xref: /openbmc/linux/kernel/kallsyms.c (revision a10c9ede)
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 #include <linux/bsearch.h>
33 
34 #include "kallsyms_internal.h"
35 
36 /*
37  * Expand a compressed symbol data into the resulting uncompressed string,
38  * if uncompressed string is too long (>= maxlen), it will be truncated,
39  * given the offset to where the symbol is in the compressed stream.
40  */
41 static unsigned int kallsyms_expand_symbol(unsigned int off,
42 					   char *result, size_t maxlen)
43 {
44 	int len, skipped_first = 0;
45 	const char *tptr;
46 	const u8 *data;
47 
48 	/* Get the compressed symbol length from the first symbol byte. */
49 	data = &kallsyms_names[off];
50 	len = *data;
51 	data++;
52 
53 	/*
54 	 * Update the offset to return the offset for the next symbol on
55 	 * the compressed stream.
56 	 */
57 	off += len + 1;
58 
59 	/*
60 	 * For every byte on the compressed symbol data, copy the table
61 	 * entry for that byte.
62 	 */
63 	while (len) {
64 		tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
65 		data++;
66 		len--;
67 
68 		while (*tptr) {
69 			if (skipped_first) {
70 				if (maxlen <= 1)
71 					goto tail;
72 				*result = *tptr;
73 				result++;
74 				maxlen--;
75 			} else
76 				skipped_first = 1;
77 			tptr++;
78 		}
79 	}
80 
81 tail:
82 	if (maxlen)
83 		*result = '\0';
84 
85 	/* Return to offset to the next symbol. */
86 	return off;
87 }
88 
89 /*
90  * Get symbol type information. This is encoded as a single char at the
91  * beginning of the symbol name.
92  */
93 static char kallsyms_get_symbol_type(unsigned int off)
94 {
95 	/*
96 	 * Get just the first code, look it up in the token table,
97 	 * and return the first char from this token.
98 	 */
99 	return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
100 }
101 
102 
103 /*
104  * Find the offset on the compressed stream given and index in the
105  * kallsyms array.
106  */
107 static unsigned int get_symbol_offset(unsigned long pos)
108 {
109 	const u8 *name;
110 	int i;
111 
112 	/*
113 	 * Use the closest marker we have. We have markers every 256 positions,
114 	 * so that should be close enough.
115 	 */
116 	name = &kallsyms_names[kallsyms_markers[pos >> 8]];
117 
118 	/*
119 	 * Sequentially scan all the symbols up to the point we're searching
120 	 * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
121 	 * so we just need to add the len to the current pointer for every
122 	 * symbol we wish to skip.
123 	 */
124 	for (i = 0; i < (pos & 0xFF); i++)
125 		name = name + (*name) + 1;
126 
127 	return name - kallsyms_names;
128 }
129 
130 static unsigned long kallsyms_sym_address(int idx)
131 {
132 	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
133 		return kallsyms_addresses[idx];
134 
135 	/* values are unsigned offsets if --absolute-percpu is not in effect */
136 	if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
137 		return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
138 
139 	/* ...otherwise, positive offsets are absolute values */
140 	if (kallsyms_offsets[idx] >= 0)
141 		return kallsyms_offsets[idx];
142 
143 	/* ...and negative offsets are relative to kallsyms_relative_base - 1 */
144 	return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
145 }
146 
147 static bool cleanup_symbol_name(char *s)
148 {
149 	char *res;
150 
151 	if (!IS_ENABLED(CONFIG_LTO_CLANG))
152 		return false;
153 
154 	/*
155 	 * LLVM appends various suffixes for local functions and variables that
156 	 * must be promoted to global scope as part of LTO.  This can break
157 	 * hooking of static functions with kprobes. '.' is not a valid
158 	 * character in an identifier in C. Suffixes observed:
