1 // SPDX-License-Identifier: GPL-2.0-only
3 * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
5 * Rewritten and vastly simplified by Rusty Russell for in-kernel
7 * Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
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)
15 #include <linux/kallsyms.h>
16 #include <linux/init.h>
17 #include <linux/seq_file.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>
34 * These will be re-linked against their real values
35 * during the second link stage.
37 extern const unsigned long kallsyms_addresses[] __weak;
38 extern const int kallsyms_offsets[] __weak;
39 extern const u8 kallsyms_names[] __weak;
42 * Tell the compiler that the count isn't in the small data section if the arch
45 extern const unsigned int kallsyms_num_syms
46 __section(".rodata") __attribute__((weak));
48 extern const unsigned long kallsyms_relative_base
49 __section(".rodata") __attribute__((weak));
51 extern const char kallsyms_token_table[] __weak;
52 extern const u16 kallsyms_token_index[] __weak;
54 extern const unsigned int kallsyms_markers[] __weak;
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.
61 static unsigned int kallsyms_expand_symbol(unsigned int off,
62 char *result, size_t maxlen)
64 int len, skipped_first = 0;
68 /* Get the compressed symbol length from the first symbol byte. */
69 data = &kallsyms_names[off];
74 * Update the offset to return the offset for the next symbol on
75 * the compressed stream.
80 * For every byte on the compressed symbol data, copy the table
81 * entry for that byte.
84 tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
105 /* Return to offset to the next symbol. */
110 * Get symbol type information. This is encoded as a single char at the
111 * beginning of the symbol name.
113 static char kallsyms_get_symbol_type(unsigned int off)
116 * Get just the first code, look it up in the token table,
117 * and return the first char from this token.
119 return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
124 * Find the offset on the compressed stream given and index in the
127 static unsigned int get_symbol_offset(unsigned long pos)
133 * Use the closest marker we have. We have markers every 256 positions,
134 * so that should be close enough.
136 name = &kallsyms_names[kallsyms_markers[pos >> 8]];
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.
144 for (i = 0; i < (pos & 0xFF); i++)
145 name = name + (*name) + 1;
147 return name - kallsyms_names;
150 static unsigned long kallsyms_sym_address(int idx)
152 if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
153 return kallsyms_addresses[idx];
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];
159 /* ...otherwise, positive offsets are absolute values */
160 if (kallsyms_offsets[idx] >= 0)
161 return kallsyms_offsets[idx];
163 /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
164 return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
167 static bool cleanup_symbol_name(char *s)
171 if (!IS_ENABLED(CONFIG_LTO_CLANG))
175 * LLVM appends various suffixes for local functions and variables that
176 * must be promoted to global scope as part of LTO. This can break
177 * hooking of static functions with kprobes. '.' is not a valid
178 * character in an identifier in C. Suffixes observed:
179 * - foo.llvm.[0-9a-f]+
181 * - foo.[0-9a-f]+.cfi_jt
183 res = strchr(s, '.');
189 if (!IS_ENABLED(CONFIG_CFI_CLANG) ||
190 !IS_ENABLED(CONFIG_LTO_CLANG_THIN) ||
191 CONFIG_CLANG_VERSION >= 130000)
195 * Prior to LLVM 13, the following suffixes were observed when thinLTO
196 * and CFI are both enabled:
199 res = strrchr(s, '$');
208 /* Lookup the address for this symbol. Returns 0 if not found. */
209 unsigned long kallsyms_lookup_name(const char *name)
211 char namebuf[KSYM_NAME_LEN];
215 for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
216 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
218 if (strcmp(namebuf, name) == 0)
219 return kallsyms_sym_address(i);
221 if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
222 return kallsyms_sym_address(i);
224 return module_kallsyms_lookup_name(name);
227 #ifdef CONFIG_LIVEPATCH
229 * Iterate over all symbols in vmlinux. For symbols from modules use
230 * module_kallsyms_on_each_symbol instead.
