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442f04c3 JP |
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 | #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 | ||
43 | struct 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 | ||
56 | struct alternative { | |
57 | struct list_head list; | |
58 | struct instruction *insn; | |
59 | }; | |
60 | ||
61 | struct objtool_file { | |
62 | struct elf *elf; | |
63 | struct list_head insns; | |
64 | }; | |
65 | ||
66 | const char *objname; | |
67 | static bool nofp; | |
68 | ||
69 | static 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 | */ | |
87 | static 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, ¯o_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. | |
124 | */ | |
125 | static bool dead_end_function(struct objtool_file *file, struct symbol *func) | |
126 | { | |
127 | int i; | |
128 | struct instruction *insn; | |
129 | bool empty = true; | |
130 | ||
131 | /* | |
132 | * Unfortunately these have to be hard coded because the noreturn | |
133 | * attribute isn't provided in ELF data. | |
134 | */ | |
135 | static const char * const global_noreturns[] = { | |
136 | "__stack_chk_fail", | |
137 | "panic", | |
138 | "do_exit", | |
139 | "__module_put_and_exit", | |
140 | "complete_and_exit", | |
141 | "kvm_spurious_fault", | |
142 | "__reiserfs_panic", | |
143 | "lbug_with_loc" | |
144 | }; | |
145 | ||
146 | if (func->bind == STB_WEAK) | |
147 | return false; | |
148 | ||
149 | if (func->bind == STB_GLOBAL) | |
150 | for (i = 0; i < ARRAY_SIZE(global_noreturns); i++) | |
151 | if (!strcmp(func->name, global_noreturns[i])) | |
152 | return true; | |
153 | ||
154 | if (!func->sec) | |
155 | return false; | |
156 | ||
157 | insn = find_instruction(file, func->sec, func->offset); | |
158 | if (!insn) | |
159 | return false; | |
160 | ||
161 | list_for_each_entry_from(insn, &file->insns, list) { | |
162 | if (insn->sec != func->sec || | |
163 | insn->offset >= func->offset + func->len) | |
164 | break; | |
165 | ||
166 | empty = false; | |
167 | ||
168 | if (insn->type == INSN_RETURN) | |
169 | return false; | |
170 | ||
171 | if (insn->type == INSN_JUMP_UNCONDITIONAL) { | |
172 | struct instruction *dest = insn->jump_dest; | |
173 | struct symbol *dest_func; | |
174 | ||
175 | if (!dest) | |
176 | /* sibling call to another file */ | |
177 | return false; | |
178 | ||
179 | if (dest->sec != func->sec || | |
180 | dest->offset < func->offset || | |
181 | dest->offset >= func->offset + func->len) { | |
182 | /* local sibling call */ | |
183 | dest_func = find_symbol_by_offset(dest->sec, | |
184 | dest->offset); | |
185 | if (!dest_func) | |
186 | continue; | |
187 | ||
188 | return dead_end_function(file, dest_func); | |
189 | } | |
190 | } | |
191 | ||
192 | if (insn->type == INSN_JUMP_DYNAMIC) | |
193 | /* sibling call */ | |
194 | return false; | |
195 | } | |
196 | ||
197 | return !empty; | |
198 | } | |
199 | ||
200 | /* | |
201 | * Call the arch-specific instruction decoder for all the instructions and add | |
202 | * them to the global insns list. | |
203 | */ | |
204 | static int decode_instructions(struct objtool_file *file) | |
205 | { | |
206 | struct section *sec; | |
207 | unsigned long offset; | |
208 | struct instruction *insn; | |
209 | int ret; | |
210 | ||
211 | INIT_LIST_HEAD(&file->insns); | |
212 | ||
213 | list_for_each_entry(sec, &file->elf->sections, list) { | |
214 | ||
215 | if (!(sec->sh.sh_flags & SHF_EXECINSTR)) | |
216 | continue; | |
217 | ||
218 | for (offset = 0; offset < sec->len; offset += insn->len) { | |
219 | insn = malloc(sizeof(*insn)); | |
220 | memset(insn, 0, sizeof(*insn)); | |
221 | ||
222 | INIT_LIST_HEAD(&insn->alts); | |
223 | insn->sec = sec; | |
224 | insn->offset = offset; | |
