summaryrefslogtreecommitdiffstats
path: root/tools/objtool/builtin-check.c
blob: e8a1e69eb92c5235735d42847e4f34b2e737a972 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
/*
 * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

/*
 * objtool check:
 *
 * This command analyzes every .o file and ensures the validity of its stack
 * trace metadata.  It enforces a set of rules on asm code and C inline
 * assembly code so that stack traces can be reliable.
 *
 * For more information, see tools/objtool/Documentation/stack-validation.txt.
 */

#include <string.h>
#include <subcmd/parse-options.h>

#include "builtin.h"
#include "elf.h"
#include "special.h"
#include "arch.h"
#include "warn.h"

#include <linux/hashtable.h>

#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))

#define STATE_FP_SAVED		0x1
#define STATE_FP_SETUP		0x2
#define STATE_FENTRY		0x4

struct instruction {
	struct list_head list;
	struct hlist_node hash;
	struct section *sec;
	unsigned long offset;
	unsigned int len, state;
	unsigned char type;
	unsigned long immediate;
	bool alt_group, visited;
	struct symbol *call_dest;
	struct instruction *jump_dest;
	struct list_head alts;
	struct symbol *func;
};

struct alternative {
	struct list_head list;
	struct instruction *insn;
};

struct objtool_file {
	struct elf *elf;
	struct list_head insn_list;
	DECLARE_HASHTABLE(insn_hash, 16);
	struct section *rodata, *whitelist;
	bool ignore_unreachables, c_file;
};

const char *objname;
static bool nofp;

static struct instruction *find_insn(struct objtool_file *file,
				     struct section *sec, unsigned long offset)
{
	struct instruction *insn;

	hash_for_each_possible(file->insn_hash, insn, hash, offset)
		if (insn->sec == sec && insn->offset == offset)
			return insn;

	return NULL;
}

static struct instruction *next_insn_same_sec(struct objtool_file *file,
					      struct instruction *insn)
{
	struct instruction *next = list_next_entry(insn, list);

	if (&next->list == &file->insn_list || next->sec != insn->sec)
		return NULL;

	return next;
}

#define for_each_insn(file, insn)					\
	list_for_each_entry(insn, &file->insn_list, list)

#define func_for_each_insn(file, func, insn)				\
	for (insn = find_insn(file, func->sec, func->offset);		\
	     insn && &insn->list != &file->insn_list &&			\
		insn->sec == func->sec &&				\
		insn->offset < func->offset + func->len;		\
	     insn = list_next_entry(insn, list))

#define sec_for_each_insn_from(file, insn)				\
	for (; insn; insn = next_insn_same_sec(file, insn))


/*
 * Check if the function has been manually whitelisted with the
 * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
 * due to its use of a context switching instruction.
 */
static bool ignore_func(struct objtool_file *file, struct symbol *func)
{
	struct rela *rela;
	struct instruction *insn;

	/* check for STACK_FRAME_NON_STANDARD */
	if (file->whitelist && file->whitelist->rela)
		list_for_each_entry(rela, &file->whitelist->rela->rela_list, list)
			if (rela->sym->sec == func->sec &&
			    rela->addend == func->offset)
				return true;

	/* check if it has a context switching instruction */
	func_for_each_insn(file, func, insn)
		if (insn->type == INSN_CONTEXT_SWITCH)
			return true;

	return false;
}

/*
 * This checks to see if the given function is a "noreturn" function.
 *
 * For global functions which are outside the scope of this object file, we
 * have to keep a manual list of them.
 *
 * For local functions, we have to detect them manually by simply looking for
 * the lack of a return instruction.
 *
 * Returns:
 *  -1: error
 *   0: no dead end
 *   1: dead end
 */
static int __dead_end_function(struct objtool_file *file, struct symbol *func,
			       int recursion)
{
	int i;
	struct instruction *insn;
	bool empty = true;

