1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
  4 *
  5 * Rewritten and vastly simplified by Rusty Russell for in-kernel
  6 * module loader:
  7 *   Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
  8 *
  9 * ChangeLog:
 10 *
 11 * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
 12 *      Changed the compression method from stem compression to "table lookup"
 13 *      compression (see scripts/kallsyms.c for a more complete description)
 14 */
 15#include <linux/kallsyms.h>
 16#include <linux/init.h>
 17#include <linux/seq_file.h>
 18#include <linux/fs.h>
 19#include <linux/kdb.h>
 20#include <linux/err.h>
 21#include <linux/proc_fs.h>
 22#include <linux/sched.h>	/* for cond_resched */
 23#include <linux/ctype.h>
 24#include <linux/slab.h>
 25#include <linux/filter.h>
 26#include <linux/ftrace.h>
 27#include <linux/kprobes.h>
 28#include <linux/build_bug.h>
 29#include <linux/compiler.h>
 30#include <linux/module.h>
 31#include <linux/kernel.h>
 32
 33/*
 34 * These will be re-linked against their real values
 35 * during the second link stage.
 36 */
 37extern const unsigned long kallsyms_addresses[] __weak;
 38extern const int kallsyms_offsets[] __weak;
 39extern const u8 kallsyms_names[] __weak;
 40
 41/*
 42 * Tell the compiler that the count isn't in the small data section if the arch
 43 * has one (eg: FRV).
 44 */
 45extern const unsigned int kallsyms_num_syms
 46__section(".rodata") __attribute__((weak));
 47
 48extern const unsigned long kallsyms_relative_base
 49__section(".rodata") __attribute__((weak));
 50
 51extern const char kallsyms_token_table[] __weak;
 52extern const u16 kallsyms_token_index[] __weak;
 53
 54extern const unsigned int kallsyms_markers[] __weak;
 55
 56/*
 57 * Expand a compressed symbol data into the resulting uncompressed string,
 58 * if uncompressed string is too long (>= maxlen), it will be truncated,
 59 * given the offset to where the symbol is in the compressed stream.
 60 */
 61static unsigned int kallsyms_expand_symbol(unsigned int off,
 62					   char *result, size_t maxlen)
 63{
 64	int len, skipped_first = 0;
 65	const char *tptr;
 66	const u8 *data;
 67
 68	/* Get the compressed symbol length from the first symbol byte. */
 69	data = &kallsyms_names[off];
 70	len = *data;
 71	data++;
 72
 73	/*
 74	 * Update the offset to return the offset for the next symbol on
 75	 * the compressed stream.
 76	 */
 77	off += len + 1;
 78
 79	/*
 80	 * For every byte on the compressed symbol data, copy the table
 81	 * entry for that byte.
 82	 */
 83	while (len) {
 84		tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
 85		data++;
 86		len--;
 87
 88		while (*tptr) {
 89			if (skipped_first) {
 90				if (maxlen <= 1)
 91					goto tail;
 92				*result = *tptr;
 93				result++;
 94				maxlen--;
 95			} else
 96				skipped_first = 1;
 97			tptr++;
 98		}
 99	}
100
101tail:
102	if (maxlen)
103		*result = '\0';
104
105	/* Return to offset to the next symbol. */
106	return off;
107}
108
109/*
110 * Get symbol type information. This is encoded as a single char at the
111 * beginning of the symbol name.
112 */
113static char kallsyms_get_symbol_type(unsigned int off)
114{
115	/*
116	 * Get just the first code, look it up in the token table,
117	 * and return the first char from this token.
118	 */
119	return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
120}
121
122
123/*
124 * Find the offset on the compressed stream given and index in the
125 * kallsyms array.
126 */
127static unsigned int get_symbol_offset(unsigned long pos)
128{
129	const u8 *name;
130	int i;
131
132	/*
133	 * Use the closest marker we have. We have markers every 256 positions,
134	 * so that should be close enough.
135	 */
136	name = &kallsyms_names[kallsyms_markers[pos >> 8]];
137
138	/*
139	 * Sequentially scan all the symbols up to the point we're searching
140	 * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
141	 * so we just need to add the len to the current pointer for every
142	 * symbol we wish to skip.