225 | ||
226 | ret = arch_decode_instruction(file->elf, sec, offset, | |
227 | sec->len - offset, | |
228 | &insn->len, &insn->type, | |
229 | &insn->immediate); | |
230 | if (ret) | |
231 | return ret; | |
232 | ||
233 | if (!insn->type || insn->type > INSN_LAST) { | |
234 | WARN_FUNC("invalid instruction type %d", | |
235 | insn->sec, insn->offset, insn->type); | |
236 | return -1; | |
237 | } | |
238 | ||
239 | list_add_tail(&insn->list, &file->insns); | |
240 | } | |
241 | } | |
242 | ||
243 | return 0; | |
244 | } | |
245 | ||
246 | /* | |
247 | * Warnings shouldn't be reported for ignored functions. | |
248 | */ | |
249 | static void get_ignores(struct objtool_file *file) | |
250 | { | |
251 | struct instruction *insn; | |
252 | struct section *sec; | |
253 | struct symbol *func; | |
254 | ||
255 | list_for_each_entry(sec, &file->elf->sections, list) { | |
256 | list_for_each_entry(func, &sec->symbols, list) { | |
257 | if (func->type != STT_FUNC) | |
258 | continue; | |
259 | ||
260 | if (!ignore_func(file, func)) | |
261 | continue; | |
262 | ||
263 | insn = find_instruction(file, sec, func->offset); | |
264 | if (!insn) | |
265 | continue; | |
266 | ||
267 | list_for_each_entry_from(insn, &file->insns, list) { | |
268 | if (insn->sec != func->sec || | |
269 | insn->offset >= func->offset + func->len) | |
270 | break; | |
271 | ||
272 | insn->visited = true; | |
273 | } | |
274 | } | |
275 | } | |
276 | } | |
277 | ||
278 | /* | |
279 | * Find the destination instructions for all jumps. | |
280 | */ | |
281 | static int get_jump_destinations(struct objtool_file *file) | |
282 | { | |
283 | struct instruction *insn; | |
284 | struct rela *rela; | |
285 | struct section *dest_sec; | |
286 | unsigned long dest_off; | |
287 | ||
288 | list_for_each_entry(insn, &file->insns, list) { | |
289 | if (insn->type != INSN_JUMP_CONDITIONAL && | |
290 | insn->type != INSN_JUMP_UNCONDITIONAL) | |
291 | continue; | |
292 | ||
293 | /* skip ignores */ | |
294 | if (insn->visited) | |
295 | continue; | |
296 | ||
297 | rela = find_rela_by_dest_range(insn->sec, insn->offset, | |
298 | insn->len); | |
299 | if (!rela) { | |
300 | dest_sec = insn->sec; | |
301 | dest_off = insn->offset + insn->len + insn->immediate; | |
302 | } else if (rela->sym->type == STT_SECTION) { | |
303 | dest_sec = rela->sym->sec; | |
304 | dest_off = rela->addend + 4; | |
305 | } else if (rela->sym->sec->idx) { | |
306 | dest_sec = rela->sym->sec; | |
307 | dest_off = rela->sym->sym.st_value + rela->addend + 4; | |
308 | } else { | |
309 | /* sibling call */ | |
310 | insn->jump_dest = 0; | |
311 | continue; | |
312 | } | |
313 | ||
314 | insn->jump_dest = find_instruction(file, dest_sec, dest_off); | |
315 | if (!insn->jump_dest) { | |
316 | ||
317 | /* | |
318 | * This is a special case where an alt instruction | |
319 | * jumps past the end of the section. These are | |
320 | * handled later in handle_group_alt(). | |
321 | */ | |
322 | if (!strcmp(insn->sec->name, ".altinstr_replacement")) | |
323 | continue; | |
324 | ||
325 | WARN_FUNC("can't find jump dest instruction at %s+0x%lx", | |
326 | insn->sec, insn->offset, dest_sec->name, | |
327 | dest_off); | |
328 | return -1; | |
329 | } | |
330 | } | |
331 | ||
332 | return 0; | |
333 | } | |
334 | ||
335 | /* | |
336 | * Find the destination instructions for all calls. | |
337 | */ | |
338 | static int get_call_destinations(struct objtool_file *file) | |
339 | { | |
340 | struct instruction *insn; | |
341 | unsigned long dest_off; | |
342 | struct rela *rela; | |
343 | ||
344 | list_for_each_entry(insn, &file->insns, list) { | |
345 | if (insn->type != INSN_CALL) | |
346 | continue; | |
347 | ||
348 | rela = find_rela_by_dest_range(insn->sec, insn->offset, | |
349 | insn->len); | |
