aboutsummaryrefslogtreecommitdiff
path: root/kernel/kallsyms.c
blob: 60c20f301a6ba2c794c7716c87e7bde61de196e7 (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
// SPDX-License-Identifier: GPL-2.0-only
/*
 * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
 *
 * Rewritten and vastly simplified by Rusty Russell for in-kernel
 * module loader:
 *   Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
 *
 * ChangeLog:
 *
 * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
 *      Changed the compression method from stem compression to "table lookup"
 *      compression (see scripts/kallsyms.c for a more complete description)
 */
#include <linux/kallsyms.h>
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/fs.h>
#include <linux/kdb.h>
#include <linux/err.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>	/* for cond_resched */
#include <linux/ctype.h>
#include <linux/slab.h>
#include <linux/filter.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <linux/build_bug.h>
#include <linux/compiler.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bsearch.h>
#include <linux/btf_ids.h>

#include "kallsyms_internal.h"

/*
 * Expand a compressed symbol data into the resulting uncompressed string,
 * if uncompressed string is too long (>= maxlen), it will be truncated,
 * given the offset to where the symbol is in the compressed stream.
 */
static unsigned int kallsyms_expand_symbol(unsigned int off,
					   char *result, size_t maxlen)
{
	int len, skipped_first = 0;
	const char *tptr;
	const u8 *data;

	/* Get the compressed symbol length from the first symbol byte. */
	data = &kallsyms_names[off];
	len = *data;
	data++;
	off++;

	/* If MSB is 1, it is a "big" symbol, so needs an additional byte. */
	if ((len & 0x80) != 0) {
		len = (len & 0x7F) | (*data << 7);
		data++;
		off++;
	}

	/*
	 * Update the offset to return the offset for the next symbol on
	 * the compressed stream.
	 */
	off += len;

	/*
	 * For every byte on the compressed symbol data, copy the table
	 * entry for that byte.
	 */
	while (len) {
		tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
		data++;
		len--;

		while (*tptr) {
			if (skipped_first) {
				if (maxlen <= 1)
					goto tail;
				*result = *tptr;
				result++;
				maxlen--;
			} else
				skipped_first = 1;
			tptr++;
		}
	}

tail:
	if (maxlen)
		*result = '\0';

	/* Return to offset to the next symbol. */
	return off;
}

/*
 * Get symbol type information. This is encoded as a single char at the
 * beginning of the symbol name.
 */
static char kallsyms_get_symbol_type(unsigned int off)
{
	/*
	 * Get just the first code, look it up in the token table,
	 * and return the first char from this token.
	 */
	return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
}


/*
 * Find the offset on the compressed stream given and index in the
 * kallsyms array.
 */
static unsigned int get_symbol_offset(unsigned long pos)
{
	const u8 *name;
	int i, len;

	/*
	 * Use the closest marker we have. We have markers every 256 positions,
	 * so that should be close enough.
	 */
	name = &kallsyms_names[kallsyms_markers[pos >> 8]];

	/*
	 * Sequentially scan all the symbols up to the point we're searching
	 * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
	 * so we just need to add the len to the current pointer for every
	 * symbol we wish to skip.
	 */
	for (i = 0; i < (pos & 0xFF); i++) {
		len = *name;

		/*
		 * If MSB is 1, it is a "big" symbol, so we need to look into
		 * the next byte (and skip it, too).
		 */
		if ((len & 0x80) != 0)
			len = ((len & 0x7F) | (name[1] << 7)) + 1;

		name = name + len + 1;
	}

	return name - kallsyms_names;
}

static unsigned long kallsyms_sym_address(int idx)
{
	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
		return kallsyms_addresses[idx];

	/* values are unsigned offsets if --absolute-percpu is not in effect */
	if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
		return kallsyms_relative_base + (u32)kallsyms_offsets[idx];

	/* ...otherwise, positive offsets are absolute values */
	if (kallsyms_offsets[idx] >= 0)
		return kallsyms_offsets[idx];