	/*
	 * Unfortunately these have to be hard coded because the noreturn
	 * attribute isn't provided in ELF data.
	 */
	static const char * const global_noreturns[] = {
		"__stack_chk_fail",
		"panic",
		"do_exit",
		"__module_put_and_exit",
		"complete_and_exit",
		"kvm_spurious_fault",
		"__reiserfs_panic",
		"lbug_with_loc"
	};

	if (func->bind == STB_WEAK)
		return 0;

	if (func->bind == STB_GLOBAL)
		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
			if (!strcmp(func->name, global_noreturns[i]))
				return 1;

	if (!func->sec)
		return 0;

	func_for_each_insn(file, func, insn) {
		empty = false;

		if (insn->type == INSN_RETURN)
			return 0;
	}

	if (empty)
		return 0;

	/*
	 * A function can have a sibling call instead of a return.  In that
	 * case, the function's dead-end status depends on whether the target
	 * of the sibling call returns.
	 */
	func_for_each_insn(file, func, insn) {
		if (insn->sec != func->sec ||
		    insn->offset >= func->offset + func->len)
			break;

		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
			struct instruction *dest = insn->jump_dest;
			struct symbol *dest_func;

			if (!dest)
				/* sibling call to another file */
				return 0;

			if (dest->sec != func->sec ||
			    dest->offset < func->offset ||
			    dest->offset >= func->offset + func->len) {
				/* local sibling call */
				dest_func = find_symbol_by_offset(dest->sec,
								  dest->offset);
				if (!dest_func)
					continue;

				if (recursion == 5) {
					WARN_FUNC("infinite recursion (objtool bug!)",
						  dest->sec, dest->offset);
					return -1;
				}

				return __dead_end_function(file, dest_func,
							   recursion + 1);
			}
		}

		if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
			/* sibling call */
			return 0;
	}

	return 1;
}

static int dead_end_function(struct objtool_file *file, struct symbol *func)
{
	return __dead_end_function(file, func, 0);
}

/*
 * Call the arch-specific instruction decoder for all the instructions and add
 * them to the global instruction list.
 */
static int decode_instructions(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	unsigned long offset;
	struct instruction *insn;
	int ret;

	list_for_each_entry(sec, &file->elf->sections, list) {

		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
			continue;

		for (offset = 0; offset < sec->len; offset += insn->len) {
			insn = malloc(sizeof(*insn));
			memset(insn, 0, sizeof(*insn));

			INIT_LIST_HEAD(&insn->alts);
			insn->sec = sec;
			insn->offset = offset;

			ret = arch_decode_instruction(file->elf, sec, offset,
						      sec->len - offset,
						      &insn->len, &insn->type,
						      &insn->immediate);
			if (ret)
				return ret;

			if (!insn->type || insn->type > INSN_LAST) {
				WARN_FUNC("invalid instruction type %d",
					  insn->sec, insn->offset, insn->type);
				return -1;
			}

			hash_add(file->insn_hash, &insn->hash, insn->offset);
			list_add_tail(&insn->list, &file->insn_list);
		}

		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			if (!find_insn(file, sec, func->offset)) {
				WARN("%s(): can't find starting instruction",
				     func->name);
				return -1;
			}

			func_for_each_insn(file, func, insn)
				if (!insn->func)
					insn->func = func;
		}
	}

	return 0;
}

/*
 * Warnings shouldn't be reported for ignored functions.
 */
static void add_ignores(struct objtool_file *file)
{
	struct instruction *insn;
	struct section *sec;
	struct symbol *func;

	list_for_each_entry(sec, &file->elf->sections, list) {
		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			if (!ignore_func(file, func))
				continue;

			func_for_each_insn(file, func, insn)
				insn->visited = true;
		}
	}
}

/*
 * Find the destination instructions for all jumps.
 */
static int add_jump_destinations(struct objtool_file *file)
{
	struct instruction *insn;
	struct rela *rela;
	struct section *dest_sec;
	unsigned long dest_off;

	for_each_insn(file, insn) {
		if (insn->type != INSN_JUMP_CONDITIONAL &&
		    insn->type != INSN_JUMP_UNCONDITIONAL)
			continue;