143	 */
144	for (i = 0; i < (pos & 0xFF); i++)
145		name = name + (*name) + 1;
146
147	return name - kallsyms_names;
148}
149
150static unsigned long kallsyms_sym_address(int idx)
151{
152	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
153		return kallsyms_addresses[idx];
154
155	/* values are unsigned offsets if --absolute-percpu is not in effect */
156	if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
157		return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
158
159	/* ...otherwise, positive offsets are absolute values */
160	if (kallsyms_offsets[idx] >= 0)
161		return kallsyms_offsets[idx];
162
163	/* ...and negative offsets are relative to kallsyms_relative_base - 1 */
164	return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
165}
166
167#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
168/*
169 * LLVM appends a hash to static function names when ThinLTO and CFI are
170 * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
171 * This causes confusion and potentially breaks user space tools, so we
172 * strip the suffix from expanded symbol names.
173 */
174static inline bool cleanup_symbol_name(char *s)
175{
176	char *res;
177
178	res = strrchr(s, '$');
179	if (res)
180		*res = '\0';
181
182	return res != NULL;
183}
184#else
185static inline bool cleanup_symbol_name(char *s) { return false; }
186#endif
187
188/* Lookup the address for this symbol. Returns 0 if not found. */
189unsigned long kallsyms_lookup_name(const char *name)
190{
191	char namebuf[KSYM_NAME_LEN];
192	unsigned long i;
193	unsigned int off;
194
195	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
196		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
197
198		if (strcmp(namebuf, name) == 0)
199			return kallsyms_sym_address(i);
200
201		if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
202			return kallsyms_sym_address(i);
203	}
204	return module_kallsyms_lookup_name(name);
205}
206
207#ifdef CONFIG_LIVEPATCH
208/*
209 * Iterate over all symbols in vmlinux.  For symbols from modules use
210 * module_kallsyms_on_each_symbol instead.
211 */
212int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
213				      unsigned long),
214			    void *data)
215{
216	char namebuf[KSYM_NAME_LEN];
217	unsigned long i;
218	unsigned int off;
219	int ret;
220
221	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
222		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
223		ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
224		if (ret != 0)
225			return ret;
226	}
227	return 0;
228}
229#endif /* CONFIG_LIVEPATCH */
230
231static unsigned long get_symbol_pos(unsigned long addr,
232				    unsigned long *symbolsize,
233				    unsigned long *offset)
234{
235	unsigned long symbol_start = 0, symbol_end = 0;
236	unsigned long i, low, high, mid;
237
238	/* This kernel should never had been booted. */
239	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
240		BUG_ON(!kallsyms_addresses);
241	else
242		BUG_ON(!kallsyms_offsets);
243
244	/* Do a binary search on the sorted kallsyms_addresses array. */
245	low = 0;
246	high = kallsyms_num_syms;
247
248	while (high - low > 1) {
249		mid = low + (high - low) / 2;
250		if (kallsyms_sym_address(mid) <= addr)
251			low = mid;
252		else
253			high = mid;
254	}
255
256	/*
257	 * Search for the first aliased symbol. Aliased
258	 * symbols are symbols with the same address.
259	 */
260	while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
261		--low;
262
263	symbol_start = kallsyms_sym_address(low);
264
265	/* Search for next non-aliased symbol. */
266	for (i = low + 1; i < kallsyms_num_syms; i++) {
267		if (kallsyms_sym_address(i) > symbol_start) {
268			symbol_end = kallsyms_sym_address(i);
269			break;
270		}
271	}
272
273	/* If we found no next symbol, we use the end of the section. */
274	if (!symbol_end) {
275		if (is_kernel_inittext(addr))
276			symbol_end = (unsigned long)_einittext;
277		else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
278			symbol_end = (unsigned long)_end;
279		else
280			symbol_end = (unsigned long)_etext;
281	}
282
283	if (symbolsize)
284		*symbolsize = symbol_end - symbol_start;
285	if (offset)
286		*offset = addr - symbol_start;
287
288	return low;
289}
290
291/*
292 * Lookup an address but don't bother to find any names.
