objtool: Add Clang support
[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->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1390                                  cfa->base == CFI_BP) {
1391
1392                                 /*
1393                                  * mov %rbp, %rsp
1394                                  *
1395                                  * Restore the original stack pointer (Clang).
1396                                  */
1397                                 state->stack_size = -state->regs[CFI_BP].offset;
1398                         }
1399
1400                         else if (op->dest.reg == cfa->base) {
1401
1402                                 /* mov %reg, %rsp */
1403                                 if (cfa->base == CFI_SP &&
1404                                     state->vals[op->src.reg].base == CFI_CFA) {
1405
1406                                         /*
1407                                          * This is needed for the rare case
1408                                          * where GCC does something dumb like:
1409                                          *
1410                                          *   lea    0x8(%rsp), %rcx
1411                                          *   ...
1412                                          *   mov    %rcx, %rsp
1413                                          */
1414                                         cfa->offset = -state->vals[op->src.reg].offset;
1415                                         state->stack_size = cfa->offset;
1416
1417                                 } else {
1418                                         cfa->base = CFI_UNDEFINED;
1419                                         cfa->offset = 0;
1420                                 }
1421                         }
1422
1423                         break;
1424
1425                 case OP_SRC_ADD:
1426                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1427
1428                                 /* add imm, %rsp */
1429                                 state->stack_size -= op->src.offset;
1430                                 if (cfa->base == CFI_SP)
1431                                         cfa->offset -= op->src.offset;
1432                                 break;
1433                         }
1434
1435                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1436
1437                                 /* lea disp(%rbp), %rsp */
1438                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1439                                 break;
1440                         }
1441
1442                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1443
1444                                 /* drap: lea disp(%rsp), %drap */
1445                                 state->drap_reg = op->dest.reg;
1446
1447                                 /*
1448                                  * lea disp(%rsp), %reg
1449                                  *
1450                                  * This is needed for the rare case where GCC
1451                                  * does something dumb like:
1452                                  *
1453                                  *   lea    0x8(%rsp), %rcx
1454                                  *   ...
1455                                  *   mov    %rcx, %rsp
1456                                  */
1457                                 state->vals[op->dest.reg].base = CFI_CFA;
1458                                 state->vals[op->dest.reg].offset = \
1459                                         -state->stack_size + op->src.offset;
1460
1461                                 break;
1462                         }
1463
1464                         if (state->drap && op->dest.reg == CFI_SP &&
1465                             op->src.reg == state->drap_reg) {
1466
1467                                  /* drap: lea disp(%drap), %rsp */
1468                                 cfa->base = CFI_SP;
1469                                 cfa->offset = state->stack_size = -op->src.offset;
1470                                 state->drap_reg = CFI_UNDEFINED;
1471                                 state->drap = false;
1472                                 break;
1473                         }
1474
1475                         if (op->dest.reg == state->cfa.base) {
1476                                 WARN_FUNC("unsupported stack register modification",
1477                                           insn->sec, insn->offset);
1478                                 return -1;
1479                         }
1480
1481                         break;
1482
1483                 case OP_SRC_AND:
1484                         if (op->dest.reg != CFI_SP ||
1485                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1486                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1487                                 WARN_FUNC("unsupported stack pointer realignment",
1488                                           insn->sec, insn->offset);
1489                                 return -1;
1490                         }
1491
1492                         if (state->drap_reg != CFI_UNDEFINED) {
1493                                 /* drap: and imm, %rsp */
1494                                 cfa->base = state->drap_reg;
1495                                 cfa->offset = state->stack_size = 0;
1496                                 state->drap = true;
1497                         }
1498
1499                         /*
1500                          * Older versions of GCC (4.8ish) realign the stack
1501                          * without DRAP, with a frame pointer.
