blob: 51da270758f01cd50d6ce37091229252d1004f83 [file] [log] [blame]
Josh Poimboeuf442f04c2016-02-28 22:22:41 -06001/*
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#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
38
39#define STATE_FP_SAVED 0x1
40#define STATE_FP_SETUP 0x2
41#define STATE_FENTRY 0x4
42
43struct instruction {
44 struct list_head list;
45 struct section *sec;
46 unsigned long offset;
47 unsigned int len, state;
48 unsigned char type;
49 unsigned long immediate;
50 bool alt_group, visited;
51 struct symbol *call_dest;
52 struct instruction *jump_dest;
53 struct list_head alts;
54};
55
56struct alternative {
57 struct list_head list;
58 struct instruction *insn;
59};
60
61struct objtool_file {
62 struct elf *elf;
63 struct list_head insns;
64};
65
66const char *objname;
67static bool nofp;
68
69static struct instruction *find_instruction(struct objtool_file *file,
70 struct section *sec,
71 unsigned long offset)
72{
73 struct instruction *insn;
74
75 list_for_each_entry(insn, &file->insns, list)
76 if (insn->sec == sec && insn->offset == offset)
77 return insn;
78
79 return NULL;
80}
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 */
87static bool ignore_func(struct objtool_file *file, struct symbol *func)
88{
89 struct section *macro_sec;
90 struct rela *rela;
91 struct instruction *insn;
92
93 /* check for STACK_FRAME_NON_STANDARD */
94 macro_sec = find_section_by_name(file->elf, "__func_stack_frame_non_standard");
95 if (macro_sec && macro_sec->rela)
96 list_for_each_entry(rela, &macro_sec->rela->relas, list)
97 if (rela->sym->sec == func->sec &&
98 rela->addend == func->offset)
99 return true;
100
101 /* check if it has a context switching instruction */
102 insn = find_instruction(file, func->sec, func->offset);
103 if (!insn)
104 return false;
105 list_for_each_entry_from(insn, &file->insns, list) {
106 if (insn->sec != func->sec ||
107 insn->offset >= func->offset + func->len)
108 break;
109 if (insn->type == INSN_CONTEXT_SWITCH)
110 return true;
111 }
112
113 return false;
114}
115
116/*
117 * This checks to see if the given function is a "noreturn" function.
118 *
119 * For global functions which are outside the scope of this object file, we
120 * have to keep a manual list of them.
121 *
122 * For local functions, we have to detect them manually by simply looking for
123 * the lack of a return instruction.
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600124 *
125 * Returns:
126 * -1: error
127 * 0: no dead end
128 * 1: dead end
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600129 */
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600130static int __dead_end_function(struct objtool_file *file, struct symbol *func,
131 int recursion)
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600132{
133 int i;
Josh Poimboeuf81bfafc2016-03-09 00:06:51 -0600134 struct instruction *insn, *func_insn;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600135 bool empty = true;
136
137 /*
138 * Unfortunately these have to be hard coded because the noreturn
139 * attribute isn't provided in ELF data.
140 */
141 static const char * const global_noreturns[] = {
142 "__stack_chk_fail",
143 "panic",
144 "do_exit",
145 "__module_put_and_exit",
146 "complete_and_exit",
147 "kvm_spurious_fault",
148 "__reiserfs_panic",
149 "lbug_with_loc"
150 };
151
152 if (func->bind == STB_WEAK)
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600153 return 0;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600154
155 if (func->bind == STB_GLOBAL)
156 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
157 if (!strcmp(func->name, global_noreturns[i]))
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600158 return 1;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600159
160 if (!func->sec)
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600161 return 0;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600162
Josh Poimboeuf81bfafc2016-03-09 00:06:51 -0600163 func_insn = find_instruction(file, func->sec, func->offset);
164 if (!func_insn)
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600165 return 0;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600166
Josh Poimboeuf81bfafc2016-03-09 00:06:51 -0600167 insn = func_insn;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600168 list_for_each_entry_from(insn, &file->insns, list) {
169 if (insn->sec != func->sec ||
170 insn->offset >= func->offset + func->len)
171 break;
172
173 empty = false;
174
175 if (insn->type == INSN_RETURN)
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600176 return 0;
Josh Poimboeuf81bfafc2016-03-09 00:06:51 -0600177 }
178
179 if (empty)
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600180 return 0;
Josh Poimboeuf81bfafc2016-03-09 00:06:51 -0600181
182 /*
183 * A function can have a sibling call instead of a return. In that
184 * case, the function's dead-end status depends on whether the target
185 * of the sibling call returns.