293 */
294int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
295				unsigned long *offset)
296{
297	char namebuf[KSYM_NAME_LEN];
298
299	if (is_ksym_addr(addr)) {
300		get_symbol_pos(addr, symbolsize, offset);
301		return 1;
302	}
303	return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
304	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
305}
306
307static const char *kallsyms_lookup_buildid(unsigned long addr,
308			unsigned long *symbolsize,
309			unsigned long *offset, char **modname,
310			const unsigned char **modbuildid, char *namebuf)
 
 
 
 
 
 
 
311{
312	const char *ret;
313
314	namebuf[KSYM_NAME_LEN - 1] = 0;
315	namebuf[0] = 0;
316
317	if (is_ksym_addr(addr)) {
318		unsigned long pos;
319
320		pos = get_symbol_pos(addr, symbolsize, offset);
321		/* Grab name */
322		kallsyms_expand_symbol(get_symbol_offset(pos),
323				       namebuf, KSYM_NAME_LEN);
324		if (modname)
325			*modname = NULL;
326		if (modbuildid)
327			*modbuildid = NULL;
328
329		ret = namebuf;
330		goto found;
331	}
332
333	/* See if it's in a module or a BPF JITed image. */
334	ret = module_address_lookup(addr, symbolsize, offset,
335				    modname, modbuildid, namebuf);
336	if (!ret)
337		ret = bpf_address_lookup(addr, symbolsize,
338					 offset, modname, namebuf);
339
340	if (!ret)
341		ret = ftrace_mod_address_lookup(addr, symbolsize,
342						offset, modname, namebuf);
343
344found:
345	cleanup_symbol_name(namebuf);
346	return ret;
347}
348
349/*
350 * Lookup an address
351 * - modname is set to NULL if it's in the kernel.
352 * - We guarantee that the returned name is valid until we reschedule even if.
353 *   It resides in a module.
354 * - We also guarantee that modname will be valid until rescheduled.
355 */
356const char *kallsyms_lookup(unsigned long addr,
357			    unsigned long *symbolsize,
358			    unsigned long *offset,
359			    char **modname, char *namebuf)
360{
361	return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
362				       NULL, namebuf);
363}
364
365int lookup_symbol_name(unsigned long addr, char *symname)
366{
367	int res;
368
369	symname[0] = '\0';
370	symname[KSYM_NAME_LEN - 1] = '\0';
371
372	if (is_ksym_addr(addr)) {
373		unsigned long pos;
374
375		pos = get_symbol_pos(addr, NULL, NULL);
376		/* Grab name */
377		kallsyms_expand_symbol(get_symbol_offset(pos),
378				       symname, KSYM_NAME_LEN);
379		goto found;
380	}
381	/* See if it's in a module. */
382	res = lookup_module_symbol_name(addr, symname);
383	if (res)
384		return res;
385
386found:
387	cleanup_symbol_name(symname);
388	return 0;
389}
390
391int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
392			unsigned long *offset, char *modname, char *name)
393{
394	int res;
395
396	name[0] = '\0';
397	name[KSYM_NAME_LEN - 1] = '\0';
398
399	if (is_ksym_addr(addr)) {
400		unsigned long pos;
401
402		pos = get_symbol_pos(addr, size, offset);
403		/* Grab name */
404		kallsyms_expand_symbol(get_symbol_offset(pos),
405				       name, KSYM_NAME_LEN);
406		modname[0] = '\0';
407		goto found;
408	}
409	/* See if it's in a module. */
410	res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
411	if (res)
412		return res;
413
414found:
415	cleanup_symbol_name(name);
416	return 0;
417}
418
419/* Look up a kernel symbol and return it in a text buffer. */
420static int __sprint_symbol(char *buffer, unsigned long address,
421			   int symbol_offset, int add_offset, int add_buildid)
422{
423	char *modname;
424	const unsigned char *buildid;
425	const char *name;
426	unsigned long offset, size;
427	int len;
428
429	address += symbol_offset;
430	name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
431				       buffer);
432	if (!name)
433		return sprintf(buffer, "0x%lx", address - symbol_offset);
434
435	if (name != buffer)
436		strcpy(buffer, name);
437	len = strlen(buffer);
438	offset -= symbol_offset;
439
440	if (add_offset)
441		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
442
443	if (modname) {
444		len += sprintf(buffer + len, " [%s", modname);
445#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
446		if (add_buildid && buildid) {
447			/* build ID should match length of sprintf */
448#if IS_ENABLED(CONFIG_MODULES)
449			static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
450#endif
451			len += sprintf(buffer + len, " %20phN", buildid);
452		}
453#endif
454		len += sprintf(buffer + len, "]");
455	}
456
457	return len;
458}
459
460/**
461 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
462 * @buffer: buffer to be stored
463 * @address: address to lookup
464 *
465 * This function looks up a kernel symbol with @address and stores its name,
466 * offset, size and module name to @buffer if possible. If no symbol was found,
467 * just saves its @address as is.
