]> git.proxmox.com Git - mirror_ubuntu-jammy-kernel.git/blob - tools/objtool/check.c
projects / mirror_ubuntu-jammy-kernel.git / blob
? search:
summary | shortlog | log | commit | commitdiff | tree
blame | history | raw | HEAD
objtool: Fix noreturn detection for ignored functions
[mirror_ubuntu-jammy-kernel.git] / tools / objtool / check.c
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
4 */
5
6 #include <string.h>
7 #include <stdlib.h>
8
9 #include "builtin.h"
10 #include "cfi.h"
11 #include "arch.h"
12 #include "check.h"
13 #include "special.h"
14 #include "warn.h"
15 #include "arch_elf.h"
16
17 #include <linux/hashtable.h>
18 #include <linux/kernel.h>
19
20 #define FAKE_JUMP_OFFSET -1
21
22 #define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
23
24 struct alternative {
25 struct list_head list;
26 struct instruction *insn;
27 bool skip_orig;
28 };
29
30 const char *objname;
31 struct cfi_init_state initial_func_cfi;
32
33 struct instruction *find_insn(struct objtool_file *file,
34 struct section *sec, unsigned long offset)
35 {
36 struct instruction *insn;
37
38 hash_for_each_possible(file->insn_hash, insn, hash, sec_offset_hash(sec, offset)) {
39 if (insn->sec == sec && insn->offset == offset)
40 return insn;
41 }
42
43 return NULL;
44 }
45
46 static struct instruction *next_insn_same_sec(struct objtool_file *file,
47 struct instruction *insn)
48 {
49 struct instruction *next = list_next_entry(insn, list);
50
51 if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
52 return NULL;
53
54 return next;
55 }
56
57 static struct instruction *next_insn_same_func(struct objtool_file *file,
58 struct instruction *insn)
59 {
60 struct instruction *next = list_next_entry(insn, list);
61 struct symbol *func = insn->func;
62
63 if (!func)
64 return NULL;
65
66 if (&next->list != &file->insn_list && next->func == func)
67 return next;
68
69 /* Check if we're already in the subfunction: */
70 if (func == func->cfunc)
71 return NULL;
72
73 /* Move to the subfunction: */
74 return find_insn(file, func->cfunc->sec, func->cfunc->offset);
75 }
76
77 static struct instruction *prev_insn_same_sym(struct objtool_file *file,
78 struct instruction *insn)
79 {
80 struct instruction *prev = list_prev_entry(insn, list);
81
82 if (&prev->list != &file->insn_list && prev->func == insn->func)
83 return prev;
84
85 return NULL;
86 }
87
88 #define func_for_each_insn(file, func, insn) \
89 for (insn = find_insn(file, func->sec, func->offset); \
90 insn; \
91 insn = next_insn_same_func(file, insn))
92
93 #define sym_for_each_insn(file, sym, insn) \
94 for (insn = find_insn(file, sym->sec, sym->offset); \
95 insn && &insn->list != &file->insn_list && \
96 insn->sec == sym->sec && \
97 insn->offset < sym->offset + sym->len; \
98 insn = list_next_entry(insn, list))
99
100 #define sym_for_each_insn_continue_reverse(file, sym, insn) \
101 for (insn = list_prev_entry(insn, list); \
102 &insn->list != &file->insn_list && \
103 insn->sec == sym->sec && insn->offset >= sym->offset; \
104 insn = list_prev_entry(insn, list))
105
106 #define sec_for_each_insn_from(file, insn) \
107 for (; insn; insn = next_insn_same_sec(file, insn))
108
109 #define sec_for_each_insn_continue(file, insn) \
110 for (insn = next_insn_same_sec(file, insn); insn; \
111 insn = next_insn_same_sec(file, insn))
112
113 static bool is_static_jump(struct instruction *insn)
114 {
115 return insn->type == INSN_JUMP_CONDITIONAL ||
116 insn->type == INSN_JUMP_UNCONDITIONAL;
117 }
118
119 static bool is_sibling_call(struct instruction *insn)
120 {
121 /* An indirect jump is either a sibling call or a jump to a table. */
122 if (insn->type == INSN_JUMP_DYNAMIC)
123 return list_empty(&insn->alts);
124
125 if (!is_static_jump(insn))
126 return false;
127
128 /* add_jump_destinations() sets insn->call_dest for sibling calls. */
129 return !!insn->call_dest;
130 }
131
132 /*
133 * This checks to see if the given function is a "noreturn" function.
134 *
135 * For global functions which are outside the scope of this object file, we
136 * have to keep a manual list of them.
137 *
138 * For local functions, we have to detect them manually by simply looking for
139 * the lack of a return instruction.
140 */
141 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
142 int recursion)
143 {
144 int i;
145 struct instruction *insn;
146 bool empty = true;
147
148 /*
149 * Unfortunately these have to be hard coded because the noreturn
150 * attribute isn't provided in ELF data.
151 */
152 static const char * const global_noreturns[] = {
153 "__stack_chk_fail",
154 "panic",
155 "do_exit",
156 "do_task_dead",
157 "__module_put_and_exit",
158 "complete_and_exit",
159 "__reiserfs_panic",
160 "lbug_with_loc",
161 "fortify_panic",
162 "usercopy_abort",
163 "machine_real_restart",
164 "rewind_stack_do_exit",
165 "kunit_try_catch_throw",
166 };
167
168 if (!func)
169 return false;
170
171 if (func->bind == STB_WEAK)
172 return false;
173
174 if (func->bind == STB_GLOBAL)
175 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
176 if (!strcmp(func->name, global_noreturns[i]))
177 return true;
178
179 if (!func->len)
180 return false;
181
182 insn = find_insn(file, func->sec, func->offset);
183 if (!insn->func)
184 return false;
185
186 func_for_each_insn(file, func, insn) {
187 empty = false;
188
189 if (insn->type == INSN_RETURN)
190 return false;
191 }
192
193 if (empty)
194 return false;
195
196 /*
197 * A function can have a sibling call instead of a return. In that
198 * case, the function's dead-end status depends on whether the target
199 * of the sibling call returns.
200 */
201 func_for_each_insn(file, func, insn) {
202 if (is_sibling_call(insn)) {
203 struct instruction *dest = insn->jump_dest;
204
205 if (!dest)
206 /* sibling call to another file */
207 return false;
208
209 /* local sibling call */
210 if (recursion == 5) {
211 /*
212 * Infinite recursion: two functions have
213 * sibling calls to each other. This is a very
214 * rare case. It means they aren't dead ends.
215 */
216 return false;
217 }
218
219 return __dead_end_function(file, dest->func, recursion+1);
220 }
221 }
222
223 return true;
224 }
225
226 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
227 {
228 return __dead_end_function(file, func, 0);
229 }
230
231 static void init_cfi_state(struct cfi_state *cfi)
232 {
233 int i;
234
235 for (i = 0; i < CFI_NUM_REGS; i++) {
236 cfi->regs[i].base = CFI_UNDEFINED;
237 cfi->vals[i].base = CFI_UNDEFINED;
238 }
239 cfi->cfa.base = CFI_UNDEFINED;
240 cfi->drap_reg = CFI_UNDEFINED;
241 cfi->drap_offset = -1;
242 }
243
244 static void init_insn_state(struct insn_state *state, struct section *sec)
245 {
246 memset(state, 0, sizeof(*state));
247 init_cfi_state(&state->cfi);
248
249 /*
250 * We need the full vmlinux for noinstr validation, otherwise we can
251 * not correctly determine insn->call_dest->sec (external symbols do
252 * not have a section).
253 */
254 if (vmlinux && sec)
255 state->noinstr = sec->noinstr;
256 }
257
258 /*
259 * Call the arch-specific instruction decoder for all the instructions and add
260 * them to the global instruction list.
261 */
262 static int decode_instructions(struct objtool_file *file)
263 {
264 struct section *sec;
265 struct symbol *func;
266 unsigned long offset;
267 struct instruction *insn;
268 unsigned long nr_insns = 0;
269 int ret;
270
271 for_each_sec(file, sec) {
272
273 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
274 continue;
275
276 if (strcmp(sec->name, ".altinstr_replacement") &&
277 strcmp(sec->name, ".altinstr_aux") &&
278 strncmp(sec->name, ".discard.", 9))
279 sec->text = true;
280
281 if (!strcmp(sec->name, ".noinstr.text") ||
282 !strcmp(sec->name, ".entry.text"))
283 sec->noinstr = true;
284
285 for (offset = 0; offset < sec->len; offset += insn->len) {
286 insn = malloc(sizeof(*insn));
287 if (!insn) {
288 WARN("malloc failed");
289 return -1;
290 }
291 memset(insn, 0, sizeof(*insn));
292 INIT_LIST_HEAD(&insn->alts);
293 INIT_LIST_HEAD(&insn->stack_ops);
294 init_cfi_state(&insn->cfi);
295
296 insn->sec = sec;
297 insn->offset = offset;
298
299 ret = arch_decode_instruction(file->elf, sec, offset,
300 sec->len - offset,
301 &insn->len, &insn->type,
302 &insn->immediate,
303 &insn->stack_ops);
304 if (ret)
305 goto err;
306
307 hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
308 list_add_tail(&insn->list, &file->insn_list);
309 nr_insns++;
310 }
311
312 list_for_each_entry(func, &sec->symbol_list, list) {
313 if (func->type != STT_FUNC || func->alias != func)
314 continue;
315
316 if (!find_insn(file, sec, func->offset)) {
317 WARN("%s(): can't find starting instruction",
318 func->name);
319 return -1;
320 }
321
322 sym_for_each_insn(file, func, insn)
323 insn->func = func;
324 }
325 }
326
327 if (stats)
328 printf("nr_insns: %lu\n", nr_insns);
329
330 return 0;
331
332 err:
333 free(insn);
334 return ret;
335 }
336
337 static struct instruction *find_last_insn(struct objtool_file *file,
338 struct section *sec)
339 {
340 struct instruction *insn = NULL;
341 unsigned int offset;
342 unsigned int end = (sec->len > 10) ? sec->len - 10 : 0;
343
344 for (offset = sec->len - 1; offset >= end && !insn; offset--)
345 insn = find_insn(file, sec, offset);
346
347 return insn;
348 }
349
350 /*
351 * Mark "ud2" instructions and manually annotated dead ends.
352 */
353 static int add_dead_ends(struct objtool_file *file)
354 {
355 struct section *sec;
356 struct reloc *reloc;
357 struct instruction *insn;
358
359 /*
360 * By default, "ud2" is a dead end unless otherwise annotated, because
361 * GCC 7 inserts it for certain divide-by-zero cases.
362 */
363 for_each_insn(file, insn)
364 if (insn->type == INSN_BUG)
365 insn->dead_end = true;
366
367 /*
368 * Check for manually annotated dead ends.