		/* skip ignores */
		if (insn->visited)
			continue;

		rela = find_rela_by_dest_range(insn->sec, insn->offset,
					       insn->len);
		if (!rela) {
			dest_sec = insn->sec;
			dest_off = insn->offset + insn->len + insn->immediate;
		} else if (rela->sym->type == STT_SECTION) {
			dest_sec = rela->sym->sec;
			dest_off = rela->addend + 4;
		} else if (rela->sym->sec->idx) {
			dest_sec = rela->sym->sec;
			dest_off = rela->sym->sym.st_value + rela->addend + 4;
		} else {
			/* sibling call */
			insn->jump_dest = 0;
			continue;
		}

		insn->jump_dest = find_insn(file, dest_sec, dest_off);
		if (!insn->jump_dest) {

			/*
			 * This is a special case where an alt instruction
			 * jumps past the end of the section.  These are
			 * handled later in handle_group_alt().
			 */
			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
				continue;

			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
				  insn->sec, insn->offset, dest_sec->name,
				  dest_off);
			return -1;
		}
	}

	return 0;
}

/*
 * Find the destination instructions for all calls.
 */
static int add_call_destinations(struct objtool_file *file)
{
	struct instruction *insn;
	unsigned long dest_off;
	struct rela *rela;

	for_each_insn(file, insn) {
		if (insn->type != INSN_CALL)
			continue;

		rela = find_rela_by_dest_range(insn->sec, insn->offset,
					       insn->len);
		if (!rela) {
			dest_off = insn->offset + insn->len + insn->immediate;
			insn->call_dest = find_symbol_by_offset(insn->sec,
								dest_off);
			if (!insn->call_dest) {
				WARN_FUNC("can't find call dest symbol at offset 0x%lx",
					  insn->sec, insn->offset, dest_off);
				return -1;
			}
		} else if (rela->sym->type == STT_SECTION) {
			insn->call_dest = find_symbol_by_offset(rela->sym->sec,
								rela->addend+4);
			if (!insn->call_dest ||
			    insn->call_dest->type != STT_FUNC) {
				WARN_FUNC("can't find call dest symbol at %s+0x%x",
					  insn->sec, insn->offset,
					  rela->sym->sec->name,
					  rela->addend + 4);
				return -1;
			}
		} else
			insn->call_dest = rela->sym;
	}

	return 0;
}

/*
 * The .alternatives section requires some extra special care, over and above
 * what other special sections require:
 *
 * 1. Because alternatives are patched in-place, we need to insert a fake jump
 *    instruction at the end so that validate_branch() skips all the original
 *    replaced instructions when validating the new instruction path.
 *
 * 2. An added wrinkle is that the new instruction length might be zero.  In
 *    that case the old instructions are replaced with noops.  We simulate that
 *    by creating a fake jump as the only new instruction.
 *
 * 3. In some cases, the alternative section includes an instruction which
 *    conditionally jumps to the _end_ of the entry.  We have to modify these
 *    jumps' destinations to point back to .text rather than the end of the
 *    entry in .altinstr_replacement.
 *
 * 4. It has been requested that we don't validate the !POPCNT feature path
 *    which is a "very very small percentage of machines".
 */
static int handle_group_alt(struct objtool_file *file,
			    struct special_alt *special_alt,
			    struct instruction *orig_insn,
			    struct instruction **new_insn)
{
	struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
	unsigned long dest_off;

	last_orig_insn = NULL;
	insn = orig_insn;
	sec_for_each_insn_from(file, insn) {
		if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
			break;

		if (special_alt->skip_orig)
			insn->type = INSN_NOP;

		insn->alt_group = true;
		last_orig_insn = insn;
	}

	if (!next_insn_same_sec(file, last_orig_insn)) {
		WARN("%s: don't know how to handle alternatives at end of section",
		     special_alt->orig_sec->name);
		return -1;
	}

	fake_jump = malloc(sizeof(*fake_jump));
	if (!fake_jump) {
		WARN("malloc failed");
		return -1;
	}
	memset(fake_jump, 0, sizeof(*fake_jump));
	INIT_LIST_HEAD(&fake_jump->alts);
	fake_jump->sec = special_alt->new_sec;
	fake_jump->offset = -1;
	fake_jump->type = INSN_JUMP_UNCONDITIONAL;
	fake_jump->jump_dest = list_next_entry(last_orig_insn, list);

