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1/*
2 * Copyright (C) 2015 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/*
19 * objtool check:
20 *
21 * This command analyzes every .o file and ensures the validity of its stack
22 * trace metadata. It enforces a set of rules on asm code and C inline
23 * assembly code so that stack traces can be reliable.
24 *
25 * For more information, see tools/objtool/Documentation/stack-validation.txt.
26 */
27
28#include <string.h>
29#include <subcmd/parse-options.h>
30
31#include "builtin.h"
32#include "elf.h"
33#include "special.h"
34#include "arch.h"
35#include "warn.h"
36
37#include <linux/hashtable.h>
38
39#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
40
41#define STATE_FP_SAVED 0x1
42#define STATE_FP_SETUP 0x2
43#define STATE_FENTRY 0x4
44
45struct instruction {
46 struct list_head list;
47 struct hlist_node hash;
48 struct section *sec;
49 unsigned long offset;
50 unsigned int len, state;
51 unsigned char type;
52 unsigned long immediate;
53 bool alt_group, visited;
54 struct symbol *call_dest;
55 struct instruction *jump_dest;
56 struct list_head alts;
57 struct symbol *func;
58};
59
60struct alternative {
61 struct list_head list;
62 struct instruction *insn;
63};
64
65struct objtool_file {
66 struct elf *elf;
67 struct list_head insn_list;
68 DECLARE_HASHTABLE(insn_hash, 16);
69 struct section *rodata, *whitelist;
70 bool ignore_unreachables, c_file;
71};
72
73const char *objname;
74static bool nofp;
75
76static struct instruction *find_insn(struct objtool_file *file,
77 struct section *sec, unsigned long offset)
78{
79 struct instruction *insn;
80
81 hash_for_each_possible(file->insn_hash, insn, hash, offset)
82 if (insn->sec == sec && insn->offset == offset)
83 return insn;
84
85 return NULL;
86}
87
88static struct instruction *next_insn_same_sec(struct objtool_file *file,
89 struct instruction *insn)
90{
91 struct instruction *next = list_next_entry(insn, list);
92
93 if (&next->list == &file->insn_list || next->sec != insn->sec)
94 return NULL;
95
96 return next;
97}
98
99#define for_each_insn(file, insn) \
100 list_for_each_entry(insn, &file->insn_list, list)
101
102#define func_for_each_insn(file, func, insn) \
103 for (insn = find_insn(file, func->sec, func->offset); \
104 insn && &insn->list != &file->insn_list && \
105 insn->sec == func->sec && \
106 insn->offset < func->offset + func->len; \
107 insn = list_next_entry(insn, list))
108
109#define sec_for_each_insn_from(file, insn) \
110 for (; insn; insn = next_insn_same_sec(file, insn))
111
112
113/*
114 * Check if the function has been manually whitelisted with the
115 * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
116 * due to its use of a context switching instruction.
117 */
118static bool ignore_func(struct objtool_file *file, struct symbol *func)
119{
120 struct rela *rela;
121 struct instruction *insn;
122
123 /* check for STACK_FRAME_NON_STANDARD */
124 if (file->whitelist && file->whitelist->rela)
125 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list)
126 if (rela->sym->sec == func->sec &&
127 rela->addend == func->offset)
128 return true;
129
130 /* check if it has a context switching instruction */
131 func_for_each_insn(file, func, insn)
132 if (insn->type == INSN_CONTEXT_SWITCH)
133 return true;
134
135 return false;
136}
137
138/*
139 * This checks to see if the given function is a "noreturn" function.
140 *
141 * For global functions which are outside the scope of this object file, we
142 * have to keep a manual list of them.
143 *
144 * For local functions, we have to detect them manually by simply looking for
145 * the lack of a return instruction.
146 *
147 * Returns:
148 * -1: error
149 * 0: no dead end
150 * 1: dead end
151 */
152static int __dead_end_function(struct objtool_file *file, struct symbol *func,
153 int recursion)
154{
155 int i;
156 struct instruction *insn;
157 bool empty = true;
158
159 /*
160 * Unfortunately these have to be hard coded because the noreturn
161 * attribute isn't provided in ELF data.