369 */
370 sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
371 if (!sec)
372 goto reachable;
373
374 list_for_each_entry(reloc, &sec->reloc_list, list) {
375 if (reloc->sym->type != STT_SECTION) {
376 WARN("unexpected relocation symbol type in %s", sec->name);
377 return -1;
378 }
379 insn = find_insn(file, reloc->sym->sec, reloc->addend);
380 if (insn)
381 insn = list_prev_entry(insn, list);
382 else if (reloc->addend == reloc->sym->sec->len) {
383 insn = find_last_insn(file, reloc->sym->sec);
384 if (!insn) {
385 WARN("can't find unreachable insn at %s+0x%x",
386 reloc->sym->sec->name, reloc->addend);
387 return -1;
388 }
389 } else {
390 WARN("can't find unreachable insn at %s+0x%x",
391 reloc->sym->sec->name, reloc->addend);
392 return -1;
393 }
394
395 insn->dead_end = true;
396 }
397
398 reachable:
399 /*
400 * These manually annotated reachable checks are needed for GCC 4.4,
401 * where the Linux unreachable() macro isn't supported. In that case
402 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
403 * not a dead end.
404 */
405 sec = find_section_by_name(file->elf, ".rela.discard.reachable");
406 if (!sec)
407 return 0;
408
409 list_for_each_entry(reloc, &sec->reloc_list, list) {
410 if (reloc->sym->type != STT_SECTION) {
411 WARN("unexpected relocation symbol type in %s", sec->name);
412 return -1;
413 }
414 insn = find_insn(file, reloc->sym->sec, reloc->addend);
415 if (insn)
416 insn = list_prev_entry(insn, list);
417 else if (reloc->addend == reloc->sym->sec->len) {
418 insn = find_last_insn(file, reloc->sym->sec);
419 if (!insn) {
420 WARN("can't find reachable insn at %s+0x%x",
421 reloc->sym->sec->name, reloc->addend);
422 return -1;
423 }
424 } else {
425 WARN("can't find reachable insn at %s+0x%x",
426 reloc->sym->sec->name, reloc->addend);
427 return -1;
428 }
429
430 insn->dead_end = false;
431 }
432
433 return 0;
434 }
435
436 /*
437 * Warnings shouldn't be reported for ignored functions.
438 */
439 static void add_ignores(struct objtool_file *file)
440 {
441 struct instruction *insn;
442 struct section *sec;
443 struct symbol *func;
444 struct reloc *reloc;
445
446 sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
447 if (!sec)
448 return;
449
450 list_for_each_entry(reloc, &sec->reloc_list, list) {
451 switch (reloc->sym->type) {
452 case STT_FUNC:
453 func = reloc->sym;
454 break;
455
456 case STT_SECTION:
457 func = find_func_by_offset(reloc->sym->sec, reloc->addend);
458 if (!func)
459 continue;
460 break;
461
462 default:
463 WARN("unexpected relocation symbol type in %s: %d", sec->name, reloc->sym->type);
464 continue;
465 }
466
467 func_for_each_insn(file, func, insn)
468 insn->ignore = true;
469 }
470 }
471
472 /*
473 * This is a whitelist of functions that is allowed to be called with AC set.
474 * The list is meant to be minimal and only contains compiler instrumentation
475 * ABI and a few functions used to implement *_{to,from}_user() functions.
476 *
477 * These functions must not directly change AC, but may PUSHF/POPF.
478 */
479 static const char *uaccess_safe_builtin[] = {
480 /* KASAN */
481 "kasan_report",
482 "check_memory_region",
483 /* KASAN out-of-line */
484 "__asan_loadN_noabort",
485 "__asan_load1_noabort",
486 "__asan_load2_noabort",
487 "__asan_load4_noabort",
488 "__asan_load8_noabort",
489 "__asan_load16_noabort",
490 "__asan_storeN_noabort",
491 "__asan_store1_noabort",
492 "__asan_store2_noabort",
493 "__asan_store4_noabort",
494 "__asan_store8_noabort",
495 "__asan_store16_noabort",
496 /* KASAN in-line */
497 "__asan_report_load_n_noabort",
498 "__asan_report_load1_noabort",
499 "__asan_report_load2_noabort",
500 "__asan_report_load4_noabort",
501 "__asan_report_load8_noabort",
502 "__asan_report_load16_noabort",
503 "__asan_report_store_n_noabort",
504 "__asan_report_store1_noabort",
505 "__asan_report_store2_noabort",
506 "__asan_report_store4_noabort",
507 "__asan_report_store8_noabort",
508 "__asan_report_store16_noabort",
509 /* KCSAN */
510 "__kcsan_check_access",
511 "kcsan_found_watchpoint",
512 "kcsan_setup_watchpoint",
513 "kcsan_check_scoped_accesses",
514 "kcsan_disable_current",
515 "kcsan_enable_current_nowarn",
516 /* KCSAN/TSAN */
517 "__tsan_func_entry",
518 "__tsan_func_exit",
519 "__tsan_read_range",
520 "__tsan_write_range",
521 "__tsan_read1",
522 "__tsan_read2",
523 "__tsan_read4",
524 "__tsan_read8",
525 "__tsan_read16",
526 "__tsan_write1",
527 "__tsan_write2",
528 "__tsan_write4",
529 "__tsan_write8",
530 "__tsan_write16",
531 /* KCOV */
532 "write_comp_data",
533 "check_kcov_mode",
534 "__sanitizer_cov_trace_pc",
535 "__sanitizer_cov_trace_const_cmp1",
536 "__sanitizer_cov_trace_const_cmp2",
537 "__sanitizer_cov_trace_const_cmp4",
538 "__sanitizer_cov_trace_const_cmp8",
539 "__sanitizer_cov_trace_cmp1",
540 "__sanitizer_cov_trace_cmp2",
541 "__sanitizer_cov_trace_cmp4",
542 "__sanitizer_cov_trace_cmp8",
543 "__sanitizer_cov_trace_switch",
544 /* UBSAN */
545 "ubsan_type_mismatch_common",
546 "__ubsan_handle_type_mismatch",
547 "__ubsan_handle_type_mismatch_v1",
548 "__ubsan_handle_shift_out_of_bounds",
549 /* misc */
550 "csum_partial_copy_generic",
551 "__memcpy_mcsafe",
552 "mcsafe_handle_tail",
553 "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
554 NULL
555 };
556
557 static void add_uaccess_safe(struct objtool_file *file)
558 {
559 struct symbol *func;
560 const char **name;
561
562 if (!uaccess)
563 return;
564
565 for (name = uaccess_safe_builtin; *name; name++) {
566 func = find_symbol_by_name(file->elf, *name);
567 if (!func)
568 continue;
569
570 func->uaccess_safe = true;
571 }
572 }
573
574 /*
575 * FIXME: For now, just ignore any alternatives which add retpolines. This is
576 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
577 * But it at least allows objtool to understand the control flow *around* the
578 * retpoline.
579 */
580 static int add_ignore_alternatives(struct objtool_file *file)
581 {
582 struct section *sec;
583 struct reloc *reloc;
584 struct instruction *insn;
585
586 sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
587 if (!sec)
588 return 0;
589
590 list_for_each_entry(reloc, &sec->reloc_list, list) {
591 if (reloc->sym->type != STT_SECTION) {
592 WARN("unexpected relocation symbol type in %s", sec->name);
593 return -1;
594 }
595
596 insn = find_insn(file, reloc->sym->sec, reloc->addend);
597 if (!insn) {
598 WARN("bad .discard.ignore_alts entry");
599 return -1;
600 }
601
602 insn->ignore_alts = true;
603 }
604
605 return 0;
606 }
607
608 /*
609 * Find the destination instructions for all jumps.
610 */
611 static int add_jump_destinations(struct objtool_file *file)
612 {
613 struct instruction *insn;
614 struct reloc *reloc;
615 struct section *dest_sec;
616 unsigned long dest_off;
617
618 for_each_insn(file, insn) {
619 if (!is_static_jump(insn))
620 continue;
621
622 if (insn->offset == FAKE_JUMP_OFFSET)
623 continue;
624
625 reloc = find_reloc_by_dest_range(file->elf, insn->sec,
626 insn->offset, insn->len);
627 if (!reloc) {
628 dest_sec = insn->sec;
629 dest_off = arch_jump_destination(insn);
630 } else if (reloc->sym->type == STT_SECTION) {
631 dest_sec = reloc->sym->sec;
632 dest_off = arch_dest_reloc_offset(reloc->addend);
633 } else if (reloc->sym->sec->idx) {
634 dest_sec = reloc->sym->sec;
635 dest_off = reloc->sym->sym.st_value +
636 arch_dest_reloc_offset(reloc->addend);
637 } else if (strstr(reloc->sym->name, "_indirect_thunk_")) {
638 /*
639 * Retpoline jumps are really dynamic jumps in
640 * disguise, so convert them accordingly.
641 */
642 if (insn->type == INSN_JUMP_UNCONDITIONAL)
643 insn->type = INSN_JUMP_DYNAMIC;
644 else
645 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
646
647 insn->retpoline_safe = true;
648 continue;
649 } else {
650 /* external sibling call */
651 insn->call_dest = reloc->sym;
652 continue;
653 }
654
655 insn->jump_dest = find_insn(file, dest_sec, dest_off);
656 if (!insn->jump_dest) {
657
658 /*
659 * This is a special case where an alt instruction
660 * jumps past the end of the section. These are
661 * handled later in handle_group_alt().
662 */
663 if (!strcmp(insn->sec->name, ".altinstr_replacement"))
664 continue;
665
666 WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
667 insn->sec, insn->offset, dest_sec->name,
668 dest_off);
669 return -1;
670 }
671
672 /*
673 * Cross-function jump.
674 */
675 if (insn->func && insn->jump_dest->func &&
676 insn->func != insn->jump_dest->func) {
677
678 /*
679 * For GCC 8+, create parent/child links for any cold
680 * subfunctions. This is _mostly_ redundant with a
681 * similar initialization in read_symbols().
682 *
683 * If a function has aliases, we want the *first* such
684 * function in the symbol table to be the subfunction's
685 * parent. In that case we overwrite the
686 * initialization done in read_symbols().
687 *
688 * However this code can't completely replace the
689 * read_symbols() code because this doesn't detect the
690 * case where the parent function's only reference to a
691 * subfunction is through a jump table.
692 */
693 if (!strstr(insn->func->name, ".cold.") &&
694 strstr(insn->jump_dest->func->name, ".cold.")) {
695 insn->func->cfunc = insn->jump_dest->func;
696 insn->jump_dest->func->pfunc = insn->func;
697
698 } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
699 insn->jump_dest->offset == insn->jump_dest->func->offset) {
700
701 /* internal sibling call */
702 insn->call_dest = insn->jump_dest->func;
703 }
704 }
705 }
706
707 return 0;
708 }
709
710 static void remove_insn_ops(struct instruction *insn)
711 {
712 struct stack_op *op, *tmp;
713
714 list_for_each_entry_safe(op, tmp, &insn->stack_ops, list) {
715 list_del(&op->list);
716 free(op);
717 }
718 }
719
720 /*
721 * Find the destination instructions for all calls.
