata->rela)
1033 return 0;
1034
1035 for_each_sec(file, sec) {
1036 list_for_each_entry(func, &sec->symbol_list, list) {
1037 if (func->type != STT_FUNC)
1038 continue;
1039
1040 ret = add_func_switch_tables(file, func);
1041 if (ret)
1042 return ret;
1043 }
1044 }
1045
1046 return 0;
1047}
1048
1049static int read_unwind_hints(struct objtool_file *file)
1050{
1051 struct section *sec, *relasec;
1052 struct rela *rela;
1053 struct unwind_hint *hint;
1054 struct instruction *insn;
1055 struct cfi_reg *cfa;
1056 int i;
1057
1058 sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1059 if (!sec)
1060 return 0;
1061
1062 relasec = sec->rela;
1063 if (!relasec) {
1064 WARN("missing .rela.discard.unwind_hints section");
1065 return -1;
1066 }
1067
1068 if (sec->len % sizeof(struct unwind_hint)) {
1069 WARN("struct unwind_hint size mismatch");
1070 return -1;
1071 }
1072
1073 file->hints = true;
1074
1075 for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1076 hint = (struct unwind_hint *)sec->data->d_buf + i;
1077
1078 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1079 if (!rela) {
1080 WARN("can't find rela for unwind_hints[%d]", i);
1081 return -1;
1082 }
1083
1084 insn = find_insn(file, rela->sym->sec, rela->addend);
1085 if (!insn) {
1086 WARN("can't find insn for unwind_hints[%d]", i);
1087 return -1;
1088 }
1089
1090 cfa = &insn->state.cfa;
1091
1092 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1093 insn->save = true;
1094 continue;
1095
1096 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1097 insn->restore = true;
1098 insn->hint = true;
1099 continue;
1100 }
1101
1102 insn->hint = true;
1103
1104 switch (hint->sp_reg) {
1105 case ORC_REG_UNDEFINED:
1106 cfa->base = CFI_UNDEFINED;
1107 break;
1108 case ORC_REG_SP:
1109 cfa->base = CFI_SP;
1110 break;
1111 case ORC_REG_BP:
1112 cfa->base = CFI_BP;
1113 break;
1114 case ORC_REG_SP_INDIRECT:
1115 cfa->base = CFI_SP_INDIRECT;
1116 break;
1117 case ORC_REG_R10:
1118 cfa->base = CFI_R10;
1119 break;
1120 case ORC_REG_R13:
1121 cfa->base = CFI_R13;
1122 break;
1123 case ORC_REG_DI:
1124 cfa->base = CFI_DI;
1125 break;
1126 case ORC_REG_DX:
1127 cfa->base = CFI_DX;
1128 break;
1129 default:
1130 WARN_FUNC("unsupported unwind_hint sp base reg %d",
1131 insn->sec, insn->offset, hint->sp_reg);
1132 return -1;
1133 }
1134
1135 cfa->offset = hint->sp_offset;
1136 insn->state.type = hint->type;
1137 }
1138
1139 return 0;
1140}
1141
1142static int read_retpoline_hints(struct objtool_file *file)
1143{
1144 struct section *sec;
1145 struct instruction *insn;
1146 struct rela *rela;
1147
1148 sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1149 if (!sec)
1150 return 0;
1151
1152 list_for_each_entry(rela, &sec->rela_list, list) {
1153 if (rela->sym->type != STT_SECTION) {
1154 WARN("unexpected relocation symbol type in %s", sec->name);
1155 return -1;
1156 }
1157
1158 insn = find_insn(file, rela->sym->sec, rela->addend);
1159 if (!insn) {
1160 WARN("bad .discard.retpoline_safe entry");
1161 return -1;
1162 }
1163
1164 if (insn->type != INSN_JUMP_DYNAMIC &&
1165 insn->type != INSN_CALL_DYNAMIC) {
1166 WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1167 insn->sec, insn->offset);
1168 return -1;
1169 }
1170
1171 insn->retpoline_safe = true;
1172 }
1173
1174 return 0;
1175}
1176
1177static int decode_sections(struct objtool_file *file)