162 */
163 static const char * const global_noreturns[] = {
164 "__stack_chk_fail",
165 "panic",
166 "do_exit",
167 "__module_put_and_exit",
168 "complete_and_exit",
169 "kvm_spurious_fault",
170 "__reiserfs_panic",
171 "lbug_with_loc"
172 };
173
174 if (func->bind == STB_WEAK)
175 return 0;
176
177 if (func->bind == STB_GLOBAL)
178 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
179 if (!strcmp(func->name, global_noreturns[i]))
180 return 1;
181
182 if (!func->sec)
183 return 0;
184
185 func_for_each_insn(file, func, insn) {
186 empty = false;
187
188 if (insn->type == INSN_RETURN)
189 return 0;
190 }
191
192 if (empty)
193 return 0;
194
195 /*
196 * A function can have a sibling call instead of a return. In that
197 * case, the function's dead-end status depends on whether the target
198 * of the sibling call returns.
199 */
200 func_for_each_insn(file, func, insn) {
201 if (insn->sec != func->sec ||
202 insn->offset >= func->offset + func->len)
203 break;
204
205 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
206 struct instruction *dest = insn->jump_dest;
207 struct symbol *dest_func;
208
209 if (!dest)
210 /* sibling call to another file */
211 return 0;
212
213 if (dest->sec != func->sec ||
214 dest->offset < func->offset ||
215 dest->offset >= func->offset + func->len) {
216 /* local sibling call */
217 dest_func = find_symbol_by_offset(dest->sec,
218 dest->offset);
219 if (!dest_func)
220 continue;
221
222 if (recursion == 5) {
223 WARN_FUNC("infinite recursion (objtool bug!)",
224 dest->sec, dest->offset);
225 return -1;
226 }
227
228 return __dead_end_function(file, dest_func,
229 recursion + 1);
230 }
231 }
232
233 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
234 /* sibling call */
235 return 0;
236 }
237
238 return 1;
239}
240
241static int dead_end_function(struct objtool_file *file, struct symbol *func)
242{
243 return __dead_end_function(file, func, 0);
244}
245
246/*
247 * Call the arch-specific instruction decoder for all the instructions and add
248 * them to the global instruction list.
249 */
250static int decode_instructions(struct objtool_file *file)
251{
252 struct section *sec;
253 struct symbol *func;
254 unsigned long offset;
255 struct instruction *insn;
256 int ret;
257
258 list_for_each_entry(sec, &file->elf->sections, list) {
259
260 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
261 continue;
262
263 for (offset = 0; offset < sec->len; offset += insn->len) {
264 insn = malloc(sizeof(*insn));
265 memset(insn, 0, sizeof(*insn));
266
267 INIT_LIST_HEAD(&insn->alts);
268 insn->sec = sec;
269 insn->offset = offset;
270
271 ret = arch_decode_instruction(file->elf, sec, offset,
272 sec->len - offset,
273 &insn->len, &insn->type,
274 &insn->immediate);
275 if (ret)
276 return ret;
277
278 if (!insn->type || insn->type > INSN_LAST) {
279 WARN_FUNC("invalid instruction type %d",
280 insn->sec, insn->offset, insn->type);
281 return -1;
282 }
283
284 hash_add(file->insn_hash, &insn->hash, insn->offset);
285 list_add_tail(&insn->list, &file->insn_list);
286 }
287
288 list_for_each_entry(func, &sec->symbol_list, list) {
289 if (func->type != STT_FUNC)
290 continue;
291
292 if (!find_insn(file, sec, func->offset)) {
293 WARN("%s(): can't find starting instruction",
294 func->name);
295 return -1;
296 }
297
298 func_for_each_insn(file, func, insn)
299 if (!insn->func)
300 insn->func = func;
301 }
302 }
303
304 return 0;
305}
306
307/*
308 * Warnings shouldn't be reported for ignored functions.
309 */
310static void add_ignores(struct objtool_file *file)
311{
312 struct instruction *insn;
313 struct section *sec;
314 struct symbol *func;
315
316 list_for_each_entry(sec, &file->elf->sections, list) {
317 list_for_each_entry(func, &sec->symbol_list, list) {
318 if (func->type != STT_FUNC)
319 continue;
320
321 if (!ignore_func(file, func))
322 continue;
323
324 func_for_each_insn(file, func, insn)
325 insn->visited = true;
326 }
327 }
328}
329
330/*
331 * Find the destination instructions for all jumps.