722 */
723 static int add_call_destinations(struct objtool_file *file)
724 {
725 struct instruction *insn;
726 unsigned long dest_off;
727 struct reloc *reloc;
728
729 for_each_insn(file, insn) {
730 if (insn->type != INSN_CALL)
731 continue;
732
733 reloc = find_reloc_by_dest_range(file->elf, insn->sec,
734 insn->offset, insn->len);
735 if (!reloc) {
736 dest_off = arch_jump_destination(insn);
737 insn->call_dest = find_func_by_offset(insn->sec, dest_off);
738 if (!insn->call_dest)
739 insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
740
741 if (insn->ignore)
742 continue;
743
744 if (!insn->call_dest) {
745 WARN_FUNC("unannotated intra-function call", insn->sec, insn->offset);
746 return -1;
747 }
748
749 if (insn->func && insn->call_dest->type != STT_FUNC) {
750 WARN_FUNC("unsupported call to non-function",
751 insn->sec, insn->offset);
752 return -1;
753 }
754
755 } else if (reloc->sym->type == STT_SECTION) {
756 dest_off = arch_dest_reloc_offset(reloc->addend);
757 insn->call_dest = find_func_by_offset(reloc->sym->sec,
758 dest_off);
759 if (!insn->call_dest) {
760 WARN_FUNC("can't find call dest symbol at %s+0x%lx",
761 insn->sec, insn->offset,
762 reloc->sym->sec->name,
763 dest_off);
764 return -1;
765 }
766 } else
767 insn->call_dest = reloc->sym;
768
769 /*
770 * Many compilers cannot disable KCOV with a function attribute
771 * so they need a little help, NOP out any KCOV calls from noinstr
772 * text.
773 */
774 if (insn->sec->noinstr &&
775 !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
776 if (reloc) {
777 reloc->type = R_NONE;
778 elf_write_reloc(file->elf, reloc);
779 }
780
781 elf_write_insn(file->elf, insn->sec,
782 insn->offset, insn->len,
783 arch_nop_insn(insn->len));
784 insn->type = INSN_NOP;
785 }
786
787 /*
788 * Whatever stack impact regular CALLs have, should be undone
789 * by the RETURN of the called function.
790 *
791 * Annotated intra-function calls retain the stack_ops but
792 * are converted to JUMP, see read_intra_function_calls().
793 */
794 remove_insn_ops(insn);
795 }
796
797 return 0;
798 }
799
800 /*
801 * The .alternatives section requires some extra special care, over and above
802 * what other special sections require:
803 *
804 * 1. Because alternatives are patched in-place, we need to insert a fake jump
805 * instruction at the end so that validate_branch() skips all the original
806 * replaced instructions when validating the new instruction path.
807 *
808 * 2. An added wrinkle is that the new instruction length might be zero. In
809 * that case the old instructions are replaced with noops. We simulate that
810 * by creating a fake jump as the only new instruction.
811 *
812 * 3. In some cases, the alternative section includes an instruction which
813 * conditionally jumps to the _end_ of the entry. We have to modify these
814 * jumps' destinations to point back to .text rather than the end of the
815 * entry in .altinstr_replacement.
816 */
817 static int handle_group_alt(struct objtool_file *file,
818 struct special_alt *special_alt,
819 struct instruction *orig_insn,
820 struct instruction **new_insn)
821 {
822 static unsigned int alt_group_next_index = 1;
823 struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
824 unsigned int alt_group = alt_group_next_index++;
825 unsigned long dest_off;
826
827 last_orig_insn = NULL;
828 insn = orig_insn;
829 sec_for_each_insn_from(file, insn) {
830 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
831 break;
832
833 insn->alt_group = alt_group;
834 last_orig_insn = insn;
835 }
836
837 if (next_insn_same_sec(file, last_orig_insn)) {
838 fake_jump = malloc(sizeof(*fake_jump));
839 if (!fake_jump) {
840 WARN("malloc failed");
841 return -1;
842 }
843 memset(fake_jump, 0, sizeof(*fake_jump));
844 INIT_LIST_HEAD(&fake_jump->alts);
845 INIT_LIST_HEAD(&fake_jump->stack_ops);
846 init_cfi_state(&fake_jump->cfi);
847
848 fake_jump->sec = special_alt->new_sec;
849 fake_jump->offset = FAKE_JUMP_OFFSET;
850 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
851 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
852 fake_jump->func = orig_insn->func;
853 }
854
855 if (!special_alt->new_len) {
856 if (!fake_jump) {
857 WARN("%s: empty alternative at end of section",
858 special_alt->orig_sec->name);
859 return -1;
860 }
861
862 *new_insn = fake_jump;
863 return 0;
864 }
865
866 last_new_insn = NULL;
867 alt_group = alt_group_next_index++;
868 insn = *new_insn;
869 sec_for_each_insn_from(file, insn) {
870 if (insn->offset >= special_alt->new_off + special_alt->new_len)
871 break;
872
873 last_new_insn = insn;
874
875 insn->ignore = orig_insn->ignore_alts;
876 insn->func = orig_insn->func;
877 insn->alt_group = alt_group;
878
879 /*
880 * Since alternative replacement code is copy/pasted by the
881 * kernel after applying relocations, generally such code can't
882 * have relative-address relocation references to outside the
883 * .altinstr_replacement section, unless the arch's
884 * alternatives code can adjust the relative offsets
885 * accordingly.
886 *
887 * The x86 alternatives code adjusts the offsets only when it
888 * encounters a branch instruction at the very beginning of the
889 * replacement group.
890 */
891 if ((insn->offset != special_alt->new_off ||
892 (insn->type != INSN_CALL && !is_static_jump(insn))) &&
893 find_reloc_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
894
895 WARN_FUNC("unsupported relocation in alternatives section",
896 insn->sec, insn->offset);
897 return -1;
898 }
899
900 if (!is_static_jump(insn))
901 continue;
902
903 if (!insn->immediate)
904 continue;
905
906 dest_off = arch_jump_destination(insn);
907 if (dest_off == special_alt->new_off + special_alt->new_len) {
908 if (!fake_jump) {
909 WARN("%s: alternative jump to end of section",
910 special_alt->orig_sec->name);
911 return -1;
912 }
913 insn->jump_dest = fake_jump;
914 }
915
916 if (!insn->jump_dest) {
917 WARN_FUNC("can't find alternative jump destination",
918 insn->sec, insn->offset);
919 return -1;
920 }
921 }
922
923 if (!last_new_insn) {
924 WARN_FUNC("can't find last new alternative instruction",
925 special_alt->new_sec, special_alt->new_off);
926 return -1;
927 }
928
929 if (fake_jump)
930 list_add(&fake_jump->list, &last_new_insn->list);
931
932 return 0;
933 }
934
935 /*
936 * A jump table entry can either convert a nop to a jump or a jump to a nop.
937 * If the original instruction is a jump, make the alt entry an effective nop
938 * by just skipping the original instruction.
939 */
940 static int handle_jump_alt(struct objtool_file *file,
941 struct special_alt *special_alt,
942 struct instruction *orig_insn,
943 struct instruction **new_insn)
944 {
945 if (orig_insn->type == INSN_NOP)
946 return 0;
947
948 if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
949 WARN_FUNC("unsupported instruction at jump label",
950 orig_insn->sec, orig_insn->offset);
951 return -1;
952 }
953
954 *new_insn = list_next_entry(orig_insn, list);
955 return 0;
956 }
957
958 /*
959 * Read all the special sections which have alternate instructions which can be
960 * patched in or redirected to at runtime. Each instruction having alternate
961 * instruction(s) has them added to its insn->alts list, which will be
962 * traversed in validate_branch().
963 */
964 static int add_special_section_alts(struct objtool_file *file)
965 {
966 struct list_head special_alts;
967 struct instruction *orig_insn, *new_insn;
968 struct special_alt *special_alt, *tmp;
969 struct alternative *alt;
970 int ret;
971
972 ret = special_get_alts(file->elf, &special_alts);
973 if (ret)
974 return ret;
975
976 list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
977
978 orig_insn = find_insn(file, special_alt->orig_sec,
979 special_alt->orig_off);
980 if (!orig_insn) {
981 WARN_FUNC("special: can't find orig instruction",
982 special_alt->orig_sec, special_alt->orig_off);
983 ret = -1;
984 goto out;
985 }
986
987 new_insn = NULL;
988 if (!special_alt->group || special_alt->new_len) {
989 new_insn = find_insn(file, special_alt->new_sec,
990 special_alt->new_off);
991 if (!new_insn) {
992 WARN_FUNC("special: can't find new instruction",
993 special_alt->new_sec,
994 special_alt->new_off);
995 ret = -1;
996 goto out;
997 }
998 }
999
1000 if (special_alt->group) {
1001 if (!special_alt->orig_len) {
1002 WARN_FUNC("empty alternative entry",
1003 orig_insn->sec, orig_insn->offset);
1004 continue;
1005 }
1006
1007 ret = handle_group_alt(file, special_alt, orig_insn,
1008 &new_insn);
1009 if (ret)
1010 goto out;
1011 } else if (special_alt->jump_or_nop) {
1012 ret = handle_jump_alt(file, special_alt, orig_insn,
1013 &new_insn);
1014 if (ret)
1015 goto out;
1016 }
1017
1018 alt = malloc(sizeof(*alt));
1019 if (!alt) {
1020 WARN("malloc failed");
1021 ret = -1;
1022 goto out;
1023 }
1024
1025 alt->insn = new_insn;
1026 alt->skip_orig = special_alt->skip_orig;
1027 orig_insn->ignore_alts |= special_alt->skip_alt;
1028 list_add_tail(&alt->list, &orig_insn->alts);
1029
1030 list_del(&special_alt->list);
1031 free(special_alt);
1032 }
1033
1034 out:
1035 return ret;
1036 }
1037
1038 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
1039 struct reloc *table)
1040 {
1041 struct reloc *reloc = table;
1042 struct instruction *dest_insn;
1043 struct alternative *alt;
1044 struct symbol *pfunc = insn->func->pfunc;
1045 unsigned int prev_offset = 0;
1046
1047 /*
1048 * Each @reloc is a switch table relocation which points to the target
1049 * instruction.