1178{
1179 int ret;
1180
1181 ret = decode_instructions(file);
1182 if (ret)
1183 return ret;
1184
1185 ret = add_dead_ends(file);
1186 if (ret)
1187 return ret;
1188
1189 add_ignores(file);
1190
1191 ret = add_nospec_ignores(file);
1192 if (ret)
1193 return ret;
1194
1195 ret = add_jump_destinations(file);
1196 if (ret)
1197 return ret;
1198
1199 ret = add_special_section_alts(file);
1200 if (ret)
1201 return ret;
1202
1203 ret = add_call_destinations(file);
1204 if (ret)
1205 return ret;
1206
1207 ret = add_switch_table_alts(file);
1208 if (ret)
1209 return ret;
1210
1211 ret = read_unwind_hints(file);
1212 if (ret)
1213 return ret;
1214
1215 ret = read_retpoline_hints(file);
1216 if (ret)
1217 return ret;
1218
1219 return 0;
1220}
1221
1222static bool is_fentry_call(struct instruction *insn)
1223{
1224 if (insn->type == INSN_CALL &&
1225 insn->call_dest->type == STT_NOTYPE &&
1226 !strcmp(insn->call_dest->name, "__fentry__"))
1227 return true;
1228
1229 return false;
1230}
1231
1232static bool has_modified_stack_frame(struct insn_state *state)
1233{
1234 int i;
1235
1236 if (state->cfa.base != initial_func_cfi.cfa.base ||
1237 state->cfa.offset != initial_func_cfi.cfa.offset ||
1238 state->stack_size != initial_func_cfi.cfa.offset ||
1239 state->drap)
1240 return true;
1241
1242 for (i = 0; i < CFI_NUM_REGS; i++)
1243 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1244 state->regs[i].offset != initial_func_cfi.regs[i].offset)
1245 return true;
1246
1247 return false;
1248}
1249
1250static bool has_valid_stack_frame(struct insn_state *state)
1251{
1252 if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1253 state->regs[CFI_BP].offset == -16)
1254 return true;
1255
1256 if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1257 return true;
1258
1259 return false;
1260}
1261
1262static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1263{
1264 struct cfi_reg *cfa = &state->cfa;
1265 struct stack_op *op = &insn->stack_op;
1266
1267 if (cfa->base != CFI_SP)
1268 return 0;
1269
1270 /* push */
1271 if (op->dest.type == OP_DEST_PUSH)
1272 cfa->offset += 8;
1273
1274 /* pop */
1275 if (op->src.type == OP_SRC_POP)
1276 cfa->offset -= 8;
1277
1278 /* add immediate to sp */
1279 if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1280 op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1281 cfa->offset -= op->src.offset;
1282
1283 return 0;
1284}
1285
1286static void save_reg(struct insn_state *state, unsigned char reg, int base,
1287 int offset)
1288{
1289 if (arch_callee_saved_reg(reg) &&
1290 state->regs[reg].base == CFI_UNDEFINED) {
1291 state->regs[reg].base = base;
1292 state->regs[reg].offset = offset;
1293 }
1294}
1295
1296static void restore_reg(struct insn_state *state, unsigned char reg)
1297{
1298 state->regs[reg].base = CFI_UNDEFINED;
1299 state->regs[reg].offset = 0;
1300}
1301
1302/*
1303 * A note about DRAP stack alignment:
1304 *
1305 * GCC has the concept of a DRAP register, which is used to help keep track of
1306 * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
1307 * register. The typical DRAP pattern is:
1308 *
1309 * 4c 8d 54 24 08 lea 0x8(%rsp),%r10
1310 * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
1311 * 41 ff 72 f8 pushq -0x8(%r10)
1312 * 55 push %rbp
1313 * 48 89 e5 mov %rsp,%rbp
1314 * (more pushes)
1315 * 41 52 push %r10
1316 * ...