350 | if (!rela) { | |
351 | dest_off = insn->offset + insn->len + insn->immediate; | |
352 | insn->call_dest = find_symbol_by_offset(insn->sec, | |
353 | dest_off); | |
354 | if (!insn->call_dest) { | |
355 | WARN_FUNC("can't find call dest symbol at offset 0x%lx", | |
356 | insn->sec, insn->offset, dest_off); | |
357 | return -1; | |
358 | } | |
359 | } else if (rela->sym->type == STT_SECTION) { | |
360 | insn->call_dest = find_symbol_by_offset(rela->sym->sec, | |
361 | rela->addend+4); | |
362 | if (!insn->call_dest || | |
363 | insn->call_dest->type != STT_FUNC) { | |
364 | WARN_FUNC("can't find call dest symbol at %s+0x%x", | |
365 | insn->sec, insn->offset, | |
366 | rela->sym->sec->name, | |
367 | rela->addend + 4); | |
368 | return -1; | |
369 | } | |
370 | } else | |
371 | insn->call_dest = rela->sym; | |
372 | } | |
373 | ||
374 | return 0; | |
375 | } | |
376 | ||
377 | /* | |
378 | * The .alternatives section requires some extra special care, over and above | |
379 | * what other special sections require: | |
380 | * | |
381 | * 1. Because alternatives are patched in-place, we need to insert a fake jump | |
382 | * instruction at the end so that validate_branch() skips all the original | |
383 | * replaced instructions when validating the new instruction path. | |
384 | * | |
385 | * 2. An added wrinkle is that the new instruction length might be zero. In | |
386 | * that case the old instructions are replaced with noops. We simulate that | |
387 | * by creating a fake jump as the only new instruction. | |
388 | * | |
389 | * 3. In some cases, the alternative section includes an instruction which | |
390 | * conditionally jumps to the _end_ of the entry. We have to modify these | |
391 | * jumps' destinations to point back to .text rather than the end of the | |
392 | * entry in .altinstr_replacement. | |
393 | * | |
394 | * 4. It has been requested that we don't validate the !POPCNT feature path | |
395 | * which is a "very very small percentage of machines". | |
396 | */ | |
397 | static int handle_group_alt(struct objtool_file *file, | |
398 | struct special_alt *special_alt, | |
399 | struct instruction *orig_insn, | |
400 | struct instruction **new_insn) | |
401 | { | |
402 | struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump; | |
403 | unsigned long dest_off; | |
404 | ||
405 | last_orig_insn = NULL; | |
406 | insn = orig_insn; | |
407 | list_for_each_entry_from(insn, &file->insns, list) { | |
408 | if (insn->sec != special_alt->orig_sec || | |
409 | insn->offset >= special_alt->orig_off + special_alt->orig_len) | |
410 | break; | |
411 | ||
412 | if (special_alt->skip_orig) | |
413 | insn->type = INSN_NOP; | |
414 | ||
415 | insn->alt_group = true; | |
416 | last_orig_insn = insn; | |
417 | } | |
418 | ||
419 | if (list_is_last(&last_orig_insn->list, &file->insns) || | |
420 | list_next_entry(last_orig_insn, list)->sec != special_alt->orig_sec) { | |
421 | WARN("%s: don't know how to handle alternatives at end of section", | |
422 | special_alt->orig_sec->name); | |
423 | return -1; | |
424 | } | |
425 | ||
426 | fake_jump = malloc(sizeof(*fake_jump)); | |
427 | if (!fake_jump) { | |
428 | WARN("malloc failed"); | |
429 | return -1; | |
430 | } | |
431 | memset(fake_jump, 0, sizeof(*fake_jump)); | |
432 | INIT_LIST_HEAD(&fake_jump->alts); | |
433 | fake_jump->sec = special_alt->new_sec; | |
434 | fake_jump->offset = -1; | |
435 | fake_jump->type = INSN_JUMP_UNCONDITIONAL; | |
436 | fake_jump->jump_dest = list_next_entry(last_orig_insn, list); | |
437 | ||
438 | if (!special_alt->new_len) { | |
439 | *new_insn = fake_jump; | |
440 | return 0; | |
441 | } | |
442 | ||
443 | last_new_insn = NULL; | |
444 | insn = *new_insn; | |
445 | list_for_each_entry_from(insn, &file->insns, list) { | |