159 	 * - foo.llvm.[0-9a-f]+
160 	 * - foo.[0-9a-f]+
161 	 * - foo.[0-9a-f]+.cfi_jt
162 	 */
163 	res = strchr(s, '.');
164 	if (res) {
165 		*res = '\0';
166 		return true;
167 	}
168 
169 	if (!IS_ENABLED(CONFIG_CFI_CLANG) ||
170 	    !IS_ENABLED(CONFIG_LTO_CLANG_THIN) ||
171 	    CONFIG_CLANG_VERSION >= 130000)
172 		return false;
173 
174 	/*
175 	 * Prior to LLVM 13, the following suffixes were observed when thinLTO
176 	 * and CFI are both enabled:
177 	 * - foo$[0-9]+
178 	 */
179 	res = strrchr(s, '$');
180 	if (res) {
181 		*res = '\0';
182 		return true;
183 	}
184 
185 	return false;
186 }
187 
188 /* Lookup the address for this symbol. Returns 0 if not found. */
189 unsigned long kallsyms_lookup_name(const char *name)
190 {
191 	char namebuf[KSYM_NAME_LEN];
192 	unsigned long i;
193 	unsigned int off;
194 
195 	/* Skip the search for empty string. */
196 	if (!*name)
197 		return 0;
198 
199 	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
200 		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
201 
202 		if (strcmp(namebuf, name) == 0)
203 			return kallsyms_sym_address(i);
204 
205 		if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
206 			return kallsyms_sym_address(i);
207 	}
208 	return module_kallsyms_lookup_name(name);
209 }
210 
211 /*
212  * Iterate over all symbols in vmlinux.  For symbols from modules use
213  * module_kallsyms_on_each_symbol instead.
214  */
215 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
216 				      unsigned long),
217 			    void *data)
218 {
219 	char namebuf[KSYM_NAME_LEN];
220 	unsigned long i;
221 	unsigned int off;
222 	int ret;
223 
224 	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
225 		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
226 		ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
227 		if (ret != 0)
228 			return ret;
229 		cond_resched();
230 	}
231 	return 0;
232 }
233 
234 static unsigned long get_symbol_pos(unsigned long addr,
235 				    unsigned long *symbolsize,
236 				    unsigned long *offset)
237 {
238 	unsigned long symbol_start = 0, symbol_end = 0;
239 	unsigned long i, low, high, mid;
240 
241 	/* This kernel should never had been booted. */
242 	if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
243 		BUG_ON(!kallsyms_addresses);
244 	else
245 		BUG_ON(!kallsyms_offsets);
246 
247 	/* Do a binary search on the sorted kallsyms_addresses array. */
248 	low = 0;
249 	high = kallsyms_num_syms;
250 
251 	while (high - low > 1) {
252 		mid = low + (high - low) / 2;
253 		if (kallsyms_sym_address(mid) <= addr)
254 			low = mid;
255 		else
256 			high = mid;
257 	}
258 
259 	/*
260 	 * Search for the first aliased symbol. Aliased
261 	 * symbols are symbols with the same address.
262 	 */
263 	while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
264 		--low;
265 
266 	symbol_start = kallsyms_sym_address(low);
267 
268 	/* Search for next non-aliased symbol. */
269 	for (i = low + 1; i < kallsyms_num_syms; i++) {
270 		if (kallsyms_sym_address(i) > symbol_start) {
271 			symbol_end = kallsyms_sym_address(i);
272 			break;
273 		}
274 	}
275 
276 	/* If we found no next symbol, we use the end of the section. */
277 	if (!symbol_end) {
278 		if (is_kernel_inittext(addr))
279 			symbol_end = (unsigned long)_einittext;
280 		else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
281 			symbol_end = (unsigned long)_end;
282 		else
283 			symbol_end = (unsigned long)_etext;
284 	}
285 
286 	if (symbolsize)
287 		*symbolsize = symbol_end - symbol_start;
288 	if (offset)
289 		*offset = addr - symbol_start;
290 
291 	return low;
292 }
293 
294 /*
295  * Lookup an address but don't bother to find any names.