	/* ...and negative offsets are relative to kallsyms_relative_base - 1 */
	return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
}

static bool cleanup_symbol_name(char *s)
{
	char *res;

	if (!IS_ENABLED(CONFIG_LTO_CLANG))
		return false;

	/*
	 * LLVM appends various suffixes for local functions and variables that
	 * must be promoted to global scope as part of LTO.  This can break
	 * hooking of static functions with kprobes. '.' is not a valid
	 * character in an identifier in C. Suffixes observed:
	 * - foo.llvm.[0-9a-f]+
	 * - foo.[0-9a-f]+
	 */
	res = strchr(s, '.');
	if (res) {
		*res = '\0';
		return true;
	}

	return false;
}

/* Lookup the address for this symbol. Returns 0 if not found. */
unsigned long kallsyms_lookup_name(const char *name)
{
	char namebuf[KSYM_NAME_LEN];
	unsigned long i;
	unsigned int off;

	/* Skip the search for empty string. */
	if (!*name)
		return 0;

	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));

		if (strcmp(namebuf, name) == 0)
			return kallsyms_sym_address(i);

		if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
			return kallsyms_sym_address(i);
	}
	return module_kallsyms_lookup_name(name);
}

/*
 * Iterate over all symbols in vmlinux.  For symbols from modules use
 * module_kallsyms_on_each_symbol instead.
 */
int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
				      unsigned long),
			    void *data)
{
	char namebuf[KSYM_NAME_LEN];
	unsigned long i;
	unsigned int off;
	int ret;

	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
		ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
		if (ret != 0)
			return ret;
		cond_resched();
	}
	return 0;
}

static unsigned long get_symbol_pos(unsigned long addr,
				    unsigned long *symbolsize,
				    unsigned long *offset)
{
	unsigned long symbol_start = 0, symbol_end = 0;
	unsigned long i, low, high, mid;

	/* This kernel should never had been booted. */
	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
		BUG_ON(!kallsyms_addresses);
	else
		BUG_ON(!kallsyms_offsets);

	/* Do a binary search on the sorted kallsyms_addresses array. */
	low = 0;
	high = kallsyms_num_syms;

	while (high - low > 1) {
		mid = low + (high - low) / 2;
		if (kallsyms_sym_address(mid) <= addr)
			low = mid;
		else
			high = mid;
	}

	/*
	 * Search for the first aliased symbol. Aliased
	 * symbols are symbols with the same address.
	 */
	while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
		--low;

	symbol_start = kallsyms_sym_address(low);

	/* Search for next non-aliased symbol. */
	for (i = low + 1; i < kallsyms_num_syms; i++) {
		if (kallsyms_sym_address(i) > symbol_start) {
			symbol_end = kallsyms_sym_address(i);
			break;
		}
	}

	/* If we found no next symbol, we use the end of the section. */
	if (!symbol_end) {
		if (is_kernel_inittext(addr))
			symbol_end = (unsigned long)_einittext;
		else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
			symbol_end = (unsigned long)_end;
		else
			symbol_end = (unsigned long)_etext;
	}

	if (symbolsize)
		*symbolsize = symbol_end - symbol_start;
	if (offset)
		*offset = addr - symbol_start;

	return low;
}

/*
 * Lookup an address but don't bother to find any names.
 */
int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
				unsigned long *offset)
{
	char namebuf[KSYM_NAME_LEN];

	if (is_ksym_addr(addr)) {
		get_symbol_pos(addr, symbolsize, offset);
		return 1;
	}
	return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
}

static const char *kallsyms_lookup_buildid(unsigned long addr,
			unsigned long *symbolsize,
			unsigned long *offset, char **modname,
			const unsigned char **modbuildid, char *namebuf)
{
	const char *ret;

	namebuf[KSYM_NAME_LEN - 1] = 0;
	namebuf[0] = 0;

	if (is_ksym_addr(addr)) {
		unsigned long pos;

		pos = get_symbol_pos(addr, symbolsize, offset);
		/* Grab name */
		kallsyms_expand_symbol(get_symbol_offset(pos),
				       namebuf, KSYM_NAME_LEN);
		if (modname)
			*modname = NULL;
		if (modbuildid)
			*modbuildid = NULL;