446 | if (insn->sec != special_alt->new_sec || | |
447 | insn->offset >= special_alt->new_off + special_alt->new_len) | |
448 | break; | |
449 | ||
450 | last_new_insn = insn; | |
451 | ||
452 | if (insn->type != INSN_JUMP_CONDITIONAL && | |
453 | insn->type != INSN_JUMP_UNCONDITIONAL) | |
454 | continue; | |
455 | ||
456 | if (!insn->immediate) | |
457 | continue; | |
458 | ||
459 | dest_off = insn->offset + insn->len + insn->immediate; | |
460 | if (dest_off == special_alt->new_off + special_alt->new_len) | |
461 | insn->jump_dest = fake_jump; | |
462 | ||
463 | if (!insn->jump_dest) { | |
464 | WARN_FUNC("can't find alternative jump destination", | |
465 | insn->sec, insn->offset); | |
466 | return -1; | |
467 | } | |
468 | } | |
469 | ||
470 | if (!last_new_insn) { | |
471 | WARN_FUNC("can't find last new alternative instruction", | |
472 | special_alt->new_sec, special_alt->new_off); | |
473 | return -1; | |
474 | } | |
475 | ||
476 | list_add(&fake_jump->list, &last_new_insn->list); | |
477 | ||
478 | return 0; | |
479 | } | |
480 | ||
481 | /* | |
482 | * A jump table entry can either convert a nop to a jump or a jump to a nop. | |
483 | * If the original instruction is a jump, make the alt entry an effective nop | |
484 | * by just skipping the original instruction. | |
485 | */ | |
486 | static int handle_jump_alt(struct objtool_file *file, | |
487 | struct special_alt *special_alt, | |
488 | struct instruction *orig_insn, | |
489 | struct instruction **new_insn) | |
490 | { | |
491 | if (orig_insn->type == INSN_NOP) | |
492 | return 0; | |
493 | ||
494 | if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) { | |
495 | WARN_FUNC("unsupported instruction at jump label", | |
496 | orig_insn->sec, orig_insn->offset); | |
497 | return -1; | |
498 | } | |
499 | ||
500 | *new_insn = list_next_entry(orig_insn, list); | |
501 | return 0; | |
502 | } | |
503 | ||
504 | /* | |
505 | * Read all the special sections which have alternate instructions which can be | |
506 | * patched in or redirected to at runtime. Each instruction having alternate | |
507 | * instruction(s) has them added to its insn->alts list, which will be | |
508 | * traversed in validate_branch(). | |
509 | */ | |
510 | static int get_special_section_alts(struct objtool_file *file) | |
511 | { | |
512 | struct list_head special_alts; | |
513 | struct instruction *orig_insn, *new_insn; | |
514 | struct special_alt *special_alt, *tmp; | |
515 | struct alternative *alt; | |
516 | int ret; | |
517 | ||
518 | ret = special_get_alts(file->elf, &special_alts); | |
519 | if (ret) | |
520 | return ret; | |
521 | ||
522 | list_for_each_entry_safe(special_alt, tmp, &special_alts, list) { | |
523 | alt = malloc(sizeof(*alt)); | |
524 | if (!alt) { | |
525 | WARN("malloc failed"); | |
526 | ret = -1; | |
527 | goto out; | |
528 | } | |
529 | ||
530 | orig_insn = find_instruction(file, special_alt->orig_sec, | |
531 | special_alt->orig_off); | |
532 | if (!orig_insn) { | |
533 | WARN_FUNC("special: can't find orig instruction", | |
534 | special_alt->orig_sec, special_alt->orig_off); | |
535 | ret = -1; | |
536 | goto out; | |
537 | } | |
538 | ||
539 | new_insn = NULL; | |
540 | if (!special_alt->group || special_alt->new_len) { | |
541 | new_insn = find_instruction(file, special_alt->new_sec, | |
542 | special_alt->new_off); | |
543 | if (!new_insn) { | |
544 | WARN_FUNC("special: can't find new instruction", | |
545 | special_alt->new_sec, | |
546 | special_alt->new_off); | |
547 | ret = -1; | |
548 | goto out; | |
549 | } | |
550 | } | |
551 | ||
552 | if (special_alt->group) { | |
553 | ret = handle_group_alt(file, special_alt, orig_insn, | |
554 | &new_insn); | |
555 | if (ret) | |
556 | goto out; | |