232 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
236 char namebuf[KSYM_NAME_LEN];
241 for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
242 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
243 ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
250 #endif /* CONFIG_LIVEPATCH */
252 static unsigned long get_symbol_pos(unsigned long addr,
253 unsigned long *symbolsize,
254 unsigned long *offset)
256 unsigned long symbol_start = 0, symbol_end = 0;
257 unsigned long i, low, high, mid;
259 /* This kernel should never had been booted. */
260 if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
261 BUG_ON(!kallsyms_addresses);
263 BUG_ON(!kallsyms_offsets);
265 /* Do a binary search on the sorted kallsyms_addresses array. */
267 high = kallsyms_num_syms;
269 while (high - low > 1) {
270 mid = low + (high - low) / 2;
271 if (kallsyms_sym_address(mid) <= addr)
278 * Search for the first aliased symbol. Aliased
279 * symbols are symbols with the same address.
281 while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
284 symbol_start = kallsyms_sym_address(low);
286 /* Search for next non-aliased symbol. */
287 for (i = low + 1; i < kallsyms_num_syms; i++) {
288 if (kallsyms_sym_address(i) > symbol_start) {
289 symbol_end = kallsyms_sym_address(i);
294 /* If we found no next symbol, we use the end of the section. */
296 if (is_kernel_inittext(addr))
297 symbol_end = (unsigned long)_einittext;
298 else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
299 symbol_end = (unsigned long)_end;
301 symbol_end = (unsigned long)_etext;
305 *symbolsize = symbol_end - symbol_start;
307 *offset = addr - symbol_start;
313 * Lookup an address but don't bother to find any names.
315 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
316 unsigned long *offset)
318 char namebuf[KSYM_NAME_LEN];
320 if (is_ksym_addr(addr)) {
321 get_symbol_pos(addr, symbolsize, offset);
324 return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
325 !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
328 static const char *kallsyms_lookup_buildid(unsigned long addr,
329 unsigned long *symbolsize,
330 unsigned long *offset, char **modname,
331 const unsigned char **modbuildid, char *namebuf)
335 namebuf[KSYM_NAME_LEN - 1] = 0;
338 if (is_ksym_addr(addr)) {
341 pos = get_symbol_pos(addr, symbolsize, offset);
343 kallsyms_expand_symbol(get_symbol_offset(pos),
344 namebuf, KSYM_NAME_LEN);
354 /* See if it's in a module or a BPF JITed image. */
355 ret = module_address_lookup(addr, symbolsize, offset,
356 modname, modbuildid, namebuf);
358 ret = bpf_address_lookup(addr, symbolsize,
359 offset, modname, namebuf);
362 ret = ftrace_mod_address_lookup(addr, symbolsize,
363 offset, modname, namebuf);
366 cleanup_symbol_name(namebuf);
372 * - modname is set to NULL if it's in the kernel.
373 * - We guarantee that the returned name is valid until we reschedule even if.
374 * It resides in a module.
375 * - We also guarantee that modname will be valid until rescheduled.
377 const char *kallsyms_lookup(unsigned long addr,
378 unsigned long *symbolsize,
379 unsigned long *offset,
380 char **modname, char *namebuf)
382 return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
386 int lookup_symbol_name(unsigned long addr, char *symname)
391 symname[KSYM_NAME_LEN - 1] = '\0';
393 if (is_ksym_addr(addr)) {
396 pos = get_symbol_pos(addr, NULL, NULL);
398 kallsyms_expand_symbol(get_symbol_offset(pos),
399 symname, KSYM_NAME_LEN);
402 /* See if it's in a module. */
403 res = lookup_module_symbol_name(addr, symname);
408 cleanup_symbol_name(symname);
412 int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
413 unsigned long *offset, char *modname, char *name)
418 name[KSYM_NAME_LEN - 1] = '\0';
420 if (is_ksym_addr(addr)) {
423 pos = get_symbol_pos(addr, size, offset);
425 kallsyms_expand_symbol(get_symbol_offset(pos),
426 name, KSYM_NAME_LEN);
430 /* See if it's in a module. */
431 res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
436 cleanup_symbol_name(name);
440 /* Look up a kernel symbol and return it in a text buffer. */
441 static int __sprint_symbol(char *buffer, unsigned long address,
442 int symbol_offset, int add_offset, int add_buildid)
445 const unsigned char *buildid;
447 unsigned long offset, size;
450 address += symbol_offset;
451 name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
454 return sprintf(buffer, "0x%lx", address - symbol_offset);
457 strcpy(buffer, name);
458 len = strlen(buffer);
459 offset -= symbol_offset;
462 len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
465 len += sprintf(buffer + len, " [%s", modname);
466 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
467 if (add_buildid && buildid) {
468 /* build ID should match length of sprintf */
469 #if IS_ENABLED(CONFIG_MODULES)
470 static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
472 len += sprintf(buffer + len, " %20phN", buildid);
475 len += sprintf(buffer + len, "]");
482 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
483 * @buffer: buffer to be stored
484 * @address: address to lookup
486 * This function looks up a kernel symbol with @address and stores its name,
487 * offset, size and module name to @buffer if possible. If no symbol was found,
488 * just saves its @address as is.