332 */
333static int add_jump_destinations(struct objtool_file *file)
334{
335 struct instruction *insn;
336 struct rela *rela;
337 struct section *dest_sec;
338 unsigned long dest_off;
339
340 for_each_insn(file, insn) {
341 if (insn->type != INSN_JUMP_CONDITIONAL &&
342 insn->type != INSN_JUMP_UNCONDITIONAL)
343 continue;
344
345 /* skip ignores */
346 if (insn->visited)
347 continue;
348
349 rela = find_rela_by_dest_range(insn->sec, insn->offset,
350 insn->len);
351 if (!rela) {
352 dest_sec = insn->sec;
353 dest_off = insn->offset + insn->len + insn->immediate;
354 } else if (rela->sym->type == STT_SECTION) {
355 dest_sec = rela->sym->sec;
356 dest_off = rela->addend + 4;
357 } else if (rela->sym->sec->idx) {
358 dest_sec = rela->sym->sec;
359 dest_off = rela->sym->sym.st_value + rela->addend + 4;
360 } else {
361 /* sibling call */
362 insn->jump_dest = 0;
363 continue;
364 }
365
366 insn->jump_dest = find_insn(file, dest_sec, dest_off);
367 if (!insn->jump_dest) {
368
369 /*
370 * This is a special case where an alt instruction
371 * jumps past the end of the section. These are
372 * handled later in handle_group_alt().
373 */
374 if (!strcmp(insn->sec->name, ".altinstr_replacement"))
375 continue;
376
377 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
378 insn->sec, insn->offset, dest_sec->name,
379 dest_off);
380 return -1;
381 }
382 }
383
384 return 0;
385}
386
387/*
388 * Find the destination instructions for all calls.
389 */
390static int add_call_destinations(struct objtool_file *file)
391{
392 struct instruction *insn;
393 unsigned long dest_off;
394 struct rela *rela;
395
396 for_each_insn(file, insn) {
397 if (insn->type != INSN_CALL)
398 continue;
399
400 rela = find_rela_by_dest_range(insn->sec, insn->offset,
401 insn->len);
402 if (!rela) {
403 dest_off = insn->offset + insn->len + insn->immediate;
404 insn->call_dest = find_symbol_by_offset(insn->sec,
405 dest_off);
406 if (!insn->call_dest) {
407 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
408 insn->sec, insn->offset, dest_off);
409 return -1;
410 }
411 } else if (rela->sym->type == STT_SECTION) {
412 insn->call_dest = find_symbol_by_offset(rela->sym->sec,
413 rela->addend+4);
414 if (!insn->call_dest ||
415 insn->call_dest->type != STT_FUNC) {
416 WARN_FUNC("can't find call dest symbol at %s+0x%x",
417 insn->sec, insn->offset,
418 rela->sym->sec->name,
419 rela->addend + 4);
420 return -1;
421 }
422 } else
423 insn->call_dest = rela->sym;
424 }
425
426 return 0;
427}
428
429/*
430 * The .alternatives section requires some extra special care, over and above
431 * what other special sections require:
432 *
433 * 1. Because alternatives are patched in-place, we need to insert a fake jump
434 * instruction at the end so that validate_branch() skips all the original
435 * replaced instructions when validating the new instruction path.
436 *
437 * 2. An added wrinkle is that the new instruction length might be zero. In
438 * that case the old instructions are replaced with noops. We simulate that
439 * by creating a fake jump as the only new instruction.
440 *
441 * 3. In some cases, the alternative section includes an instruction which
442 * conditionally jumps to the _end_ of the entry. We have to modify these
443 * jumps' destinations to point back to .text rather than the end of the
444 * entry in .altinstr_replacement.
445 *
446 * 4. It has been requested that we don't validate the !POPCNT feature path
447 * which is a "very very small percentage of machines".