1502                          */
1503
1504                         break;
1505
1506                 case OP_SRC_POP:
1507                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1508                             op->dest.reg == cfa->base) {
1509
1510                                 /* pop %rbp */
1511                                 cfa->base = CFI_SP;
1512                         }
1513
1514                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1515                             op->dest.type == OP_DEST_REG &&
1516                             op->dest.reg == state->drap_reg &&
1517                             state->drap_offset == -state->stack_size) {
1518
1519                                 /* drap: pop %drap */
1520                                 cfa->base = state->drap_reg;
1521                                 cfa->offset = 0;
1522                                 state->drap_offset = -1;
1523
1524                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1525
1526                                 /* pop %reg */
1527                                 restore_reg(state, op->dest.reg);
1528                         }
1529
1530                         state->stack_size -= 8;
1531                         if (cfa->base == CFI_SP)
1532                                 cfa->offset -= 8;
1533
1534                         break;
1535
1536                 case OP_SRC_REG_INDIRECT:
1537                         if (state->drap && op->src.reg == CFI_BP &&
1538                             op->src.offset == state->drap_offset) {
1539
1540                                 /* drap: mov disp(%rbp), %drap */
1541                                 cfa->base = state->drap_reg;
1542                                 cfa->offset = 0;
1543                                 state->drap_offset = -1;
1544                         }
1545
1546                         if (state->drap && op->src.reg == CFI_BP &&
1547                             op->src.offset == regs[op->dest.reg].offset) {
1548
1549                                 /* drap: mov disp(%rbp), %reg */
1550                                 restore_reg(state, op->dest.reg);
1551
1552                         } else if (op->src.reg == cfa->base &&
1553                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1554
1555                                 /* mov disp(%rbp), %reg */
1556                                 /* mov disp(%rsp), %reg */
1557                                 restore_reg(state, op->dest.reg);
1558                         }
1559
1560                         break;
1561
1562                 default:
1563                         WARN_FUNC("unknown stack-related instruction",
1564                                   insn->sec, insn->offset);
1565                         return -1;
1566                 }
1567
1568                 break;
1569
1570         case OP_DEST_PUSH:
1571                 state->stack_size += 8;
1572                 if (cfa->base == CFI_SP)
1573                         cfa->offset += 8;
1574
1575                 if (op->src.type != OP_SRC_REG)
1576                         break;
1577
1578                 if (state->drap) {
1579                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1580
1581                                 /* drap: push %drap */
1582                                 cfa->base = CFI_BP_INDIRECT;
1583                                 cfa->offset = -state->stack_size;
1584
1585                                 /* save drap so we know when to restore it */
1586                                 state->drap_offset = -state->stack_size;
1587
1588                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1589
1590                                 /* drap: push %rbp */
1591                                 state->stack_size = 0;
1592
1593                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1594
1595                                 /* drap: push %reg */
1596                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1597                         }
1598
1599                 } else {
1600
1601                         /* push %reg */
1602                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1603                 }
1604
1605                 /* detect when asm code uses rbp as a scratch register */
1606                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1607                     cfa->base != CFI_BP)
1608                         state->bp_scratch = true;
1609                 break;
1610
1611         case OP_DEST_REG_INDIRECT:
1612
1613                 if (state->drap) {
1614                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1615
1616                                 /* drap: mov %drap, disp(%rbp) */
1617                                 cfa->base = CFI_BP_INDIRECT;
1618                                 cfa->offset = op->dest.offset;
1619
1620                                 /* save drap offset so we know when to restore it */
1621                                 state->drap_offset = op->dest.offset;
1622                         }
1623
1624                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1625
1626                                 /* drap: mov reg, disp(%rbp) */
1627                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1628                         }
1629
1630                 } else if (op->dest.reg == cfa->base) {
1631
1632                         /* mov reg, disp(%rbp) */
1633                         /* mov reg, disp(%rsp) */
1634                         save_reg(state, op->src.reg, CFI_CFA,
1635                                  op->dest.offset - state->cfa.offset);
1636                 }
1637
1638                 break;
1639
1640         case OP_DEST_LEAVE:
1641                 if ((!state->drap && cfa->base != CFI_BP) ||
1642                     (state->drap && cfa->base != state->drap_reg)) {
1643                         WARN_FUNC("leave instruction with modified stack frame",
1644                                   insn->sec, insn->offset);
1645                         return -1;
1646                 }
1647