1317 * 41 5a pop %r10
1318 * (more pops)
1319 * 5d pop %rbp
1320 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1321 * c3 retq
1322 *
1323 * There are some variations in the epilogues, like:
1324 *
1325 * 5b pop %rbx
1326 * 41 5a pop %r10
1327 * 41 5c pop %r12
1328 * 41 5d pop %r13
1329 * 41 5e pop %r14
1330 * c9 leaveq
1331 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1332 * c3 retq
1333 *
1334 * and:
1335 *
1336 * 4c 8b 55 e8 mov -0x18(%rbp),%r10
1337 * 48 8b 5d e0 mov -0x20(%rbp),%rbx
1338 * 4c 8b 65 f0 mov -0x10(%rbp),%r12
1339 * 4c 8b 6d f8 mov -0x8(%rbp),%r13
1340 * c9 leaveq
1341 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1342 * c3 retq
1343 *
1344 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1345 * restored beforehand:
1346 *
1347 * 41 55 push %r13
1348 * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
1349 * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
1350 * ...
1351 * 49 8d 65 f0 lea -0x10(%r13),%rsp
1352 * 41 5d pop %r13
1353 * c3 retq
1354 */
1355static int update_insn_state(struct instruction *insn, struct insn_state *state)
1356{
1357 struct stack_op *op = &insn->stack_op;
1358 struct cfi_reg *cfa = &state->cfa;
1359 struct cfi_reg *regs = state->regs;
1360
1361 /* stack operations don't make sense with an undefined CFA */
1362 if (cfa->base == CFI_UNDEFINED) {
1363 if (insn->func) {
1364 WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1365 return -1;
1366 }
1367 return 0;
1368 }
1369
1370 if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1371 return update_insn_state_regs(insn, state);
1372
1373 switch (op->dest.type) {
1374
1375 case OP_DEST_REG:
1376 switch (op->src.type) {
1377
1378 case OP_SRC_REG:
1379 if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1380 cfa->base == CFI_SP &&
1381 regs[CFI_BP].base == CFI_CFA &&
1382 regs[CFI_BP].offset == -cfa->offset) {
1383
1384 /* mov %rsp, %rbp */
1385 cfa->base = op->dest.reg;
1386 state->bp_scratch = false;
1387 }
1388
1389 else if (op->src.reg == CFI_SP &&
1390 op->dest.reg == CFI_BP && state->drap) {
1391
1392 /* drap: mov %rsp, %rbp */
1393 regs[CFI_BP].base = CFI_BP;
1394 regs[CFI_BP].offset = -state->stack_size;
1395 state->bp_scratch = false;
1396 }
1397
1398 else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1399
1400 /*
1401 * mov %rsp, %reg
1402 *
1403 * This is needed for the rare case where GCC
1404 * does:
1405 *
1406 * mov %rsp, %rax
1407 * ...
1408 * mov %rax, %rsp
1409 */
1410 state->vals[op->dest.reg].base = CFI_CFA;
1411 state->vals[op->dest.reg].offset = -state->stack_size;
1412 }
1413
1414 else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1415 cfa->base == CFI_BP) {
1416
1417 /*
1418 * mov %rbp, %rsp
1419 *
1420 * Restore the original stack pointer (Clang).
1421 */
1422 state->stack_size = -state->regs[CFI_BP].offset;
1423 }
1424
1425 else if (op->dest.reg == cfa->base) {
1426
1427 /* mov %reg, %rsp */
1428 if (cfa->base == CFI_SP &&
1429 state->vals[op->src.reg].base == CFI_CFA) {
1430
1431 /*
1432 * This is needed for the rare case
1433 * where GCC does something dumb like:
1434 *
1435 * lea 0x8(%rsp), %rcx
1436 * ...
1437 * mov %rcx, %rsp
1438 */
1439 cfa->offset = -state->vals[op->src.reg].offset;
1440 state->stack_size = cfa->offset;
1441
1442 } else {
1443 cfa->base = CFI_UNDEFINED;
1444 cfa->offset = 0;
1445 }
1446 }
1447
1448 break;
1449
1450 case OP_SRC_ADD:
1451 if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1452
1453 /* add imm, %rsp */
1454 state->stack_size -= op->src.offset;
1455 if (cfa->base == CFI_SP)
1456 cfa->offset -= op->src.offset;
1457 break;
1458 }
1459
1460 if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1461
1462 /* lea disp(%rbp), %rsp */
1463 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1464 break;
1465 }
1466
1467 if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1468
1469 /* drap: lea disp(%rsp), %drap */
1470 state->drap_reg = op->dest.reg;
1471
1472 /*
1473 * lea disp(%rsp), %reg
1474 *
1475 * This is needed for the rare case where GCC
1476 * does something dumb like:
1477 *
1478 * lea 0x8(%rsp), %rcx
1479 * ...
