92b6a2c21631d810cda14a79ef3fa2d906e6cb50
[muen/linux.git] / tools / objtool / check.c
1 /*
2  * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
3  *
4  * This program is free software; you can redistribute it and/or
5  * modify it under the terms of the GNU General Public License
6  * as published by the Free Software Foundation; either version 2
7  * of the License, or (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
16  */
17
18 #include <string.h>
19 #include <stdlib.h>
20
21 #include "builtin.h"
22 #include "check.h"
23 #include "elf.h"
24 #include "special.h"
25 #include "arch.h"
26 #include "warn.h"
27
28 #include <linux/hashtable.h>
29 #include <linux/kernel.h>
30
31 struct alternative {
32         struct list_head list;
33         struct instruction *insn;
34 };
35
36 const char *objname;
37 struct cfi_state initial_func_cfi;
38
39 struct instruction *find_insn(struct objtool_file *file,
40                               struct section *sec, unsigned long offset)
41 {
42         struct instruction *insn;
43
44         hash_for_each_possible(file->insn_hash, insn, hash, offset)
45                 if (insn->sec == sec && insn->offset == offset)
46                         return insn;
47
48         return NULL;
49 }
50
51 static struct instruction *next_insn_same_sec(struct objtool_file *file,
52                                               struct instruction *insn)
53 {
54         struct instruction *next = list_next_entry(insn, list);
55
56         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
57                 return NULL;
58
59         return next;
60 }
61
62 #define func_for_each_insn(file, func, insn)                            \
63         for (insn = find_insn(file, func->sec, func->offset);           \
64              insn && &insn->list != &file->insn_list &&                 \
65                 insn->sec == func->sec &&                               \
66                 insn->offset < func->offset + func->len;                \
67              insn = list_next_entry(insn, list))
68
69 #define func_for_each_insn_continue_reverse(file, func, insn)           \
70         for (insn = list_prev_entry(insn, list);                        \
71              &insn->list != &file->insn_list &&                         \
72                 insn->sec == func->sec && insn->offset >= func->offset; \
73              insn = list_prev_entry(insn, list))
74
75 #define sec_for_each_insn_from(file, insn)                              \
76         for (; insn; insn = next_insn_same_sec(file, insn))
77
78 #define sec_for_each_insn_continue(file, insn)                          \
79         for (insn = next_insn_same_sec(file, insn); insn;               \
80              insn = next_insn_same_sec(file, insn))
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 rela *rela;
90
91         /* check for STACK_FRAME_NON_STANDARD */
92         if (file->whitelist && file->whitelist->rela)
93                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
94                         if (rela->sym->type == STT_SECTION &&
95                             rela->sym->sec == func->sec &&
96                             rela->addend == func->offset)
97                                 return true;
98                         if (rela->sym->type == STT_FUNC && rela->sym == func)
99                                 return true;
100                 }
101
102         return false;
103 }
104
105 /*
106  * This checks to see if the given function is a "noreturn" function.
107  *
108  * For global functions which are outside the scope of this object file, we
109  * have to keep a manual list of them.
110  *
111  * For local functions, we have to detect them manually by simply looking for
112  * the lack of a return instruction.
113  *
114  * Returns:
115  *  -1: error
116  *   0: no dead end
117  *   1: dead end
118  */
119 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
120                                int recursion)
121 {
122         int i;
123         struct instruction *insn;
124         bool empty = true;
125
126         /*
127          * Unfortunately these have to be hard coded because the noreturn
128          * attribute isn't provided in ELF data.
129          */
130         static const char * const global_noreturns[] = {
131                 "__stack_chk_fail",
132                 "panic",
133                 "do_exit",
134                 "do_task_dead",
135                 "__module_put_and_exit",
136                 "complete_and_exit",
137                 "kvm_spurious_fault",
138                 "__reiserfs_panic",
139                 "lbug_with_loc",
140                 "fortify_panic",
141                 "usercopy_abort",
142         };
143
144         if (func->bind == STB_WEAK)
145                 return 0;
146
147         if (func->bind == STB_GLOBAL)
148                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
149                         if (!strcmp(func->name, global_noreturns[i]))
150                                 return 1;
151
152         if (!func->sec)
153                 return 0;
154
155         func_for_each_insn(file, func, insn) {
156                 empty = false;
157
158                 if (insn->type == INSN_RETURN)
159                         return 0;
160         }
161
162         if (empty)
163                 return 0;
164
165         /*
166          * A function can have a sibling call instead of a return.  In that
167          * case, the function's dead-end status depends on whether the target
168          * of the sibling call returns.
169          */
170         func_for_each_insn(file, func, insn) {
171                 if (insn->sec != func->sec ||
172                     insn->offset >= func->offset + func->len)
173                         break;
174
175                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
176                         struct instruction *dest = insn->jump_dest;
177                         struct symbol *dest_func;
178
179                         if (!dest)
180                                 /* sibling call to another file */
181                                 return 0;
182
183                         if (dest->sec != func->sec ||
184                             dest->offset < func->offset ||
185                             dest->offset >= func->offset + func->len) {
186                                 /* local sibling call */
187                                 dest_func = find_symbol_by_offset(dest->sec,
188                                                                   dest->offset);
189                                 if (!dest_func)
190                                         continue;
191
192                                 if (recursion == 5) {
193                                         WARN_FUNC("infinite recursion (objtool bug!)",
194                                                   dest->sec, dest->offset);
195                                         return -1;
196                                 }
197
198                                 return __dead_end_function(file, dest_func,
199                                                            recursion + 1);
200                         }
201                 }
202
203                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
204                         /* sibling call */
205                         return 0;
206         }
207
208         return 1;
209 }
210
211 static int dead_end_function(struct objtool_file *file, struct symbol *func)
212 {
213         return __dead_end_function(file, func, 0);
214 }
215
216 static void clear_insn_state(struct insn_state *state)
217 {
218         int i;
219
220         memset(state, 0, sizeof(*state));
221         state->cfa.base = CFI_UNDEFINED;
222         for (i = 0; i < CFI_NUM_REGS; i++) {
223                 state->regs[i].base = CFI_UNDEFINED;
224                 state->vals[i].base = CFI_UNDEFINED;
225         }
226         state->drap_reg = CFI_UNDEFINED;
227         state->drap_offset = -1;
228 }
229
230 /*
231  * Call the arch-specific instruction decoder for all the instructions and add
232  * them to the global instruction list.
233  */
234 static int decode_instructions(struct objtool_file *file)
235 {
236         struct section *sec;
237         struct symbol *func;
238         unsigned long offset;
239         struct instruction *insn;
240         int ret;
241
242         for_each_sec(file, sec) {
243
244                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
245                         continue;
246
247                 if (strcmp(sec->name, ".altinstr_replacement") &&
248                     strcmp(sec->name, ".altinstr_aux") &&
249                     strncmp(sec->name, ".discard.", 9))
250                         sec->text = true;
251
252                 for (offset = 0; offset < sec->len; offset += insn->len) {
253                         insn = malloc(sizeof(*insn));
254                         if (!insn) {
255                                 WARN("malloc failed");
256                                 return -1;
257                         }
258                         memset(insn, 0, sizeof(*insn));
259                         INIT_LIST_HEAD(&insn->alts);
260                         clear_insn_state(&insn->state);
261
262                         insn->sec = sec;
263                         insn->offset = offset;
264
265                         ret = arch_decode_instruction(file->elf, sec, offset,
266                                                       sec->len - offset,
267                                                       &insn->len, &insn->type,
268                                                       &insn->immediate,
269                                                       &insn->stack_op);
270                         if (ret)
271                                 goto err;
272
273                         if (!insn->type || insn->type > INSN_LAST) {
274                                 WARN_FUNC("invalid instruction type %d",
275                                           insn->sec, insn->offset, insn->type);
276                                 ret = -1;
277                                 goto err;
278                         }
279
280                         hash_add(file->insn_hash, &insn->hash, insn->offset);
281                         list_add_tail(&insn->list, &file->insn_list);
282                 }
283
284                 list_for_each_entry(func, &sec->symbol_list, list) {
285                         if (func->type != STT_FUNC)
286                                 continue;
287
288                         if (!find_insn(file, sec, func->offset)) {
289                                 WARN("%s(): can't find starting instruction",
290                                      func->name);
291                                 return -1;
292                         }
293
294                         func_for_each_insn(file, func, insn)
295                                 if (!insn->func)
296                                         insn->func = func;
297                 }
298         }
299
300         return 0;
301
302 err:
303         free(insn);
304         return ret;
305 }
306
307 /*
308  * Mark "ud2" instructions and manually annotated dead ends.