1648                 /* leave (mov %rbp, %rsp; pop %rbp) */
1649
1650                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1651                 restore_reg(state, CFI_BP);
1652
1653                 if (!state->drap) {
1654                         cfa->base = CFI_SP;
1655                         cfa->offset -= 8;
1656                 }
1657
1658                 break;
1659
1660         case OP_DEST_MEM:
1661                 if (op->src.type != OP_SRC_POP) {
1662                         WARN_FUNC("unknown stack-related memory operation",
1663                                   insn->sec, insn->offset);
1664                         return -1;
1665                 }
1666
1667                 /* pop mem */
1668                 state->stack_size -= 8;
1669                 if (cfa->base == CFI_SP)
1670                         cfa->offset -= 8;
1671
1672                 break;
1673
1674         default:
1675                 WARN_FUNC("unknown stack-related instruction",
1676                           insn->sec, insn->offset);
1677                 return -1;
1678         }
1679
1680         return 0;
1681 }
1682
1683 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1684 {
1685         struct insn_state *state1 = &insn->state, *state2 = state;
1686         int i;
1687
1688         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1689                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1690                           insn->sec, insn->offset,
1691                           state1->cfa.base, state1->cfa.offset,
1692                           state2->cfa.base, state2->cfa.offset);
1693
1694         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1695                 for (i = 0; i < CFI_NUM_REGS; i++) {
1696                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1697                                     sizeof(struct cfi_reg)))
1698                                 continue;
1699
1700                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1701                                   insn->sec, insn->offset,
1702                                   i, state1->regs[i].base, state1->regs[i].offset,
1703                                   i, state2->regs[i].base, state2->regs[i].offset);
1704                         break;
1705                 }
1706
1707         } else if (state1->type != state2->type) {
1708                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1709                           insn->sec, insn->offset, state1->type, state2->type);
1710
1711         } else if (state1->drap != state2->drap ||
1712                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1713                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1714                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1715                           insn->sec, insn->offset,
1716                           state1->drap, state1->drap_reg, state1->drap_offset,
1717                           state2->drap, state2->drap_reg, state2->drap_offset);
1718
1719         } else
1720                 return true;
1721
1722         return false;
1723 }
1724
1725 /*
1726  * Follow the branch starting at the given instruction, and recursively follow
1727  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1728  * each instruction and validate all the rules described in
1729  * tools/objtool/Documentation/stack-validation.txt.
1730  */
1731 static int validate_branch(struct objtool_file *file, struct instruction *first,
1732                            struct insn_state state)
1733 {
1734         struct alternative *alt;
1735         struct instruction *insn, *next_insn;
1736         struct section *sec;
1737         struct symbol *func = NULL;
1738         int ret;
1739
1740         insn = first;
1741         sec = insn->sec;
1742
1743         if (insn->alt_group && list_empty(&insn->alts)) {
1744                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1745                           sec, insn->offset);
1746                 return 1;
1747         }
1748
1749         while (1) {
1750                 next_insn = next_insn_same_sec(file, insn);
1751
1752
1753                 if (file->c_file && func && insn->func && func != insn->func) {
1754                         WARN("%s() falls through to next function %s()",
1755                              func->name, insn->func->name);
1756                         return 1;
1757                 }
1758
1759                 if (insn->func)
1760                         func = insn->func;
1761
1762                 if (func && insn->ignore) {
1763                         WARN_FUNC("BUG: why am I validating an ignored function?",
1764                                   sec, insn->offset);
1765                         return 1;
1766                 }
1767
1768                 if (insn->visited) {
1769                         if (!insn->hint && !insn_state_match(insn, &state))
1770                                 return 1;
1771
1772                         return 0;
1773                 }
1774
1775                 if (insn->hint) {
1776                         if (insn->restore) {
1777                                 struct instruction *save_insn, *i;
1778
1779                                 i = insn;
1780                                 save_insn = NULL;
1781                                 func_for_each_insn_continue_reverse(file, func, i) {
1782                                         if (i->save) {
1783                                                 save_insn = i;
1784                                                 break;
1785                                         }
1786                                 }
1787
1788                                 if (!save_insn) {
1789                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1790                                                   sec, insn->offset);
1791                                         return 1;
1792                                 }
1793
1794                                 if (!save_insn->visited) {
1795                                         /*
1796                                          * Oops, no state to copy yet.