	if (!special_alt->new_len) {
		*new_insn = fake_jump;
		return 0;
	}

	last_new_insn = NULL;
	insn = *new_insn;
	sec_for_each_insn_from(file, insn) {
		if (insn->offset >= special_alt->new_off + special_alt->new_len)
			break;

		last_new_insn = insn;

		if (insn->type != INSN_JUMP_CONDITIONAL &&
		    insn->type != INSN_JUMP_UNCONDITIONAL)
			continue;

		if (!insn->immediate)
			continue;

		dest_off = insn->offset + insn->len + insn->immediate;
		if (dest_off == special_alt->new_off + special_alt->new_len)
			insn->jump_dest = fake_jump;

		if (!insn->jump_dest) {
			WARN_FUNC("can't find alternative jump destination",
				  insn->sec, insn->offset);
			return -1;
		}
	}

	if (!last_new_insn) {
		WARN_FUNC("can't find last new alternative instruction",
			  special_alt->new_sec, special_alt->new_off);
		return -1;
	}

	list_add(&fake_jump->list, &last_new_insn->list);

	return 0;
}

/*
 * A jump table entry can either convert a nop to a jump or a jump to a nop.
 * If the original instruction is a jump, make the alt entry an effective nop
 * by just skipping the original instruction.
 */
static int handle_jump_alt(struct objtool_file *file,
			   struct special_alt *special_alt,
			   struct instruction *orig_insn,
			   struct instruction **new_insn)
{
	if (orig_insn->type == INSN_NOP)
		return 0;

	if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
		WARN_FUNC("unsupported instruction at jump label",
			  orig_insn->sec, orig_insn->offset);
		return -1;
	}

	*new_insn = list_next_entry(orig_insn, list);
	return 0;
}

/*
 * Read all the special sections which have alternate instructions which can be
 * patched in or redirected to at runtime.  Each instruction having alternate
 * instruction(s) has them added to its insn->alts list, which will be
 * traversed in validate_branch().
 */
static int add_special_section_alts(struct objtool_file *file)
{
	struct list_head special_alts;
	struct instruction *orig_insn, *new_insn;
	struct special_alt *special_alt, *tmp;
	struct alternative *alt;
	int ret;

	ret = special_get_alts(file->elf, &special_alts);
	if (ret)
		return ret;

	list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
		alt = malloc(sizeof(*alt));
		if (!alt) {
			WARN("malloc failed");
			ret = -1;
			goto out;
		}

		orig_insn = find_insn(file, special_alt->orig_sec,
				      special_alt->orig_off);
		if (!orig_insn) {
			WARN_FUNC("special: can't find orig instruction",
				  special_alt->orig_sec, special_alt->orig_off);
			ret = -1;
			goto out;
		}

		new_insn = NULL;
		if (!special_alt->group || special_alt->new_len) {
			new_insn = find_insn(file, special_alt->new_sec,
					     special_alt->new_off);
			if (!new_insn) {
				WARN_FUNC("special: can't find new instruction",
					  special_alt->new_sec,
					  special_alt->new_off);
				ret = -1;
				goto out;
			}
		}

		if (special_alt->group) {
			ret = handle_group_alt(file, special_alt, orig_insn,
					       &new_insn);
			if (ret)
				goto out;
		} else if (special_alt->jump_or_nop) {
			ret = handle_jump_alt(file, special_alt, orig_insn,
					      &new_insn);
			if (ret)
				goto out;
		}

		alt->insn = new_insn;
		list_add_tail(&alt->list, &orig_insn->alts);

		list_del(&special_alt->list);
		free(special_alt);
	}

out:
	return ret;
}

static int add_switch_table(struct objtool_file *file, struct symbol *func,
			    struct instruction *insn, struct rela *table,
			    struct rela *next_table)
{
	struct rela *rela = table;
	struct instruction *alt_insn;
	struct alternative *alt;

	list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
		if (rela == next_table)
			break;

		if (rela->sym->sec != insn->sec ||
		    rela->addend <= func->offset ||
		    rela->addend >= func->offset + func->len)
			break;

		alt_insn = find_insn(file, insn->sec, rela->addend);
		if (!alt_insn) {
			WARN("%s: can't find instruction at %s+0x%x",
			     file->rodata->rela->name, insn->sec->name,
			     rela->addend);
			return -1;
		}