1480 * mov %rcx, %rsp
1481 */
1482 state->vals[op->dest.reg].base = CFI_CFA;
1483 state->vals[op->dest.reg].offset = \
1484 -state->stack_size + op->src.offset;
1485
1486 break;
1487 }
1488
1489 if (state->drap && op->dest.reg == CFI_SP &&
1490 op->src.reg == state->drap_reg) {
1491
1492 /* drap: lea disp(%drap), %rsp */
1493 cfa->base = CFI_SP;
1494 cfa->offset = state->stack_size = -op->src.offset;
1495 state->drap_reg = CFI_UNDEFINED;
1496 state->drap = false;
1497 break;
1498 }
1499
1500 if (op->dest.reg == state->cfa.base) {
1501 WARN_FUNC("unsupported stack register modification",
1502 insn->sec, insn->offset);
1503 return -1;
1504 }
1505
1506 break;
1507
1508 case OP_SRC_AND:
1509 if (op->dest.reg != CFI_SP ||
1510 (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1511 (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1512 WARN_FUNC("unsupported stack pointer realignment",
1513 insn->sec, insn->offset);
1514 return -1;
1515 }
1516
1517 if (state->drap_reg != CFI_UNDEFINED) {
1518 /* drap: and imm, %rsp */
1519 cfa->base = state->drap_reg;
1520 cfa->offset = state->stack_size = 0;
1521 state->drap = true;
1522 }
1523
1524 /*
1525 * Older versions of GCC (4.8ish) realign the stack
1526 * without DRAP, with a frame pointer.
1527 */
1528
1529 break;
1530
1531 case OP_SRC_POP:
1532 if (!state->drap && op->dest.type == OP_DEST_REG &&
1533 op->dest.reg == cfa->base) {
1534
1535 /* pop %rbp */
1536 cfa->base = CFI_SP;
1537 }
1538
1539 if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1540 op->dest.type == OP_DEST_REG &&
1541 op->dest.reg == state->drap_reg &&
1542 state->drap_offset == -state->stack_size) {
1543
1544 /* drap: pop %drap */
1545 cfa->base = state->drap_reg;
1546 cfa->offset = 0;
1547 state->drap_offset = -1;
1548
1549 } else if (regs[op->dest.reg].offset == -state->stack_size) {
1550
1551 /* pop %reg */
1552 restore_reg(state, op->dest.reg);
1553 }
1554
1555 state->stack_size -= 8;
1556 if (cfa->base == CFI_SP)
1557 cfa->offset -= 8;
1558
1559 break;
1560
1561 case OP_SRC_REG_INDIRECT:
1562 if (state->drap && op->src.reg == CFI_BP &&
1563 op->src.offset == state->drap_offset) {
1564
1565 /* drap: mov disp(%rbp), %drap */
1566 cfa->base = state->drap_reg;
1567 cfa->offset = 0;
1568 state->drap_offset = -1;
1569 }
1570
1571 if (state->drap && op->src.reg == CFI_BP &&
1572 op->src.offset == regs[op->dest.reg].offset) {
1573
1574 /* drap: mov disp(%rbp), %reg */
1575 restore_reg(state, op->dest.reg);
1576
1577 } else if (op->src.reg == cfa->base &&
1578 op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1579
1580 /* mov disp(%rbp), %reg */
1581 /* mov disp(%rsp), %reg */
1582 restore_reg(state, op->dest.reg);
1583 }
1584
1585 break;
1586
1587 default:
1588 WARN_FUNC("unknown stack-related instruction",
1589 insn->sec, insn->offset);
1590 return -1;
1591 }
1592
1593 break;
1594
1595 case OP_DEST_PUSH:
1596 state->stack_size += 8;
1597 if (cfa->base == CFI_SP)
1598 cfa->offset += 8;
1599
1600 if (op->src.type != OP_SRC_REG)
1601 break;
1602
1603 if (state->drap) {
1604 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1605
1606 /* drap: push %drap */
1607 cfa->base = CFI_BP_INDIRECT;
1608 cfa->offset = -state->stack_size;
1609
1610 /* save drap so we know when to restore it */
1611 state->drap_offset = -state->stack_size;
1612
1613 } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1614
1615 /* drap: push %rbp */
1616 state->stack_size = 0;
1617
1618 } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1619
1620 /* drap: push %reg */
1621 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1622 }
1623
1624 } else {
1625
1626 /* push %reg */