		ret = namebuf;
		goto found;
	}

	/* See if it's in a module or a BPF JITed image. */
	ret = module_address_lookup(addr, symbolsize, offset,
				    modname, modbuildid, namebuf);
	if (!ret)
		ret = bpf_address_lookup(addr, symbolsize,
					 offset, modname, namebuf);

	if (!ret)
		ret = ftrace_mod_address_lookup(addr, symbolsize,
						offset, modname, namebuf);

found:
	cleanup_symbol_name(namebuf);
	return ret;
}

/*
 * Lookup an address
 * - modname is set to NULL if it's in the kernel.
 * - We guarantee that the returned name is valid until we reschedule even if.
 *   It resides in a module.
 * - We also guarantee that modname will be valid until rescheduled.
 */
const char *kallsyms_lookup(unsigned long addr,
			    unsigned long *symbolsize,
			    unsigned long *offset,
			    char **modname, char *namebuf)
{
	return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
				       NULL, namebuf);
}

int lookup_symbol_name(unsigned long addr, char *symname)
{
	int res;

	symname[0] = '\0';
	symname[KSYM_NAME_LEN - 1] = '\0';

	if (is_ksym_addr(addr)) {
		unsigned long pos;

		pos = get_symbol_pos(addr, NULL, NULL);
		/* Grab name */
		kallsyms_expand_symbol(get_symbol_offset(pos),
				       symname, KSYM_NAME_LEN);
		goto found;
	}
	/* See if it's in a module. */
	res = lookup_module_symbol_name(addr, symname);
	if (res)
		return res;

found:
	cleanup_symbol_name(symname);
	return 0;
}

int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
			unsigned long *offset, char *modname, char *name)
{
	int res;

	name[0] = '\0';
	name[KSYM_NAME_LEN - 1] = '\0';

	if (is_ksym_addr(addr)) {
		unsigned long pos;

		pos = get_symbol_pos(addr, size, offset);
		/* Grab name */
		kallsyms_expand_symbol(get_symbol_offset(pos),
				       name, KSYM_NAME_LEN);
		modname[0] = '\0';
		goto found;
	}
	/* See if it's in a module. */
	res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
	if (res)
		return res;

found:
	cleanup_symbol_name(name);
	return 0;
}

/* Look up a kernel symbol and return it in a text buffer. */
static int __sprint_symbol(char *buffer, unsigned long address,
			   int symbol_offset, int add_offset, int add_buildid)
{
	char *modname;
	const unsigned char *buildid;
	const char *name;
	unsigned long offset, size;
	int len;

	address += symbol_offset;
	name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
				       buffer);
	if (!name)
		return sprintf(buffer, "0x%lx", address - symbol_offset);

	if (name != buffer)
		strcpy(buffer, name);
	len = strlen(buffer);
	offset -= symbol_offset;

	if (add_offset)
		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);

	if (modname) {
		len += sprintf(buffer + len, " [%s", modname);
#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
		if (add_buildid && buildid) {
			/* build ID should match length of sprintf */
#if IS_ENABLED(CONFIG_MODULES)
			static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
#endif
			len += sprintf(buffer + len, " %20phN", buildid);
		}
#endif
		len += sprintf(buffer + len, "]");
	}

	return len;
}

/**
 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function looks up a kernel symbol with @address and stores its name,
 * offset, size and module name to @buffer if possible. If no symbol was found,
 * just saves its @address as is.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_symbol(char *buffer, unsigned long address)
{
	return __sprint_symbol(buffer, address, 0, 1, 0);
}
EXPORT_SYMBOL_GPL(sprint_symbol);

/**
 * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function looks up a kernel symbol with @address and stores its name,
 * offset, size, module name and module build ID to @buffer if possible. If no
 * symbol was found, just saves its @address as is.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_symbol_build_id(char *buffer, unsigned long address)
{
	return __sprint_symbol(buffer, address, 0, 1, 1);
}
EXPORT_SYMBOL_GPL(sprint_symbol_build_id);