		alt = malloc(sizeof(*alt));
		if (!alt) {
			WARN("malloc failed");
			return -1;
		}

		alt->insn = alt_insn;
		list_add_tail(&alt->list, &insn->alts);
	}

	return 0;
}

static int add_func_switch_tables(struct objtool_file *file,
				  struct symbol *func)
{
	struct instruction *insn, *prev_jump;
	struct rela *text_rela, *rodata_rela, *prev_rela;
	int ret;

	prev_jump = NULL;

	func_for_each_insn(file, func, insn) {
		if (insn->type != INSN_JUMP_DYNAMIC)
			continue;

		text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
						    insn->len);
		if (!text_rela || text_rela->sym != file->rodata->sym)
			continue;

		/* common case: jmpq *[addr](,%rax,8) */
		rodata_rela = find_rela_by_dest(file->rodata,
						text_rela->addend);

		/*
		 * rare case:   jmpq *[addr](%rip)
		 *
		 * This check is for a rare gcc quirk, currently only seen in
		 * three driver functions in the kernel, only with certain
		 * obscure non-distro configs.
		 *
		 * As part of an optimization, gcc makes a copy of an existing
		 * switch jump table, modifies it, and then hard-codes the jump
		 * (albeit with an indirect jump) to use a single entry in the
		 * table.  The rest of the jump table and some of its jump
		 * targets remain as dead code.
		 *
		 * In such a case we can just crudely ignore all unreachable
		 * instruction warnings for the entire object file.  Ideally we
		 * would just ignore them for the function, but that would
		 * require redesigning the code quite a bit.  And honestly
		 * that's just not worth doing: unreachable instruction
		 * warnings are of questionable value anyway, and this is such
		 * a rare issue.
		 *
		 * kbuild reports:
		 * - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com
		 * - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com
		 * - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com
		 *
		 * gcc bug:
		 * - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604
		 */
		if (!rodata_rela) {
			rodata_rela = find_rela_by_dest(file->rodata,
							text_rela->addend + 4);
			if (rodata_rela)
				file->ignore_unreachables = true;
		}

		if (!rodata_rela)
			continue;

		/*
		 * We found a switch table, but we don't know yet how big it
		 * is.  Don't add it until we reach the end of the function or
		 * the beginning of another switch table in the same function.
		 */
		if (prev_jump) {
			ret = add_switch_table(file, func, prev_jump, prev_rela,
					       rodata_rela);
			if (ret)
				return ret;
		}

		prev_jump = insn;
		prev_rela = rodata_rela;
	}

	if (prev_jump) {
		ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
		if (ret)
			return ret;
	}

	return 0;
}

/*
 * For some switch statements, gcc generates a jump table in the .rodata
 * section which contains a list of addresses within the function to jump to.
 * This finds these jump tables and adds them to the insn->alts lists.
 */
static int add_switch_table_alts(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	int ret;

	if (!file->rodata || !file->rodata->rela)
		return 0;

	list_for_each_entry(sec, &file->elf->sections, list) {
		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			ret = add_func_switch_tables(file, func);
			if (ret)
				return ret;
		}
	}

	return 0;
}

static int decode_sections(struct objtool_file *file)
{
	int ret;

	ret = decode_instructions(file);
	if (ret)
		return ret;

	add_ignores(file);

	ret = add_jump_destinations(file);
	if (ret)
		return ret;

	ret = add_call_destinations(file);
	if (ret)
		return ret;

	ret = add_special_section_alts(file);
	if (ret)
		return ret;

	ret = add_switch_table_alts(file);
	if (ret)
		return ret;

	return 0;
}

static bool is_fentry_call(struct instruction *insn)
{
	if (insn->type == INSN_CALL &&
	    insn->call_dest->type == STT_NOTYPE &&
	    !strcmp(insn->call_dest->name, "__fentry__"))
		return true;

	return false;
}

static bool has_modified_stack_frame(struct instruction *insn)
{
	return (insn->state & STATE_FP_SAVED) ||
	       (insn->state & STATE_FP_SETUP);
}

static bool has_valid_stack_frame(struct instruction *insn)
{
	return (insn->state & STATE_FP_SAVED) &&
	       (insn->state & STATE_FP_SETUP);
}

static unsigned int frame_state(unsigned long state)
{
	return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
}