296  */
297 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
298 				unsigned long *offset)
299 {
300 	char namebuf[KSYM_NAME_LEN];
301 
302 	if (is_ksym_addr(addr)) {
303 		get_symbol_pos(addr, symbolsize, offset);
304 		return 1;
305 	}
306 	return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
307 	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
308 }
309 
310 static const char *kallsyms_lookup_buildid(unsigned long addr,
311 			unsigned long *symbolsize,
312 			unsigned long *offset, char **modname,
313 			const unsigned char **modbuildid, char *namebuf)
314 {
315 	const char *ret;
316 
317 	namebuf[KSYM_NAME_LEN - 1] = 0;
318 	namebuf[0] = 0;
319 
320 	if (is_ksym_addr(addr)) {
321 		unsigned long pos;
322 
323 		pos = get_symbol_pos(addr, symbolsize, offset);
324 		/* Grab name */
325 		kallsyms_expand_symbol(get_symbol_offset(pos),
326 				       namebuf, KSYM_NAME_LEN);
327 		if (modname)
328 			*modname = NULL;
329 		if (modbuildid)
330 			*modbuildid = NULL;
331 
332 		ret = namebuf;
333 		goto found;
334 	}
335 
336 	/* See if it's in a module or a BPF JITed image. */
337 	ret = module_address_lookup(addr, symbolsize, offset,
338 				    modname, modbuildid, namebuf);
339 	if (!ret)
340 		ret = bpf_address_lookup(addr, symbolsize,
341 					 offset, modname, namebuf);
342 
343 	if (!ret)
344 		ret = ftrace_mod_address_lookup(addr, symbolsize,
345 						offset, modname, namebuf);
346 
347 found:
348 	cleanup_symbol_name(namebuf);
349 	return ret;
350 }
351 
352 /*
353  * Lookup an address
354  * - modname is set to NULL if it's in the kernel.
355  * - We guarantee that the returned name is valid until we reschedule even if.
356  *   It resides in a module.
357  * - We also guarantee that modname will be valid until rescheduled.
358  */
359 const char *kallsyms_lookup(unsigned long addr,
360 			    unsigned long *symbolsize,
361 			    unsigned long *offset,
362 			    char **modname, char *namebuf)
363 {
364 	return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
365 				       NULL, namebuf);
366 }
367 
368 int lookup_symbol_name(unsigned long addr, char *symname)
369 {
370 	int res;
371 
372 	symname[0] = '\0';
373 	symname[KSYM_NAME_LEN - 1] = '\0';
374 
375 	if (is_ksym_addr(addr)) {
376 		unsigned long pos;
377 
378 		pos = get_symbol_pos(addr, NULL, NULL);
379 		/* Grab name */
380 		kallsyms_expand_symbol(get_symbol_offset(pos),
381 				       symname, KSYM_NAME_LEN);
382 		goto found;
383 	}
384 	/* See if it's in a module. */
385 	res = lookup_module_symbol_name(addr, symname);
386 	if (res)
387 		return res;
388 
389 found:
390 	cleanup_symbol_name(symname);
391 	return 0;
392 }
393 
394 int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
395 			unsigned long *offset, char *modname, char *name)
396 {
397 	int res;
398 
399 	name[0] = '\0';
400 	name[KSYM_NAME_LEN - 1] = '\0';
401 
402 	if (is_ksym_addr(addr)) {
403 		unsigned long pos;
404 
405 		pos = get_symbol_pos(addr, size, offset);
406 		/* Grab name */
407 		kallsyms_expand_symbol(get_symbol_offset(pos),
408 				       name, KSYM_NAME_LEN);
409 		modname[0] = '\0';
410 		goto found;
411 	}
412 	/* See if it's in a module. */
413 	res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
414 	if (res)
415 		return res;
416 
417 found:
418 	cleanup_symbol_name(name);
419 	return 0;
420 }
421 
422 /* Look up a kernel symbol and return it in a text buffer. */
423 static int __sprint_symbol(char *buffer, unsigned long address,
424 			   int symbol_offset, int add_offset, int add_buildid)
425 {
426 	char *modname;
427 	const unsigned char *buildid;
428 	const char *name;
429 	unsigned long offset, size;
430 	int len;
431 
432 	address += symbol_offset;
433 	name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
434 				       buffer);
435 	if (!name)
436 		return sprintf(buffer, "0x%lx", address - symbol_offset);
437 
438 	if (name != buffer)
439 		strcpy(buffer, name);
440 	len = strlen(buffer);
441 	offset -= symbol_offset;
442 
443 	if (add_offset)
444 		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
445 
446 	if (modname) {
447 		len += sprintf(buffer + len, " [%s", modname);
448 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
449 		if (add_buildid && buildid) {
450 			/* build ID should match length of sprintf */
451 #if IS_ENABLED(CONFIG_MODULES)
452 			static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
453 #endif
454 			len += sprintf(buffer + len, " %20phN", buildid);
455 		}
456 #endif
457 		len += sprintf(buffer + len, "]");
458 	}
459 
460 	return len;
461 }
462 
463 /**
464  * sprint_symbol - Look up a kernel symbol and return it in a text buffer
465  * @buffer: buffer to be stored
466  * @address: address to lookup
467  *
468  * This function looks up a kernel symbol with @address and stores its name,
469  * offset, size and module name to @buffer if possible. If no symbol was found,
470  * just saves its @address as is.