186 */
187 insn = func_insn;
188 list_for_each_entry_from(insn, &file->insns, list) {
189 if (insn->sec != func->sec ||
190 insn->offset >= func->offset + func->len)
191 break;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600192
193 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
194 struct instruction *dest = insn->jump_dest;
195 struct symbol *dest_func;
196
197 if (!dest)
198 /* sibling call to another file */
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600199 return 0;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600200
201 if (dest->sec != func->sec ||
202 dest->offset < func->offset ||
203 dest->offset >= func->offset + func->len) {
204 /* local sibling call */
205 dest_func = find_symbol_by_offset(dest->sec,
206 dest->offset);
207 if (!dest_func)
208 continue;
209
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600210 if (recursion == 5) {
211 WARN_FUNC("infinite recursion (objtool bug!)",
212 dest->sec, dest->offset);
213 return -1;
214 }
215
216 return __dead_end_function(file, dest_func,
217 recursion + 1);
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600218 }
219 }
220
221 if (insn->type == INSN_JUMP_DYNAMIC)
222 /* sibling call */
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600223 return 0;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600224 }
225
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600226 return 1;
227}
228
229static int dead_end_function(struct objtool_file *file, struct symbol *func)
230{
231 return __dead_end_function(file, func, 0);
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600232}
233
234/*
235 * Call the arch-specific instruction decoder for all the instructions and add
236 * them to the global insns list.
237 */
238static int decode_instructions(struct objtool_file *file)
239{
240 struct section *sec;
241 unsigned long offset;
242 struct instruction *insn;
243 int ret;
244
245 INIT_LIST_HEAD(&file->insns);
246
247 list_for_each_entry(sec, &file->elf->sections, list) {
248
249 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
250 continue;
251
252 for (offset = 0; offset < sec->len; offset += insn->len) {
253 insn = malloc(sizeof(*insn));
254 memset(insn, 0, sizeof(*insn));
255
256 INIT_LIST_HEAD(&insn->alts);
257 insn->sec = sec;
258 insn->offset = offset;
259
260 ret = arch_decode_instruction(file->elf, sec, offset,
261 sec->len - offset,
262 &insn->len, &insn->type,
263 &insn->immediate);
264 if (ret)
265 return ret;
266
267 if (!insn->type || insn->type > INSN_LAST) {
268 WARN_FUNC("invalid instruction type %d",
269 insn->sec, insn->offset, insn->type);
270 return -1;
271 }
272
273 list_add_tail(&insn->list, &file->insns);
274 }
275 }
276
277 return 0;
278}
279
280/*
281 * Warnings shouldn't be reported for ignored functions.
282 */
283static void get_ignores(struct objtool_file *file)
284{
285 struct instruction *insn;
286 struct section *sec;
287 struct symbol *func;
288
289 list_for_each_entry(sec, &file->elf->sections, list) {
290 list_for_each_entry(func, &sec->symbols, list) {
291 if (func->type != STT_FUNC)
292 continue;
293
294 if (!ignore_func(file, func))
295 continue;
296
297 insn = find_instruction(file, sec, func->offset);
298 if (!insn)
299 continue;
300
301 list_for_each_entry_from(insn, &file->insns, list) {
302 if (insn->sec != func->sec ||
303 insn->offset >= func->offset + func->len)
304 break;
305
306 insn->visited = true;
307 }
308 }
309 }
310}
311
312/*
313 * Find the destination instructions for all jumps.