309  */
310 static int add_dead_ends(struct objtool_file *file)
311 {
312         struct section *sec;
313         struct rela *rela;
314         struct instruction *insn;
315         bool found;
316
317         /*
318          * By default, "ud2" is a dead end unless otherwise annotated, because
319          * GCC 7 inserts it for certain divide-by-zero cases.
320          */
321         for_each_insn(file, insn)
322                 if (insn->type == INSN_BUG)
323                         insn->dead_end = true;
324
325         /*
326          * Check for manually annotated dead ends.
327          */
328         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
329         if (!sec)
330                 goto reachable;
331
332         list_for_each_entry(rela, &sec->rela_list, list) {
333                 if (rela->sym->type != STT_SECTION) {
334                         WARN("unexpected relocation symbol type in %s", sec->name);
335                         return -1;
336                 }
337                 insn = find_insn(file, rela->sym->sec, rela->addend);
338                 if (insn)
339                         insn = list_prev_entry(insn, list);
340                 else if (rela->addend == rela->sym->sec->len) {
341                         found = false;
342                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
343                                 if (insn->sec == rela->sym->sec) {
344                                         found = true;
345                                         break;
346                                 }
347                         }
348
349                         if (!found) {
350                                 WARN("can't find unreachable insn at %s+0x%x",
351                                      rela->sym->sec->name, rela->addend);
352                                 return -1;
353                         }
354                 } else {
355                         WARN("can't find unreachable insn at %s+0x%x",
356                              rela->sym->sec->name, rela->addend);
357                         return -1;
358                 }
359
360                 insn->dead_end = true;
361         }
362
363 reachable:
364         /*
365          * These manually annotated reachable checks are needed for GCC 4.4,
366          * where the Linux unreachable() macro isn't supported.  In that case
367          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
368          * not a dead end.
369          */
370         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
371         if (!sec)
372                 return 0;
373
374         list_for_each_entry(rela, &sec->rela_list, list) {
375                 if (rela->sym->type != STT_SECTION) {
376                         WARN("unexpected relocation symbol type in %s", sec->name);
377                         return -1;
378                 }
379                 insn = find_insn(file, rela->sym->sec, rela->addend);
380                 if (insn)
381                         insn = list_prev_entry(insn, list);
382                 else if (rela->addend == rela->sym->sec->len) {
383                         found = false;
384                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
385                                 if (insn->sec == rela->sym->sec) {
386                                         found = true;
387                                         break;
388                                 }
389                         }
390
391                         if (!found) {
392                                 WARN("can't find reachable insn at %s+0x%x",
393                                      rela->sym->sec->name, rela->addend);
394                                 return -1;
395                         }
396                 } else {
397                         WARN("can't find reachable insn at %s+0x%x",
398                              rela->sym->sec->name, rela->addend);
399                         return -1;
400                 }
401
402                 insn->dead_end = false;
403         }
404
405         return 0;
406 }
407
408 /*
409  * Warnings shouldn't be reported for ignored functions.
410  */
411 static void add_ignores(struct objtool_file *file)
412 {
413         struct instruction *insn;
414         struct section *sec;
415         struct symbol *func;
416
417         for_each_sec(file, sec) {
418                 list_for_each_entry(func, &sec->symbol_list, list) {
419                         if (func->type != STT_FUNC)
420                                 continue;
421
422                         if (!ignore_func(file, func))
423                                 continue;
424
425                         func_for_each_insn(file, func, insn)
426                                 insn->ignore = true;
427                 }
428         }
429 }
430
431 /*
432  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
433  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
434  * But it at least allows objtool to understand the control flow *around* the
435  * retpoline.
436  */
437 static int add_nospec_ignores(struct objtool_file *file)
438 {
439         struct section *sec;
440         struct rela *rela;
441         struct instruction *insn;
442
443         sec = find_section_by_name(file->elf, ".rela.discard.nospec");
444         if (!sec)
445                 return 0;
446
447         list_for_each_entry(rela, &sec->rela_list, list) {
448                 if (rela->sym->type != STT_SECTION) {
449                         WARN("unexpected relocation symbol type in %s", sec->name);
450                         return -1;
451                 }
452
453                 insn = find_insn(file, rela->sym->sec, rela->addend);
454                 if (!insn) {
455                         WARN("bad .discard.nospec entry");
456                         return -1;
457                 }
458
459                 insn->ignore_alts = true;
460         }
461
462         return 0;
463 }
464
465 /*
466  * Find the destination instructions for all jumps.
467  */
468 static int add_jump_destinations(struct objtool_file *file)
469 {
470         struct instruction *insn;
471         struct rela *rela;
472         struct section *dest_sec;
473         unsigned long dest_off;
474
475         for_each_insn(file, insn) {
476                 if (insn->type != INSN_JUMP_CONDITIONAL &&
477                     insn->type != INSN_JUMP_UNCONDITIONAL)
478                         continue;
479
480                 if (insn->ignore)
481                         continue;
482
483                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
484                                                insn->len);
485                 if (!rela) {
486                         dest_sec = insn->sec;
487                         dest_off = insn->offset + insn->len + insn->immediate;
488                 } else if (rela->sym->type == STT_SECTION) {
489                         dest_sec = rela->sym->sec;
490                         dest_off = rela->addend + 4;
491                 } else if (rela->sym->sec->idx) {
492                         dest_sec = rela->sym->sec;
493                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
494                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
495                         /*
496                          * Retpoline jumps are really dynamic jumps in
497                          * disguise, so convert them accordingly.
498                          */
499                         insn->type = INSN_JUMP_DYNAMIC;
500                         insn->retpoline_safe = true;
501                         continue;
502                 } else {
503                         /* sibling call */
504                         insn->jump_dest = 0;
505                         continue;
506                 }
507
508                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
509                 if (!insn->jump_dest) {
510
511                         /*
512                          * This is a special case where an alt instruction
513                          * jumps past the end of the section.  These are
514                          * handled later in handle_group_alt().
515                          */
516                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
517                                 continue;
518
519                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
520                                   insn->sec, insn->offset, dest_sec->name,
521                                   dest_off);
522                         return -1;
523                 }
524         }
525
526         return 0;
527 }
528
529 /*
530  * Find the destination instructions for all calls.
531  */
532 static int add_call_destinations(struct objtool_file *file)
533 {
534         struct instruction *insn;
535         unsigned long dest_off;
536         struct rela *rela;
537
538         for_each_insn(file, insn) {
539                 if (insn->type != INSN_CALL)
540                         continue;
541
542                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
543                                                insn->len);
544                 if (!rela) {
545                         dest_off = insn->offset + insn->len + insn->immediate;
546                         insn->call_dest = find_symbol_by_offset(insn->sec,
547                                                                 dest_off);
548
549                         if (!insn->call_dest && !insn->ignore) {
550                                 WARN_FUNC("unsupported intra-function call",
551                                           insn->sec, insn->offset);
552                                 if (retpoline)
553                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
554                                 return -1;
555                         }
556
557                 } else if (rela->sym->type == STT_SECTION) {
558                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
559                                                                 rela->addend+4);
560                         if (!insn->call_dest ||
561                             insn->call_dest->type != STT_FUNC) {
562                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
563                                           insn->sec, insn->offset,
564                                           rela->sym->sec->name,
565                                           rela->addend + 4);
566                                 return -1;
567                         }
568                 } else
569                         insn->call_dest = rela->sym;
570         }
571
572         return 0;
573 }
574
575 /*
576  * The .alternatives section requires some extra special care, over and above
577  * what other special sections require:
578  *
579  * 1. Because alternatives are patched in-place, we need to insert a fake jump
580  *    instruction at the end so that validate_branch() skips all the original
581  *    replaced instructions when validating the new instruction path.