471  *
472  * This function returns the number of bytes stored in @buffer.
473  */
474 int sprint_symbol(char *buffer, unsigned long address)
475 {
476 	return __sprint_symbol(buffer, address, 0, 1, 0);
477 }
478 EXPORT_SYMBOL_GPL(sprint_symbol);
479 
480 /**
481  * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
482  * @buffer: buffer to be stored
483  * @address: address to lookup
484  *
485  * This function looks up a kernel symbol with @address and stores its name,
486  * offset, size, module name and module build ID to @buffer if possible. If no
487  * symbol was found, just saves its @address as is.
488  *
489  * This function returns the number of bytes stored in @buffer.
490  */
491 int sprint_symbol_build_id(char *buffer, unsigned long address)
492 {
493 	return __sprint_symbol(buffer, address, 0, 1, 1);
494 }
495 EXPORT_SYMBOL_GPL(sprint_symbol_build_id);
496 
497 /**
498  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
499  * @buffer: buffer to be stored
500  * @address: address to lookup
501  *
502  * This function looks up a kernel symbol with @address and stores its name
503  * and module name to @buffer if possible. If no symbol was found, just saves
504  * its @address as is.
505  *
506  * This function returns the number of bytes stored in @buffer.
507  */
508 int sprint_symbol_no_offset(char *buffer, unsigned long address)
509 {
510 	return __sprint_symbol(buffer, address, 0, 0, 0);
511 }
512 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
513 
514 /**
515  * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
516  * @buffer: buffer to be stored
517  * @address: address to lookup
518  *
519  * This function is for stack backtrace and does the same thing as
520  * sprint_symbol() but with modified/decreased @address. If there is a
521  * tail-call to the function marked "noreturn", gcc optimized out code after
522  * the call so that the stack-saved return address could point outside of the
523  * caller. This function ensures that kallsyms will find the original caller
524  * by decreasing @address.
525  *
526  * This function returns the number of bytes stored in @buffer.
527  */
528 int sprint_backtrace(char *buffer, unsigned long address)
529 {
530 	return __sprint_symbol(buffer, address, -1, 1, 0);
531 }
532 
533 /**
534  * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
535  * @buffer: buffer to be stored
536  * @address: address to lookup
537  *
538  * This function is for stack backtrace and does the same thing as
539  * sprint_symbol() but with modified/decreased @address. If there is a
540  * tail-call to the function marked "noreturn", gcc optimized out code after
541  * the call so that the stack-saved return address could point outside of the
542  * caller. This function ensures that kallsyms will find the original caller
543  * by decreasing @address. This function also appends the module build ID to
544  * the @buffer if @address is within a kernel module.
545  *
546  * This function returns the number of bytes stored in @buffer.
547  */
548 int sprint_backtrace_build_id(char *buffer, unsigned long address)
549 {
550 	return __sprint_symbol(buffer, address, -1, 1, 1);
551 }
552 
553 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
554 struct kallsym_iter {
555 	loff_t pos;
556 	loff_t pos_arch_end;
557 	loff_t pos_mod_end;
558 	loff_t pos_ftrace_mod_end;
559 	loff_t pos_bpf_end;
560 	unsigned long value;
561 	unsigned int nameoff; /* If iterating in core kernel symbols. */
562 	char type;
563 	char name[KSYM_NAME_LEN];
564 	char module_name[MODULE_NAME_LEN];
565 	int exported;
566 	int show_value;
567 };
568 
569 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
570 			    char *type, char *name)
571 {
572 	return -EINVAL;
573 }
574 
575 static int get_ksymbol_arch(struct kallsym_iter *iter)
576 {
577 	int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
578 				   &iter->value, &iter->type,
579 				   iter->name);
580 
581 	if (ret < 0) {
582 		iter->pos_arch_end = iter->pos;
583 		return 0;
584 	}
585 
586 	return 1;
587 }
588 
589 static int get_ksymbol_mod(struct kallsym_iter *iter)
590 {
591 	int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
592 				     &iter->value, &iter->type,
593 				     iter->name, iter->module_name,
594 				     &iter->exported);
595 	if (ret < 0) {
596 		iter->pos_mod_end = iter->pos;
597 		return 0;
598 	}
599 
600 	return 1;
601 }
602 
603 /*
604  * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
605  * purposes. In that case "__builtin__ftrace" is used as a module name, even
606  * though "__builtin__ftrace" is not a module.