1797                                          * Hopefully we can reach this
1798                                          * instruction from another branch
1799                                          * after the save insn has been
1800                                          * visited.
1801                                          */
1802                                         if (insn == first)
1803                                                 return 0;
1804
1805                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1806                                                   sec, insn->offset);
1807                                         return 1;
1808                                 }
1809
1810                                 insn->state = save_insn->state;
1811                         }
1812
1813                         state = insn->state;
1814
1815                 } else
1816                         insn->state = state;
1817
1818                 insn->visited = true;
1819
1820                 if (!insn->ignore_alts) {
1821                         list_for_each_entry(alt, &insn->alts, list) {
1822                                 ret = validate_branch(file, alt->insn, state);
1823                                 if (ret)
1824                                         return 1;
1825                         }
1826                 }
1827
1828                 switch (insn->type) {
1829
1830                 case INSN_RETURN:
1831                         if (func && has_modified_stack_frame(&state)) {
1832                                 WARN_FUNC("return with modified stack frame",
1833                                           sec, insn->offset);
1834                                 return 1;
1835                         }
1836
1837                         if (state.bp_scratch) {
1838                                 WARN("%s uses BP as a scratch register",
1839                                      insn->func->name);
1840                                 return 1;
1841                         }
1842
1843                         return 0;
1844
1845                 case INSN_CALL:
1846                         if (is_fentry_call(insn))
1847                                 break;
1848
1849                         ret = dead_end_function(file, insn->call_dest);
1850                         if (ret == 1)
1851                                 return 0;
1852                         if (ret == -1)
1853                                 return 1;
1854
1855                         /* fallthrough */
1856                 case INSN_CALL_DYNAMIC:
1857                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
1858                                 WARN_FUNC("call without frame pointer save/setup",
1859                                           sec, insn->offset);
1860                                 return 1;
1861                         }
1862                         break;
1863
1864                 case INSN_JUMP_CONDITIONAL:
1865                 case INSN_JUMP_UNCONDITIONAL:
1866                         if (insn->jump_dest &&
1867                             (!func || !insn->jump_dest->func ||
1868                              func == insn->jump_dest->func)) {
1869                                 ret = validate_branch(file, insn->jump_dest,
1870                                                       state);
1871                                 if (ret)
1872                                         return 1;
1873
1874                         } else if (func && has_modified_stack_frame(&state)) {
1875                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1876                                           sec, insn->offset);
1877                                 return 1;
1878                         }
1879
1880                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1881                                 return 0;
1882
1883                         break;
1884
1885                 case INSN_JUMP_DYNAMIC:
1886                         if (func && list_empty(&insn->alts) &&
1887                             has_modified_stack_frame(&state)) {
1888                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1889                                           sec, insn->offset);
1890                                 return 1;
1891                         }
1892
1893                         return 0;
1894