468 *
469 * This function returns the number of bytes stored in @buffer.
470 */
471int sprint_symbol(char *buffer, unsigned long address)
472{
473	return __sprint_symbol(buffer, address, 0, 1, 0);
474}
475EXPORT_SYMBOL_GPL(sprint_symbol);
476
477/**
478 * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
479 * @buffer: buffer to be stored
480 * @address: address to lookup
481 *
482 * This function looks up a kernel symbol with @address and stores its name,
483 * offset, size, module name and module build ID to @buffer if possible. If no
484 * symbol was found, just saves its @address as is.
485 *
486 * This function returns the number of bytes stored in @buffer.
487 */
488int sprint_symbol_build_id(char *buffer, unsigned long address)
489{
490	return __sprint_symbol(buffer, address, 0, 1, 1);
491}
492EXPORT_SYMBOL_GPL(sprint_symbol_build_id);
493
494/**
495 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
496 * @buffer: buffer to be stored
497 * @address: address to lookup
498 *
499 * This function looks up a kernel symbol with @address and stores its name
500 * and module name to @buffer if possible. If no symbol was found, just saves
501 * its @address as is.
502 *
503 * This function returns the number of bytes stored in @buffer.
504 */
505int sprint_symbol_no_offset(char *buffer, unsigned long address)
506{
507	return __sprint_symbol(buffer, address, 0, 0, 0);
508}
509EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
510
511/**
512 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
513 * @buffer: buffer to be stored
514 * @address: address to lookup
515 *
516 * This function is for stack backtrace and does the same thing as
517 * sprint_symbol() but with modified/decreased @address. If there is a
518 * tail-call to the function marked "noreturn", gcc optimized out code after
519 * the call so that the stack-saved return address could point outside of the
520 * caller. This function ensures that kallsyms will find the original caller
521 * by decreasing @address.
522 *
523 * This function returns the number of bytes stored in @buffer.
524 */
525int sprint_backtrace(char *buffer, unsigned long address)
526{
527	return __sprint_symbol(buffer, address, -1, 1, 0);
528}
529
530/**
531 * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
532 * @buffer: buffer to be stored
533 * @address: address to lookup
534 *
535 * This function is for stack backtrace and does the same thing as
536 * sprint_symbol() but with modified/decreased @address. If there is a
537 * tail-call to the function marked "noreturn", gcc optimized out code after
538 * the call so that the stack-saved return address could point outside of the
539 * caller. This function ensures that kallsyms will find the original caller
540 * by decreasing @address. This function also appends the module build ID to
541 * the @buffer if @address is within a kernel module.
542 *
543 * This function returns the number of bytes stored in @buffer.