582  *
583  * 2. An added wrinkle is that the new instruction length might be zero.  In
584  *    that case the old instructions are replaced with noops.  We simulate that
585  *    by creating a fake jump as the only new instruction.
586  *
587  * 3. In some cases, the alternative section includes an instruction which
588  *    conditionally jumps to the _end_ of the entry.  We have to modify these
589  *    jumps' destinations to point back to .text rather than the end of the
590  *    entry in .altinstr_replacement.
591  *
592  * 4. It has been requested that we don't validate the !POPCNT feature path
593  *    which is a "very very small percentage of machines".
594  */
595 static int handle_group_alt(struct objtool_file *file,
596                             struct special_alt *special_alt,
597                             struct instruction *orig_insn,
598                             struct instruction **new_insn)
599 {
600         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
601         unsigned long dest_off;
602
603         last_orig_insn = NULL;
604         insn = orig_insn;
605         sec_for_each_insn_from(file, insn) {
606                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
607                         break;
608
609                 if (special_alt->skip_orig)
610                         insn->type = INSN_NOP;
611
612                 insn->alt_group = true;
613                 last_orig_insn = insn;
614         }
615
616         if (next_insn_same_sec(file, last_orig_insn)) {
617                 fake_jump = malloc(sizeof(*fake_jump));
618                 if (!fake_jump) {
619                         WARN("malloc failed");
620                         return -1;
621                 }
622                 memset(fake_jump, 0, sizeof(*fake_jump));
623                 INIT_LIST_HEAD(&fake_jump->alts);
624                 clear_insn_state(&fake_jump->state);
625
626                 fake_jump->sec = special_alt->new_sec;
627                 fake_jump->offset = -1;
628                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
629                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
630                 fake_jump->ignore = true;
631         }
632
633         if (!special_alt->new_len) {
634                 if (!fake_jump) {
635                         WARN("%s: empty alternative at end of section",
636                              special_alt->orig_sec->name);
637                         return -1;
638                 }
639
640                 *new_insn = fake_jump;
641                 return 0;
642         }
643
644         last_new_insn = NULL;
645         insn = *new_insn;
646         sec_for_each_insn_from(file, insn) {
647                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
648                         break;
649
650                 last_new_insn = insn;
651
652                 insn->ignore = orig_insn->ignore_alts;
653
654                 if (insn->type != INSN_JUMP_CONDITIONAL &&
655                     insn->type != INSN_JUMP_UNCONDITIONAL)
656                         continue;
657
658                 if (!insn->immediate)
659                         continue;
660
661                 dest_off = insn->offset + insn->len + insn->immediate;
662                 if (dest_off == special_alt->new_off + special_alt->new_len) {
663                         if (!fake_jump) {
664                                 WARN("%s: alternative jump to end of section",
665                                      special_alt->orig_sec->name);
666                                 return -1;
667                         }
668                         insn->jump_dest = fake_jump;
669                 }
670
671                 if (!insn->jump_dest) {
672                         WARN_FUNC("can't find alternative jump destination",
673                                   insn->sec, insn->offset);
674                         return -1;
675                 }
676         }
677
678         if (!last_new_insn) {
679                 WARN_FUNC("can't find last new alternative instruction",
680                           special_alt->new_sec, special_alt->new_off);
681                 return -1;
682         }
683
684         if (fake_jump)
685                 list_add(&fake_jump->list, &last_new_insn->list);
686
687         return 0;
688 }
689
690 /*
691  * A jump table entry can either convert a nop to a jump or a jump to a nop.
692  * If the original instruction is a jump, make the alt entry an effective nop
693  * by just skipping the original instruction.
694  */
695 static int handle_jump_alt(struct objtool_file *file,
696                            struct special_alt *special_alt,
697                            struct instruction *orig_insn,
698                            struct instruction **new_insn)
699 {
700         if (orig_insn->type == INSN_NOP)
701                 return 0;
702
703         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
704                 WARN_FUNC("unsupported instruction at jump label",
705                           orig_insn->sec, orig_insn->offset);
706                 return -1;
707         }
708
709         *new_insn = list_next_entry(orig_insn, list);
710         return 0;
711 }
712
713 /*
714  * Read all the special sections which have alternate instructions which can be
715  * patched in or redirected to at runtime.  Each instruction having alternate
716  * instruction(s) has them added to its insn->alts list, which will be
717  * traversed in validate_branch().
718  */
719 static int add_special_section_alts(struct objtool_file *file)
720 {
721         struct list_head special_alts;
722         struct instruction *orig_insn, *new_insn;
723         struct special_alt *special_alt, *tmp;
724         struct alternative *alt;
725         int ret;
726
727         ret = special_get_alts(file->elf, &special_alts);
728         if (ret)
729                 return ret;
730
731         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
732
733                 orig_insn = find_insn(file, special_alt->orig_sec,
734                                       special_alt->orig_off);
735                 if (!orig_insn) {
736                         WARN_FUNC("special: can't find orig instruction",
737                                   special_alt->orig_sec, special_alt->orig_off);
738                         ret = -1;
739                         goto out;
740                 }
741
742                 new_insn = NULL;
743                 if (!special_alt->group || special_alt->new_len) {
744                         new_insn = find_insn(file, special_alt->new_sec,
745                                              special_alt->new_off);
746                         if (!new_insn) {
747                                 WARN_FUNC("special: can't find new instruction",
748                                           special_alt->new_sec,
749                                           special_alt->new_off);
750                                 ret = -1;
751                                 goto out;
752                         }
753                 }
754
755                 if (special_alt->group) {
756                         ret = handle_group_alt(file, special_alt, orig_insn,
757                                                &new_insn);
758                         if (ret)
759                                 goto out;
760                 } else if (special_alt->jump_or_nop) {
761                         ret = handle_jump_alt(file, special_alt, orig_insn,
762                                               &new_insn);
763                         if (ret)
764                                 goto out;
765                 }
766
767                 alt = malloc(sizeof(*alt));
768                 if (!alt) {
769                         WARN("malloc failed");
770                         ret = -1;
771                         goto out;
772                 }
773
774                 alt->insn = new_insn;
775                 list_add_tail(&alt->list, &orig_insn->alts);
776
777                 list_del(&special_alt->list);
778                 free(special_alt);
779         }
780
781 out:
782         return ret;
783 }
784
785 static int add_switch_table(struct objtool_file *file, struct symbol *func,
786                             struct instruction *insn, struct rela *table,
787                             struct rela *next_table)
788 {
789         struct rela *rela = table;
790         struct instruction *alt_insn;
791         struct alternative *alt;
792
793         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
794                 if (rela == next_table)
795                         break;
796
797                 if (rela->sym->sec != insn->sec ||
798                     rela->addend <= func->offset ||
799                     rela->addend >= func->offset + func->len)
800                         break;
801
802                 alt_insn = find_insn(file, insn->sec, rela->addend);
803                 if (!alt_insn) {
804                         WARN("%s: can't find instruction at %s+0x%x",
805                              file->rodata->rela->name, insn->sec->name,
806                              rela->addend);
807                         return -1;
808                 }
809
810                 alt = malloc(sizeof(*alt));
811                 if (!alt) {
812                         WARN("malloc failed");
813                         return -1;
814                 }
815
816                 alt->insn = alt_insn;
817                 list_add_tail(&alt->list, &insn->alts);
818         }
819
820         return 0;
821 }
822
823 /*
824  * find_switch_table() - Given a dynamic jump, find the switch jump table in
825  * .rodata associated with it.