1050 */
1051 list_for_each_entry_from(reloc, &table->sec->reloc_list, list) {
1052
1053 /* Check for the end of the table: */
1054 if (reloc != table && reloc->jump_table_start)
1055 break;
1056
1057 /* Make sure the table entries are consecutive: */
1058 if (prev_offset && reloc->offset != prev_offset + 8)
1059 break;
1060
1061 /* Detect function pointers from contiguous objects: */
1062 if (reloc->sym->sec == pfunc->sec &&
1063 reloc->addend == pfunc->offset)
1064 break;
1065
1066 dest_insn = find_insn(file, reloc->sym->sec, reloc->addend);
1067 if (!dest_insn)
1068 break;
1069
1070 /* Make sure the destination is in the same function: */
1071 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
1072 break;
1073
1074 alt = malloc(sizeof(*alt));
1075 if (!alt) {
1076 WARN("malloc failed");
1077 return -1;
1078 }
1079
1080 alt->insn = dest_insn;
1081 list_add_tail(&alt->list, &insn->alts);
1082 prev_offset = reloc->offset;
1083 }
1084
1085 if (!prev_offset) {
1086 WARN_FUNC("can't find switch jump table",
1087 insn->sec, insn->offset);
1088 return -1;
1089 }
1090
1091 return 0;
1092 }
1093
1094 /*
1095 * find_jump_table() - Given a dynamic jump, find the switch jump table in
1096 * .rodata associated with it.
1097 *
1098 * There are 3 basic patterns:
1099 *
1100 * 1. jmpq *[rodata addr](,%reg,8)
1101 *
1102 * This is the most common case by far. It jumps to an address in a simple
1103 * jump table which is stored in .rodata.
1104 *
1105 * 2. jmpq *[rodata addr](%rip)
1106 *
1107 * This is caused by a rare GCC quirk, currently only seen in three driver
1108 * functions in the kernel, only with certain obscure non-distro configs.
1109 *
1110 * As part of an optimization, GCC makes a copy of an existing switch jump
1111 * table, modifies it, and then hard-codes the jump (albeit with an indirect
1112 * jump) to use a single entry in the table. The rest of the jump table and
1113 * some of its jump targets remain as dead code.
1114 *
1115 * In such a case we can just crudely ignore all unreachable instruction
1116 * warnings for the entire object file. Ideally we would just ignore them
1117 * for the function, but that would require redesigning the code quite a
1118 * bit. And honestly that's just not worth doing: unreachable instruction
1119 * warnings are of questionable value anyway, and this is such a rare issue.
1120 *
1121 * 3. mov [rodata addr],%reg1
1122 * ... some instructions ...
1123 * jmpq *(%reg1,%reg2,8)
1124 *
1125 * This is a fairly uncommon pattern which is new for GCC 6. As of this
1126 * writing, there are 11 occurrences of it in the allmodconfig kernel.
1127 *
1128 * As of GCC 7 there are quite a few more of these and the 'in between' code
1129 * is significant. Esp. with KASAN enabled some of the code between the mov
1130 * and jmpq uses .rodata itself, which can confuse things.
1131 *
1132 * TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1133 * ensure the same register is used in the mov and jump instructions.
1134 *
1135 * NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1136 */
1137 static struct reloc *find_jump_table(struct objtool_file *file,
1138 struct symbol *func,
1139 struct instruction *insn)
1140 {
1141 struct reloc *text_reloc, *table_reloc;
1142 struct instruction *dest_insn, *orig_insn = insn;
1143 struct section *table_sec;
1144 unsigned long table_offset;
1145
1146 /*
1147 * Backward search using the @first_jump_src links, these help avoid
1148 * much of the 'in between' code. Which avoids us getting confused by
1149 * it.
1150 */
1151 for (;
1152 insn && insn->func && insn->func->pfunc == func;
1153 insn = insn->first_jump_src ?: prev_insn_same_sym(file, insn)) {
1154
1155 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1156 break;
1157
1158 /* allow small jumps within the range */
1159 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1160 insn->jump_dest &&
1161 (insn->jump_dest->offset <= insn->offset ||
1162 insn->jump_dest->offset > orig_insn->offset))
1163 break;
1164
1165 /* look for a relocation which references .rodata */
1166 text_reloc = find_reloc_by_dest_range(file->elf, insn->sec,
1167 insn->offset, insn->len);
1168 if (!text_reloc || text_reloc->sym->type != STT_SECTION ||
1169 !text_reloc->sym->sec->rodata)
1170 continue;
1171
1172 table_offset = text_reloc->addend;
1173 table_sec = text_reloc->sym->sec;
1174
1175 if (text_reloc->type == R_X86_64_PC32)
1176 table_offset += 4;
1177
1178 /*
1179 * Make sure the .rodata address isn't associated with a
1180 * symbol. GCC jump tables are anonymous data.
1181 *
1182 * Also support C jump tables which are in the same format as
1183 * switch jump tables. For objtool to recognize them, they
1184 * need to be placed in the C_JUMP_TABLE_SECTION section. They
1185 * have symbols associated with them.
1186 */
1187 if (find_symbol_containing(table_sec, table_offset) &&
1188 strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1189 continue;
1190
1191 /*
1192 * Each table entry has a reloc associated with it. The reloc
1193 * should reference text in the same function as the original
1194 * instruction.
1195 */
1196 table_reloc = find_reloc_by_dest(file->elf, table_sec, table_offset);
1197 if (!table_reloc)
1198 continue;
1199 dest_insn = find_insn(file, table_reloc->sym->sec, table_reloc->addend);
1200 if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1201 continue;
1202
1203 /*
1204 * Use of RIP-relative switch jumps is quite rare, and
1205 * indicates a rare GCC quirk/bug which can leave dead code
1206 * behind.
1207 */
1208 if (text_reloc->type == R_X86_64_PC32)
1209 file->ignore_unreachables = true;
1210
1211 return table_reloc;
1212 }
1213
1214 return NULL;
1215 }
1216
1217 /*
1218 * First pass: Mark the head of each jump table so that in the next pass,
1219 * we know when a given jump table ends and the next one starts.
1220 */
1221 static void mark_func_jump_tables(struct objtool_file *file,
1222 struct symbol *func)
1223 {
1224 struct instruction *insn, *last = NULL;
1225 struct reloc *reloc;
1226
1227 func_for_each_insn(file, func, insn) {
1228 if (!last)
1229 last = insn;
1230
1231 /*
1232 * Store back-pointers for unconditional forward jumps such
1233 * that find_jump_table() can back-track using those and
1234 * avoid some potentially confusing code.
1235 */
1236 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1237 insn->offset > last->offset &&
1238 insn->jump_dest->offset > insn->offset &&
1239 !insn->jump_dest->first_jump_src) {
1240
1241 insn->jump_dest->first_jump_src = insn;
1242 last = insn->jump_dest;
1243 }
1244
1245 if (insn->type != INSN_JUMP_DYNAMIC)
1246 continue;
1247
1248 reloc = find_jump_table(file, func, insn);
1249 if (reloc) {
1250 reloc->jump_table_start = true;
1251 insn->jump_table = reloc;
1252 }
1253 }
1254 }
1255
1256 static int add_func_jump_tables(struct objtool_file *file,
1257 struct symbol *func)
1258 {
1259 struct instruction *insn;
1260 int ret;
1261
1262 func_for_each_insn(file, func, insn) {
1263 if (!insn->jump_table)
1264 continue;
1265
1266 ret = add_jump_table(file, insn, insn->jump_table);
1267 if (ret)
1268 return ret;
1269 }
1270
1271 return 0;
1272 }
1273
1274 /*
1275 * For some switch statements, gcc generates a jump table in the .rodata
1276 * section which contains a list of addresses within the function to jump to.
1277 * This finds these jump tables and adds them to the insn->alts lists.
1278 */
1279 static int add_jump_table_alts(struct objtool_file *file)
1280 {
1281 struct section *sec;
1282 struct symbol *func;
1283 int ret;
1284
1285 if (!file->rodata)
1286 return 0;
1287
1288 for_each_sec(file, sec) {
1289 list_for_each_entry(func, &sec->symbol_list, list) {
1290 if (func->type != STT_FUNC)
1291 continue;
1292
1293 mark_func_jump_tables(file, func);
1294 ret = add_func_jump_tables(file, func);
1295 if (ret)
1296 return ret;
1297 }
1298 }
1299
1300 return 0;
1301 }
1302
1303 static int read_unwind_hints(struct objtool_file *file)
1304 {
1305 struct section *sec, *relocsec;
1306 struct reloc *reloc;
1307 struct unwind_hint *hint;
1308 struct instruction *insn;
1309 struct cfi_reg *cfa;
1310 int i;
1311
1312 sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1313 if (!sec)
1314 return 0;
1315
1316 relocsec = sec->reloc;
1317 if (!relocsec) {
1318 WARN("missing .rela.discard.unwind_hints section");
1319 return -1;
1320 }
1321
1322 if (sec->len % sizeof(struct unwind_hint)) {
1323 WARN("struct unwind_hint size mismatch");
1324 return -1;
1325 }
1326
1327 file->hints = true;
1328
1329 for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1330 hint = (struct unwind_hint *)sec->data->d_buf + i;
1331
1332 reloc = find_reloc_by_dest(file->elf, sec, i * sizeof(*hint));
1333 if (!reloc) {
1334 WARN("can't find reloc for unwind_hints[%d]", i);
1335 return -1;
1336 }
1337
1338 insn = find_insn(file, reloc->sym->sec, reloc->addend);
1339 if (!insn) {
1340 WARN("can't find insn for unwind_hints[%d]", i);
1341 return -1;
1342 }
1343
1344 cfa = &insn->cfi.cfa;
1345
1346 if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
1347 insn->ret_offset = hint->sp_offset;
1348 continue;
1349 }
1350
1351 insn->hint = true;
1352
1353 switch (hint->sp_reg) {
1354 case ORC_REG_UNDEFINED:
1355 cfa->base = CFI_UNDEFINED;
1356 break;
1357 case ORC_REG_SP:
1358 cfa->base = CFI_SP;
1359 break;
1360 case ORC_REG_BP:
1361 cfa->base = CFI_BP;
1362 break;
1363 case ORC_REG_SP_INDIRECT:
1364 cfa->base = CFI_SP_INDIRECT;
1365 break;
1366 case ORC_REG_R10:
1367 cfa->base = CFI_R10;
1368 break;
1369 case ORC_REG_R13:
1370 cfa->base = CFI_R13;
1371 break;
1372 case ORC_REG_DI:
1373 cfa->base = CFI_DI;
1374 break;
1375 case ORC_REG_DX:
1376 cfa->base = CFI_DX;
1377 break;
1378 default:
1379 WARN_FUNC("unsupported unwind_hint sp base reg %d",
1380 insn->sec, insn->offset, hint->sp_reg);
1381 return -1;
1382 }
1383
1384 cfa->offset = hint->sp_offset;
1385 insn->cfi.type = hint->type;
1386 insn->cfi.end = hint->end;
1387 }
1388
1389 return 0;
1390 }
1391
1392 static int read_retpoline_hints(struct objtool_file *file)
1393 {
1394 struct section *sec;
1395 struct instruction *insn;
1396 struct reloc *reloc;
1397
1398 sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1399 if (!sec)
1400 return 0;
1401
1402 list_for_each_entry(reloc, &sec->reloc_list, list) {
1403 if (reloc->sym->type != STT_SECTION) {
1404 WARN("unexpected relocation symbol type in %s", sec->name);
1405 return -1;
1406 }
1407
1408 insn = find_insn(file, reloc->sym->sec, reloc->addend);
1409 if (!insn) {
1410 WARN("bad .discard.retpoline_safe entry");
1411 return -1;
1412 }
1413
1414 if (insn->type != INSN_JUMP_DYNAMIC &&
1415 insn->type != INSN_CALL_DYNAMIC) {
1416 WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1417 insn->sec, insn->offset);
1418 return -1;
1419 }
1420
1421 insn->retpoline_safe = true;
1422 }
1423
1424 return 0;
1425 }
1426
1427 static int read_instr_hints(struct objtool_file *file)
1428 {
1429 struct section *sec;
1430 struct instruction *insn;
1431 struct reloc *reloc;
1432
1433 sec = find_section_by_name(file->elf, ".rela.discard.instr_end");
1434 if (!sec)
1435 return 0;
1436
1437 list_for_each_entry(reloc, &sec->reloc_list, list) {
1438 if (reloc->sym->type != STT_SECTION) {
1439 WARN("unexpected relocation symbol type in %s", sec->name);
1440 return -1;
1441 }
1442
1443 insn = find_insn(file, reloc->sym->sec, reloc->addend);
1444 if (!insn) {
1445 WARN("bad .discard.instr_end entry");
1446 return -1;
1447 }
1448
1449 insn->instr--;
1450 }
1451
1452 sec = find_section_by_name(file->elf, ".rela.discard.instr_begin");
1453 if (!sec)
1454 return 0;
1455
1456 list_for_each_entry(reloc, &sec->reloc_list, list) {
1457 if (reloc->sym->type != STT_SECTION) {
1458 WARN("unexpected relocation symbol type in %s", sec->name);
1459 return -1;
1460 }
1461
1462 insn = find_insn(file, reloc->sym->sec, reloc->addend);
1463 if (!insn) {
1464 WARN("bad .discard.instr_begin entry");
1465 return -1;
1466 }
1467
1468 insn->instr++;
1469 }
1470
1471 return 0;
1472 }
1473
1474 static int read_intra_function_calls(struct objtool_file *file)
1475 {
1476 struct instruction *insn;
1477 struct section *sec;
1478 struct reloc *reloc;
1479
1480 sec = find_section_by_name(file->elf, ".rela.discard.intra_function_calls");
1481 if (!sec)
1482 return 0;
1483
1484 list_for_each_entry(reloc, &sec->reloc_list, list) {
1485 unsigned long dest_off;
1486
1487 if (reloc->sym->type != STT_SECTION) {
1488 WARN("unexpected relocation symbol type in %s",
1489 sec->name);
1490 return -1;
1491 }
1492
1493 insn = find_insn(file, reloc->sym->sec, reloc->addend);
1494 if (!insn) {
1495 WARN("bad .discard.intra_function_call entry");
1496 return -1;
1497 }
1498
1499 if (insn->type != INSN_CALL) {
1500 WARN_FUNC("intra_function_call not a direct call",
1501 insn->sec, insn->offset);
1502 return -1;
1503 }
1504
1505 /*
1506 * Treat intra-function CALLs as JMPs, but with a stack_op.