314 */
315static int get_jump_destinations(struct objtool_file *file)
316{
317 struct instruction *insn;
318 struct rela *rela;
319 struct section *dest_sec;
320 unsigned long dest_off;
321
322 list_for_each_entry(insn, &file->insns, list) {
323 if (insn->type != INSN_JUMP_CONDITIONAL &&
324 insn->type != INSN_JUMP_UNCONDITIONAL)
325 continue;
326
327 /* skip ignores */
328 if (insn->visited)
329 continue;
330
331 rela = find_rela_by_dest_range(insn->sec, insn->offset,
332 insn->len);
333 if (!rela) {
334 dest_sec = insn->sec;
335 dest_off = insn->offset + insn->len + insn->immediate;
336 } else if (rela->sym->type == STT_SECTION) {
337 dest_sec = rela->sym->sec;
338 dest_off = rela->addend + 4;
339 } else if (rela->sym->sec->idx) {
340 dest_sec = rela->sym->sec;
341 dest_off = rela->sym->sym.st_value + rela->addend + 4;
342 } else {
343 /* sibling call */
344 insn->jump_dest = 0;
345 continue;
346 }
347
348 insn->jump_dest = find_instruction(file, dest_sec, dest_off);
349 if (!insn->jump_dest) {
350
351 /*
352 * This is a special case where an alt instruction
353 * jumps past the end of the section. These are
354 * handled later in handle_group_alt().
355 */
356 if (!strcmp(insn->sec->name, ".altinstr_replacement"))
357 continue;
358
359 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
360 insn->sec, insn->offset, dest_sec->name,
361 dest_off);
362 return -1;
363 }
364 }
365
366 return 0;
367}
368
369/*
370 * Find the destination instructions for all calls.
371 */
372static int get_call_destinations(struct objtool_file *file)
373{
374 struct instruction *insn;
375 unsigned long dest_off;
376 struct rela *rela;
377
378 list_for_each_entry(insn, &file->insns, list) {
379 if (insn->type != INSN_CALL)
380 continue;
381
382 rela = find_rela_by_dest_range(insn->sec, insn->offset,
383 insn->len);
384 if (!rela) {
385 dest_off = insn->offset + insn->len + insn->immediate;
386 insn->call_dest = find_symbol_by_offset(insn->sec,
387 dest_off);
388 if (!insn->call_dest) {
389 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
390 insn->sec, insn->offset, dest_off);
391 return -1;
392 }
393 } else if (rela->sym->type == STT_SECTION) {
394 insn->call_dest = find_symbol_by_offset(rela->sym->sec,
395 rela->addend+4);
396 if (!insn->call_dest ||
397 insn->call_dest->type != STT_FUNC) {
398 WARN_FUNC("can't find call dest symbol at %s+0x%x",
399 insn->sec, insn->offset,
400 rela->sym->sec->name,
401 rela->addend + 4);
402 return -1;
403 }
404 } else
405 insn->call_dest = rela->sym;
406 }
407
408 return 0;
409}
410
411/*
412 * The .alternatives section requires some extra special care, over and above
413 * what other special sections require:
414 *
415 * 1. Because alternatives are patched in-place, we need to insert a fake jump
416 * instruction at the end so that validate_branch() skips all the original
417 * replaced instructions when validating the new instruction path.
418 *
419 * 2. An added wrinkle is that the new instruction length might be zero. In
420 * that case the old instructions are replaced with noops. We simulate that
421 * by creating a fake jump as the only new instruction.
422 *
423 * 3. In some cases, the alternative section includes an instruction which
424 * conditionally jumps to the _end_ of the entry. We have to modify these
425 * jumps' destinations to point back to .text rather than the end of the
426 * entry in .altinstr_replacement.