607  */
608 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
609 {
610 	int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
611 					 &iter->value, &iter->type,
612 					 iter->name, iter->module_name,
613 					 &iter->exported);
614 	if (ret < 0) {
615 		iter->pos_ftrace_mod_end = iter->pos;
616 		return 0;
617 	}
618 
619 	return 1;
620 }
621 
622 static int get_ksymbol_bpf(struct kallsym_iter *iter)
623 {
624 	int ret;
625 
626 	strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
627 	iter->exported = 0;
628 	ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
629 			      &iter->value, &iter->type,
630 			      iter->name);
631 	if (ret < 0) {
632 		iter->pos_bpf_end = iter->pos;
633 		return 0;
634 	}
635 
636 	return 1;
637 }
638 
639 /*
640  * This uses "__builtin__kprobes" as a module name for symbols for pages
641  * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
642  * module.
643  */
644 static int get_ksymbol_kprobe(struct kallsym_iter *iter)
645 {
646 	strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
647 	iter->exported = 0;
648 	return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
649 				  &iter->value, &iter->type,
650 				  iter->name) < 0 ? 0 : 1;
651 }
652 
653 /* Returns space to next name. */
654 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
655 {
656 	unsigned off = iter->nameoff;
657 
658 	iter->module_name[0] = '\0';
659 	iter->value = kallsyms_sym_address(iter->pos);
660 
661 	iter->type = kallsyms_get_symbol_type(off);
662 
663 	off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
664 
665 	return off - iter->nameoff;
666 }
667 
668 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
669 {
670 	iter->name[0] = '\0';
671 	iter->nameoff = get_symbol_offset(new_pos);
672 	iter->pos = new_pos;
673 	if (new_pos == 0) {
674 		iter->pos_arch_end = 0;
675 		iter->pos_mod_end = 0;
676 		iter->pos_ftrace_mod_end = 0;
677 		iter->pos_bpf_end = 0;
678 	}
679 }
680 
681 /*
682  * The end position (last + 1) of each additional kallsyms section is recorded
683  * in iter->pos_..._end as each section is added, and so can be used to
684  * determine which get_ksymbol_...() function to call next.
685  */
686 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
687 {
688 	iter->pos = pos;
689 
690 	if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
691 	    get_ksymbol_arch(iter))
692 		return 1;
693 
694 	if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
695 	    get_ksymbol_mod(iter))
696 		return 1;
697 
698 	if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
699 	    get_ksymbol_ftrace_mod(iter))
700 		return 1;
701 
702 	if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
703 	    get_ksymbol_bpf(iter))
704 		return 1;
705 
706 	return get_ksymbol_kprobe(iter);
707 }
708 
709 /* Returns false if pos at or past end of file. */
710 static int update_iter(struct kallsym_iter *iter, loff_t pos)
711 {
712 	/* Module symbols can be accessed randomly. */
713 	if (pos >= kallsyms_num_syms)
714 		return update_iter_mod(iter, pos);
715 
716 	/* If we're not on the desired position, reset to new position. */
717 	if (pos != iter->pos)
718 		reset_iter(iter, pos);
719 
720 	iter->nameoff += get_ksymbol_core(iter);
721 	iter->pos++;
722 
723 	return 1;
724 }
725 
726 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
727 {
728 	(*pos)++;
729 
730 	if (!update_iter(m->private, *pos))
731 		return NULL;
732 	return p;
733 }
734 
735 static void *s_start(struct seq_file *m, loff_t *pos)
736 {
737 	if (!update_iter(m->private, *pos))
738 		return NULL;
739 	return m->private;
740 }
741 
742 static void s_stop(struct seq_file *m, void *p)
743 {
744 }
745 
746 static int s_show(struct seq_file *m, void *p)
747 {
748 	void *value;
749 	struct kallsym_iter *iter = m->private;
750 
751 	/* Some debugging symbols have no name.  Ignore them. */
752 	if (!iter->name[0])
753 		return 0;
754 
755 	value = iter->show_value ? (void *)iter->value : NULL;
756 
757 	if (iter->module_name[0]) {
758 		char type;
759 
760 		/*
761 		 * Label it "global" if it is exported,
762 		 * "local" if not exported.