1627 save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1628 }
1629
1630 /* detect when asm code uses rbp as a scratch register */
1631 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1632 cfa->base != CFI_BP)
1633 state->bp_scratch = true;
1634 break;
1635
1636 case OP_DEST_REG_INDIRECT:
1637
1638 if (state->drap) {
1639 if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1640
1641 /* drap: mov %drap, disp(%rbp) */
1642 cfa->base = CFI_BP_INDIRECT;
1643 cfa->offset = op->dest.offset;
1644
1645 /* save drap offset so we know when to restore it */
1646 state->drap_offset = op->dest.offset;
1647 }
1648
1649 else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1650
1651 /* drap: mov reg, disp(%rbp) */
1652 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1653 }
1654
1655 } else if (op->dest.reg == cfa->base) {
1656
1657 /* mov reg, disp(%rbp) */
1658 /* mov reg, disp(%rsp) */
1659 save_reg(state, op->src.reg, CFI_CFA,
1660 op->dest.offset - state->cfa.offset);
1661 }
1662
1663 break;
1664
1665 case OP_DEST_LEAVE:
1666 if ((!state->drap && cfa->base != CFI_BP) ||
1667 (state->drap && cfa->base != state->drap_reg)) {
1668 WARN_FUNC("leave instruction with modified stack frame",
1669 insn->sec, insn->offset);
1670 return -1;
1671 }
1672
1673 /* leave (mov %rbp, %rsp; pop %rbp) */
1674
1675 state->stack_size = -state->regs[CFI_BP].offset - 8;
1676 restore_reg(state, CFI_BP);
1677
1678 if (!state->drap) {
1679 cfa->base = CFI_SP;
1680 cfa->offset -= 8;
1681 }
1682
1683 break;
1684
1685 case OP_DEST_MEM:
1686 if (op->src.type != OP_SRC_POP) {
1687 WARN_FUNC("unknown stack-related memory operation",
1688 insn->sec, insn->offset);
1689 return -1;
1690 }
1691
1692 /* pop mem */
1693 state->stack_size -= 8;
1694 if (cfa->base == CFI_SP)
1695 cfa->offset -= 8;
1696
1697 break;
1698
1699 default:
1700 WARN_FUNC("unknown stack-related instruction",
1701 insn->sec, insn->offset);
1702 return -1;
1703 }
1704
1705 return 0;
1706}
1707
1708static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1709{
1710 struct insn_state *state1 = &insn->state, *state2 = state;
1711 int i;
1712
1713 if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1714 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1715 insn->sec, insn->offset,
1716 state1->cfa.base, state1->cfa.offset,
1717 state2->cfa.base, state2->cfa.offset);
1718
1719 } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1720 for (i = 0; i < CFI_NUM_REGS; i++) {
1721 if (!memcmp(&state1->regs[i], &state2->regs[i],
1722 sizeof(struct cfi_reg)))
1723 continue;
1724
1725 WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1726 insn->sec, insn->offset,
1727 i, state1->regs[i].base, state1->regs[i].offset,
1728 i, state2->regs[i].base, state2->regs[i].offset);
1729 break;
1730 }
1731
1732 } else if (state1->type != state2->type) {
1733 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1734 insn->sec, insn->offset, state1->type, state2->type);
1735
1736 } else if (state1->drap != state2->drap ||
1737 (state1->drap && state1->drap_reg != state2->drap_reg) ||
1738 (state1->drap && state1->drap_offset != state2->drap_offset)) {
1739 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1740 insn->sec, insn->offset,
1741 state1->drap, state1->drap_reg, state1->drap_offset,
1742 state2->drap, state2->drap_reg, state2->drap_offset);
1743
1744 } else
1745 return true;
1746
1747 return false;
1748}
1749
1750/*
1751 * Follow the branch starting at the given instruction, and recursively follow
1752 * any other branches (jumps). Meanwhile, track the frame pointer state at
1753 * each instruction and validate all the rules described in
1754 * tools/objtool/Documentation/stack-validation.txt.