1895                 case INSN_CONTEXT_SWITCH:
1896                         if (func && (!next_insn || !next_insn->hint)) {
1897                                 WARN_FUNC("unsupported instruction in callable function",
1898                                           sec, insn->offset);
1899                                 return 1;
1900                         }
1901                         return 0;
1902
1903                 case INSN_STACK:
1904                         if (update_insn_state(insn, &state))
1905                                 return 1;
1906
1907                         break;
1908
1909                 default:
1910                         break;
1911                 }
1912
1913                 if (insn->dead_end)
1914                         return 0;
1915
1916                 if (!next_insn) {
1917                         if (state.cfa.base == CFI_UNDEFINED)
1918                                 return 0;
1919                         WARN("%s: unexpected end of section", sec->name);
1920                         return 1;
1921                 }
1922
1923                 insn = next_insn;
1924         }
1925
1926         return 0;
1927 }
1928
1929 static int validate_unwind_hints(struct objtool_file *file)
1930 {
1931         struct instruction *insn;
1932         int ret, warnings = 0;
1933         struct insn_state state;
1934
1935         if (!file->hints)
1936                 return 0;
1937
1938         clear_insn_state(&state);
1939
1940         for_each_insn(file, insn) {
1941                 if (insn->hint && !insn->visited) {
1942                         ret = validate_branch(file, insn, state);
1943                         warnings += ret;
1944                 }
1945         }
1946
1947         return warnings;
1948 }
1949
1950 static int validate_retpoline(struct objtool_file *file)
1951 {
1952         struct instruction *insn;
1953         int warnings = 0;
1954
1955         for_each_insn(file, insn) {
1956                 if (insn->type != INSN_JUMP_DYNAMIC &&
1957                     insn->type != INSN_CALL_DYNAMIC)
1958                         continue;
1959
1960                 if (insn->retpoline_safe)
1961                         continue;
1962
1963                 /*
1964                  * .init.text code is ran before userspace and thus doesn't
1965                  * strictly need retpolines, except for modules which are
1966                  * loaded late, they very much do need retpoline in their
1967                  * .init.text
1968                  */
1969                 if (!strcmp(insn->sec->name, ".init.text") && !module)
1970                         continue;
1971
1972                 WARN_FUNC("indirect %s found in RETPOLINE build",
1973                           insn->sec, insn->offset,
1974                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
1975
1976                 warnings++;
1977         }
1978
1979         return warnings;
1980 }
1981
1982 static bool is_kasan_insn(struct instruction *insn)
1983 {
1984         return (insn->type == INSN_CALL &&
1985                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1986 }
1987
1988 static bool is_ubsan_insn(struct instruction *insn)
1989 {
1990         return (insn->type == INSN_CALL &&
1991                 !strcmp(insn->call_dest->name,
1992                         "__ubsan_handle_builtin_unreachable"));
1993 }
1994
1995 static bool ignore_unreachable_insn(struct instruction *insn)
1996 {
1997         int i;
1998
1999         if (insn->ignore || insn->type == INSN_NOP)
2000                 return true;
2001
2002         /*
2003          * Ignore any unused exceptions.  This can happen when a whitelisted
2004          * function has an exception table entry.
2005          *
2006          * Also ignore alternative replacement instructions.  This can happen
2007          * when a whitelisted function uses one of the ALTERNATIVE macros.
2008          */
2009         if (!strcmp(insn->sec->name, ".fixup") ||
2010             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2011             !strcmp(insn->sec->name, ".altinstr_aux"))
2012                 return true;
2013
2014         /*
2015          * Check if this (or a subsequent) instruction is related to
2016          * CONFIG_UBSAN or CONFIG_KASAN.
2017          *
2018          * End the search at 5 instructions to avoid going into the weeds.