557 | } else if (special_alt->jump_or_nop) { | |
558 | ret = handle_jump_alt(file, special_alt, orig_insn, | |
559 | &new_insn); | |
560 | if (ret) | |
561 | goto out; | |
562 | } | |
563 | ||
564 | alt->insn = new_insn; | |
565 | list_add_tail(&alt->list, &orig_insn->alts); | |
566 | ||
567 | list_del(&special_alt->list); | |
568 | free(special_alt); | |
569 | } | |
570 | ||
571 | out: | |
572 | return ret; | |
573 | } | |
574 | ||
575 | /* | |
576 | * For some switch statements, gcc generates a jump table in the .rodata | |
577 | * section which contains a list of addresses within the function to jump to. | |
578 | * This finds these jump tables and adds them to the insn->alts lists. | |
579 | */ | |
580 | static int get_switch_alts(struct objtool_file *file) | |
581 | { | |
582 | struct instruction *insn, *alt_insn; | |
583 | struct rela *rodata_rela, *rela; | |
584 | struct section *rodata; | |
585 | struct symbol *func; | |
586 | struct alternative *alt; | |
587 | ||
588 | list_for_each_entry(insn, &file->insns, list) { | |
589 | if (insn->type != INSN_JUMP_DYNAMIC) | |
590 | continue; | |
591 | ||
592 | rodata_rela = find_rela_by_dest_range(insn->sec, insn->offset, | |
593 | insn->len); | |
594 | if (!rodata_rela || strcmp(rodata_rela->sym->name, ".rodata")) | |
595 | continue; | |
596 | ||
597 | rodata = find_section_by_name(file->elf, ".rodata"); | |
598 | if (!rodata || !rodata->rela) | |
599 | continue; | |
600 | ||
601 | /* common case: jmpq *[addr](,%rax,8) */ | |
602 | rela = find_rela_by_dest(rodata, rodata_rela->addend); | |
603 | ||
604 | /* rare case: jmpq *[addr](%rip) */ | |
605 | if (!rela) | |
606 | rela = find_rela_by_dest(rodata, | |
607 | rodata_rela->addend + 4); | |
608 | if (!rela) | |
609 | continue; | |
610 | ||
611 | func = find_containing_func(insn->sec, insn->offset); | |
612 | if (!func) { | |
613 | WARN_FUNC("can't find containing func", | |
614 | insn->sec, insn->offset); | |
615 | return -1; | |
616 | } | |
617 | ||
618 | list_for_each_entry_from(rela, &rodata->rela->relas, list) { | |
619 | if (rela->sym->sec != insn->sec || | |
620 | rela->addend <= func->offset || | |
621 | rela->addend >= func->offset + func->len) | |
622 | break; | |
623 | ||
624 | alt_insn = find_instruction(file, insn->sec, | |
625 | rela->addend); | |
626 | if (!alt_insn) { | |
627 | WARN("%s: can't find instruction at %s+0x%x", | |
628 | rodata->rela->name, insn->sec->name, | |
629 | rela->addend); | |
630 | return -1; | |
631 | } | |
632 | ||
633 | alt = malloc(sizeof(*alt)); | |
634 | if (!alt) { | |
635 | WARN("malloc failed"); | |
636 | return -1; | |
637 | } | |
638 | ||
639 | alt->insn = alt_insn; | |
640 | list_add_tail(&alt->list, &insn->alts); | |
641 | } | |
642 | } | |
643 | ||
644 | return 0; | |
645 | } | |
646 | ||
647 | static int decode_sections(struct objtool_file *file) | |
648 | { | |
649 | int ret; | |
650 | ||
651 | ret = decode_instructions(file); | |
652 | if (ret) | |
653 | return ret; | |
654 | ||
655 | get_ignores(file); | |
656 | ||
657 | ret = get_jump_destinations(file); | |
658 | if (ret) | |
659 | return ret; | |
660 | ||
661 | ret = get_call_destinations(file); | |
662 | if (ret) | |
663 | return ret; | |
664 | ||
665 | ret = get_special_section_alts(file); | |
666 | if (ret) | |
667 | return ret; | |
668 | ||
669 | ret = get_switch_alts(file); | |
670 | if (ret) | |
671 | return ret; | |
672 | ||
673 | return 0; | |
674 | } | |
675 | ||
676 | static bool is_fentry_call(struct instruction *insn) | |
677 | { | |
678 | if (insn->type == INSN_CALL && | |
679 | insn->call_dest->type == STT_NOTYPE && | |
680 | !strcmp(insn->call_dest->name, "__fentry__")) | |
681 | return true; | |
682 | ||
683 | return false; | |
684 | } | |
685 | ||
686 | static bool has_modified_stack_frame(struct instruction *insn) | |