/*
 * Follow the branch starting at the given instruction, and recursively follow
 * any other branches (jumps).  Meanwhile, track the frame pointer state at
 * each instruction and validate all the rules described in
 * tools/objtool/Documentation/stack-validation.txt.
 */
static int validate_branch(struct objtool_file *file,
			   struct instruction *first, unsigned char first_state)
{
	struct alternative *alt;
	struct instruction *insn;
	struct section *sec;
	struct symbol *func = NULL;
	unsigned char state;
	int ret;

	insn = first;
	sec = insn->sec;
	state = first_state;

	if (insn->alt_group && list_empty(&insn->alts)) {
		WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
			  sec, insn->offset);
		return 1;
	}

	while (1) {
		if (file->c_file && insn->func) {
			if (func && func != insn->func) {
				WARN("%s() falls through to next function %s()",
				     func->name, insn->func->name);
				return 1;
			}

			func = insn->func;
		}

		if (insn->visited) {
			if (frame_state(insn->state) != frame_state(state)) {
				WARN_FUNC("frame pointer state mismatch",
					  sec, insn->offset);
				return 1;
			}

			return 0;
		}

		insn->visited = true;
		insn->state = state;

		list_for_each_entry(alt, &insn->alts, list) {
			ret = validate_branch(file, alt->insn, state);
			if (ret)
				return 1;
		}

		switch (insn->type) {

		case INSN_FP_SAVE:
			if (!nofp) {
				if (state & STATE_FP_SAVED) {
					WARN_FUNC("duplicate frame pointer save",
						  sec, insn->offset);
					return 1;
				}
				state |= STATE_FP_SAVED;
			}
			break;

		case INSN_FP_SETUP:
			if (!nofp) {
				if (state & STATE_FP_SETUP) {
					WARN_FUNC("duplicate frame pointer setup",
						  sec, insn->offset);
					return 1;
				}
				state |= STATE_FP_SETUP;
			}
			break;

		case INSN_FP_RESTORE:
			if (!nofp) {
				if (has_valid_stack_frame(insn))
					state &= ~STATE_FP_SETUP;

				state &= ~STATE_FP_SAVED;
			}
			break;

		case INSN_RETURN:
			if (!nofp && has_modified_stack_frame(insn)) {
				WARN_FUNC("return without frame pointer restore",
					  sec, insn->offset);
				return 1;
			}
			return 0;

		case INSN_CALL:
			if (is_fentry_call(insn)) {
				state |= STATE_FENTRY;
				break;
			}

			ret = dead_end_function(file, insn->call_dest);
			if (ret == 1)
				return 0;
			if (ret == -1)
				return 1;

			/* fallthrough */
		case INSN_CALL_DYNAMIC:
			if (!nofp && !has_valid_stack_frame(insn)) {
				WARN_FUNC("call without frame pointer save/setup",
					  sec, insn->offset);
				return 1;
			}
			break;

		case INSN_JUMP_CONDITIONAL:
		case INSN_JUMP_UNCONDITIONAL:
			if (insn->jump_dest) {
				ret = validate_branch(file, insn->jump_dest,
						      state);
				if (ret)
					return 1;
			} else if (has_modified_stack_frame(insn)) {
				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
					  sec, insn->offset);
				return 1;
			} /* else it's a sibling call */

			if (insn->type == INSN_JUMP_UNCONDITIONAL)
				return 0;

			break;

		case INSN_JUMP_DYNAMIC:
			if (list_empty(&insn->alts) &&
			    has_modified_stack_frame(insn)) {
				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
					  sec, insn->offset);
				return 1;
			}

			return 0;

		case INSN_BUG:
			return 0;

		default:
			break;
		}

		insn = next_insn_same_sec(file, insn);
		if (!insn) {
			WARN("%s: unexpected end of section", sec->name);
			return 1;
		}
	}

	return 0;
}

static bool is_gcov_insn(struct instruction *insn)
{
	struct rela *rela;
	struct section *sec;
	struct symbol *sym;
	unsigned long offset;

	rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
	if (!rela)
		return false;