1507 * See add_call_destinations(), which strips stack_ops from
1508 * normal CALLs.
1509 */
1510 insn->type = INSN_JUMP_UNCONDITIONAL;
1511
1512 dest_off = insn->offset + insn->len + insn->immediate;
1513 insn->jump_dest = find_insn(file, insn->sec, dest_off);
1514 if (!insn->jump_dest) {
1515 WARN_FUNC("can't find call dest at %s+0x%lx",
1516 insn->sec, insn->offset,
1517 insn->sec->name, dest_off);
1518 return -1;
1519 }
1520 }
1521
1522 return 0;
1523 }
1524
1525 static void mark_rodata(struct objtool_file *file)
1526 {
1527 struct section *sec;
1528 bool found = false;
1529
1530 /*
1531 * Search for the following rodata sections, each of which can
1532 * potentially contain jump tables:
1533 *
1534 * - .rodata: can contain GCC switch tables
1535 * - .rodata.<func>: same, if -fdata-sections is being used
1536 * - .rodata..c_jump_table: contains C annotated jump tables
1537 *
1538 * .rodata.str1.* sections are ignored; they don't contain jump tables.
1539 */
1540 for_each_sec(file, sec) {
1541 if (!strncmp(sec->name, ".rodata", 7) &&
1542 !strstr(sec->name, ".str1.")) {
1543 sec->rodata = true;
1544 found = true;
1545 }
1546 }
1547
1548 file->rodata = found;
1549 }
1550
1551 static int decode_sections(struct objtool_file *file)
1552 {
1553 int ret;
1554
1555 mark_rodata(file);
1556
1557 ret = decode_instructions(file);
1558 if (ret)
1559 return ret;
1560
1561 ret = add_dead_ends(file);
1562 if (ret)
1563 return ret;
1564
1565 add_ignores(file);
1566 add_uaccess_safe(file);
1567
1568 ret = add_ignore_alternatives(file);
1569 if (ret)
1570 return ret;
1571
1572 ret = add_jump_destinations(file);
1573 if (ret)
1574 return ret;
1575
1576 ret = add_special_section_alts(file);
1577 if (ret)
1578 return ret;
1579
1580 ret = read_intra_function_calls(file);
1581 if (ret)
1582 return ret;
1583
1584 ret = add_call_destinations(file);
1585 if (ret)
1586 return ret;
1587
1588 ret = add_jump_table_alts(file);
1589 if (ret)
1590 return ret;
1591
1592 ret = read_unwind_hints(file);
1593 if (ret)
1594 return ret;
1595
1596 ret = read_retpoline_hints(file);
1597 if (ret)
1598 return ret;
1599
1600 ret = read_instr_hints(file);
1601 if (ret)
1602 return ret;
1603
1604 return 0;
1605 }
1606
1607 static bool is_fentry_call(struct instruction *insn)
1608 {
1609 if (insn->type == INSN_CALL && insn->call_dest &&
1610 insn->call_dest->type == STT_NOTYPE &&
1611 !strcmp(insn->call_dest->name, "__fentry__"))
1612 return true;
1613
1614 return false;
1615 }
1616
1617 static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
1618 {
1619 u8 ret_offset = insn->ret_offset;
1620 struct cfi_state *cfi = &state->cfi;
1621 int i;
1622
1623 if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
1624 return true;
1625
1626 if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
1627 return true;
1628
1629 if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
1630 return true;
1631
1632 /*
1633 * If there is a ret offset hint then don't check registers
1634 * because a callee-saved register might have been pushed on
1635 * the stack.
1636 */
1637 if (ret_offset)
1638 return false;
1639
1640 for (i = 0; i < CFI_NUM_REGS; i++) {
1641 if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
1642 cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
1643 return true;
1644 }
1645
1646 return false;
1647 }
1648
1649 static bool has_valid_stack_frame(struct insn_state *state)
1650 {
1651 struct cfi_state *cfi = &state->cfi;
1652
1653 if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
1654 cfi->regs[CFI_BP].offset == -16)
1655 return true;
1656
1657 if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
1658 return true;
1659
1660 return false;
1661 }
1662
1663 static int update_cfi_state_regs(struct instruction *insn,
1664 struct cfi_state *cfi,
1665 struct stack_op *op)
1666 {
1667 struct cfi_reg *cfa = &cfi->cfa;
1668
1669 if (cfa->base != CFI_SP && cfa->base != CFI_SP_INDIRECT)
1670 return 0;
1671
1672 /* push */
1673 if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1674 cfa->offset += 8;
1675
1676 /* pop */
1677 if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1678 cfa->offset -= 8;
1679
1680 /* add immediate to sp */
1681 if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1682 op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1683 cfa->offset -= op->src.offset;
1684
1685 return 0;
1686 }
1687
1688 static void save_reg(struct cfi_state *cfi, unsigned char reg, int base, int offset)
1689 {
1690 if (arch_callee_saved_reg(reg) &&
1691 cfi->regs[reg].base == CFI_UNDEFINED) {
1692 cfi->regs[reg].base = base;
1693 cfi->regs[reg].offset = offset;
1694 }
1695 }
1696
1697 static void restore_reg(struct cfi_state *cfi, unsigned char reg)
1698 {
1699 cfi->regs[reg].base = initial_func_cfi.regs[reg].base;
1700 cfi->regs[reg].offset = initial_func_cfi.regs[reg].offset;
1701 }
1702
1703 /*
1704 * A note about DRAP stack alignment:
1705 *
1706 * GCC has the concept of a DRAP register, which is used to help keep track of
1707 * the stack pointer when aligning the stack. r10 or r13 is used as the DRAP
1708 * register. The typical DRAP pattern is:
1709 *
1710 * 4c 8d 54 24 08 lea 0x8(%rsp),%r10
1711 * 48 83 e4 c0 and $0xffffffffffffffc0,%rsp
1712 * 41 ff 72 f8 pushq -0x8(%r10)
1713 * 55 push %rbp
1714 * 48 89 e5 mov %rsp,%rbp
1715 * (more pushes)
1716 * 41 52 push %r10
1717 * ...
1718 * 41 5a pop %r10
1719 * (more pops)
1720 * 5d pop %rbp
1721 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1722 * c3 retq
1723 *
1724 * There are some variations in the epilogues, like:
1725 *
1726 * 5b pop %rbx
1727 * 41 5a pop %r10
1728 * 41 5c pop %r12
1729 * 41 5d pop %r13
1730 * 41 5e pop %r14
1731 * c9 leaveq
1732 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1733 * c3 retq
1734 *
1735 * and:
1736 *
1737 * 4c 8b 55 e8 mov -0x18(%rbp),%r10
1738 * 48 8b 5d e0 mov -0x20(%rbp),%rbx
1739 * 4c 8b 65 f0 mov -0x10(%rbp),%r12
1740 * 4c 8b 6d f8 mov -0x8(%rbp),%r13
1741 * c9 leaveq
1742 * 49 8d 62 f8 lea -0x8(%r10),%rsp
1743 * c3 retq
1744 *
1745 * Sometimes r13 is used as the DRAP register, in which case it's saved and
1746 * restored beforehand:
1747 *
1748 * 41 55 push %r13
1749 * 4c 8d 6c 24 10 lea 0x10(%rsp),%r13
1750 * 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
1751 * ...