687 | { | |
688 | return (insn->state & STATE_FP_SAVED) || | |
689 | (insn->state & STATE_FP_SETUP); | |
690 | } | |
691 | ||
692 | static bool has_valid_stack_frame(struct instruction *insn) | |
693 | { | |
694 | return (insn->state & STATE_FP_SAVED) && | |
695 | (insn->state & STATE_FP_SETUP); | |
696 | } | |
697 | ||
698 | /* | |
699 | * Follow the branch starting at the given instruction, and recursively follow | |
700 | * any other branches (jumps). Meanwhile, track the frame pointer state at | |
701 | * each instruction and validate all the rules described in | |
702 | * tools/objtool/Documentation/stack-validation.txt. | |
703 | */ | |
704 | static int validate_branch(struct objtool_file *file, | |
705 | struct instruction *first, unsigned char first_state) | |
706 | { | |
707 | struct alternative *alt; | |
708 | struct instruction *insn; | |
709 | struct section *sec; | |
710 | unsigned char state; | |
711 | int ret, warnings = 0; | |
712 | ||
713 | insn = first; | |
714 | sec = insn->sec; | |
715 | state = first_state; | |
716 | ||
717 | if (insn->alt_group && list_empty(&insn->alts)) { | |
718 | WARN_FUNC("don't know how to handle branch to middle of alternative instruction group", | |
719 | sec, insn->offset); | |
720 | warnings++; | |
721 | } | |
722 | ||
723 | while (1) { | |
724 | if (insn->visited) { | |
725 | if (insn->state != state) { | |
726 | WARN_FUNC("frame pointer state mismatch", | |
727 | sec, insn->offset); | |
728 | warnings++; | |
729 | } | |
730 | ||
731 | return warnings; | |
732 | } | |
733 | ||
734 | /* | |
735 | * Catch a rare case where a noreturn function falls through to | |
736 | * the next function. | |
737 | */ | |
738 | if (is_fentry_call(insn) && (state & STATE_FENTRY)) | |
739 | return warnings; | |
740 | ||
741 | insn->visited = true; | |
742 | insn->state = state; | |
743 | ||
744 | list_for_each_entry(alt, &insn->alts, list) { | |
745 | ret = validate_branch(file, alt->insn, state); | |
746 | warnings += ret; | |
747 | } | |
748 | ||
749 | switch (insn->type) { | |
750 | ||
751 | case INSN_FP_SAVE: | |
752 | if (!nofp) { | |
753 | if (state & STATE_FP_SAVED) { | |
754 | WARN_FUNC("duplicate frame pointer save", | |
755 | sec, insn->offset); | |
756 | warnings++; | |
757 | } | |
758 | state |= STATE_FP_SAVED; | |
759 | } | |
760 | break; | |
761 | ||
762 | case INSN_FP_SETUP: | |
763 | if (!nofp) { | |
764 | if (state & STATE_FP_SETUP) { | |
765 | WARN_FUNC("duplicate frame pointer setup", | |
766 | sec, insn->offset); | |
767 | warnings++; | |
768 | } | |
769 | state |= STATE_FP_SETUP; | |
770 | } | |
771 | break; | |
772 | ||
773 | case INSN_FP_RESTORE: | |
774 | if (!nofp) { | |
775 | if (has_valid_stack_frame(insn)) | |
776 | state &= ~STATE_FP_SETUP; | |
777 | ||
778 | state &= ~STATE_FP_SAVED; | |
779 | } | |
780 | break; | |
781 | ||
782 | case INSN_RETURN: | |
783 | if (!nofp && has_modified_stack_frame(insn)) { | |
784 | WARN_FUNC("return without frame pointer restore", | |
785 | sec, insn->offset); | |
786 | warnings++; | |
787 | } | |
788 | return warnings; | |
789 | ||
790 | case INSN_CALL: | |
791 | if (is_fentry_call(insn)) { | |
792 | state |= STATE_FENTRY; | |
793 | break; | |
794 | } | |
795 | ||
796 | if (dead_end_function(file, insn->call_dest)) | |
797 | return warnings; | |
798 | ||
799 | /* fallthrough */ | |
800 | case INSN_CALL_DYNAMIC: | |
801 | if (!nofp && !has_valid_stack_frame(insn)) { | |
802 | WARN_FUNC("call without frame pointer save/setup", | |
803 | sec, insn->offset); | |
804 | warnings++; | |
805 | } | |
806 | break; | |
807 | ||
808 | case INSN_JUMP_CONDITIONAL: | |
809 | case INSN_JUMP_UNCONDITIONAL: | |
810 | if (insn->jump_dest) { | |
811 | ret = validate_branch(file, insn->jump_dest, | |
812 | state); | |