427 *
428 * 4. It has been requested that we don't validate the !POPCNT feature path
429 * which is a "very very small percentage of machines".
430 */
431static int handle_group_alt(struct objtool_file *file,
432 struct special_alt *special_alt,
433 struct instruction *orig_insn,
434 struct instruction **new_insn)
435{
436 struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
437 unsigned long dest_off;
438
439 last_orig_insn = NULL;
440 insn = orig_insn;
441 list_for_each_entry_from(insn, &file->insns, list) {
442 if (insn->sec != special_alt->orig_sec ||
443 insn->offset >= special_alt->orig_off + special_alt->orig_len)
444 break;
445
446 if (special_alt->skip_orig)
447 insn->type = INSN_NOP;
448
449 insn->alt_group = true;
450 last_orig_insn = insn;
451 }
452
453 if (list_is_last(&last_orig_insn->list, &file->insns) ||
454 list_next_entry(last_orig_insn, list)->sec != special_alt->orig_sec) {
455 WARN("%s: don't know how to handle alternatives at end of section",
456 special_alt->orig_sec->name);
457 return -1;
458 }
459
460 fake_jump = malloc(sizeof(*fake_jump));
461 if (!fake_jump) {
462 WARN("malloc failed");
463 return -1;
464 }
465 memset(fake_jump, 0, sizeof(*fake_jump));
466 INIT_LIST_HEAD(&fake_jump->alts);
467 fake_jump->sec = special_alt->new_sec;
468 fake_jump->offset = -1;
469 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
470 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
471
472 if (!special_alt->new_len) {
473 *new_insn = fake_jump;
474 return 0;
475 }
476
477 last_new_insn = NULL;
478 insn = *new_insn;
479 list_for_each_entry_from(insn, &file->insns, list) {
480 if (insn->sec != special_alt->new_sec ||
481 insn->offset >= special_alt->new_off + special_alt->new_len)
482 break;
483
484 last_new_insn = insn;
485
486 if (insn->type != INSN_JUMP_CONDITIONAL &&
487 insn->type != INSN_JUMP_UNCONDITIONAL)
488 continue;
489
490 if (!insn->immediate)
491 continue;
492
493 dest_off = insn->offset + insn->len + insn->immediate;
494 if (dest_off == special_alt->new_off + special_alt->new_len)
495 insn->jump_dest = fake_jump;
496
497 if (!insn->jump_dest) {
498 WARN_FUNC("can't find alternative jump destination",
499 insn->sec, insn->offset);
500 return -1;
501 }
502 }
503
504 if (!last_new_insn) {
505 WARN_FUNC("can't find last new alternative instruction",
506 special_alt->new_sec, special_alt->new_off);
507 return -1;
508 }
509
510 list_add(&fake_jump->list, &last_new_insn->list);
511
512 return 0;
513}
514
515/*
516 * A jump table entry can either convert a nop to a jump or a jump to a nop.
517 * If the original instruction is a jump, make the alt entry an effective nop
518 * by just skipping the original instruction.
519 */
520static int handle_jump_alt(struct objtool_file *file,
521 struct special_alt *special_alt,
522 struct instruction *orig_insn,
523 struct instruction **new_insn)
524{
525 if (orig_insn->type == INSN_NOP)
526 return 0;
527
528 if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
529 WARN_FUNC("unsupported instruction at jump label",
530 orig_insn->sec, orig_insn->offset);
531 return -1;
532 }
533
534 *new_insn = list_next_entry(orig_insn, list);
535 return 0;
536}
537
538/*
539 * Read all the special sections which have alternate instructions which can be
540 * patched in or redirected to at runtime. Each instruction having alternate
541 * instruction(s) has them added to its insn->alts list, which will be
542 * traversed in validate_branch().