826  *
827  * There are 3 basic patterns:
828  *
829  * 1. jmpq *[rodata addr](,%reg,8)
830  *
831  *    This is the most common case by far.  It jumps to an address in a simple
832  *    jump table which is stored in .rodata.
833  *
834  * 2. jmpq *[rodata addr](%rip)
835  *
836  *    This is caused by a rare GCC quirk, currently only seen in three driver
837  *    functions in the kernel, only with certain obscure non-distro configs.
838  *
839  *    As part of an optimization, GCC makes a copy of an existing switch jump
840  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
841  *    jump) to use a single entry in the table.  The rest of the jump table and
842  *    some of its jump targets remain as dead code.
843  *
844  *    In such a case we can just crudely ignore all unreachable instruction
845  *    warnings for the entire object file.  Ideally we would just ignore them
846  *    for the function, but that would require redesigning the code quite a
847  *    bit.  And honestly that's just not worth doing: unreachable instruction
848  *    warnings are of questionable value anyway, and this is such a rare issue.
849  *
850  * 3. mov [rodata addr],%reg1
851  *    ... some instructions ...
852  *    jmpq *(%reg1,%reg2,8)
853  *
854  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
855  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
856  *
857  *    As of GCC 7 there are quite a few more of these and the 'in between' code
858  *    is significant. Esp. with KASAN enabled some of the code between the mov
859  *    and jmpq uses .rodata itself, which can confuse things.
860  *
861  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
862  *    ensure the same register is used in the mov and jump instructions.
863  *
864  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
865  */
866 static struct rela *find_switch_table(struct objtool_file *file,
867                                       struct symbol *func,
868                                       struct instruction *insn)
869 {
870         struct rela *text_rela, *rodata_rela;
871         struct instruction *orig_insn = insn;
872
873         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
874         if (text_rela && text_rela->sym == file->rodata->sym) {
875                 /* case 1 */
876                 rodata_rela = find_rela_by_dest(file->rodata,
877                                                 text_rela->addend);
878                 if (rodata_rela)
879                         return rodata_rela;
880
881                 /* case 2 */
882                 rodata_rela = find_rela_by_dest(file->rodata,
883                                                 text_rela->addend + 4);
884                 if (!rodata_rela)
885                         return NULL;
886
887                 file->ignore_unreachables = true;
888                 return rodata_rela;
889         }
890
891         /* case 3 */
892         /*
893          * Backward search using the @first_jump_src links, these help avoid
894          * much of the 'in between' code. Which avoids us getting confused by
895          * it.
896          */
897         for (insn = list_prev_entry(insn, list);
898
899              &insn->list != &file->insn_list &&
900              insn->sec == func->sec &&
901              insn->offset >= func->offset;
902
903              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
904
905                 if (insn->type == INSN_JUMP_DYNAMIC)
906                         break;
907
908                 /* allow small jumps within the range */
909                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
910                     insn->jump_dest &&
911                     (insn->jump_dest->offset <= insn->offset ||
912                      insn->jump_dest->offset > orig_insn->offset))
913                     break;
914
915                 /* look for a relocation which references .rodata */
916                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
917                                                     insn->len);
918                 if (!text_rela || text_rela->sym != file->rodata->sym)
919                         continue;
920
921                 /*
922                  * Make sure the .rodata address isn't associated with a
923                  * symbol.  gcc jump tables are anonymous data.
924                  */
925                 if (find_symbol_containing(file->rodata, text_rela->addend))
926                         continue;
927
928                 rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend);
929                 if (!rodata_rela)
930                         continue;
931
932                 return rodata_rela;
933         }
934
935         return NULL;
936 }
937
938
939 static int add_func_switch_tables(struct objtool_file *file,
940                                   struct symbol *func)
941 {
942         struct instruction *insn, *last = NULL, *prev_jump = NULL;
943         struct rela *rela, *prev_rela = NULL;
944         int ret;
945
946         func_for_each_insn(file, func, insn) {
947                 if (!last)
948                         last = insn;
949
950                 /*
951                  * Store back-pointers for unconditional forward jumps such
952                  * that find_switch_table() can back-track using those and
953                  * avoid some potentially confusing code.
954                  */
955                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
956                     insn->offset > last->offset &&
957                     insn->jump_dest->offset > insn->offset &&
958                     !insn->jump_dest->first_jump_src) {
959
960                         insn->jump_dest->first_jump_src = insn;
961                         last = insn->jump_dest;
962                 }
963
964                 if (insn->type != INSN_JUMP_DYNAMIC)
965                         continue;
966
967                 rela = find_switch_table(file, func, insn);
968                 if (!rela)
969                         continue;
970
971                 /*
972                  * We found a switch table, but we don't know yet how big it
973                  * is.  Don't add it until we reach the end of the function or
974                  * the beginning of another switch table in the same function.
975                  */
976                 if (prev_jump) {
977                         ret = add_switch_table(file, func, prev_jump, prev_rela,
978                                                rela);
979                         if (ret)
980                                 return ret;
981                 }
982
983                 prev_jump = insn;
984                 prev_rela = rela;
985         }
986
987         if (prev_jump) {
988                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
989                 if (ret)
990                         return ret;
991         }
992
993         return 0;
994 }
995
996 /*
997  * For some switch statements, gcc generates a jump table in the .rodata
998  * section which contains a list of addresses within the function to jump to.
999  * This finds these jump tables and adds them to the insn->alts lists.