1755 */
1756static int validate_branch(struct objtool_file *file, struct instruction *first,
1757 struct insn_state state)
1758{
1759 struct alternative *alt;
1760 struct instruction *insn, *next_insn;
1761 struct section *sec;
1762 struct symbol *func = NULL;
1763 int ret;
1764
1765 insn = first;
1766 sec = insn->sec;
1767
1768 if (insn->alt_group && list_empty(&insn->alts)) {
1769 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1770 sec, insn->offset);
1771 return 1;
1772 }
1773
1774 while (1) {
1775 next_insn = next_insn_same_sec(file, insn);
1776
1777 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1778 WARN("%s() falls through to next function %s()",
1779 func->name, insn->func->name);
1780 return 1;
1781 }
1782
1783 func = insn->func ? insn->func->pfunc : NULL;
1784
1785 if (func && insn->ignore) {
1786 WARN_FUNC("BUG: why am I validating an ignored function?",
1787 sec, insn->offset);
1788 return 1;
1789 }
1790
1791 if (insn->visited) {
1792 if (!insn->hint && !insn_state_match(insn, &state))
1793 return 1;
1794
1795 return 0;
1796 }
1797
1798 if (insn->hint) {
1799 if (insn->restore) {
1800 struct instruction *save_insn, *i;
1801
1802 i = insn;
1803 save_insn = NULL;
1804 func_for_each_insn_continue_reverse(file, insn->func, i) {
1805 if (i->save) {
1806 save_insn = i;
1807 break;
1808 }
1809 }
1810
1811 if (!save_insn) {
1812 WARN_FUNC("no corresponding CFI save for CFI restore",
1813 sec, insn->offset);
1814 return 1;
1815 }
1816
1817 if (!save_insn->visited) {
1818 /*
1819 * Oops, no state to copy yet.
1820 * Hopefully we can reach this
1821 * instruction from another branch
1822 * after the save insn has been
1823 * visited.
1824 */
1825 if (insn == first)
1826 return 0;
1827
1828 WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1829 sec, insn->offset);
1830 return 1;
1831 }
1832
1833 insn->state = save_insn->state;
1834 }
1835
1836 state = insn->state;
1837
1838 } else
1839 insn->state = state;
1840
1841 insn->visited = true;
1842
1843 if (!insn->ignore_alts) {
1844 list_for_each_entry(alt, &insn->alts, list) {
1845 ret = validate_branch(file, alt->insn, state);
1846 if (ret)
1847 return 1;
1848 }
1849 }
1850
1851 switch (insn->type) {
1852
1853 case INSN_RETURN:
1854 if (func && has_modified_stack_frame(&state)) {
1855 WARN_FUNC("return with modified stack frame",
1856 sec, insn->offset);
1857 return 1;
1858 }
1859
1860 if (state.bp_scratch) {
1861 WARN("%s uses BP as a scratch register",
1862 insn->func->name);
1863 return 1;
1864 }
1865
1866 return 0;
1867
1868 case INSN_CALL:
1869 if (is_fentry_call(insn))
1870 break;
1871
1872 ret = dead_end_function(file, insn->call_dest);
1873 if (ret == 1)
1874 return 0;
1875 if (ret == -1)
1876 return 1;
1877
1878 /* fallthrough */
1879 case INSN_CALL_DYNAMIC:
1880 if (!no_fp && func && !has_valid_stack_frame(&state)) {
1881 WARN_FUNC("call without frame pointer save/setup",
1882 sec, insn->offset);
1883 return 1;
1884 }
1885 break;
1886
1887 case INSN_JUMP_CONDITIONAL:
1888 case INSN_JUMP_UNCONDITIONAL:
1889 if (insn->jump_dest &&
1890 (!func || !insn->jump_dest->func ||
1891 insn->jump_dest->func->pfunc == func)) {
1892 ret = validate_branch(file, insn->jump_dest,
1893 state);
1894 if (ret)
1895 return 1;
1896
1897 } else if (func && has_modified_stack_frame(&state)) {
1898 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1899 sec, insn->offset);
1900 return 1;