448 */
449static int handle_group_alt(struct objtool_file *file,
450 struct special_alt *special_alt,
451 struct instruction *orig_insn,
452 struct instruction **new_insn)
453{
454 struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
455 unsigned long dest_off;
456
457 last_orig_insn = NULL;
458 insn = orig_insn;
459 sec_for_each_insn_from(file, insn) {
460 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
461 break;
462
463 if (special_alt->skip_orig)
464 insn->type = INSN_NOP;
465
466 insn->alt_group = true;
467 last_orig_insn = insn;
468 }
469
470 if (!next_insn_same_sec(file, last_orig_insn)) {
471 WARN("%s: don't know how to handle alternatives at end of section",
472 special_alt->orig_sec->name);
473 return -1;
474 }
475
476 fake_jump = malloc(sizeof(*fake_jump));
477 if (!fake_jump) {
478 WARN("malloc failed");
479 return -1;
480 }
481 memset(fake_jump, 0, sizeof(*fake_jump));
482 INIT_LIST_HEAD(&fake_jump->alts);
483 fake_jump->sec = special_alt->new_sec;
484 fake_jump->offset = -1;
485 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
486 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
487
488 if (!special_alt->new_len) {
489 *new_insn = fake_jump;
490 return 0;
491 }
492
493 last_new_insn = NULL;
494 insn = *new_insn;
495 sec_for_each_insn_from(file, insn) {
496 if (insn->offset >= special_alt->new_off + special_alt->new_len)
497 break;
498
499 last_new_insn = insn;
500
501 if (insn->type != INSN_JUMP_CONDITIONAL &&
502 insn->type != INSN_JUMP_UNCONDITIONAL)
503 continue;
504
505 if (!insn->immediate)
506 continue;
507
508 dest_off = insn->offset + insn->len + insn->immediate;
509 if (dest_off == special_alt->new_off + special_alt->new_len)
510 insn->jump_dest = fake_jump;
511
512 if (!insn->jump_dest) {
513 WARN_FUNC("can't find alternative jump destination",
514 insn->sec, insn->offset);
515 return -1;
516 }
517 }
518
519 if (!last_new_insn) {
520 WARN_FUNC("can't find last new alternative instruction",
521 special_alt->new_sec, special_alt->new_off);
522 return -1;
523 }
524
525 list_add(&fake_jump->list, &last_new_insn->list);
526
527 return 0;
528}
529
530/*
531 * A jump table entry can either convert a nop to a jump or a jump to a nop.
532 * If the original instruction is a jump, make the alt entry an effective nop
533 * by just skipping the original instruction.
534 */
535static int handle_jump_alt(struct objtool_file *file,
536 struct special_alt *special_alt,
537 struct instruction *orig_insn,
538 struct instruction **new_insn)
539{
540 if (orig_insn->type == INSN_NOP)
541 return 0;
542
543 if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
544 WARN_FUNC("unsupported instruction at jump label",
545 orig_insn->sec, orig_insn->offset);
546 return -1;
547 }
548
549 *new_insn = list_next_entry(orig_insn, list);
550 return 0;
551}
552
553/*
554 * Read all the special sections which have alternate instructions which can be
555 * patched in or redirected to at runtime. Each instruction having alternate
556 * instruction(s) has them added to its insn->alts list, which will be
557 * traversed in validate_branch().