813 | warnings += ret; | |
814 | } else if (has_modified_stack_frame(insn)) { | |
815 | WARN_FUNC("sibling call from callable instruction with changed frame pointer", | |
816 | sec, insn->offset); | |
817 | warnings++; | |
818 | } /* else it's a sibling call */ | |
819 | ||
820 | if (insn->type == INSN_JUMP_UNCONDITIONAL) | |
821 | return warnings; | |
822 | ||
823 | break; | |
824 | ||
825 | case INSN_JUMP_DYNAMIC: | |
826 | if (list_empty(&insn->alts) && | |
827 | has_modified_stack_frame(insn)) { | |
828 | WARN_FUNC("sibling call from callable instruction with changed frame pointer", | |
829 | sec, insn->offset); | |
830 | warnings++; | |
831 | } | |
832 | ||
833 | return warnings; | |
834 | ||
835 | case INSN_BUG: | |
836 | return warnings; | |
837 | ||
838 | default: | |
839 | break; | |
840 | } | |
841 | ||
842 | insn = list_next_entry(insn, list); | |
843 | ||
844 | if (&insn->list == &file->insns || insn->sec != sec) { | |
845 | WARN("%s: unexpected end of section", sec->name); | |
846 | warnings++; | |
847 | return warnings; | |
848 | } | |
849 | } | |
850 | ||
851 | return warnings; | |
852 | } | |
853 | ||
854 | static bool is_gcov_insn(struct instruction *insn) | |
855 | { | |
856 | struct rela *rela; | |
857 | struct section *sec; | |
858 | struct symbol *sym; | |
859 | unsigned long offset; | |
860 | ||
861 | rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); | |
862 | if (!rela) | |
863 | return false; | |
864 | ||
865 | if (rela->sym->type != STT_SECTION) | |
866 | return false; | |
867 | ||
868 | sec = rela->sym->sec; | |
869 | offset = rela->addend + insn->offset + insn->len - rela->offset; | |
870 | ||
871 | list_for_each_entry(sym, &sec->symbols, list) { | |
872 | if (sym->type != STT_OBJECT) | |
873 | continue; | |
874 | ||
875 | if (offset >= sym->offset && offset < sym->offset + sym->len) | |
876 | return (!memcmp(sym->name, "__gcov0.", 8)); | |
877 | } | |
878 | ||
879 | return false; | |
880 | } | |
881 | ||
882 | static bool is_kasan_insn(struct instruction *insn) | |
883 | { | |
884 | return (insn->type == INSN_CALL && | |
885 | !strcmp(insn->call_dest->name, "__asan_handle_no_return")); | |
886 | } | |
887 | ||
888 | static bool is_ubsan_insn(struct instruction *insn) | |
889 | { | |
890 | return (insn->type == INSN_CALL && | |
891 | !strcmp(insn->call_dest->name, | |
892 | "__ubsan_handle_builtin_unreachable")); | |
893 | } | |
894 | ||
895 | static bool ignore_unreachable_insn(struct instruction *insn, | |
896 | unsigned long func_end) | |
897 | { | |
898 | int i; | |
899 | ||
900 | if (insn->type == INSN_NOP) | |
901 | return true; | |
902 | ||
903 | if (is_gcov_insn(insn)) | |
904 | return true; | |
905 | ||
906 | /* | |
907 | * Check if this (or a subsequent) instruction is related to | |
908 | * CONFIG_UBSAN or CONFIG_KASAN. | |
909 | * | |
910 | * End the search at 5 instructions to avoid going into the weeds. | |
911 | */ | |
912 | for (i = 0; i < 5; i++) { | |
913 | ||
914 | if (is_kasan_insn(insn) || is_ubsan_insn(insn)) | |
915 | return true; | |
916 | ||
917 | if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) { | |
918 | insn = insn->jump_dest; | |
919 | continue; | |
920 | } | |
921 | ||
922 | if (insn->offset + insn->len >= func_end) | |
923 | break; | |
924 | insn = list_next_entry(insn, list); | |
925 | } | |
926 | ||
927 | return false; | |
928 | } | |
929 | ||
930 | static int validate_functions(struct objtool_file *file) | |
931 | { | |
932 | struct section *sec; | |
933 | struct symbol *func; | |
934 | struct instruction *insn; | |
935 | unsigned long func_end; | |
936 | int ret, warnings = 0; | |
937 | ||
938 | list_for_each_entry(sec, &file->elf->sections, list) { | |
939 | list_for_each_entry(func, &sec->symbols, list) { | |