/**
 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function looks up a kernel symbol with @address and stores its name
 * and module name to @buffer if possible. If no symbol was found, just saves
 * its @address as is.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_symbol_no_offset(char *buffer, unsigned long address)
{
	return __sprint_symbol(buffer, address, 0, 0, 0);
}
EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);

/**
 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function is for stack backtrace and does the same thing as
 * sprint_symbol() but with modified/decreased @address. If there is a
 * tail-call to the function marked "noreturn", gcc optimized out code after
 * the call so that the stack-saved return address could point outside of the
 * caller. This function ensures that kallsyms will find the original caller
 * by decreasing @address.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_backtrace(char *buffer, unsigned long address)
{
	return __sprint_symbol(buffer, address, -1, 1, 0);
}

/**
 * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
 * @buffer: buffer to be stored
 * @address: address to lookup
 *
 * This function is for stack backtrace and does the same thing as
 * sprint_symbol() but with modified/decreased @address. If there is a
 * tail-call to the function marked "noreturn", gcc optimized out code after
 * the call so that the stack-saved return address could point outside of the
 * caller. This function ensures that kallsyms will find the original caller
 * by decreasing @address. This function also appends the module build ID to
 * the @buffer if @address is within a kernel module.
 *
 * This function returns the number of bytes stored in @buffer.
 */
int sprint_backtrace_build_id(char *buffer, unsigned long address)
{
	return __sprint_symbol(buffer, address, -1, 1, 1);
}

/* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
struct kallsym_iter {
	loff_t pos;
	loff_t pos_arch_end;
	loff_t pos_mod_end;
	loff_t pos_ftrace_mod_end;
	loff_t pos_bpf_end;
	unsigned long value;
	unsigned int nameoff; /* If iterating in core kernel symbols. */
	char type;
	char name[KSYM_NAME_LEN];
	char module_name[MODULE_NAME_LEN];
	int exported;
	int show_value;
};

int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
			    char *type, char *name)
{
	return -EINVAL;
}

static int get_ksymbol_arch(struct kallsym_iter *iter)
{
	int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
				   &iter->value, &iter->type,
				   iter->name);

	if (ret < 0) {
		iter->pos_arch_end = iter->pos;
		return 0;
	}

	return 1;
}

static int get_ksymbol_mod(struct kallsym_iter *iter)
{
	int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
				     &iter->value, &iter->type,
				     iter->name, iter->module_name,
				     &iter->exported);
	if (ret < 0) {
		iter->pos_mod_end = iter->pos;
		return 0;
	}

	return 1;
}

/*
 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
 * purposes. In that case "__builtin__ftrace" is used as a module name, even
 * though "__builtin__ftrace" is not a module.
 */
static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
{
	int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
					 &iter->value, &iter->type,
					 iter->name, iter->module_name,
					 &iter->exported);
	if (ret < 0) {
		iter->pos_ftrace_mod_end = iter->pos;
		return 0;
	}

	return 1;
}

static int get_ksymbol_bpf(struct kallsym_iter *iter)
{
	int ret;

	strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
	iter->exported = 0;
	ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
			      &iter->value, &iter->type,
			      iter->name);
	if (ret < 0) {
		iter->pos_bpf_end = iter->pos;
		return 0;
	}

	return 1;
}

/*
 * This uses "__builtin__kprobes" as a module name for symbols for pages
 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
 * module.
 */
static int get_ksymbol_kprobe(struct kallsym_iter *iter)
{
	strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
	iter->exported = 0;
	return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
				  &iter->value, &iter->type,
				  iter->name) < 0 ? 0 : 1;
}

/* Returns space to next name. */
static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
{
	unsigned off = iter->nameoff;

	iter->module_name[0] = '\0';
	iter->value = kallsyms_sym_address(iter->pos);

	iter->type = kallsyms_get_symbol_type(off);

	off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));

	return off - iter->nameoff;
}

static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
{
	iter->name[0] = '\0';
	iter->nameoff = get_symbol_offset(new_pos);
	iter->pos = new_pos;
	if (new_pos == 0) {
		iter->pos_arch_end = 0;
		iter->pos_mod_end = 0;
		iter->pos_ftrace_mod_end = 0;
		iter->pos_bpf_end = 0;
	}
}