763 		 */
764 		type = iter->exported ? toupper(iter->type) :
765 					tolower(iter->type);
766 		seq_printf(m, "%px %c %s\t[%s]\n", value,
767 			   type, iter->name, iter->module_name);
768 	} else
769 		seq_printf(m, "%px %c %s\n", value,
770 			   iter->type, iter->name);
771 	return 0;
772 }
773 
774 static const struct seq_operations kallsyms_op = {
775 	.start = s_start,
776 	.next = s_next,
777 	.stop = s_stop,
778 	.show = s_show
779 };
780 
781 static inline int kallsyms_for_perf(void)
782 {
783 #ifdef CONFIG_PERF_EVENTS
784 	extern int sysctl_perf_event_paranoid;
785 	if (sysctl_perf_event_paranoid <= 1)
786 		return 1;
787 #endif
788 	return 0;
789 }
790 
791 /*
792  * We show kallsyms information even to normal users if we've enabled
793  * kernel profiling and are explicitly not paranoid (so kptr_restrict
794  * is clear, and sysctl_perf_event_paranoid isn't set).
795  *
796  * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
797  * block even that).
798  */
799 bool kallsyms_show_value(const struct cred *cred)
800 {
801 	switch (kptr_restrict) {
802 	case 0:
803 		if (kallsyms_for_perf())
804 			return true;
805 		fallthrough;
806 	case 1:
807 		if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
808 				     CAP_OPT_NOAUDIT) == 0)
809 			return true;
810 		fallthrough;
811 	default:
812 		return false;
813 	}
814 }
815 
816 static int kallsyms_open(struct inode *inode, struct file *file)
817 {
818 	/*
819 	 * We keep iterator in m->private, since normal case is to
820 	 * s_start from where we left off, so we avoid doing
821 	 * using get_symbol_offset for every symbol.
822 	 */
823 	struct kallsym_iter *iter;
824 	iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
825 	if (!iter)
826 		return -ENOMEM;
827 	reset_iter(iter, 0);
828 
829 	/*
830 	 * Instead of checking this on every s_show() call, cache
831 	 * the result here at open time.
832 	 */
833 	iter->show_value = kallsyms_show_value(file->f_cred);
834 	return 0;
835 }
836 
837 #ifdef	CONFIG_KGDB_KDB
838 const char *kdb_walk_kallsyms(loff_t *pos)
839 {
840 	static struct kallsym_iter kdb_walk_kallsyms_iter;
841 	if (*pos == 0) {
842 		memset(&kdb_walk_kallsyms_iter, 0,
843 		       sizeof(kdb_walk_kallsyms_iter));
844 		reset_iter(&kdb_walk_kallsyms_iter, 0);
845 	}
846 	while (1) {
847 		if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
848 			return NULL;
849 		++*pos;
850 		/* Some debugging symbols have no name.  Ignore them. */
851 		if (kdb_walk_kallsyms_iter.name[0])
852 			return kdb_walk_kallsyms_iter.name;
853 	}
854 }
855 #endif	/* CONFIG_KGDB_KDB */
856 
857 static const struct proc_ops kallsyms_proc_ops = {
858 	.proc_open	= kallsyms_open,
859 	.proc_read	= seq_read,
860 	.proc_lseek	= seq_lseek,
861 	.proc_release	= seq_release_private,
862 };
863 
864 static int __init kallsyms_init(void)
865 {
866 	proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
867 	return 0;
868 }
869 device_initcall(kallsyms_init);
870