544 */
545int sprint_backtrace_build_id(char *buffer, unsigned long address)
546{
547	return __sprint_symbol(buffer, address, -1, 1, 1);
548}
549
550/* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
551struct kallsym_iter {
552	loff_t pos;
553	loff_t pos_arch_end;
554	loff_t pos_mod_end;
555	loff_t pos_ftrace_mod_end;
556	loff_t pos_bpf_end;
557	unsigned long value;
558	unsigned int nameoff; /* If iterating in core kernel symbols. */
559	char type;
560	char name[KSYM_NAME_LEN];
561	char module_name[MODULE_NAME_LEN];
562	int exported;
563	int show_value;
564};
565
566int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
567			    char *type, char *name)
568{
569	return -EINVAL;
570}
571
572static int get_ksymbol_arch(struct kallsym_iter *iter)
573{
574	int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
575				   &iter->value, &iter->type,
576				   iter->name);
577
578	if (ret < 0) {
579		iter->pos_arch_end = iter->pos;
580		return 0;
581	}
582
583	return 1;
584}
585
586static int get_ksymbol_mod(struct kallsym_iter *iter)
587{
588	int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
589				     &iter->value, &iter->type,
590				     iter->name, iter->module_name,
591				     &iter->exported);
592	if (ret < 0) {
593		iter->pos_mod_end = iter->pos;
594		return 0;
595	}
596
597	return 1;
598}
599
600/*
601 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
602 * purposes. In that case "__builtin__ftrace" is used as a module name, even
603 * though "__builtin__ftrace" is not a module.
604 */
605static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
606{
607	int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
608					 &iter->value, &iter->type,
609					 iter->name, iter->module_name,
610					 &iter->exported);
611	if (ret < 0) {
612		iter->pos_ftrace_mod_end = iter->pos;
613		return 0;
614	}
615
616	return 1;
617}
618
619static int get_ksymbol_bpf(struct kallsym_iter *iter)
620{
621	int ret;
622
623	strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
624	iter->exported = 0;
625	ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
626			      &iter->value, &iter->type,
627			      iter->name);
628	if (ret < 0) {
629		iter->pos_bpf_end = iter->pos;
630		return 0;
631	}
632
633	return 1;
634}
635
636/*
637 * This uses "__builtin__kprobes" as a module name for symbols for pages
638 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
639 * module.
640 */
641static int get_ksymbol_kprobe(struct kallsym_iter *iter)
642{
643	strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
644	iter->exported = 0;
645	return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
646				  &iter->value, &iter->type,
647				  iter->name) < 0 ? 0 : 1;
648}
649
650/* Returns space to next name. */
651static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
652{
653	unsigned off = iter->nameoff;
654
655	iter->module_name[0] = '\0';
656	iter->value = kallsyms_sym_address(iter->pos);
657
658	iter->type = kallsyms_get_symbol_type(off);
659
660	off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
661
662	return off - iter->nameoff;
663}
664
665static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
666{
667	iter->name[0] = '\0';
668	iter->nameoff = get_symbol_offset(new_pos);
669	iter->pos = new_pos;
670	if (new_pos == 0) {
671		iter->pos_arch_end = 0;
672		iter->pos_mod_end = 0;
673		iter->pos_ftrace_mod_end = 0;
674		iter->pos_bpf_end = 0;
675	}
676}
677
678/*
679 * The end position (last + 1) of each additional kallsyms section is recorded
680 * in iter->pos_..._end as each section is added, and so can be used to
681 * determine which get_ksymbol_...() function to call next.
682 */
683static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
684{
685	iter->pos = pos;
686
687	if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
688	    get_ksymbol_arch(iter))
689		return 1;
690
691	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
692	    get_ksymbol_mod(iter))
693		return 1;
694
695	if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
696	    get_ksymbol_ftrace_mod(iter))
697		return 1;
698
699	if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
700	    get_ksymbol_bpf(iter))
701		return 1;
702
703	return get_ksymbol_kprobe(iter);
704}
705
706/* Returns false if pos at or past end of file. */
707static int update_iter(struct kallsym_iter *iter, loff_t pos)
708{
709	/* Module symbols can be accessed randomly. */
710	if (pos >= kallsyms_num_syms)
711		return update_iter_mod(iter, pos);
712
713	/* If we're not on the desired position, reset to new position. */
714	if (pos != iter->pos)
715		reset_iter(iter, pos);
716
717	iter->nameoff += get_ksymbol_core(iter);
718	iter->pos++;
719
720	return 1;
721}
722
723static void *s_next(struct seq_file *m, void *p, loff_t *pos)
724{
725	(*pos)++;
726
727	if (!update_iter(m->private, *pos))
728		return NULL;
729	return p;
730}
731
732static void *s_start(struct seq_file *m, loff_t *pos)
733{
734	if (!update_iter(m->private, *pos))
735		return NULL;
736	return m->private;
737}
738
739static void s_stop(struct seq_file *m, void *p)
740{
741}
742
743static int s_show(struct seq_file *m, void *p)
744{
745	void *value;
746	struct kallsym_iter *iter = m->private;
747
748	/* Some debugging symbols have no name.  Ignore them. */
749	if (!iter->name[0])
750		return 0;
751
752	value = iter->show_value ? (void *)iter->value : NULL;
753
754	if (iter->module_name[0]) {
755		char type;
756
757		/*
758		 * Label it "global" if it is exported,
759		 * "local" if not exported.