1752 * 49 8d 65 f0 lea -0x10(%r13),%rsp
1753 * 41 5d pop %r13
1754 * c3 retq
1755 */
1756 static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
1757 struct stack_op *op)
1758 {
1759 struct cfi_reg *cfa = &cfi->cfa;
1760 struct cfi_reg *regs = cfi->regs;
1761
1762 /* stack operations don't make sense with an undefined CFA */
1763 if (cfa->base == CFI_UNDEFINED) {
1764 if (insn->func) {
1765 WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1766 return -1;
1767 }
1768 return 0;
1769 }
1770
1771 if (cfi->type == ORC_TYPE_REGS || cfi->type == ORC_TYPE_REGS_IRET)
1772 return update_cfi_state_regs(insn, cfi, op);
1773
1774 switch (op->dest.type) {
1775
1776 case OP_DEST_REG:
1777 switch (op->src.type) {
1778
1779 case OP_SRC_REG:
1780 if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1781 cfa->base == CFI_SP &&
1782 regs[CFI_BP].base == CFI_CFA &&
1783 regs[CFI_BP].offset == -cfa->offset) {
1784
1785 /* mov %rsp, %rbp */
1786 cfa->base = op->dest.reg;
1787 cfi->bp_scratch = false;
1788 }
1789
1790 else if (op->src.reg == CFI_SP &&
1791 op->dest.reg == CFI_BP && cfi->drap) {
1792
1793 /* drap: mov %rsp, %rbp */
1794 regs[CFI_BP].base = CFI_BP;
1795 regs[CFI_BP].offset = -cfi->stack_size;
1796 cfi->bp_scratch = false;
1797 }
1798
1799 else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1800
1801 /*
1802 * mov %rsp, %reg
1803 *
1804 * This is needed for the rare case where GCC
1805 * does:
1806 *
1807 * mov %rsp, %rax
1808 * ...
1809 * mov %rax, %rsp
1810 */
1811 cfi->vals[op->dest.reg].base = CFI_CFA;
1812 cfi->vals[op->dest.reg].offset = -cfi->stack_size;
1813 }
1814
1815 else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1816 cfa->base == CFI_BP) {
1817
1818 /*
1819 * mov %rbp, %rsp
1820 *
1821 * Restore the original stack pointer (Clang).
1822 */
1823 cfi->stack_size = -cfi->regs[CFI_BP].offset;
1824 }
1825
1826 else if (op->dest.reg == cfa->base) {
1827
1828 /* mov %reg, %rsp */
1829 if (cfa->base == CFI_SP &&
1830 cfi->vals[op->src.reg].base == CFI_CFA) {
1831
1832 /*
1833 * This is needed for the rare case
1834 * where GCC does something dumb like:
1835 *
1836 * lea 0x8(%rsp), %rcx
1837 * ...
1838 * mov %rcx, %rsp
1839 */
1840 cfa->offset = -cfi->vals[op->src.reg].offset;
1841 cfi->stack_size = cfa->offset;
1842
1843 } else {
1844 cfa->base = CFI_UNDEFINED;
1845 cfa->offset = 0;
1846 }
1847 }
1848
1849 break;
1850
1851 case OP_SRC_ADD:
1852 if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1853
1854 /* add imm, %rsp */
1855 cfi->stack_size -= op->src.offset;
1856 if (cfa->base == CFI_SP)
1857 cfa->offset -= op->src.offset;
1858 break;
1859 }
1860
1861 if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1862
1863 /* lea disp(%rbp), %rsp */
1864 cfi->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1865 break;
1866 }
1867
1868 if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1869
1870 /* drap: lea disp(%rsp), %drap */
1871 cfi->drap_reg = op->dest.reg;
1872
1873 /*
1874 * lea disp(%rsp), %reg
1875 *
1876 * This is needed for the rare case where GCC
1877 * does something dumb like:
1878 *
1879 * lea 0x8(%rsp), %rcx
1880 * ...
1881 * mov %rcx, %rsp
1882 */
1883 cfi->vals[op->dest.reg].base = CFI_CFA;
1884 cfi->vals[op->dest.reg].offset = \
1885 -cfi->stack_size + op->src.offset;
1886
1887 break;
1888 }
1889
1890 if (cfi->drap && op->dest.reg == CFI_SP &&
1891 op->src.reg == cfi->drap_reg) {
1892
1893 /* drap: lea disp(%drap), %rsp */
1894 cfa->base = CFI_SP;
1895 cfa->offset = cfi->stack_size = -op->src.offset;
1896 cfi->drap_reg = CFI_UNDEFINED;
1897 cfi->drap = false;
1898 break;
1899 }
1900
1901 if (op->dest.reg == cfi->cfa.base) {
1902 WARN_FUNC("unsupported stack register modification",
1903 insn->sec, insn->offset);
1904 return -1;
1905 }
1906
1907 break;
1908
1909 case OP_SRC_AND:
1910 if (op->dest.reg != CFI_SP ||
1911 (cfi->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1912 (cfi->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1913 WARN_FUNC("unsupported stack pointer realignment",
1914 insn->sec, insn->offset);
1915 return -1;
1916 }
1917
1918 if (cfi->drap_reg != CFI_UNDEFINED) {
1919 /* drap: and imm, %rsp */
1920 cfa->base = cfi->drap_reg;
1921 cfa->offset = cfi->stack_size = 0;
1922 cfi->drap = true;
1923 }
1924
1925 /*
1926 * Older versions of GCC (4.8ish) realign the stack
1927 * without DRAP, with a frame pointer.
1928 */
1929
1930 break;
1931
1932 case OP_SRC_POP:
1933 case OP_SRC_POPF:
1934 if (!cfi->drap && op->dest.reg == cfa->base) {
1935
1936 /* pop %rbp */
1937 cfa->base = CFI_SP;
1938 }
1939
1940 if (cfi->drap && cfa->base == CFI_BP_INDIRECT &&
1941 op->dest.reg == cfi->drap_reg &&
1942 cfi->drap_offset == -cfi->stack_size) {
1943
1944 /* drap: pop %drap */
1945 cfa->base = cfi->drap_reg;
1946 cfa->offset = 0;
1947 cfi->drap_offset = -1;
1948
1949 } else if (regs[op->dest.reg].offset == -cfi->stack_size) {
1950
1951 /* pop %reg */
1952 restore_reg(cfi, op->dest.reg);
1953 }
1954
1955 cfi->stack_size -= 8;
1956 if (cfa->base == CFI_SP)
1957 cfa->offset -= 8;
1958
1959 break;
1960
1961 case OP_SRC_REG_INDIRECT:
1962 if (cfi->drap && op->src.reg == CFI_BP &&
1963 op->src.offset == cfi->drap_offset) {
1964
1965 /* drap: mov disp(%rbp), %drap */
1966 cfa->base = cfi->drap_reg;
1967 cfa->offset = 0;
1968 cfi->drap_offset = -1;
1969 }
1970
1971 if (cfi->drap && op->src.reg == CFI_BP &&
1972 op->src.offset == regs[op->dest.reg].offset) {
1973
1974 /* drap: mov disp(%rbp), %reg */
1975 restore_reg(cfi, op->dest.reg);
1976
1977 } else if (op->src.reg == cfa->base &&
1978 op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1979
1980 /* mov disp(%rbp), %reg */
1981 /* mov disp(%rsp), %reg */
1982 restore_reg(cfi, op->dest.reg);
1983 }
1984
1985 break;
1986
1987 default:
1988 WARN_FUNC("unknown stack-related instruction",
1989 insn->sec, insn->offset);
1990 return -1;
1991 }
1992
1993 break;
1994
1995 case OP_DEST_PUSH:
1996 case OP_DEST_PUSHF:
1997 cfi->stack_size += 8;
1998 if (cfa->base == CFI_SP)
1999 cfa->offset += 8;
2000
2001 if (op->src.type != OP_SRC_REG)
2002 break;
2003
2004 if (cfi->drap) {
2005 if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
2006
2007 /* drap: push %drap */
2008 cfa->base = CFI_BP_INDIRECT;
2009 cfa->offset = -cfi->stack_size;
2010
2011 /* save drap so we know when to restore it */
2012 cfi->drap_offset = -cfi->stack_size;
2013
2014 } else if (op->src.reg == CFI_BP && cfa->base == cfi->drap_reg) {
2015
2016 /* drap: push %rbp */
2017 cfi->stack_size = 0;
2018
2019 } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
2020
2021 /* drap: push %reg */
2022 save_reg(cfi, op->src.reg, CFI_BP, -cfi->stack_size);
2023 }
2024
2025 } else {
2026
2027 /* push %reg */
2028 save_reg(cfi, op->src.reg, CFI_CFA, -cfi->stack_size);
2029 }
2030
2031 /* detect when asm code uses rbp as a scratch register */
2032 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
2033 cfa->base != CFI_BP)
2034 cfi->bp_scratch = true;
2035 break;
2036
2037 case OP_DEST_REG_INDIRECT:
2038
2039 if (cfi->drap) {
2040 if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
2041
2042 /* drap: mov %drap, disp(%rbp) */
2043 cfa->base = CFI_BP_INDIRECT;
2044 cfa->offset = op->dest.offset;
2045
2046 /* save drap offset so we know when to restore it */
2047 cfi->drap_offset = op->dest.offset;
2048 }
2049
2050 else if (regs[op->src.reg].base == CFI_UNDEFINED) {
2051
2052 /* drap: mov reg, disp(%rbp) */
2053 save_reg(cfi, op->src.reg, CFI_BP, op->dest.offset);
2054 }
2055
2056 } else if (op->dest.reg == cfa->base) {
2057
2058 /* mov reg, disp(%rbp) */
2059 /* mov reg, disp(%rsp) */
2060 save_reg(cfi, op->src.reg, CFI_CFA,
2061 op->dest.offset - cfi->cfa.offset);
2062 }
2063
2064 break;
2065
2066 case OP_DEST_LEAVE:
2067 if ((!cfi->drap && cfa->base != CFI_BP) ||
2068 (cfi->drap && cfa->base != cfi->drap_reg)) {
2069 WARN_FUNC("leave instruction with modified stack frame",
2070 insn->sec, insn->offset);
2071 return -1;
2072 }
2073
2074 /* leave (mov %rbp, %rsp; pop %rbp) */
2075
2076 cfi->stack_size = -cfi->regs[CFI_BP].offset - 8;
2077 restore_reg(cfi, CFI_BP);
2078
2079 if (!cfi->drap) {
2080 cfa->base = CFI_SP;
2081 cfa->offset -= 8;
2082 }
2083
2084 break;
2085
2086 case OP_DEST_MEM:
2087 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
2088 WARN_FUNC("unknown stack-related memory operation",
2089 insn->sec, insn->offset);
2090 return -1;
2091 }
2092
2093 /* pop mem */
2094 cfi->stack_size -= 8;
2095 if (cfa->base == CFI_SP)
2096 cfa->offset -= 8;
2097
2098 break;
2099
2100 default:
2101 WARN_FUNC("unknown stack-related instruction",
2102 insn->sec, insn->offset);
2103 return -1;
2104 }
2105
2106 return 0;
2107 }
2108
2109 static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
2110 {
2111 struct stack_op *op;
2112
2113 list_for_each_entry(op, &insn->stack_ops, list) {
2114 struct cfi_state old_cfi = state->cfi;
2115 int res;
2116
2117 res = update_cfi_state(insn, &state->cfi, op);
2118 if (res)
2119 return res;
2120
2121 if (insn->alt_group && memcmp(&state->cfi, &old_cfi, sizeof(struct cfi_state))) {
2122 WARN_FUNC("alternative modifies stack", insn->sec, insn->offset);
2123 return -1;
2124 }
2125
2126 if (op->dest.type == OP_DEST_PUSHF) {
2127 if (!state->uaccess_stack) {
2128 state->uaccess_stack = 1;
2129 } else if (state->uaccess_stack >> 31) {
2130 WARN_FUNC("PUSHF stack exhausted",
2131 insn->sec, insn->offset);
2132 return 1;
2133 }
2134 state->uaccess_stack <<= 1;
2135 state->uaccess_stack |= state->uaccess;
2136 }
2137
2138 if (op->src.type == OP_SRC_POPF) {
2139 if (state->uaccess_stack) {
2140 state->uaccess = state->uaccess_stack & 1;
2141 state->uaccess_stack >>= 1;
2142 if (state->uaccess_stack == 1)
2143 state->uaccess_stack = 0;
2144 }
2145 }
2146 }
2147
2148 return 0;
2149 }
2150
2151 static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
2152 {
2153 struct cfi_state *cfi1 = &insn->cfi;
2154 int i;
2155
2156 if (memcmp(&cfi1->cfa, &cfi2->cfa, sizeof(cfi1->cfa))) {
2157
2158 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
2159 insn->sec, insn->offset,
2160 cfi1->cfa.base, cfi1->cfa.offset,
2161 cfi2->cfa.base, cfi2->cfa.offset);
2162
2163 } else if (memcmp(&cfi1->regs, &cfi2->regs, sizeof(cfi1->regs))) {
2164 for (i = 0; i < CFI_NUM_REGS; i++) {
2165 if (!memcmp(&cfi1->regs[i], &cfi2->regs[i],
2166 sizeof(struct cfi_reg)))
2167 continue;
2168
2169 WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
2170 insn->sec, insn->offset,
2171 i, cfi1->regs[i].base, cfi1->regs[i].offset,
2172 i, cfi2->regs[i].base, cfi2->regs[i].offset);
2173 break;
2174 }
2175
2176 } else if (cfi1->type != cfi2->type) {
2177
2178 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
2179 insn->sec, insn->offset, cfi1->type, cfi2->type);
2180
2181 } else if (cfi1->drap != cfi2->drap ||
2182 (cfi1->drap && cfi1->drap_reg != cfi2->drap_reg) ||
2183 (cfi1->drap && cfi1->drap_offset != cfi2->drap_offset)) {
2184
2185 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
2186 insn->sec, insn->offset,
2187 cfi1->drap, cfi1->drap_reg, cfi1->drap_offset,
2188 cfi2->drap, cfi2->drap_reg, cfi2->drap_offset);
2189
2190 } else
2191 return true;
2192
2193 return false;
2194 }
2195
2196 static inline bool func_uaccess_safe(struct symbol *func)
2197 {
2198 if (func)
2199 return func->uaccess_safe;
2200
2201 return false;
2202 }
2203
2204 static inline const char *call_dest_name(struct instruction *insn)
2205 {
2206 if (insn->call_dest)
2207 return insn->call_dest->name;
2208
2209 return "{dynamic}";
2210 }
2211
2212 static inline bool noinstr_call_dest(struct symbol *func)
2213 {
2214 /*
2215 * We can't deal with indirect function calls at present;
2216 * assume they're instrumented.