1901 }
1902
1903 if (insn->type == INSN_JUMP_UNCONDITIONAL)
1904 return 0;
1905
1906 break;
1907
1908 case INSN_JUMP_DYNAMIC:
1909 if (func && list_empty(&insn->alts) &&
1910 has_modified_stack_frame(&state)) {
1911 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1912 sec, insn->offset);
1913 return 1;
1914 }
1915
1916 return 0;
1917
1918 case INSN_CONTEXT_SWITCH:
1919 if (func && (!next_insn || !next_insn->hint)) {
1920 WARN_FUNC("unsupported instruction in callable function",
1921 sec, insn->offset);
1922 return 1;
1923 }
1924 return 0;
1925
1926 case INSN_STACK:
1927 if (update_insn_state(insn, &state))
1928 return 1;
1929
1930 break;
1931
1932 default:
1933 break;
1934 }
1935
1936 if (insn->dead_end)
1937 return 0;
1938
1939 if (!next_insn) {
1940 if (state.cfa.base == CFI_UNDEFINED)
1941 return 0;
1942 WARN("%s: unexpected end of section", sec->name);
1943 return 1;
1944 }
1945
1946 insn = next_insn;
1947 }
1948
1949 return 0;
1950}
1951
1952static int validate_unwind_hints(struct objtool_file *file)
1953{
1954 struct instruction *insn;
1955 int ret, warnings = 0;
1956 struct insn_state state;
1957
1958 if (!file->hints)
1959 return 0;
1960
1961 clear_insn_state(&state);
1962
1963 for_each_insn(file, insn) {
1964 if (insn->hint && !insn->visited) {
1965 ret = validate_branch(file, insn, state);
1966 warnings += ret;
1967 }
1968 }
1969
1970 return warnings;
1971}
1972
1973static int validate_retpoline(struct objtool_file *file)
1974{
1975 struct instruction *insn;
1976 int warnings = 0;
1977
1978 for_each_insn(file, insn) {
1979 if (insn->type != INSN_JUMP_DYNAMIC &&
1980 insn->type != INSN_CALL_DYNAMIC)
1981 continue;
1982
1983 if (insn->retpoline_safe)
1984 continue;
1985
1986 /*
1987 * .init.text code is ran before userspace and thus doesn't
1988 * strictly need retpolines, except for modules which are
1989 * loaded late, they very much do need retpoline in their
1990 * .init.text
1991 */
1992 if (!strcmp(insn->sec->name, ".init.text") && !module)
1993 continue;
1994
1995 WARN_FUNC("indirect %s found in RETPOLINE build",
1996 insn->sec, insn->offset,
1997 insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
1998
1999 warnings++;
2000 }
2001
2002 return warnings;
2003}
2004
2005static bool is_kasan_insn(struct instruction *insn)
2006{
2007 return (insn->type == INSN_CALL &&
2008 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2009}
2010
2011static bool is_ubsan_insn(struct instruction *insn)
2012{
2013 return (insn->type == INSN_CALL &&
2014 !strcmp(insn->call_dest->name,
2015 "__ubsan_handle_builtin_unreachable"));
2016}
2017
2018static bool ignore_unreachable_insn(struct instruction *insn)
2019{
2020 int i;
2021
2022 if (insn->ignore || insn->type == INSN_NOP)
2023 return true;
2024
2025 /*
2026 * Ignore any unused exceptions. This can happen when a whitelisted
2027 * function has an exception table entry.
2028 *
2029 * Also ignore alternative replacement instructions. This can happen
2030 * when a whitelisted function uses one of the ALTERNATIVE macros.
2031 */
2032 if (!strcmp(insn->sec->name, ".fixup") ||
2033 !strcmp(insn->sec->name, ".altinstr_replacement") ||
2034 !strcmp(insn->sec->name, ".altinstr_aux"))
2035 return true;
2036
2037 /*
2038 * Check if this (or a subsequent) instruction is related to
2039 * CONFIG_UBSAN or CONFIG_KASAN.
2040 *
2041 * End the search at 5 instructions to avoid going into the weeds.