543 */
544static int get_special_section_alts(struct objtool_file *file)
545{
546 struct list_head special_alts;
547 struct instruction *orig_insn, *new_insn;
548 struct special_alt *special_alt, *tmp;
549 struct alternative *alt;
550 int ret;
551
552 ret = special_get_alts(file->elf, &special_alts);
553 if (ret)
554 return ret;
555
556 list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
557 alt = malloc(sizeof(*alt));
558 if (!alt) {
559 WARN("malloc failed");
560 ret = -1;
561 goto out;
562 }
563
564 orig_insn = find_instruction(file, special_alt->orig_sec,
565 special_alt->orig_off);
566 if (!orig_insn) {
567 WARN_FUNC("special: can't find orig instruction",
568 special_alt->orig_sec, special_alt->orig_off);
569 ret = -1;
570 goto out;
571 }
572
573 new_insn = NULL;
574 if (!special_alt->group || special_alt->new_len) {
575 new_insn = find_instruction(file, special_alt->new_sec,
576 special_alt->new_off);
577 if (!new_insn) {
578 WARN_FUNC("special: can't find new instruction",
579 special_alt->new_sec,
580 special_alt->new_off);
581 ret = -1;
582 goto out;
583 }
584 }
585
586 if (special_alt->group) {
587 ret = handle_group_alt(file, special_alt, orig_insn,
588 &new_insn);
589 if (ret)
590 goto out;
591 } else if (special_alt->jump_or_nop) {
592 ret = handle_jump_alt(file, special_alt, orig_insn,
593 &new_insn);
594 if (ret)
595 goto out;
596 }
597
598 alt->insn = new_insn;
599 list_add_tail(&alt->list, &orig_insn->alts);
600
601 list_del(&special_alt->list);
602 free(special_alt);
603 }
604
605out:
606 return ret;
607}
608
609/*
610 * For some switch statements, gcc generates a jump table in the .rodata
611 * section which contains a list of addresses within the function to jump to.
612 * This finds these jump tables and adds them to the insn->alts lists.
613 */
614static int get_switch_alts(struct objtool_file *file)
615{
616 struct instruction *insn, *alt_insn;
617 struct rela *rodata_rela, *rela;
618 struct section *rodata;
619 struct symbol *func;
620 struct alternative *alt;
621
622 list_for_each_entry(insn, &file->insns, list) {
623 if (insn->type != INSN_JUMP_DYNAMIC)
624 continue;
625
626 rodata_rela = find_rela_by_dest_range(insn->sec, insn->offset,
627 insn->len);
628 if (!rodata_rela || strcmp(rodata_rela->sym->name, ".rodata"))
629 continue;
630
631 rodata = find_section_by_name(file->elf, ".rodata");
632 if (!rodata || !rodata->rela)
633 continue;
634
635 /* common case: jmpq *[addr](,%rax,8) */
636 rela = find_rela_by_dest(rodata, rodata_rela->addend);
637
638 /* rare case: jmpq *[addr](%rip) */
639 if (!rela)
640 rela = find_rela_by_dest(rodata,
641 rodata_rela->addend + 4);
642 if (!rela)
643 continue;
644
645 func = find_containing_func(insn->sec, insn->offset);
646 if (!func) {
647 WARN_FUNC("can't find containing func",
648 insn->sec, insn->offset);
649 return -1;
650 }
651
652 list_for_each_entry_from(rela, &rodata->rela->relas, list) {
653 if (rela->sym->sec != insn->sec ||
654 rela->addend <= func->offset ||
655 rela->addend >= func->offset + func->len)
656 break;
657
658 alt_insn = find_instruction(file, insn->sec,
659 rela->addend);
660 if (!alt_insn) {
661 WARN("%s: can't find instruction at %s+0x%x",
662 rodata->rela->name, insn->sec->name,
663 rela->addend);