558 */
559static int add_special_section_alts(struct objtool_file *file)
560{
561 struct list_head special_alts;
562 struct instruction *orig_insn, *new_insn;
563 struct special_alt *special_alt, *tmp;
564 struct alternative *alt;
565 int ret;
566
567 ret = special_get_alts(file->elf, &special_alts);
568 if (ret)
569 return ret;
570
571 list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
572 alt = malloc(sizeof(*alt));
573 if (!alt) {
574 WARN("malloc failed");
575 ret = -1;
576 goto out;
577 }
578
579 orig_insn = find_insn(file, special_alt->orig_sec,
580 special_alt->orig_off);
581 if (!orig_insn) {
582 WARN_FUNC("special: can't find orig instruction",
583 special_alt->orig_sec, special_alt->orig_off);
584 ret = -1;
585 goto out;
586 }
587
588 new_insn = NULL;
589 if (!special_alt->group || special_alt->new_len) {
590 new_insn = find_insn(file, special_alt->new_sec,
591 special_alt->new_off);
592 if (!new_insn) {
593 WARN_FUNC("special: can't find new instruction",
594 special_alt->new_sec,
595 special_alt->new_off);
596 ret = -1;
597 goto out;
598 }
599 }
600
601 if (special_alt->group) {
602 ret = handle_group_alt(file, special_alt, orig_insn,
603 &new_insn);
604 if (ret)
605 goto out;
606 } else if (special_alt->jump_or_nop) {
607 ret = handle_jump_alt(file, special_alt, orig_insn,
608 &new_insn);
609 if (ret)
610 goto out;
611 }
612
613 alt->insn = new_insn;
614 list_add_tail(&alt->list, &orig_insn->alts);
615
616 list_del(&special_alt->list);
617 free(special_alt);
618 }
619
620out:
621 return ret;
622}
623
624static int add_switch_table(struct objtool_file *file, struct symbol *func,
625 struct instruction *insn, struct rela *table,
626 struct rela *next_table)
627{
628 struct rela *rela = table;
629 struct instruction *alt_insn;
630 struct alternative *alt;
631
632 list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
633 if (rela == next_table)
634 break;
635
636 if (rela->sym->sec != insn->sec ||
637 rela->addend <= func->offset ||
638 rela->addend >= func->offset + func->len)
639 break;
640
641 alt_insn = find_insn(file, insn->sec, rela->addend);
642 if (!alt_insn) {
643 WARN("%s: can't find instruction at %s+0x%x",
644 file->rodata->rela->name, insn->sec->name,
645 rela->addend);
646 return -1;
647 }
648
649 alt = malloc(sizeof(*alt));
650 if (!alt) {
651 WARN("malloc failed");
652 return -1;
653 }
654
655 alt->insn = alt_insn;
656 list_add_tail(&alt->list, &insn->alts);
657 }
658
659 return 0;
660}
661
662static int add_func_switch_tables(struct objtool_file *file,
663 struct symbol *func)
664{
665 struct instruction *insn, *prev_jump;
666 struct rela *text_rela, *rodata_rela, *prev_rela;
667 int ret;
668
669 prev_jump = NULL;
670
671 func_for_each_insn(file, func, insn) {
672 if (insn->type != INSN_JUMP_DYNAMIC)
673 continue;
674
675 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
676 insn->len);
677 if (!text_rela || text_rela->sym != file->rodata->sym)
678 continue;
679
680 /* common case: jmpq *[addr](,%rax,8) */
681 rodata_rela = find_rela_by_dest(file->rodata,
682 text_rela->addend);
683
684 /*
685 * rare case: jmpq *[addr](%rip)
686 *
687 * This check is for a rare gcc quirk, currently only seen in
688 * three driver functions in the kernel, only with certain
689 * obscure non-distro configs.
690 *
691 * As part of an optimization, gcc makes a copy of an existing
692 * switch jump table, modifies it, and then hard-codes the jump
693 * (albeit with an indirect jump) to use a single entry in the
694 * table. The rest of the jump table and some of its jump
695 * targets remain as dead code.
696 *
697 * In such a case we can just crudely ignore all unreachable
698 * instruction warnings for the entire object file. Ideally we
699 * would just ignore them for the function, but that would
700 * require redesigning the code quite a bit. And honestly
701 * that's just not worth doing: unreachable instruction
702 * warnings are of questionable value anyway, and this is such
703 * a rare issue.
704 *
705 * kbuild reports:
706 * - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com
707 * - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com
708 * - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com
709 *
710 * gcc bug:
711 * - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604
712 */
713 if (!rodata_rela) {
714 rodata_rela = find_rela_by_dest(file->rodata,
715 text_rela->addend + 4);
716 if (rodata_rela)
717 file->ignore_unreachables = true;
718 }
719
720 if (!rodata_rela)
721 continue;
722
723 /*
724 * We found a switch table, but we don't know yet how big it
725 * is. Don't add it until we reach the end of the function or
726 * the beginning of another switch table in the same function.