1000  */
1001 static int add_switch_table_alts(struct objtool_file *file)
1002 {
1003         struct section *sec;
1004         struct symbol *func;
1005         int ret;
1006
1007         if (!file->rodata || !file->rodata->rela)
1008                 return 0;
1009
1010         for_each_sec(file, sec) {
1011                 list_for_each_entry(func, &sec->symbol_list, list) {
1012                         if (func->type != STT_FUNC)
1013                                 continue;
1014
1015                         ret = add_func_switch_tables(file, func);
1016                         if (ret)
1017                                 return ret;
1018                 }
1019         }
1020
1021         return 0;
1022 }
1023
1024 static int read_unwind_hints(struct objtool_file *file)
1025 {
1026         struct section *sec, *relasec;
1027         struct rela *rela;
1028         struct unwind_hint *hint;
1029         struct instruction *insn;
1030         struct cfi_reg *cfa;
1031         int i;
1032
1033         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1034         if (!sec)
1035                 return 0;
1036
1037         relasec = sec->rela;
1038         if (!relasec) {
1039                 WARN("missing .rela.discard.unwind_hints section");
1040                 return -1;
1041         }
1042
1043         if (sec->len % sizeof(struct unwind_hint)) {
1044                 WARN("struct unwind_hint size mismatch");
1045                 return -1;
1046         }
1047
1048         file->hints = true;
1049
1050         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1051                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1052
1053                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1054                 if (!rela) {
1055                         WARN("can't find rela for unwind_hints[%d]", i);
1056                         return -1;
1057                 }
1058
1059                 insn = find_insn(file, rela->sym->sec, rela->addend);
1060                 if (!insn) {
1061                         WARN("can't find insn for unwind_hints[%d]", i);
1062                         return -1;
1063                 }
1064
1065                 cfa = &insn->state.cfa;
1066
1067                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1068                         insn->save = true;
1069                         continue;
1070
1071                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1072                         insn->restore = true;
1073                         insn->hint = true;
1074                         continue;
1075                 }
1076
1077                 insn->hint = true;
1078
1079                 switch (hint->sp_reg) {
1080                 case ORC_REG_UNDEFINED:
1081                         cfa->base = CFI_UNDEFINED;
1082                         break;
1083                 case ORC_REG_SP:
1084                         cfa->base = CFI_SP;
1085                         break;
1086                 case ORC_REG_BP:
1087                         cfa->base = CFI_BP;
1088                         break;
1089                 case ORC_REG_SP_INDIRECT:
1090                         cfa->base = CFI_SP_INDIRECT;
1091                         break;
1092                 case ORC_REG_R10:
1093                         cfa->base = CFI_R10;
1094                         break;
1095                 case ORC_REG_R13:
1096                         cfa->base = CFI_R13;
1097                         break;
1098                 case ORC_REG_DI:
1099                         cfa->base = CFI_DI;
1100                         break;
1101                 case ORC_REG_DX:
1102                         cfa->base = CFI_DX;
1103                         break;
1104                 default:
1105                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1106                                   insn->sec, insn->offset, hint->sp_reg);
1107                         return -1;
1108                 }
1109
1110                 cfa->offset = hint->sp_offset;
1111                 insn->state.type = hint->type;
1112         }
1113
1114         return 0;
1115 }
1116
1117 static int read_retpoline_hints(struct objtool_file *file)
1118 {
1119         struct section *sec;
1120         struct instruction *insn;
1121         struct rela *rela;
1122
1123         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1124         if (!sec)
1125                 return 0;
1126
1127         list_for_each_entry(rela, &sec->rela_list, list) {
1128                 if (rela->sym->type != STT_SECTION) {
1129                         WARN("unexpected relocation symbol type in %s", sec->name);
1130                         return -1;
1131                 }
1132
1133                 insn = find_insn(file, rela->sym->sec, rela->addend);
1134                 if (!insn) {
1135                         WARN("bad .discard.retpoline_safe entry");
1136                         return -1;
1137                 }
1138
1139                 if (insn->type != INSN_JUMP_DYNAMIC &&
1140                     insn->type != INSN_CALL_DYNAMIC) {
1141                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1142                                   insn->sec, insn->offset);
1143                         return -1;
1144                 }
1145
1146                 insn->retpoline_safe = true;
1147         }
1148
1149         return 0;
1150 }
1151
1152 static int decode_sections(struct objtool_file *file)
1153 {
1154         int ret;
1155
1156         ret = decode_instructions(file);
1157         if (ret)
1158                 return ret;
1159
1160         ret = add_dead_ends(file);
1161         if (ret)
1162                 return ret;
1163
1164         add_ignores(file);
1165
1166         ret = add_nospec_ignores(file);
1167         if (ret)
1168                 return ret;
1169
1170         ret = add_jump_destinations(file);
1171         if (ret)
1172                 return ret;
1173
1174         ret = add_special_section_alts(file);
1175         if (ret)
1176                 return ret;
1177
1178         ret = add_call_destinations(file);
1179         if (ret)
1180                 return ret;
1181
1182         ret = add_switch_table_alts(file);
1183         if (ret)
1184                 return ret;
1185
1186         ret = read_unwind_hints(file);
1187         if (ret)
1188                 return ret;
1189
1190         ret = read_retpoline_hints(file);
1191         if (ret)
1192                 return ret;
1193
1194         return 0;
1195 }
1196
1197 static bool is_fentry_call(struct instruction *insn)
1198 {
1199         if (insn->type == INSN_CALL &&
1200             insn->call_dest->type == STT_NOTYPE &&
1201             !strcmp(insn->call_dest->name, "__fentry__"))
1202                 return true;
1203
1204         return false;
1205 }
1206
1207 static bool has_modified_stack_frame(struct insn_state *state)
1208 {
1209         int i;
1210
1211         if (state->cfa.base != initial_func_cfi.cfa.base ||
1212             state->cfa.offset != initial_func_cfi.cfa.offset ||
1213             state->stack_size != initial_func_cfi.cfa.offset ||
1214             state->drap)
1215                 return true;
1216
1217         for (i = 0; i < CFI_NUM_REGS; i++)
1218                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1219                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1220                         return true;
1221
1222         return false;
1223 }
1224
1225 static bool has_valid_stack_frame(struct insn_state *state)
1226 {
1227         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1228             state->regs[CFI_BP].offset == -16)
1229                 return true;
1230
1231         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1232                 return true;
1233
1234         return false;
1235 }
1236
1237 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1238 {
1239         struct cfi_reg *cfa = &state->cfa;
1240         struct stack_op *op = &insn->stack_op;
1241
1242         if (cfa->base != CFI_SP)
1243                 return 0;
1244
1245         /* push */
1246         if (op->dest.type == OP_DEST_PUSH)
1247                 cfa->offset += 8;
1248
1249         /* pop */
1250         if (op->src.type == OP_SRC_POP)
1251                 cfa->offset -= 8;
1252
1253         /* add immediate to sp */
1254         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1255             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1256                 cfa->offset -= op->src.offset;
1257
1258         return 0;
1259 }
1260
1261 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1262                      int offset)
1263 {
1264         if (arch_callee_saved_reg(reg) &&
1265             state->regs[reg].base == CFI_UNDEFINED) {
1266                 state->regs[reg].base = base;
1267                 state->regs[reg].offset = offset;
1268         }
1269 }
1270
1271 static void restore_reg(struct insn_state *state, unsigned char reg)
1272 {
1273         state->regs[reg].base = CFI_UNDEFINED;
1274         state->regs[reg].offset = 0;
1275 }
1276
1277 /*
1278  * A note about DRAP stack alignment:
1279  *
1280  * GCC has the concept of a DRAP register, which is used to help keep track of
1281  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1282  * register.  The typical DRAP pattern is:
1283  *
1284  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1285  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1286  *   41 ff 72 f8                pushq  -0x8(%r10)
1287  *   55                         push   %rbp
1288  *   48 89 e5                   mov    %rsp,%rbp
1289  *                              (more pushes)
1290  *   41 52                      push   %r10
1291  *                              ...
1292  *   41 5a                      pop    %r10
1293  *                              (more pops)
1294  *   5d                         pop    %rbp
1295  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1296  *   c3                         retq
1297  *
1298  * There are some variations in the epilogues, like:
1299  *
1300  *   5b                         pop    %rbx
1301  *   41 5a                      pop    %r10
1302  *   41 5c                      pop    %r12
1303  *   41 5d                      pop    %r13
1304  *   41 5e                      pop    %r14
1305  *   c9                         leaveq
1306  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1307  *   c3                         retq
1308  *
1309  * and:
1310  *
1311  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1312  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1313  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1314  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1315  *   c9                         leaveq
1316  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1317  *   c3                         retq
1318  *
1319  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1320  * restored beforehand:
1321  *
1322  *   41 55                      push   %r13
1323  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1324  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1325  *                              ...
1326  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1327  *   41 5d                      pop    %r13
1328  *   c3                         retq
1329  */
1330 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1331 {
1332         struct stack_op *op = &insn->stack_op;
1333         struct cfi_reg *cfa = &state->cfa;
1334         struct cfi_reg *regs = state->regs;
1335
1336         /* stack operations don't make sense with an undefined CFA */
1337         if (cfa->base == CFI_UNDEFINED) {
1338                 if (insn->func) {
1339                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1340                         return -1;
1341                 }
1342                 return 0;
1343         }
1344
1345         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1346                 return update_insn_state_regs(insn, state);
1347
1348         switch (op->dest.type) {
1349
1350         case OP_DEST_REG:
1351                 switch (op->src.type) {
1352
1353                 case OP_SRC_REG:
1354                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1355                             cfa->base == CFI_SP &&
1356                             regs[CFI_BP].base == CFI_CFA &&
1357                             regs[CFI_BP].offset == -cfa->offset) {
1358
1359                                 /* mov %rsp, %rbp */
1360                                 cfa->base = op->dest.reg;
1361                                 state->bp_scratch = false;
1362                         }
1363
1364                         else if (op->src.reg == CFI_SP &&
1365                                  op->dest.reg == CFI_BP && state->drap) {
1366
1367                                 /* drap: mov %rsp, %rbp */
1368                                 regs[CFI_BP].base = CFI_BP;
1369                                 regs[CFI_BP].offset = -state->stack_size;
1370                                 state->bp_scratch = false;
1371                         }
1372
1373                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1374
1375                                 /*
1376                                  * mov %rsp, %reg
1377                                  *
1378                                  * This is needed for the rare case where GCC
1379                                  * does:
1380                                  *
1381                                  *   mov    %rsp, %rax
1382                                  *   ...