/*
 * The end position (last + 1) of each additional kallsyms section is recorded
 * in iter->pos_..._end as each section is added, and so can be used to
 * determine which get_ksymbol_...() function to call next.
 */
static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
{
	iter->pos = pos;

	if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
	    get_ksymbol_arch(iter))
		return 1;

	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
	    get_ksymbol_mod(iter))
		return 1;

	if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
	    get_ksymbol_ftrace_mod(iter))
		return 1;

	if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
	    get_ksymbol_bpf(iter))
		return 1;

	return get_ksymbol_kprobe(iter);
}

/* Returns false if pos at or past end of file. */
static int update_iter(struct kallsym_iter *iter, loff_t pos)
{
	/* Module symbols can be accessed randomly. */
	if (pos >= kallsyms_num_syms)
		return update_iter_mod(iter, pos);

	/* If we're not on the desired position, reset to new position. */
	if (pos != iter->pos)
		reset_iter(iter, pos);

	iter->nameoff += get_ksymbol_core(iter);
	iter->pos++;

	return 1;
}

static void *s_next(struct seq_file *m, void *p, loff_t *pos)
{
	(*pos)++;

	if (!update_iter(m->private, *pos))
		return NULL;
	return p;
}

static void *s_start(struct seq_file *m, loff_t *pos)
{
	if (!update_iter(m->private, *pos))
		return NULL;
	return m->private;
}

static void s_stop(struct seq_file *m, void *p)
{
}

static int s_show(struct seq_file *m, void *p)
{
	void *value;
	struct kallsym_iter *iter = m->private;

	/* Some debugging symbols have no name.  Ignore them. */
	if (!iter->name[0])
		return 0;

	value = iter->show_value ? (void *)iter->value : NULL;

	if (iter->module_name[0]) {
		char type;

		/*
		 * Label it "global" if it is exported,
		 * "local" if not exported.
		 */
		type = iter->exported ? toupper(iter->type) :
					tolower(iter->type);
		seq_printf(m, "%px %c %s\t[%s]\n", value,
			   type, iter->name, iter->module_name);
	} else
		seq_printf(m, "%px %c %s\n", value,
			   iter->type, iter->name);
	return 0;
}

static const struct seq_operations kallsyms_op = {
	.start = s_start,
	.next = s_next,
	.stop = s_stop,
	.show = s_show
};

#ifdef CONFIG_BPF_SYSCALL

struct bpf_iter__ksym {
	__bpf_md_ptr(struct bpf_iter_meta *, meta);
	__bpf_md_ptr(struct kallsym_iter *, ksym);
};

static int ksym_prog_seq_show(struct seq_file *m, bool in_stop)
{
	struct bpf_iter__ksym ctx;
	struct bpf_iter_meta meta;
	struct bpf_prog *prog;

	meta.seq = m;
	prog = bpf_iter_get_info(&meta, in_stop);
	if (!prog)
		return 0;

	ctx.meta = &meta;
	ctx.ksym = m ? m->private : NULL;
	return bpf_iter_run_prog(prog, &ctx);
}

static int bpf_iter_ksym_seq_show(struct seq_file *m, void *p)
{
	return ksym_prog_seq_show(m, false);
}

static void bpf_iter_ksym_seq_stop(struct seq_file *m, void *p)
{
	if (!p)
		(void) ksym_prog_seq_show(m, true);
	else
		s_stop(m, p);
}

static const struct seq_operations bpf_iter_ksym_ops = {
	.start = s_start,
	.next = s_next,
	.stop = bpf_iter_ksym_seq_stop,
	.show = bpf_iter_ksym_seq_show,
};

static int bpf_iter_ksym_init(void *priv_data, struct bpf_iter_aux_info *aux)
{
	struct kallsym_iter *iter = priv_data;

	reset_iter(iter, 0);