727 */
728 if (prev_jump) {
729 ret = add_switch_table(file, func, prev_jump, prev_rela,
730 rodata_rela);
731 if (ret)
732 return ret;
733 }
734
735 prev_jump = insn;
736 prev_rela = rodata_rela;
737 }
738
739 if (prev_jump) {
740 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
741 if (ret)
742 return ret;
743 }
744
745 return 0;
746}
747
748/*
749 * For some switch statements, gcc generates a jump table in the .rodata
750 * section which contains a list of addresses within the function to jump to.
751 * This finds these jump tables and adds them to the insn->alts lists.
752 */
753static int add_switch_table_alts(struct objtool_file *file)
754{
755 struct section *sec;
756 struct symbol *func;
757 int ret;
758
759 if (!file->rodata || !file->rodata->rela)
760 return 0;
761
762 list_for_each_entry(sec, &file->elf->sections, list) {
763 list_for_each_entry(func, &sec->symbol_list, list) {
764 if (func->type != STT_FUNC)
765 continue;
766
767 ret = add_func_switch_tables(file, func);
768 if (ret)
769 return ret;
770 }
771 }
772
773 return 0;
774}
775
776static int decode_sections(struct objtool_file *file)
777{
778 int ret;
779
780 ret = decode_instructions(file);
781 if (ret)
782 return ret;
783
784 add_ignores(file);
785
786 ret = add_jump_destinations(file);
787 if (ret)
788 return ret;
789
790 ret = add_call_destinations(file);
791 if (ret)
792 return ret;
793
794 ret = add_special_section_alts(file);
795 if (ret)
796 return ret;
797
798 ret = add_switch_table_alts(file);
799 if (ret)
800 return ret;
801
802 return 0;
803}
804
805static bool is_fentry_call(struct instruction *insn)
806{
807 if (insn->type == INSN_CALL &&
808 insn->call_dest->type == STT_NOTYPE &&
809 !strcmp(insn->call_dest->name, "__fentry__"))
810 return true;
811
812 return false;
813}
814
815static bool has_modified_stack_frame(struct instruction *insn)
816{
817 return (insn->state & STATE_FP_SAVED) ||
818 (insn->state & STATE_FP_SETUP);
819}
820
821static bool has_valid_stack_frame(struct instruction *insn)
822{
823 return (insn->state & STATE_FP_SAVED) &&
824 (insn->state & STATE_FP_SETUP);
825}
826
827static unsigned int frame_state(unsigned long state)
828{
829 return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
830}
831
832/*
833 * Follow the branch starting at the given instruction, and recursively follow
834 * any other branches (jumps). Meanwhile, track the frame pointer state at
835 * each instruction and validate all the rules described in
836 * tools/objtool/Documentation/stack-validation.txt.
837 */
838static int validate_branch(struct objtool_file *file,
839 struct instruction *first, unsigned char first_state)
840{
841 struct alternative *alt;
842 struct instruction *insn;
843 struct section *sec;
844 struct symbol *func = NULL;
845 unsigned char state;
846 int ret;
847
848 insn = first;
849 sec = insn->sec;
850 state = first_state;
851
852 if (insn->alt_group && list_empty(&insn->alts)) {
853 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
854 sec, insn->offset);
855 return 1;
856 }
857
858 while (1) {
859 if (file->c_file && insn->func) {
860 if (func && func != insn->func) {
861 WARN("%s() falls through to next function %s()",
862 func->name, insn->func->name);
863 return 1;
864 }
865
866 func = insn->func;
867 }
868
869 if (insn->visited) {
870 if (frame_state(insn->state) != frame_state(state)) {
871 WARN_FUNC("frame pointer state mismatch",
872 sec, insn->offset);
873 return 1;
874 }
875
876 return 0;
877 }
878
879 insn->visited = true;
880 insn->state = state;
881
882 list_for_each_entry(alt, &insn->alts, list) {
883 ret = validate_branch(file, alt->insn, state);
884 if (ret)