1383                                  *   mov    %rax, %rsp
1384                                  */
1385                                 state->vals[op->dest.reg].base = CFI_CFA;
1386                                 state->vals[op->dest.reg].offset = -state->stack_size;
1387                         }
1388
1389                         else if (op->dest.reg == cfa->base) {
1390
1391                                 /* mov %reg, %rsp */
1392                                 if (cfa->base == CFI_SP &&
1393                                     state->vals[op->src.reg].base == CFI_CFA) {
1394
1395                                         /*
1396                                          * This is needed for the rare case
1397                                          * where GCC does something dumb like:
1398                                          *
1399                                          *   lea    0x8(%rsp), %rcx
1400                                          *   ...
1401                                          *   mov    %rcx, %rsp
1402                                          */
1403                                         cfa->offset = -state->vals[op->src.reg].offset;
1404                                         state->stack_size = cfa->offset;
1405
1406                                 } else {
1407                                         cfa->base = CFI_UNDEFINED;
1408                                         cfa->offset = 0;
1409                                 }
1410                         }
1411
1412                         break;
1413
1414                 case OP_SRC_ADD:
1415                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1416
1417                                 /* add imm, %rsp */
1418                                 state->stack_size -= op->src.offset;
1419                                 if (cfa->base == CFI_SP)
1420                                         cfa->offset -= op->src.offset;
1421                                 break;
1422                         }
1423
1424                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1425
1426                                 /* lea disp(%rbp), %rsp */
1427                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1428                                 break;
1429                         }
1430
1431                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1432
1433                                 /* drap: lea disp(%rsp), %drap */
1434                                 state->drap_reg = op->dest.reg;
1435
1436                                 /*
1437                                  * lea disp(%rsp), %reg
1438                                  *
1439                                  * This is needed for the rare case where GCC
1440                                  * does something dumb like:
1441                                  *
1442                                  *   lea    0x8(%rsp), %rcx
1443                                  *   ...
1444                                  *   mov    %rcx, %rsp
1445                                  */
1446                                 state->vals[op->dest.reg].base = CFI_CFA;
1447                                 state->vals[op->dest.reg].offset = \
1448                                         -state->stack_size + op->src.offset;
1449
1450                                 break;
1451                         }
1452
1453                         if (state->drap && op->dest.reg == CFI_SP &&
1454                             op->src.reg == state->drap_reg) {
1455
1456                                  /* drap: lea disp(%drap), %rsp */
1457                                 cfa->base = CFI_SP;
1458                                 cfa->offset = state->stack_size = -op->src.offset;
1459                                 state->drap_reg = CFI_UNDEFINED;
1460                                 state->drap = false;
1461                                 break;
1462                         }
1463
1464                         if (op->dest.reg == state->cfa.base) {
1465                                 WARN_FUNC("unsupported stack register modification",
1466                                           insn->sec, insn->offset);
1467                                 return -1;
1468                         }
1469
1470                         break;
1471
1472                 case OP_SRC_AND:
1473                         if (op->dest.reg != CFI_SP ||
1474                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1475                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1476                                 WARN_FUNC("unsupported stack pointer realignment",
1477                                           insn->sec, insn->offset);
1478                                 return -1;
1479                         }
1480
1481                         if (state->drap_reg != CFI_UNDEFINED) {
1482                                 /* drap: and imm, %rsp */
1483                                 cfa->base = state->drap_reg;
1484                                 cfa->offset = state->stack_size = 0;
1485                                 state->drap = true;
1486                         }
1487
1488                         /*
1489                          * Older versions of GCC (4.8ish) realign the stack
1490                          * without DRAP, with a frame pointer.
1491                          */
1492
1493                         break;
1494
1495                 case OP_SRC_POP:
1496                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1497                             op->dest.reg == cfa->base) {
1498
1499                                 /* pop %rbp */
1500                                 cfa->base = CFI_SP;
1501                         }
1502
1503                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1504                             op->dest.type == OP_DEST_REG &&
1505                             op->dest.reg == state->drap_reg &&
1506                             state->drap_offset == -state->stack_size) {
1507
1508                                 /* drap: pop %drap */
1509                                 cfa->base = state->drap_reg;
1510                                 cfa->offset = 0;
1511                                 state->drap_offset = -1;
1512
1513                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1514
1515                                 /* pop %reg */
1516                                 restore_reg(state, op->dest.reg);
1517                         }
1518
1519                         state->stack_size -= 8;
1520                         if (cfa->base == CFI_SP)
1521                                 cfa->offset -= 8;
1522
1523                         break;
1524
1525                 case OP_SRC_REG_INDIRECT:
1526                         if (state->drap && op->src.reg == CFI_BP &&
1527                             op->src.offset == state->drap_offset) {
1528
1529                                 /* drap: mov disp(%rbp), %drap */
1530                                 cfa->base = state->drap_reg;
1531                                 cfa->offset = 0;
1532                                 state->drap_offset = -1;
1533                         }
1534
1535                         if (state->drap && op->src.reg == CFI_BP &&
1536                             op->src.offset == regs[op->dest.reg].offset) {
1537
1538                                 /* drap: mov disp(%rbp), %reg */
1539                                 restore_reg(state, op->dest.reg);
1540
1541                         } else if (op->src.reg == cfa->base &&
1542                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1543
1544                                 /* mov disp(%rbp), %reg */
1545                                 /* mov disp(%rsp), %reg */
1546                                 restore_reg(state, op->dest.reg);
1547                         }
1548
1549                         break;
1550
1551                 default:
1552                         WARN_FUNC("unknown stack-related instruction",
1553                                   insn->sec, insn->offset);
1554                         return -1;
1555                 }
1556
1557                 break;
1558
1559         case OP_DEST_PUSH:
1560                 state->stack_size += 8;
1561                 if (cfa->base == CFI_SP)
1562                         cfa->offset += 8;
1563
1564                 if (op->src.type != OP_SRC_REG)
1565                         break;
1566
1567                 if (state->drap) {
1568                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1569
1570                                 /* drap: push %drap */
1571                                 cfa->base = CFI_BP_INDIRECT;
1572                                 cfa->offset = -state->stack_size;
1573
1574                                 /* save drap so we know when to restore it */
1575                                 state->drap_offset = -state->stack_size;
1576
1577                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1578
1579                                 /* drap: push %rbp */
1580                                 state->stack_size = 0;
1581
1582                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1583
1584                                 /* drap: push %reg */
1585                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1586                         }
1587
1588                 } else {
1589
1590                         /* push %reg */
1591                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1592                 }
1593
1594                 /* detect when asm code uses rbp as a scratch register */
1595                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1596                     cfa->base != CFI_BP)
1597                         state->bp_scratch = true;
1598                 break;
1599
1600         case OP_DEST_REG_INDIRECT:
1601
1602                 if (state->drap) {
1603                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1604
1605                                 /* drap: mov %drap, disp(%rbp) */
1606                                 cfa->base = CFI_BP_INDIRECT;
1607                                 cfa->offset = op->dest.offset;
1608
1609                                 /* save drap offset so we know when to restore it */
1610                                 state->drap_offset = op->dest.offset;
1611                         }
1612
1613                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1614
1615                                 /* drap: mov reg, disp(%rbp) */