	if (rela->sym->type != STT_SECTION)
		return false;

	sec = rela->sym->sec;
	offset = rela->addend + insn->offset + insn->len - rela->offset;

	list_for_each_entry(sym, &sec->symbol_list, list) {
		if (sym->type != STT_OBJECT)
			continue;

		if (offset >= sym->offset && offset < sym->offset + sym->len)
			return (!memcmp(sym->name, "__gcov0.", 8));
	}

	return false;
}

static bool is_kasan_insn(struct instruction *insn)
{
	return (insn->type == INSN_CALL &&
		!strcmp(insn->call_dest->name, "__asan_handle_no_return"));
}

static bool is_ubsan_insn(struct instruction *insn)
{
	return (insn->type == INSN_CALL &&
		!strcmp(insn->call_dest->name,
			"__ubsan_handle_builtin_unreachable"));
}

static bool ignore_unreachable_insn(struct symbol *func,
				    struct instruction *insn)
{
	int i;

	if (insn->type == INSN_NOP)
		return true;

	if (is_gcov_insn(insn))
		return true;

	/*
	 * Check if this (or a subsequent) instruction is related to
	 * CONFIG_UBSAN or CONFIG_KASAN.
	 *
	 * End the search at 5 instructions to avoid going into the weeds.
	 */
	for (i = 0; i < 5; i++) {

		if (is_kasan_insn(insn) || is_ubsan_insn(insn))
			return true;

		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
			insn = insn->jump_dest;
			continue;
		}

		if (insn->offset + insn->len >= func->offset + func->len)
			break;
		insn = list_next_entry(insn, list);
	}

	return false;
}

static int validate_functions(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	struct instruction *insn;
	int ret, warnings = 0;

	list_for_each_entry(sec, &file->elf->sections, list) {
		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			insn = find_insn(file, sec, func->offset);
			if (!insn)
				continue;

			ret = validate_branch(file, insn, 0);
			warnings += ret;
		}
	}

	list_for_each_entry(sec, &file->elf->sections, list) {
		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			func_for_each_insn(file, func, insn) {
				if (insn->visited)
					continue;

				insn->visited = true;

				if (file->ignore_unreachables || warnings ||
				    ignore_unreachable_insn(func, insn))
					continue;

				WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
				warnings++;
			}
		}
	}

	return warnings;
}

static int validate_uncallable_instructions(struct objtool_file *file)
{
	struct instruction *insn;
	int warnings = 0;

	for_each_insn(file, insn) {
		if (!insn->visited && insn->type == INSN_RETURN) {
			WARN_FUNC("return instruction outside of a callable function",
				  insn->sec, insn->offset);
			warnings++;
		}
	}

	return warnings;
}

static void cleanup(struct objtool_file *file)
{
	struct instruction *insn, *tmpinsn;
	struct alternative *alt, *tmpalt;

	list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
		list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
			list_del(&alt->list);
			free(alt);
		}
		list_del(&insn->list);
		hash_del(&insn->hash);
		free(insn);
	}
	elf_close(file->elf);
}

const char * const check_usage[] = {
	"objtool check [<options>] file.o",
	NULL,
};

int cmd_check(int argc, const char **argv)
{
	struct objtool_file file;
	int ret, warnings = 0;

	const struct option options[] = {
		OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
		OPT_END(),
	};

	argc = parse_options(argc, argv, options, check_usage, 0);

	if (argc != 1)
		usage_with_options(check_usage, options);

	objname = argv[0];

	file.elf = elf_open(objname);
	if (!file.elf) {
		fprintf(stderr, "error reading elf file %s\n", objname);
		return 1;
	}

	INIT_LIST_HEAD(&file.insn_list);
	hash_init(file.insn_hash);
	file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
	file.rodata = find_section_by_name(file.elf, ".rodata");
	file.ignore_unreachables = false;
	file.c_file = find_section_by_name(file.elf, ".comment");

	ret = decode_sections(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

	ret = validate_functions(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

	ret = validate_uncallable_instructions(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

out:
	cleanup(&file);

	/* ignore warnings for now until we get all the code cleaned up */
	if (ret || warnings)
		return 0;
	return 0;
}
OpenPOWER on IntegriCloud