	/* cache here as in kallsyms_open() case; use current process
	 * credentials to tell BPF iterators if values should be shown.
	 */
	iter->show_value = kallsyms_show_value(current_cred());

	return 0;
}

DEFINE_BPF_ITER_FUNC(ksym, struct bpf_iter_meta *meta, struct kallsym_iter *ksym)

static const struct bpf_iter_seq_info ksym_iter_seq_info = {
	.seq_ops		= &bpf_iter_ksym_ops,
	.init_seq_private	= bpf_iter_ksym_init,
	.fini_seq_private	= NULL,
	.seq_priv_size		= sizeof(struct kallsym_iter),
};

static struct bpf_iter_reg ksym_iter_reg_info = {
	.target                 = "ksym",
	.feature		= BPF_ITER_RESCHED,
	.ctx_arg_info_size	= 1,
	.ctx_arg_info		= {
		{ offsetof(struct bpf_iter__ksym, ksym),
		  PTR_TO_BTF_ID_OR_NULL },
	},
	.seq_info		= &ksym_iter_seq_info,
};

BTF_ID_LIST(btf_ksym_iter_id)
BTF_ID(struct, kallsym_iter)

static int __init bpf_ksym_iter_register(void)
{
	ksym_iter_reg_info.ctx_arg_info[0].btf_id = *btf_ksym_iter_id;
	return bpf_iter_reg_target(&ksym_iter_reg_info);
}

late_initcall(bpf_ksym_iter_register);

#endif /* CONFIG_BPF_SYSCALL */

static inline int kallsyms_for_perf(void)
{
#ifdef CONFIG_PERF_EVENTS
	extern int sysctl_perf_event_paranoid;
	if (sysctl_perf_event_paranoid <= 1)
		return 1;
#endif
	return 0;
}

/*
 * We show kallsyms information even to normal users if we've enabled
 * kernel profiling and are explicitly not paranoid (so kptr_restrict
 * is clear, and sysctl_perf_event_paranoid isn't set).
 *
 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 * block even that).
 */
bool kallsyms_show_value(const struct cred *cred)
{
	switch (kptr_restrict) {
	case 0:
		if (kallsyms_for_perf())
			return true;
		fallthrough;
	case 1:
		if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
				     CAP_OPT_NOAUDIT) == 0)
			return true;
		fallthrough;
	default:
		return false;
	}
}

static int kallsyms_open(struct inode *inode, struct file *file)
{
	/*
	 * We keep iterator in m->private, since normal case is to
	 * s_start from where we left off, so we avoid doing
	 * using get_symbol_offset for every symbol.
	 */
	struct kallsym_iter *iter;
	iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
	if (!iter)
		return -ENOMEM;
	reset_iter(iter, 0);

	/*
	 * Instead of checking this on every s_show() call, cache
	 * the result here at open time.
	 */
	iter->show_value = kallsyms_show_value(file->f_cred);
	return 0;
}

#ifdef	CONFIG_KGDB_KDB
const char *kdb_walk_kallsyms(loff_t *pos)
{
	static struct kallsym_iter kdb_walk_kallsyms_iter;
	if (*pos == 0) {
		memset(&kdb_walk_kallsyms_iter, 0,
		       sizeof(kdb_walk_kallsyms_iter));
		reset_iter(&kdb_walk_kallsyms_iter, 0);
	}
	while (1) {
		if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
			return NULL;
		++*pos;
		/* Some debugging symbols have no name.  Ignore them. */
		if (kdb_walk_kallsyms_iter.name[0])
			return kdb_walk_kallsyms_iter.name;
	}
}
#endif	/* CONFIG_KGDB_KDB */

static const struct proc_ops kallsyms_proc_ops = {
	.proc_open	= kallsyms_open,
	.proc_read	= seq_read,
	.proc_lseek	= seq_lseek,
	.proc_release	= seq_release_private,
};

static int __init kallsyms_init(void)
{
	proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
	return 0;
}
device_initcall(kallsyms_init);