760		 */
761		type = iter->exported ? toupper(iter->type) :
762					tolower(iter->type);
763		seq_printf(m, "%px %c %s\t[%s]\n", value,
764			   type, iter->name, iter->module_name);
765	} else
766		seq_printf(m, "%px %c %s\n", value,
767			   iter->type, iter->name);
768	return 0;
769}
770
771static const struct seq_operations kallsyms_op = {
772	.start = s_start,
773	.next = s_next,
774	.stop = s_stop,
775	.show = s_show
776};
777
778static inline int kallsyms_for_perf(void)
779{
780#ifdef CONFIG_PERF_EVENTS
781	extern int sysctl_perf_event_paranoid;
782	if (sysctl_perf_event_paranoid <= 1)
783		return 1;
784#endif
785	return 0;
786}
787
788/*
789 * We show kallsyms information even to normal users if we've enabled
790 * kernel profiling and are explicitly not paranoid (so kptr_restrict
791 * is clear, and sysctl_perf_event_paranoid isn't set).
792 *
793 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
794 * block even that).
795 */
796bool kallsyms_show_value(const struct cred *cred)
797{
798	switch (kptr_restrict) {
799	case 0:
800		if (kallsyms_for_perf())
801			return true;
802		fallthrough;
803	case 1:
804		if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
805				     CAP_OPT_NOAUDIT) == 0)
806			return true;
807		fallthrough;
808	default:
809		return false;
810	}
811}
812
813static int kallsyms_open(struct inode *inode, struct file *file)
814{
815	/*
816	 * We keep iterator in m->private, since normal case is to
817	 * s_start from where we left off, so we avoid doing
818	 * using get_symbol_offset for every symbol.
819	 */
820	struct kallsym_iter *iter;
821	iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
822	if (!iter)
823		return -ENOMEM;
824	reset_iter(iter, 0);
825
826	/*
827	 * Instead of checking this on every s_show() call, cache
828	 * the result here at open time.
829	 */
830	iter->show_value = kallsyms_show_value(file->f_cred);
831	return 0;
832}
833
834#ifdef	CONFIG_KGDB_KDB
835const char *kdb_walk_kallsyms(loff_t *pos)
836{
837	static struct kallsym_iter kdb_walk_kallsyms_iter;
838	if (*pos == 0) {
839		memset(&kdb_walk_kallsyms_iter, 0,
840		       sizeof(kdb_walk_kallsyms_iter));
841		reset_iter(&kdb_walk_kallsyms_iter, 0);
842	}
843	while (1) {
844		if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
845			return NULL;
846		++*pos;
847		/* Some debugging symbols have no name.  Ignore them. */
848		if (kdb_walk_kallsyms_iter.name[0])
849			return kdb_walk_kallsyms_iter.name;
850	}
851}
852#endif	/* CONFIG_KGDB_KDB */
853
854static const struct proc_ops kallsyms_proc_ops = {
855	.proc_open	= kallsyms_open,
856	.proc_read	= seq_read,
857	.proc_lseek	= seq_lseek,
858	.proc_release	= seq_release_private,
859};
860
861static int __init kallsyms_init(void)
862{
863	proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
864	return 0;
865}
866device_initcall(kallsyms_init);