2217 */
2218 if (!func)
2219 return false;
2220
2221 /*
2222 * If the symbol is from a noinstr section; we good.
2223 */
2224 if (func->sec->noinstr)
2225 return true;
2226
2227 /*
2228 * The __ubsan_handle_*() calls are like WARN(), they only happen when
2229 * something 'BAD' happened. At the risk of taking the machine down,
2230 * let them proceed to get the message out.
2231 */
2232 if (!strncmp(func->name, "__ubsan_handle_", 15))
2233 return true;
2234
2235 return false;
2236 }
2237
2238 static int validate_call(struct instruction *insn, struct insn_state *state)
2239 {
2240 if (state->noinstr && state->instr <= 0 &&
2241 !noinstr_call_dest(insn->call_dest)) {
2242 WARN_FUNC("call to %s() leaves .noinstr.text section",
2243 insn->sec, insn->offset, call_dest_name(insn));
2244 return 1;
2245 }
2246
2247 if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
2248 WARN_FUNC("call to %s() with UACCESS enabled",
2249 insn->sec, insn->offset, call_dest_name(insn));
2250 return 1;
2251 }
2252
2253 if (state->df) {
2254 WARN_FUNC("call to %s() with DF set",
2255 insn->sec, insn->offset, call_dest_name(insn));
2256 return 1;
2257 }
2258
2259 return 0;
2260 }
2261
2262 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
2263 {
2264 if (has_modified_stack_frame(insn, state)) {
2265 WARN_FUNC("sibling call from callable instruction with modified stack frame",
2266 insn->sec, insn->offset);
2267 return 1;
2268 }
2269
2270 return validate_call(insn, state);
2271 }
2272
2273 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
2274 {
2275 if (state->noinstr && state->instr > 0) {
2276 WARN_FUNC("return with instrumentation enabled",
2277 insn->sec, insn->offset);
2278 return 1;
2279 }
2280
2281 if (state->uaccess && !func_uaccess_safe(func)) {
2282 WARN_FUNC("return with UACCESS enabled",
2283 insn->sec, insn->offset);
2284 return 1;
2285 }
2286
2287 if (!state->uaccess && func_uaccess_safe(func)) {
2288 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
2289 insn->sec, insn->offset);
2290 return 1;
2291 }
2292
2293 if (state->df) {
2294 WARN_FUNC("return with DF set",
2295 insn->sec, insn->offset);
2296 return 1;
2297 }
2298
2299 if (func && has_modified_stack_frame(insn, state)) {
2300 WARN_FUNC("return with modified stack frame",
2301 insn->sec, insn->offset);
2302 return 1;
2303 }
2304
2305 if (state->cfi.bp_scratch) {
2306 WARN_FUNC("BP used as a scratch register",
2307 insn->sec, insn->offset);
2308 return 1;
2309 }
2310
2311 return 0;
2312 }
2313
2314 /*
2315 * Alternatives should not contain any ORC entries, this in turn means they
2316 * should not contain any CFI ops, which implies all instructions should have
2317 * the same same CFI state.
2318 *
2319 * It is possible to constuct alternatives that have unreachable holes that go
2320 * unreported (because they're NOPs), such holes would result in CFI_UNDEFINED
2321 * states which then results in ORC entries, which we just said we didn't want.
2322 *
2323 * Avoid them by copying the CFI entry of the first instruction into the whole
2324 * alternative.
2325 */
2326 static void fill_alternative_cfi(struct objtool_file *file, struct instruction *insn)
2327 {
2328 struct instruction *first_insn = insn;
2329 int alt_group = insn->alt_group;
2330
2331 sec_for_each_insn_continue(file, insn) {
2332 if (insn->alt_group != alt_group)
2333 break;
2334 insn->cfi = first_insn->cfi;
2335 }
2336 }
2337
2338 /*
2339 * Follow the branch starting at the given instruction, and recursively follow
2340 * any other branches (jumps). Meanwhile, track the frame pointer state at
2341 * each instruction and validate all the rules described in
2342 * tools/objtool/Documentation/stack-validation.txt.
2343 */
2344 static int validate_branch(struct objtool_file *file, struct symbol *func,
2345 struct instruction *insn, struct insn_state state)
2346 {
2347 struct alternative *alt;
2348 struct instruction *next_insn;
2349 struct section *sec;
2350 u8 visited;
2351 int ret;
2352
2353 sec = insn->sec;
2354
2355 while (1) {
2356 next_insn = next_insn_same_sec(file, insn);
2357
2358 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2359 WARN("%s() falls through to next function %s()",
2360 func->name, insn->func->name);
2361 return 1;
2362 }
2363
2364 if (func && insn->ignore) {
2365 WARN_FUNC("BUG: why am I validating an ignored function?",
2366 sec, insn->offset);
2367 return 1;
2368 }
2369
2370 visited = 1 << state.uaccess;
2371 if (insn->visited) {
2372 if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
2373 return 1;
2374
2375 if (insn->visited & visited)
2376 return 0;
2377 }
2378
2379 if (state.noinstr)
2380 state.instr += insn->instr;
2381
2382 if (insn->hint)
2383 state.cfi = insn->cfi;
2384 else
2385 insn->cfi = state.cfi;
2386
2387 insn->visited |= visited;
2388
2389 if (!insn->ignore_alts && !list_empty(&insn->alts)) {
2390 bool skip_orig = false;
2391
2392 list_for_each_entry(alt, &insn->alts, list) {
2393 if (alt->skip_orig)
2394 skip_orig = true;
2395
2396 ret = validate_branch(file, func, alt->insn, state);
2397 if (ret) {
2398 if (backtrace)
2399 BT_FUNC("(alt)", insn);
2400 return ret;
2401 }
2402 }
2403
2404 if (insn->alt_group)
2405 fill_alternative_cfi(file, insn);
2406
2407 if (skip_orig)
2408 return 0;
2409 }
2410
2411 if (handle_insn_ops(insn, &state))
2412 return 1;
2413
2414 switch (insn->type) {
2415
2416 case INSN_RETURN:
2417 return validate_return(func, insn, &state);
2418
2419 case INSN_CALL:
2420 case INSN_CALL_DYNAMIC:
2421 ret = validate_call(insn, &state);
2422 if (ret)
2423 return ret;
2424
2425 if (!no_fp && func && !is_fentry_call(insn) &&
2426 !has_valid_stack_frame(&state)) {
2427 WARN_FUNC("call without frame pointer save/setup",
2428 sec, insn->offset);
2429 return 1;
2430 }
2431
2432 if (dead_end_function(file, insn->call_dest))
2433 return 0;
2434
2435 break;
2436
2437 case INSN_JUMP_CONDITIONAL:
2438 case INSN_JUMP_UNCONDITIONAL:
2439 if (func && is_sibling_call(insn)) {
2440 ret = validate_sibling_call(insn, &state);
2441 if (ret)
2442 return ret;
2443
2444 } else if (insn->jump_dest) {
2445 ret = validate_branch(file, func,
2446 insn->jump_dest, state);
2447 if (ret) {
2448 if (backtrace)
2449 BT_FUNC("(branch)", insn);
2450 return ret;
2451 }
2452 }
2453
2454 if (insn->type == INSN_JUMP_UNCONDITIONAL)
2455 return 0;
2456
2457 break;
2458
2459 case INSN_JUMP_DYNAMIC:
2460 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2461 if (func && is_sibling_call(insn)) {
2462 ret = validate_sibling_call(insn, &state);
2463 if (ret)
2464 return ret;
2465 }
2466
2467 if (insn->type == INSN_JUMP_DYNAMIC)
2468 return 0;
2469
2470 break;
2471
2472 case INSN_CONTEXT_SWITCH:
2473 if (func && (!next_insn || !next_insn->hint)) {
2474 WARN_FUNC("unsupported instruction in callable function",
2475 sec, insn->offset);
2476 return 1;
2477 }
2478 return 0;
2479
2480 case INSN_STAC:
2481 if (state.uaccess) {
2482 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2483 return 1;
2484 }
2485
2486 state.uaccess = true;
2487 break;
2488
2489 case INSN_CLAC:
2490 if (!state.uaccess && func) {
2491 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2492 return 1;
2493 }
2494
2495 if (func_uaccess_safe(func) && !state.uaccess_stack) {
2496 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2497 return 1;
2498 }
2499
2500 state.uaccess = false;
2501 break;
2502
2503 case INSN_STD:
2504 if (state.df)
2505 WARN_FUNC("recursive STD", sec, insn->offset);
2506
2507 state.df = true;
2508 break;
2509
2510 case INSN_CLD:
2511 if (!state.df && func)
2512 WARN_FUNC("redundant CLD", sec, insn->offset);
2513
2514 state.df = false;
2515 break;
2516
2517 default:
2518 break;
2519 }
2520
2521 if (insn->dead_end)
2522 return 0;
2523
2524 if (!next_insn) {
2525 if (state.cfi.cfa.base == CFI_UNDEFINED)
2526 return 0;
2527 WARN("%s: unexpected end of section", sec->name);
2528 return 1;
2529 }
2530
2531 insn = next_insn;
2532 }
2533
2534 return 0;
2535 }
2536
2537 static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
2538 {
2539 struct instruction *insn;
2540 struct insn_state state;
2541 int ret, warnings = 0;