664 return -1;
665 }
666
667 alt = malloc(sizeof(*alt));
668 if (!alt) {
669 WARN("malloc failed");
670 return -1;
671 }
672
673 alt->insn = alt_insn;
674 list_add_tail(&alt->list, &insn->alts);
675 }
676 }
677
678 return 0;
679}
680
681static int decode_sections(struct objtool_file *file)
682{
683 int ret;
684
685 ret = decode_instructions(file);
686 if (ret)
687 return ret;
688
689 get_ignores(file);
690
691 ret = get_jump_destinations(file);
692 if (ret)
693 return ret;
694
695 ret = get_call_destinations(file);
696 if (ret)
697 return ret;
698
699 ret = get_special_section_alts(file);
700 if (ret)
701 return ret;
702
703 ret = get_switch_alts(file);
704 if (ret)
705 return ret;
706
707 return 0;
708}
709
710static bool is_fentry_call(struct instruction *insn)
711{
712 if (insn->type == INSN_CALL &&
713 insn->call_dest->type == STT_NOTYPE &&
714 !strcmp(insn->call_dest->name, "__fentry__"))
715 return true;
716
717 return false;
718}
719
720static bool has_modified_stack_frame(struct instruction *insn)
721{
722 return (insn->state & STATE_FP_SAVED) ||
723 (insn->state & STATE_FP_SETUP);
724}
725
726static bool has_valid_stack_frame(struct instruction *insn)
727{
728 return (insn->state & STATE_FP_SAVED) &&
729 (insn->state & STATE_FP_SETUP);
730}
731
732/*
733 * Follow the branch starting at the given instruction, and recursively follow
734 * any other branches (jumps). Meanwhile, track the frame pointer state at
735 * each instruction and validate all the rules described in
736 * tools/objtool/Documentation/stack-validation.txt.
737 */
738static int validate_branch(struct objtool_file *file,
739 struct instruction *first, unsigned char first_state)
740{
741 struct alternative *alt;
742 struct instruction *insn;
743 struct section *sec;
744 unsigned char state;
745 int ret, warnings = 0;
746
747 insn = first;
748 sec = insn->sec;
749 state = first_state;
750
751 if (insn->alt_group && list_empty(&insn->alts)) {
752 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
753 sec, insn->offset);
754 warnings++;
755 }
756
757 while (1) {
758 if (insn->visited) {
759 if (insn->state != state) {
760 WARN_FUNC("frame pointer state mismatch",
761 sec, insn->offset);
762 warnings++;
763 }
764
765 return warnings;
766 }
767
768 /*
769 * Catch a rare case where a noreturn function falls through to
770 * the next function.
771 */
772 if (is_fentry_call(insn) && (state & STATE_FENTRY))
773 return warnings;
774
775 insn->visited = true;
776 insn->state = state;
777
778 list_for_each_entry(alt, &insn->alts, list) {
779 ret = validate_branch(file, alt->insn, state);
780 warnings += ret;
781 }
782
783 switch (insn->type) {
784
785 case INSN_FP_SAVE:
786 if (!nofp) {
787 if (state & STATE_FP_SAVED) {
788 WARN_FUNC("duplicate frame pointer save",
789 sec, insn->offset);
790 warnings++;
791 }
792 state |= STATE_FP_SAVED;
793 }
794 break;
795
796 case INSN_FP_SETUP:
797 if (!nofp) {
798 if (state & STATE_FP_SETUP) {
799 WARN_FUNC("duplicate frame pointer setup",
800 sec, insn->offset);
801 warnings++;
802 }
803 state |= STATE_FP_SETUP;
804 }
805 break;
806
807 case INSN_FP_RESTORE:
808 if (!nofp) {
809 if (has_valid_stack_frame(insn))
810 state &= ~STATE_FP_SETUP;
811
812 state &= ~STATE_FP_SAVED;
813 }
814 break;
815