885 return 1;
886 }
887
888 switch (insn->type) {
889
890 case INSN_FP_SAVE:
891 if (!nofp) {
892 if (state & STATE_FP_SAVED) {
893 WARN_FUNC("duplicate frame pointer save",
894 sec, insn->offset);
895 return 1;
896 }
897 state |= STATE_FP_SAVED;
898 }
899 break;
900
901 case INSN_FP_SETUP:
902 if (!nofp) {
903 if (state & STATE_FP_SETUP) {
904 WARN_FUNC("duplicate frame pointer setup",
905 sec, insn->offset);
906 return 1;
907 }
908 state |= STATE_FP_SETUP;
909 }
910 break;
911
912 case INSN_FP_RESTORE:
913 if (!nofp) {
914 if (has_valid_stack_frame(insn))
915 state &= ~STATE_FP_SETUP;
916
917 state &= ~STATE_FP_SAVED;
918 }
919 break;
920
921 case INSN_RETURN:
922 if (!nofp && has_modified_stack_frame(insn)) {
923 WARN_FUNC("return without frame pointer restore",
924 sec, insn->offset);
925 return 1;
926 }
927 return 0;
928
929 case INSN_CALL:
930 if (is_fentry_call(insn)) {
931 state |= STATE_FENTRY;
932 break;
933 }
934
935 ret = dead_end_function(file, insn->call_dest);
936 if (ret == 1)
937 return 0;
938 if (ret == -1)
939 return 1;
940
941 /* fallthrough */
942 case INSN_CALL_DYNAMIC:
943 if (!nofp && !has_valid_stack_frame(insn)) {
944 WARN_FUNC("call without frame pointer save/setup",
945 sec, insn->offset);
946 return 1;
947 }
948 break;
949
950 case INSN_JUMP_CONDITIONAL:
951 case INSN_JUMP_UNCONDITIONAL:
952 if (insn->jump_dest) {
953 ret = validate_branch(file, insn->jump_dest,
954 state);
955 if (ret)
956 return 1;
957 } else if (has_modified_stack_frame(insn)) {
958 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
959 sec, insn->offset);
960 return 1;
961 } /* else it's a sibling call */
962
963 if (insn->type == INSN_JUMP_UNCONDITIONAL)
964 return 0;
965
966 break;
967
968 case INSN_JUMP_DYNAMIC:
969 if (list_empty(&insn->alts) &&
970 has_modified_stack_frame(insn)) {
971 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
972 sec, insn->offset);
973 return 1;
974 }
975
976 return 0;
977
978 case INSN_BUG:
979 return 0;
980
981 default:
982 break;
983 }
984
985 insn = next_insn_same_sec(file, insn);
986 if (!insn) {
987 WARN("%s: unexpected end of section", sec->name);
988 return 1;
989 }
990 }
991
992 return 0;
993}
994
995static bool is_gcov_insn(struct instruction *insn)
996{
997 struct rela *rela;
998 struct section *sec;
999 struct symbol *sym;
1000 unsigned long offset;
1001
1002 rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
1003 if (!rela)
1004 return false;
1005
1006 if (rela->sym->type != STT_SECTION)
1007 return false;
1008
1009 sec = rela->sym->sec;
1010 offset = rela->addend + insn->offset + insn->len - rela->offset;
1011
1012 list_for_each_entry(sym, &sec->symbol_list, list) {
1013 if (sym->type != STT_OBJECT)
1014 continue;
1015
1016 if (offset >= sym->offset && offset < sym->offset + sym->len)
1017 return (!memcmp(sym->name, "__gcov0.", 8));
1018 }
1019
1020 return false;
1021}
1022
1023static bool is_kasan_insn(struct instruction *insn)
1024{
1025 return (insn->type == INSN_CALL &&
1026 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1027}
1028
1029static bool is_ubsan_insn(struct instruction *insn)
1030{
1031 return (insn->type == INSN_CALL &&
1032 !strcmp(insn->call_dest->name,
1033 "__ubsan_handle_builtin_unreachable"));
1034}
1035
1036static bool ignore_unreachable_insn(struct symbol *func,
1037 struct instruction *insn)
1038{
1039 int i;
1040
1041 if (insn->type == INSN_NOP)
1042 return true;
1043
1044 if (is_gcov_insn(insn))
1045 return true;
1046
1047 /*
1048 * Check if this (or a subsequent) instruction is related to
1049 * CONFIG_UBSAN or CONFIG_KASAN.
1050 *
1051 * End the search at 5 instructions to avoid going into the weeds.