2542
2543 if (!file->hints)
2544 return 0;
2545
2546 init_insn_state(&state, sec);
2547
2548 if (sec) {
2549 insn = find_insn(file, sec, 0);
2550 if (!insn)
2551 return 0;
2552 } else {
2553 insn = list_first_entry(&file->insn_list, typeof(*insn), list);
2554 }
2555
2556 while (&insn->list != &file->insn_list && (!sec || insn->sec == sec)) {
2557 if (insn->hint && !insn->visited) {
2558 ret = validate_branch(file, insn->func, insn, state);
2559 if (ret && backtrace)
2560 BT_FUNC("<=== (hint)", insn);
2561 warnings += ret;
2562 }
2563
2564 insn = list_next_entry(insn, list);
2565 }
2566
2567 return warnings;
2568 }
2569
2570 static int validate_retpoline(struct objtool_file *file)
2571 {
2572 struct instruction *insn;
2573 int warnings = 0;
2574
2575 for_each_insn(file, insn) {
2576 if (insn->type != INSN_JUMP_DYNAMIC &&
2577 insn->type != INSN_CALL_DYNAMIC)
2578 continue;
2579
2580 if (insn->retpoline_safe)
2581 continue;
2582
2583 /*
2584 * .init.text code is ran before userspace and thus doesn't
2585 * strictly need retpolines, except for modules which are
2586 * loaded late, they very much do need retpoline in their
2587 * .init.text
2588 */
2589 if (!strcmp(insn->sec->name, ".init.text") && !module)
2590 continue;
2591
2592 WARN_FUNC("indirect %s found in RETPOLINE build",
2593 insn->sec, insn->offset,
2594 insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2595
2596 warnings++;
2597 }
2598
2599 return warnings;
2600 }
2601
2602 static bool is_kasan_insn(struct instruction *insn)
2603 {
2604 return (insn->type == INSN_CALL &&
2605 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2606 }
2607
2608 static bool is_ubsan_insn(struct instruction *insn)
2609 {
2610 return (insn->type == INSN_CALL &&
2611 !strcmp(insn->call_dest->name,
2612 "__ubsan_handle_builtin_unreachable"));
2613 }
2614
2615 static bool ignore_unreachable_insn(struct instruction *insn)
2616 {
2617 int i;
2618
2619 if (insn->ignore || insn->type == INSN_NOP)
2620 return true;
2621
2622 /*
2623 * Ignore any unused exceptions. This can happen when a whitelisted
2624 * function has an exception table entry.
2625 *
2626 * Also ignore alternative replacement instructions. This can happen
2627 * when a whitelisted function uses one of the ALTERNATIVE macros.
2628 */
2629 if (!strcmp(insn->sec->name, ".fixup") ||
2630 !strcmp(insn->sec->name, ".altinstr_replacement") ||
2631 !strcmp(insn->sec->name, ".altinstr_aux"))
2632 return true;
2633
2634 if (!insn->func)
2635 return false;
2636
2637 /*
2638 * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2639 * __builtin_unreachable(). The BUG() macro has an unreachable() after
2640 * the UD2, which causes GCC's undefined trap logic to emit another UD2
2641 * (or occasionally a JMP to UD2).
2642 */
2643 if (list_prev_entry(insn, list)->dead_end &&
2644 (insn->type == INSN_BUG ||
2645 (insn->type == INSN_JUMP_UNCONDITIONAL &&
2646 insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2647 return true;
2648
2649 /*
2650 * Check if this (or a subsequent) instruction is related to
2651 * CONFIG_UBSAN or CONFIG_KASAN.
2652 *
2653 * End the search at 5 instructions to avoid going into the weeds.
2654 */
2655 for (i = 0; i < 5; i++) {
2656
2657 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2658 return true;
2659
2660 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2661 if (insn->jump_dest &&
2662 insn->jump_dest->func == insn->func) {
2663 insn = insn->jump_dest;
2664 continue;
2665 }
2666
2667 break;
2668 }
2669
2670 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2671 break;
2672
2673 insn = list_next_entry(insn, list);
2674 }
2675
2676 return false;
2677 }
2678
2679 static int validate_symbol(struct objtool_file *file, struct section *sec,
2680 struct symbol *sym, struct insn_state *state)
2681 {
2682 struct instruction *insn;
2683 int ret;
2684
2685 if (!sym->len) {
2686 WARN("%s() is missing an ELF size annotation", sym->name);
2687 return 1;
2688 }
2689
2690 if (sym->pfunc != sym || sym->alias != sym)
2691 return 0;
2692
2693 insn = find_insn(file, sec, sym->offset);
2694 if (!insn || insn->ignore || insn->visited)
2695 return 0;
2696
2697 state->uaccess = sym->uaccess_safe;
2698
2699 ret = validate_branch(file, insn->func, insn, *state);
2700 if (ret && backtrace)
2701 BT_FUNC("<=== (sym)", insn);
2702 return ret;
2703 }
2704
2705 static int validate_section(struct objtool_file *file, struct section *sec)
2706 {
2707 struct insn_state state;
2708 struct symbol *func;
2709 int warnings = 0;
2710
2711 list_for_each_entry(func, &sec->symbol_list, list) {
2712 if (func->type != STT_FUNC)
2713 continue;
2714
2715 init_insn_state(&state, sec);
2716 state.cfi.cfa = initial_func_cfi.cfa;
2717 memcpy(&state.cfi.regs, &initial_func_cfi.regs,
2718 CFI_NUM_REGS * sizeof(struct cfi_reg));
2719 state.cfi.stack_size = initial_func_cfi.cfa.offset;
2720
2721 warnings += validate_symbol(file, sec, func, &state);
2722 }
2723
2724 return warnings;
2725 }
2726
2727 static int validate_vmlinux_functions(struct objtool_file *file)
2728 {
2729 struct section *sec;
2730 int warnings = 0;
2731
2732 sec = find_section_by_name(file->elf, ".noinstr.text");
2733 if (sec) {
2734 warnings += validate_section(file, sec);
2735 warnings += validate_unwind_hints(file, sec);
2736 }
2737
2738 sec = find_section_by_name(file->elf, ".entry.text");
2739 if (sec) {
2740 warnings += validate_section(file, sec);
2741 warnings += validate_unwind_hints(file, sec);
2742 }
2743
2744 return warnings;
2745 }
2746
2747 static int validate_functions(struct objtool_file *file)
2748 {
2749 struct section *sec;
2750 int warnings = 0;
2751
2752 for_each_sec(file, sec) {
2753 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
2754 continue;
2755
2756 warnings += validate_section(file, sec);
2757 }
2758
2759 return warnings;
2760 }
2761
2762 static int validate_reachable_instructions(struct objtool_file *file)
2763 {
2764 struct instruction *insn;
2765
2766 if (file->ignore_unreachables)
2767 return 0;
2768
2769 for_each_insn(file, insn) {
2770 if (insn->visited || ignore_unreachable_insn(insn))
2771 continue;
2772
2773 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2774 return 1;
2775 }
2776
2777 return 0;
2778 }
2779
2780 static struct objtool_file file;
2781
2782 int check(const char *_objname, bool orc)
2783 {
2784 int ret, warnings = 0;
2785
2786 objname = _objname;
2787
2788 file.elf = elf_open_read(objname, O_RDWR);
2789 if (!file.elf)
2790 return 1;
2791
2792 INIT_LIST_HEAD(&file.insn_list);
2793 hash_init(file.insn_hash);
2794 file.c_file = !vmlinux && find_section_by_name(file.elf, ".comment");
2795 file.ignore_unreachables = no_unreachable;
2796 file.hints = false;
2797
2798 arch_initial_func_cfi_state(&initial_func_cfi);
2799
2800 ret = decode_sections(&file);
2801 if (ret < 0)
2802 goto out;
2803 warnings += ret;
2804
2805 if (list_empty(&file.insn_list))
2806 goto out;
2807
2808 if (vmlinux && !validate_dup) {
2809 ret = validate_vmlinux_functions(&file);
2810 if (ret < 0)
2811 goto out;
2812
2813 warnings += ret;
2814 goto out;
2815 }
2816
2817 if (retpoline) {
2818 ret = validate_retpoline(&file);
2819 if (ret < 0)
2820 return ret;
2821 warnings += ret;
2822 }
2823
2824 ret = validate_functions(&file);
2825 if (ret < 0)
2826 goto out;
2827 warnings += ret;
2828
2829 ret = validate_unwind_hints(&file, NULL);
2830 if (ret < 0)
2831 goto out;
2832 warnings += ret;
2833
2834 if (!warnings) {
2835 ret = validate_reachable_instructions(&file);
2836 if (ret < 0)
2837 goto out;
2838 warnings += ret;
2839 }
2840
2841 if (orc) {
2842 ret = create_orc(&file);
2843 if (ret < 0)
2844 goto out;
2845
2846 ret = create_orc_sections(&file);
2847 if (ret < 0)
2848 goto out;
2849 }
2850
2851 if (file.elf->changed) {
2852 ret = elf_write(file.elf);
2853 if (ret < 0)
2854 goto out;
2855 }
2856
2857 out:
2858 if (ret < 0) {
2859 /*
2860 * Fatal error. The binary is corrupt or otherwise broken in
2861 * some way, or objtool itself is broken. Fail the kernel
2862 * build.
2863 */
2864 return ret;
2865 }
2866
2867 return 0;
2868 }
Ubuntu Jammy Linux kernel mirror