816 case INSN_RETURN:
817 if (!nofp && has_modified_stack_frame(insn)) {
818 WARN_FUNC("return without frame pointer restore",
819 sec, insn->offset);
820 warnings++;
821 }
822 return warnings;
823
824 case INSN_CALL:
825 if (is_fentry_call(insn)) {
826 state |= STATE_FENTRY;
827 break;
828 }
829
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600830 ret = dead_end_function(file, insn->call_dest);
831 if (ret == 1)
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600832 return warnings;
Josh Poimboeufb1e03242016-03-09 00:06:52 -0600833 if (ret == -1)
834 warnings++;
Josh Poimboeuf442f04c2016-02-28 22:22:41 -0600835
836 /* fallthrough */
837 case INSN_CALL_DYNAMIC:
838 if (!nofp && !has_valid_stack_frame(insn)) {
839 WARN_FUNC("call without frame pointer save/setup",
840 sec, insn->offset);
841 warnings++;
842 }
843 break;
844
845 case INSN_JUMP_CONDITIONAL:
846 case INSN_JUMP_UNCONDITIONAL:
847 if (insn->jump_dest) {
848 ret = validate_branch(file, insn->jump_dest,
849 state);
850 warnings += ret;
851 } else if (has_modified_stack_frame(insn)) {
852 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
853 sec, insn->offset);
854 warnings++;
855 } /* else it's a sibling call */
856
857 if (insn->type == INSN_JUMP_UNCONDITIONAL)
858 return warnings;
859
860 break;
861
862 case INSN_JUMP_DYNAMIC:
863 if (list_empty(&insn->alts) &&
864 has_modified_stack_frame(insn)) {
865 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
866 sec, insn->offset);
867 warnings++;
868 }
869
870 return warnings;
871
872 case INSN_BUG:
873 return warnings;
874
875 default:
876 break;
877 }
878
879 insn = list_next_entry(insn, list);
880
881 if (&insn->list == &file->insns || insn->sec != sec) {
882 WARN("%s: unexpected end of section", sec->name);
883 warnings++;
884 return warnings;
885 }
886 }
887
888 return warnings;
889}
890
891static bool is_gcov_insn(struct instruction *insn)
892{
893 struct rela *rela;
894 struct section *sec;
895 struct symbol *sym;
896 unsigned long offset;
897
898 rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
899 if (!rela)
900 return false;
901
902 if (rela->sym->type != STT_SECTION)
903 return false;
904
905 sec = rela->sym->sec;
906 offset = rela->addend + insn->offset + insn->len - rela->offset;
907
908 list_for_each_entry(sym, &sec->symbols, list) {
909 if (sym->type != STT_OBJECT)
910 continue;
911
912 if (offset >= sym->offset && offset < sym->offset + sym->len)
913 return (!memcmp(sym->name, "__gcov0.", 8));
914 }
915
916 return false;
917}
918
919static bool is_kasan_insn(struct instruction *insn)
920{
921 return (insn->type == INSN_CALL &&
922 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
923}
924
925static bool is_ubsan_insn(struct instruction *insn)
926{
927 return (insn->type == INSN_CALL &&
928 !strcmp(insn->call_dest->name,
929 "__ubsan_handle_builtin_unreachable"));
930}
931
932static bool ignore_unreachable_insn(struct instruction *insn,
933 unsigned long func_end)
934{
935 int i;
936
937 if (insn->type == INSN_NOP)
938 return true;
939
940 if (is_gcov_insn(insn))
941 return true;
942
943 /*
944 * Check if this (or a subsequent) instruction is related to
945 * CONFIG_UBSAN or CONFIG_KASAN.
946 *
947 * End the search at 5 instructions to avoid going into the weeds.