1052 */
1053 for (i = 0; i < 5; i++) {
1054
1055 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1056 return true;
1057
1058 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1059 insn = insn->jump_dest;
1060 continue;
1061 }
1062
1063 if (insn->offset + insn->len >= func->offset + func->len)
1064 break;
1065 insn = list_next_entry(insn, list);
1066 }
1067
1068 return false;
1069}
1070
1071static int validate_functions(struct objtool_file *file)
1072{
1073 struct section *sec;
1074 struct symbol *func;
1075 struct instruction *insn;
1076 int ret, warnings = 0;
1077
1078 list_for_each_entry(sec, &file->elf->sections, list) {
1079 list_for_each_entry(func, &sec->symbol_list, list) {
1080 if (func->type != STT_FUNC)
1081 continue;
1082
1083 insn = find_insn(file, sec, func->offset);
1084 if (!insn)
1085 continue;
1086
1087 ret = validate_branch(file, insn, 0);
1088 warnings += ret;
1089 }
1090 }
1091
1092 list_for_each_entry(sec, &file->elf->sections, list) {
1093 list_for_each_entry(func, &sec->symbol_list, list) {
1094 if (func->type != STT_FUNC)
1095 continue;
1096
1097 func_for_each_insn(file, func, insn) {
1098 if (insn->visited)
1099 continue;
1100
1101 insn->visited = true;
1102
1103 if (file->ignore_unreachables || warnings ||
1104 ignore_unreachable_insn(func, insn))
1105 continue;
1106
1107 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1108 warnings++;
1109 }
1110 }
1111 }
1112
1113 return warnings;
1114}
1115
1116static int validate_uncallable_instructions(struct objtool_file *file)
1117{
1118 struct instruction *insn;
1119 int warnings = 0;
1120
1121 for_each_insn(file, insn) {
1122 if (!insn->visited && insn->type == INSN_RETURN) {
1123 WARN_FUNC("return instruction outside of a callable function",
1124 insn->sec, insn->offset);
1125 warnings++;
1126 }
1127 }
1128
1129 return warnings;
1130}
1131
1132static void cleanup(struct objtool_file *file)
1133{
1134 struct instruction *insn, *tmpinsn;
1135 struct alternative *alt, *tmpalt;
1136
1137 list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1138 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1139 list_del(&alt->list);
1140 free(alt);
1141 }
1142 list_del(&insn->list);
1143 hash_del(&insn->hash);
1144 free(insn);
1145 }
1146 elf_close(file->elf);
1147}
1148
1149const char * const check_usage[] = {
1150 "objtool check [<options>] file.o",
1151 NULL,
1152};
1153
1154int cmd_check(int argc, const char **argv)
1155{
1156 struct objtool_file file;
1157 int ret, warnings = 0;
1158
1159 const struct option options[] = {
1160 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1161 OPT_END(),
1162 };
1163
1164 argc = parse_options(argc, argv, options, check_usage, 0);
1165
1166 if (argc != 1)
1167 usage_with_options(check_usage, options);
1168
1169 objname = argv[0];
1170
1171 file.elf = elf_open(objname);
1172 if (!file.elf) {
1173 fprintf(stderr, "error reading elf file %s\n", objname);
1174 return 1;
1175 }
1176
1177 INIT_LIST_HEAD(&file.insn_list);
1178 hash_init(file.insn_hash);
1179 file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
1180 file.rodata = find_section_by_name(file.elf, ".rodata");
1181 file.ignore_unreachables = false;
1182 file.c_file = find_section_by_name(file.elf, ".comment");
1183
1184 ret = decode_sections(&file);
1185 if (ret < 0)
1186 goto out;
1187 warnings += ret;
1188
1189 ret = validate_functions(&file);
1190 if (ret < 0)
1191 goto out;
1192 warnings += ret;
1193
1194 ret = validate_uncallable_instructions(&file);
1195 if (ret < 0)
1196 goto out;
1197 warnings += ret;
1198
1199out:
1200 cleanup(&file);
1201
1202 /* ignore warnings for now until we get all the code cleaned up */
1203 if (ret || warnings)
1204 return 0;
1205 return 0;
1206}