940 | if (func->type != STT_FUNC) | |
941 | continue; | |
942 | ||
943 | insn = find_instruction(file, sec, func->offset); | |
944 | if (!insn) { | |
945 | WARN("%s(): can't find starting instruction", | |
946 | func->name); | |
947 | warnings++; | |
948 | continue; | |
949 | } | |
950 | ||
951 | ret = validate_branch(file, insn, 0); | |
952 | warnings += ret; | |
953 | } | |
954 | } | |
955 | ||
956 | list_for_each_entry(sec, &file->elf->sections, list) { | |
957 | list_for_each_entry(func, &sec->symbols, list) { | |
958 | if (func->type != STT_FUNC) | |
959 | continue; | |
960 | ||
961 | insn = find_instruction(file, sec, func->offset); | |
962 | if (!insn) | |
963 | continue; | |
964 | ||
965 | func_end = func->offset + func->len; | |
966 | ||
967 | list_for_each_entry_from(insn, &file->insns, list) { | |
968 | if (insn->sec != func->sec || | |
969 | insn->offset >= func_end) | |
970 | break; | |
971 | ||
972 | if (insn->visited) | |
973 | continue; | |
974 | ||
975 | if (!ignore_unreachable_insn(insn, func_end)) { | |
976 | WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset); | |
977 | warnings++; | |
978 | } | |
979 | ||
980 | insn->visited = true; | |
981 | } | |
982 | } | |
983 | } | |
984 | ||
985 | return warnings; | |
986 | } | |
987 | ||
988 | static int validate_uncallable_instructions(struct objtool_file *file) | |
989 | { | |
990 | struct instruction *insn; | |
991 | int warnings = 0; | |
992 | ||
993 | list_for_each_entry(insn, &file->insns, list) { | |
994 | if (!insn->visited && insn->type == INSN_RETURN) { | |
995 | WARN_FUNC("return instruction outside of a callable function", | |
996 | insn->sec, insn->offset); | |
997 | warnings++; | |
998 | } | |
999 | } | |
1000 | ||
1001 | return warnings; | |
1002 | } | |
1003 | ||
1004 | static void cleanup(struct objtool_file *file) | |
1005 | { | |
1006 | struct instruction *insn, *tmpinsn; | |
1007 | struct alternative *alt, *tmpalt; | |
1008 | ||
1009 | list_for_each_entry_safe(insn, tmpinsn, &file->insns, list) { | |
1010 | list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) { | |
1011 | list_del(&alt->list); | |
1012 | free(alt); | |
1013 | } | |
1014 | list_del(&insn->list); | |
1015 | free(insn); | |
1016 | } | |
1017 | elf_close(file->elf); | |
1018 | } | |
1019 | ||
1020 | const char * const check_usage[] = { | |
1021 | "objtool check [<options>] file.o", | |
1022 | NULL, | |
1023 | }; | |
1024 | ||
1025 | int cmd_check(int argc, const char **argv) | |
1026 | { | |
1027 | struct objtool_file file; | |
1028 | int ret, warnings = 0; | |
1029 | ||
1030 | const struct option options[] = { | |
1031 | OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"), | |
1032 | OPT_END(), | |
1033 | }; | |
1034 | ||
1035 | argc = parse_options(argc, argv, options, check_usage, 0); | |
1036 | ||
1037 | if (argc != 1) | |
1038 | usage_with_options(check_usage, options); | |
1039 | ||
1040 | objname = argv[0]; | |
1041 | ||
1042 | file.elf = elf_open(objname); | |
1043 | if (!file.elf) { | |
1044 | fprintf(stderr, "error reading elf file %s\n", objname); | |
1045 | return 1; | |
1046 | } | |
1047 | ||
1048 | INIT_LIST_HEAD(&file.insns); | |
1049 | ||
1050 | ret = decode_sections(&file); | |
1051 | if (ret < 0) | |
1052 | goto out; | |
1053 | warnings += ret; | |
1054 | ||
1055 | ret = validate_functions(&file); | |
1056 | if (ret < 0) | |
1057 | goto out; | |
1058 | warnings += ret; | |
1059 | ||
1060 | ret = validate_uncallable_instructions(&file); | |
1061 | if (ret < 0) | |
1062 | goto out; | |
1063 | warnings += ret; | |
1064 | ||
1065 | out: | |
1066 | cleanup(&file); | |
1067 | ||
1068 | /* ignore warnings for now until we get all the code cleaned up */ | |
1069 | if (ret || warnings) | |
1070 | return 0; | |
1071 | return 0; | |
1072 | } |