948 */
949 for (i = 0; i < 5; i++) {
950
951 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
952 return true;
953
954 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
955 insn = insn->jump_dest;
956 continue;
957 }
958
959 if (insn->offset + insn->len >= func_end)
960 break;
961 insn = list_next_entry(insn, list);
962 }
963
964 return false;
965}
966
967static int validate_functions(struct objtool_file *file)
968{
969 struct section *sec;
970 struct symbol *func;
971 struct instruction *insn;
972 unsigned long func_end;
973 int ret, warnings = 0;
974
975 list_for_each_entry(sec, &file->elf->sections, list) {
976 list_for_each_entry(func, &sec->symbols, list) {
977 if (func->type != STT_FUNC)
978 continue;
979
980 insn = find_instruction(file, sec, func->offset);
981 if (!insn) {
982 WARN("%s(): can't find starting instruction",
983 func->name);
984 warnings++;
985 continue;
986 }
987
988 ret = validate_branch(file, insn, 0);
989 warnings += ret;
990 }
991 }
992
993 list_for_each_entry(sec, &file->elf->sections, list) {
994 list_for_each_entry(func, &sec->symbols, list) {
995 if (func->type != STT_FUNC)
996 continue;
997
998 insn = find_instruction(file, sec, func->offset);
999 if (!insn)
1000 continue;
1001
1002 func_end = func->offset + func->len;
1003
1004 list_for_each_entry_from(insn, &file->insns, list) {
1005 if (insn->sec != func->sec ||
1006 insn->offset >= func_end)
1007 break;
1008
1009 if (insn->visited)
1010 continue;
1011
1012 if (!ignore_unreachable_insn(insn, func_end)) {
1013 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1014 warnings++;
1015 }
1016
1017 insn->visited = true;
1018 }
1019 }
1020 }
1021
1022 return warnings;
1023}
1024
1025static int validate_uncallable_instructions(struct objtool_file *file)
1026{
1027 struct instruction *insn;
1028 int warnings = 0;
1029
1030 list_for_each_entry(insn, &file->insns, list) {
1031 if (!insn->visited && insn->type == INSN_RETURN) {
1032 WARN_FUNC("return instruction outside of a callable function",
1033 insn->sec, insn->offset);
1034 warnings++;
1035 }
1036 }
1037
1038 return warnings;
1039}
1040
1041static void cleanup(struct objtool_file *file)
1042{
1043 struct instruction *insn, *tmpinsn;
1044 struct alternative *alt, *tmpalt;
1045
1046 list_for_each_entry_safe(insn, tmpinsn, &file->insns, list) {
1047 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1048 list_del(&alt->list);
1049 free(alt);
1050 }
1051 list_del(&insn->list);
1052 free(insn);
1053 }
1054 elf_close(file->elf);
1055}
1056
1057const char * const check_usage[] = {
1058 "objtool check [<options>] file.o",
1059 NULL,
1060};
1061
1062int cmd_check(int argc, const char **argv)
1063{
1064 struct objtool_file file;
1065 int ret, warnings = 0;
1066
1067 const struct option options[] = {
1068 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1069 OPT_END(),
1070 };
1071
1072 argc = parse_options(argc, argv, options, check_usage, 0);
1073
1074 if (argc != 1)
1075 usage_with_options(check_usage, options);
1076
1077 objname = argv[0];
1078
1079 file.elf = elf_open(objname);
1080 if (!file.elf) {
1081 fprintf(stderr, "error reading elf file %s\n", objname);
1082 return 1;
1083 }
1084
1085 INIT_LIST_HEAD(&file.insns);
1086
1087 ret = decode_sections(&file);
1088 if (ret < 0)
1089 goto out;
1090 warnings += ret;
1091
1092 ret = validate_functions(&file);
1093 if (ret < 0)
1094 goto out;
1095 warnings += ret;
1096
1097 ret = validate_uncallable_instructions(&file);
1098 if (ret < 0)
1099 goto out;
1100 warnings += ret;
1101
1102out:
1103 cleanup(&file);
1104
1105 /* ignore warnings for now until we get all the code cleaned up */
1106 if (ret || warnings)
1107 return 0;
1108 return 0;
1109}