1616                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1617                         }
1618
1619                 } else if (op->dest.reg == cfa->base) {
1620
1621                         /* mov reg, disp(%rbp) */
1622                         /* mov reg, disp(%rsp) */
1623                         save_reg(state, op->src.reg, CFI_CFA,
1624                                  op->dest.offset - state->cfa.offset);
1625                 }
1626
1627                 break;
1628
1629         case OP_DEST_LEAVE:
1630                 if ((!state->drap && cfa->base != CFI_BP) ||
1631                     (state->drap && cfa->base != state->drap_reg)) {
1632                         WARN_FUNC("leave instruction with modified stack frame",
1633                                   insn->sec, insn->offset);
1634                         return -1;
1635                 }
1636
1637                 /* leave (mov %rbp, %rsp; pop %rbp) */
1638
1639                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1640                 restore_reg(state, CFI_BP);
1641
1642                 if (!state->drap) {
1643                         cfa->base = CFI_SP;
1644                         cfa->offset -= 8;
1645                 }
1646
1647                 break;
1648
1649         case OP_DEST_MEM:
1650                 if (op->src.type != OP_SRC_POP) {
1651                         WARN_FUNC("unknown stack-related memory operation",
1652                                   insn->sec, insn->offset);
1653                         return -1;
1654                 }
1655
1656                 /* pop mem */
1657                 state->stack_size -= 8;
1658                 if (cfa->base == CFI_SP)
1659                         cfa->offset -= 8;
1660
1661                 break;
1662
1663         default:
1664                 WARN_FUNC("unknown stack-related instruction",
1665                           insn->sec, insn->offset);
1666                 return -1;
1667         }
1668
1669         return 0;
1670 }
1671
1672 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1673 {
1674         struct insn_state *state1 = &insn->state, *state2 = state;
1675         int i;
1676
1677         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1678                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1679                           insn->sec, insn->offset,
1680                           state1->cfa.base, state1->cfa.offset,
1681                           state2->cfa.base, state2->cfa.offset);
1682
1683         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1684                 for (i = 0; i < CFI_NUM_REGS; i++) {
1685                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1686                                     sizeof(struct cfi_reg)))
1687                                 continue;
1688
1689                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1690                                   insn->sec, insn->offset,
1691                                   i, state1->regs[i].base, state1->regs[i].offset,
1692                                   i, state2->regs[i].base, state2->regs[i].offset);
1693                         break;
1694                 }
1695
1696         } else if (state1->type != state2->type) {
1697                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1698                           insn->sec, insn->offset, state1->type, state2->type);
1699
1700         } else if (state1->drap != state2->drap ||
1701                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1702                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1703                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1704                           insn->sec, insn->offset,
1705                           state1->drap, state1->drap_reg, state1->drap_offset,
1706                           state2->drap, state2->drap_reg, state2->drap_offset);
1707
1708         } else
1709                 return true;
1710
1711         return false;
1712 }
1713
1714 /*
1715  * Follow the branch starting at the given instruction, and recursively follow
1716  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1717  * each instruction and validate all the rules described in
1718  * tools/objtool/Documentation/stack-validation.txt.
1719  */
1720 static int validate_branch(struct objtool_file *file, struct instruction *first,
1721                            struct insn_state state)
1722 {
1723         struct alternative *alt;
1724         struct instruction *insn, *next_insn;
1725         struct section *sec;
1726         struct symbol *func = NULL;
1727         int ret;
1728
1729         insn = first;
1730         sec = insn->sec;
1731
1732         if (insn->alt_group && list_empty(&insn->alts)) {
1733                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1734                           sec, insn->offset);
1735                 return 1;
1736         }
1737
1738         while (1) {
1739                 next_insn = next_insn_same_sec(file, insn);
1740
1741
1742                 if (file->c_file && func && insn->func && func != insn->func) {
1743                         WARN("%s() falls through to next function %s()",
1744                              func->name, insn->func->name);
1745                         return 1;
1746                 }
1747
1748                 if (insn->func)
1749                         func = insn->func;
1750
1751                 if (func && insn->ignore) {
1752                         WARN_FUNC("BUG: why am I validating an ignored function?",
1753                                   sec, insn->offset);
1754                         return 1;
1755                 }
1756
1757                 if (insn->visited) {
1758                         if (!insn->hint && !insn_state_match(insn, &state))
1759                                 return 1;
1760
1761                         return 0;
1762                 }
1763
1764                 if (insn->hint) {
1765                         if (insn->restore) {
1766                                 struct instruction *save_insn, *i;
1767
1768                                 i = insn;
1769                                 save_insn = NULL;
1770                                 func_for_each_insn_continue_reverse(file, func, i) {
1771                                         if (i->save) {
1772                                                 save_insn = i;
1773                                                 break;
1774                                         }
1775                                 }
1776
1777                                 if (!save_insn) {
1778                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1779                                                   sec, insn->offset);
1780                                         return 1;
1781                                 }
1782
1783                                 if (!save_insn->visited) {
1784                                         /*
1785                                          * Oops, no state to copy yet.
1786                                          * Hopefully we can reach this
1787                                          * instruction from another branch
1788                                          * after the save insn has been
1789                                          * visited.
1790                                          */
1791                                         if (insn == first)
1792                                                 return 0;
1793
1794                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1795                                                   sec, insn->offset);
1796                                         return 1;
1797                                 }
1798
1799                                 insn->state = save_insn->state;
1800                         }
1801
1802                         state = insn->state;
1803
1804                 } else
1805                         insn->state = state;
1806
1807                 insn->visited = true;
1808
1809                 if (!insn->ignore_alts) {
1810                         list_for_each_entry(alt, &insn->alts, list) {
1811                                 ret = validate_branch(file, alt->insn, state);
1812                                 if (ret)
1813                                         return 1;
1814                         }
1815                 }
1816
1817                 switch (insn->type) {
1818
1819                 case INSN_RETURN:
1820                         if (func && has_modified_stack_frame(&state)) {
1821                                 WARN_FUNC("return with modified stack frame",
1822                                           sec, insn->offset);
1823                                 return 1;
1824                         }
1825
1826                         if (state.bp_scratch) {
1827                                 WARN("%s uses BP as a scratch register",
1828                                      insn->func->name);
1829                                 return 1;
1830                         }
1831
1832                         return 0;
1833
1834                 case INSN_CALL:
1835                         if (is_fentry_call(insn))
1836                                 break;
1837
1838                         ret = dead_end_function(file, insn->call_dest);
1839                         if (ret == 1)
1840                                 return 0;
1841                         if (ret == -1)
1842                                 return 1;
1843
1844                         /* fallthrough */
1845                 case INSN_CALL_DYNAMIC:
1846                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
1847                                 WARN_FUNC("call without frame pointer save/setup",
1848                                           sec, insn->offset);
1849                                 return 1;
1850                         }
1851                         break;
1852
1853                 case INSN_JUMP_CONDITIONAL:
1854                 case INSN_JUMP_UNCONDITIONAL:
1855                         if (insn->jump_dest &&
1856                             (!func || !insn->jump_dest->func ||
1857                              func == insn->jump_dest->func)) {
1858                                 ret = validate_branch(file, insn->jump_dest,
1859                                                       state);
1860                                 if (ret)
1861                                         return 1;
1862
1863                         } else if (func && has_modified_stack_frame(&state)) {