2042 */
2043 if (!insn->func)
2044 return false;
2045 for (i = 0; i < 5; i++) {
2046
2047 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2048 return true;
2049
2050 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2051 if (insn->jump_dest &&
2052 insn->jump_dest->func == insn->func) {
2053 insn = insn->jump_dest;
2054 continue;
2055 }
2056
2057 break;
2058 }
2059
2060 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2061 break;
2062
2063 insn = list_next_entry(insn, list);
2064 }
2065
2066 return false;
2067}
2068
2069static int validate_functions(struct objtool_file *file)
2070{
2071 struct section *sec;
2072 struct symbol *func;
2073 struct instruction *insn;
2074 struct insn_state state;
2075 int ret, warnings = 0;
2076
2077 clear_insn_state(&state);
2078
2079 state.cfa = initial_func_cfi.cfa;
2080 memcpy(&state.regs, &initial_func_cfi.regs,
2081 CFI_NUM_REGS * sizeof(struct cfi_reg));
2082 state.stack_size = initial_func_cfi.cfa.offset;
2083
2084 for_each_sec(file, sec) {
2085 list_for_each_entry(func, &sec->symbol_list, list) {
2086 if (func->type != STT_FUNC || func->pfunc != func)
2087 continue;
2088
2089 insn = find_insn(file, sec, func->offset);
2090 if (!insn || insn->ignore)
2091 continue;
2092
2093 ret = validate_branch(file, insn, state);
2094 warnings += ret;
2095 }
2096 }
2097
2098 return warnings;
2099}
2100
2101static int validate_reachable_instructions(struct objtool_file *file)
2102{
2103 struct instruction *insn;
2104
2105 if (file->ignore_unreachables)
2106 return 0;
2107
2108 for_each_insn(file, insn) {
2109 if (insn->visited || ignore_unreachable_insn(insn))
2110 continue;
2111
2112 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2113 return 1;
2114 }
2115
2116 return 0;
2117}
2118
2119static void cleanup(struct objtool_file *file)
2120{
2121 struct instruction *insn, *tmpinsn;
2122 struct alternative *alt, *tmpalt;
2123
2124 list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2125 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2126 list_del(&alt->list);
2127 free(alt);
2128 }
2129 list_del(&insn->list);
2130 hash_del(&insn->hash);
2131 free(insn);
2132 }
2133 elf_close(file->elf);
2134}
2135
2136int check(const char *_objname, bool orc)
2137{
2138 struct objtool_file file;
2139 int ret, warnings = 0;
2140
2141 objname = _objname;
2142
2143 file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2144 if (!file.elf)
2145 return 1;
2146
2147 INIT_LIST_HEAD(&file.insn_list);
2148 hash_init(file.insn_hash);
2149 file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
2150 file.rodata = find_section_by_name(file.elf, ".rodata");
2151 file.c_file = find_section_by_name(file.elf, ".comment");
2152 file.ignore_unreachables = no_unreachable;
2153 file.hints = false;
2154
2155 arch_initial_func_cfi_state(&initial_func_cfi);
2156
2157 ret = decode_sections(&file);
2158 if (ret < 0)
2159 goto out;
2160 warnings += ret;
2161
2162 if (list_empty(&file.insn_list))
2163 goto out;
2164
2165 if (retpoline) {
2166 ret = validate_retpoline(&file);
2167 if (ret < 0)
2168 return ret;
2169 warnings += ret;
2170 }
2171
2172 ret = validate_functions(&file);
2173 if (ret < 0)
2174 goto out;
2175 warnings += ret;
2176
2177 ret = validate_unwind_hints(&file);
2178 if (ret < 0)
2179 goto out;
2180 warnings += ret;
2181
2182 if (!warnings) {
2183 ret = validate_reachable_instructions(&file);
2184 if (ret < 0)
2185 goto out;
2186 warnings += ret;
2187 }
2188
2189 if (orc) {
2190 ret = create_orc(&file);
2191 if (ret < 0)
2192 goto out;
2193
2194 ret = create_orc_sections(&file);
2195 if (ret < 0)
2196 goto out;
2197
2198 ret = elf_write(file.elf);
2199 if (ret < 0)
2200 goto out;
2201 }
2202
2203out:
2204 cleanup(&file);
2205
2206 /* ignore warnings for now until we get all the code cleaned up */
2207 if (ret || warnings)
2208 return 0;
2209 return 0;
2210}