2019          */
2020         if (!insn->func)
2021                 return false;
2022         for (i = 0; i < 5; i++) {
2023
2024                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2025                         return true;
2026
2027                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2028                         if (insn->jump_dest &&
2029                             insn->jump_dest->func == insn->func) {
2030                                 insn = insn->jump_dest;
2031                                 continue;
2032                         }
2033
2034                         break;
2035                 }
2036
2037                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2038                         break;
2039
2040                 insn = list_next_entry(insn, list);
2041         }
2042
2043         return false;
2044 }
2045
2046 static int validate_functions(struct objtool_file *file)
2047 {
2048         struct section *sec;
2049         struct symbol *func;
2050         struct instruction *insn;
2051         struct insn_state state;
2052         int ret, warnings = 0;
2053
2054         clear_insn_state(&state);
2055
2056         state.cfa = initial_func_cfi.cfa;
2057         memcpy(&state.regs, &initial_func_cfi.regs,
2058                CFI_NUM_REGS * sizeof(struct cfi_reg));
2059         state.stack_size = initial_func_cfi.cfa.offset;
2060
2061         for_each_sec(file, sec) {
2062                 list_for_each_entry(func, &sec->symbol_list, list) {
2063                         if (func->type != STT_FUNC)
2064                                 continue;
2065
2066                         insn = find_insn(file, sec, func->offset);
2067                         if (!insn || insn->ignore)
2068                                 continue;
2069
2070                         ret = validate_branch(file, insn, state);
2071                         warnings += ret;
2072                 }
2073         }
2074
2075         return warnings;
2076 }
2077
2078 static int validate_reachable_instructions(struct objtool_file *file)
2079 {
2080         struct instruction *insn;
2081
2082         if (file->ignore_unreachables)
2083                 return 0;
2084
2085         for_each_insn(file, insn) {
2086                 if (insn->visited || ignore_unreachable_insn(insn))
2087                         continue;
2088
2089                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2090                 return 1;
2091         }
2092
2093         return 0;
2094 }
2095
2096 static void cleanup(struct objtool_file *file)
2097 {
2098         struct instruction *insn, *tmpinsn;
2099         struct alternative *alt, *tmpalt;
2100
2101         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2102                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2103                         list_del(&alt->list);
2104                         free(alt);
2105                 }
2106                 list_del(&insn->list);
2107                 hash_del(&insn->hash);
2108                 free(insn);
2109         }
2110         elf_close(file->elf);
2111 }
2112
2113 int check(const char *_objname, bool orc)
2114 {
2115         struct objtool_file file;
2116         int ret, warnings = 0;
2117
2118         objname = _objname;
2119
2120         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2121         if (!file.elf)
2122                 return 1;
2123
2124         INIT_LIST_HEAD(&file.insn_list);
2125         hash_init(file.insn_hash);
2126         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
2127         file.rodata = find_section_by_name(file.elf, ".rodata");
2128         file.c_file = find_section_by_name(file.elf, ".comment");
2129         file.ignore_unreachables = no_unreachable;
2130         file.hints = false;
2131
2132         arch_initial_func_cfi_state(&initial_func_cfi);
2133
2134         ret = decode_sections(&file);
2135         if (ret < 0)
2136                 goto out;
2137         warnings += ret;
2138
2139         if (list_empty(&file.insn_list))
2140                 goto out;
2141
2142         if (retpoline) {
2143                 ret = validate_retpoline(&file);
2144                 if (ret < 0)
2145                         return ret;
2146                 warnings += ret;
2147         }
2148
2149         ret = validate_functions(&file);
2150         if (ret < 0)
2151                 goto out;
2152         warnings += ret;
2153
2154         ret = validate_unwind_hints(&file);
2155         if (ret < 0)
2156                 goto out;
2157         warnings += ret;
2158
2159         if (!warnings) {
2160                 ret = validate_reachable_instructions(&file);
2161                 if (ret < 0)
2162                         goto out;
2163                 warnings += ret;
2164         }
2165
2166         if (orc) {
2167                 ret = create_orc(&file);
2168                 if (ret < 0)
2169                         goto out;
2170
2171                 ret = create_orc_sections(&file);
2172                 if (ret < 0)
2173                         goto out;
2174
2175                 ret = elf_write(file.elf);
2176                 if (ret < 0)
2177                         goto out;
2178         }
2179
2180 out:
2181         cleanup(&file);
2182
2183         /* ignore warnings for now until we get all the code cleaned up */
2184         if (ret || warnings)
2185                 return 0;
2186         return 0;
2187 }