1864                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1865                                           sec, insn->offset);
1866                                 return 1;
1867                         }
1868
1869                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1870                                 return 0;
1871
1872                         break;
1873
1874                 case INSN_JUMP_DYNAMIC:
1875                         if (func && list_empty(&insn->alts) &&
1876                             has_modified_stack_frame(&state)) {
1877                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1878                                           sec, insn->offset);
1879                                 return 1;
1880                         }
1881
1882                         return 0;
1883
1884                 case INSN_CONTEXT_SWITCH:
1885                         if (func && (!next_insn || !next_insn->hint)) {
1886                                 WARN_FUNC("unsupported instruction in callable function",
1887                                           sec, insn->offset);
1888                                 return 1;
1889                         }
1890                         return 0;
1891
1892                 case INSN_STACK:
1893                         if (update_insn_state(insn, &state))
1894                                 return 1;
1895
1896                         break;
1897
1898                 default:
1899                         break;
1900                 }
1901
1902                 if (insn->dead_end)
1903                         return 0;
1904
1905                 if (!next_insn) {
1906                         if (state.cfa.base == CFI_UNDEFINED)
1907                                 return 0;
1908                         WARN("%s: unexpected end of section", sec->name);
1909                         return 1;
1910                 }
1911
1912                 insn = next_insn;
1913         }
1914
1915         return 0;
1916 }
1917
1918 static int validate_unwind_hints(struct objtool_file *file)
1919 {
1920         struct instruction *insn;
1921         int ret, warnings = 0;
1922         struct insn_state state;
1923
1924         if (!file->hints)
1925                 return 0;
1926
1927         clear_insn_state(&state);
1928
1929         for_each_insn(file, insn) {
1930                 if (insn->hint && !insn->visited) {
1931                         ret = validate_branch(file, insn, state);
1932                         warnings += ret;
1933                 }
1934         }
1935
1936         return warnings;
1937 }
1938
1939 static int validate_retpoline(struct objtool_file *file)
1940 {
1941         struct instruction *insn;
1942         int warnings = 0;
1943
1944         for_each_insn(file, insn) {
1945                 if (insn->type != INSN_JUMP_DYNAMIC &&
1946                     insn->type != INSN_CALL_DYNAMIC)
1947                         continue;
1948
1949                 if (insn->retpoline_safe)
1950                         continue;
1951
1952                 /*
1953                  * .init.text code is ran before userspace and thus doesn't
1954                  * strictly need retpolines, except for modules which are
1955                  * loaded late, they very much do need retpoline in their
1956                  * .init.text
1957                  */
1958                 if (!strcmp(insn->sec->name, ".init.text") && !module)
1959                         continue;
1960
1961                 WARN_FUNC("indirect %s found in RETPOLINE build",
1962                           insn->sec, insn->offset,
1963                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
1964
1965                 warnings++;
1966         }
1967
1968         return warnings;
1969 }
1970
1971 static bool is_kasan_insn(struct instruction *insn)
1972 {
1973         return (insn->type == INSN_CALL &&
1974                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1975 }
1976
1977 static bool is_ubsan_insn(struct instruction *insn)
1978 {
1979         return (insn->type == INSN_CALL &&
1980                 !strcmp(insn->call_dest->name,
1981                         "__ubsan_handle_builtin_unreachable"));
1982 }
1983
1984 static bool ignore_unreachable_insn(struct instruction *insn)
1985 {
1986         int i;
1987
1988         if (insn->ignore || insn->type == INSN_NOP)
1989                 return true;
1990
1991         /*
1992          * Ignore any unused exceptions.  This can happen when a whitelisted
1993          * function has an exception table entry.
1994          *
1995          * Also ignore alternative replacement instructions.  This can happen
1996          * when a whitelisted function uses one of the ALTERNATIVE macros.
1997          */
1998         if (!strcmp(insn->sec->name, ".fixup") ||
1999             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2000             !strcmp(insn->sec->name, ".altinstr_aux"))
2001                 return true;
2002
2003         /*
2004          * Check if this (or a subsequent) instruction is related to
2005          * CONFIG_UBSAN or CONFIG_KASAN.
2006          *
2007          * End the search at 5 instructions to avoid going into the weeds.
2008          */
2009         if (!insn->func)
2010                 return false;
2011         for (i = 0; i < 5; i++) {
2012
2013                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2014                         return true;
2015
2016                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2017                         if (insn->jump_dest &&
2018                             insn->jump_dest->func == insn->func) {
2019                                 insn = insn->jump_dest;
2020                                 continue;
2021                         }
2022
2023                         break;
2024                 }
2025
2026                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2027                         break;
2028
2029                 insn = list_next_entry(insn, list);
2030         }
2031
2032         return false;
2033 }
2034
2035 static int validate_functions(struct objtool_file *file)
2036 {
2037         struct section *sec;
2038         struct symbol *func;
2039         struct instruction *insn;
2040         struct insn_state state;
2041         int ret, warnings = 0;
2042
2043         clear_insn_state(&state);
2044
2045         state.cfa = initial_func_cfi.cfa;
2046         memcpy(&state.regs, &initial_func_cfi.regs,
2047                CFI_NUM_REGS * sizeof(struct cfi_reg));
2048         state.stack_size = initial_func_cfi.cfa.offset;
2049
2050         for_each_sec(file, sec) {
2051                 list_for_each_entry(func, &sec->symbol_list, list) {
2052                         if (func->type != STT_FUNC)
2053                                 continue;
2054
2055                         insn = find_insn(file, sec, func->offset);
2056                         if (!insn || insn->ignore)
2057                                 continue;
2058
2059                         ret = validate_branch(file, insn, state);
2060                         warnings += ret;
2061                 }
2062         }
2063
2064         return warnings;
2065 }
2066
2067 static int validate_reachable_instructions(struct objtool_file *file)
2068 {
2069         struct instruction *insn;
2070
2071         if (file->ignore_unreachables)
2072                 return 0;
2073
2074         for_each_insn(file, insn) {
2075                 if (insn->visited || ignore_unreachable_insn(insn))
2076                         continue;
2077
2078                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2079                 return 1;
2080         }
2081
2082         return 0;
2083 }
2084
2085 static void cleanup(struct objtool_file *file)
2086 {
2087         struct instruction *insn, *tmpinsn;
2088         struct alternative *alt, *tmpalt;
2089
2090         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2091                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2092                         list_del(&alt->list);
2093                         free(alt);
2094                 }
2095                 list_del(&insn->list);
2096                 hash_del(&insn->hash);
2097                 free(insn);
2098         }
2099         elf_close(file->elf);
2100 }
2101
2102 int check(const char *_objname, bool orc)
2103 {
2104         struct objtool_file file;
2105         int ret, warnings = 0;
2106
2107         objname = _objname;
2108
2109         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2110         if (!file.elf)
2111                 return 1;
2112
2113         INIT_LIST_HEAD(&file.insn_list);
2114         hash_init(file.insn_hash);
2115         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
2116         file.rodata = find_section_by_name(file.elf, ".rodata");
2117         file.c_file = find_section_by_name(file.elf, ".comment");
2118         file.ignore_unreachables = no_unreachable;
2119         file.hints = false;
2120
2121         arch_initial_func_cfi_state(&initial_func_cfi);
2122
2123         ret = decode_sections(&file);
2124         if (ret < 0)
2125                 goto out;
2126         warnings += ret;
2127
2128         if (list_empty(&file.insn_list))
2129                 goto out;
2130
2131         if (retpoline) {
2132                 ret = validate_retpoline(&file);
2133                 if (ret < 0)
2134                         return ret;
2135                 warnings += ret;
2136         }
2137
2138         ret = validate_functions(&file);
2139         if (ret < 0)
2140                 goto out;
2141         warnings += ret;
2142
2143         ret = validate_unwind_hints(&file);
2144         if (ret < 0)
2145                 goto out;
2146         warnings += ret;
2147
2148         if (!warnings) {
2149                 ret = validate_reachable_instructions(&file);
2150                 if (ret < 0)
2151                         goto out;
2152                 warnings += ret;
2153         }
2154
2155         if (orc) {
2156                 ret = create_orc(&file);
2157                 if (ret < 0)
2158                         goto out;
2159
2160                 ret = create_orc_sections(&file);
2161                 if (ret < 0)
2162                         goto out;
2163
2164                 ret = elf_write(file.elf);
2165                 if (ret < 0)
2166                         goto out;
2167         }
2168
2169 out:
2170         cleanup(&file);
2171
2172         /* ignore warnings for now until we get all the code cleaned up */
2173         if (ret || warnings)
2174                 return 0;
2175         return 0;
2176 }