490 * This function returns the number of bytes stored in @buffer.
492 int sprint_symbol(char *buffer, unsigned long address)
494 return __sprint_symbol(buffer, address, 0, 1, 0);
496 EXPORT_SYMBOL_GPL(sprint_symbol);
499 * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
500 * @buffer: buffer to be stored
501 * @address: address to lookup
503 * This function looks up a kernel symbol with @address and stores its name,
504 * offset, size, module name and module build ID to @buffer if possible. If no
505 * symbol was found, just saves its @address as is.
507 * This function returns the number of bytes stored in @buffer.
509 int sprint_symbol_build_id(char *buffer, unsigned long address)
511 return __sprint_symbol(buffer, address, 0, 1, 1);
513 EXPORT_SYMBOL_GPL(sprint_symbol_build_id);
516 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
517 * @buffer: buffer to be stored
518 * @address: address to lookup
520 * This function looks up a kernel symbol with @address and stores its name
521 * and module name to @buffer if possible. If no symbol was found, just saves
522 * its @address as is.
524 * This function returns the number of bytes stored in @buffer.
526 int sprint_symbol_no_offset(char *buffer, unsigned long address)
528 return __sprint_symbol(buffer, address, 0, 0, 0);
530 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
533 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
534 * @buffer: buffer to be stored
535 * @address: address to lookup
537 * This function is for stack backtrace and does the same thing as
538 * sprint_symbol() but with modified/decreased @address. If there is a
539 * tail-call to the function marked "noreturn", gcc optimized out code after
540 * the call so that the stack-saved return address could point outside of the
541 * caller. This function ensures that kallsyms will find the original caller
542 * by decreasing @address.
544 * This function returns the number of bytes stored in @buffer.
546 int sprint_backtrace(char *buffer, unsigned long address)
548 return __sprint_symbol(buffer, address, -1, 1, 0);
552 * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
553 * @buffer: buffer to be stored
554 * @address: address to lookup
556 * This function is for stack backtrace and does the same thing as
557 * sprint_symbol() but with modified/decreased @address. If there is a
558 * tail-call to the function marked "noreturn", gcc optimized out code after
559 * the call so that the stack-saved return address could point outside of the
560 * caller. This function ensures that kallsyms will find the original caller
561 * by decreasing @address. This function also appends the module build ID to
562 * the @buffer if @address is within a kernel module.
564 * This function returns the number of bytes stored in @buffer.
566 int sprint_backtrace_build_id(char *buffer, unsigned long address)
568 return __sprint_symbol(buffer, address, -1, 1, 1);
571 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
572 struct kallsym_iter {
576 loff_t pos_ftrace_mod_end;
579 unsigned int nameoff; /* If iterating in core kernel symbols. */
581 char name[KSYM_NAME_LEN];
582 char module_name[MODULE_NAME_LEN];
587 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
588 char *type, char *name)
593 static int get_ksymbol_arch(struct kallsym_iter *iter)
595 int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
596 &iter->value, &iter->type,
600 iter->pos_arch_end = iter->pos;
607 static int get_ksymbol_mod(struct kallsym_iter *iter)
609 int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
610 &iter->value, &iter->type,
611 iter->name, iter->module_name,
614 iter->pos_mod_end = iter->pos;
622 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
623 * purposes. In that case "__builtin__ftrace" is used as a module name, even
624 * though "__builtin__ftrace" is not a module.
626 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
628 int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
629 &iter->value, &iter->type,
630 iter->name, iter->module_name,
633 iter->pos_ftrace_mod_end = iter->pos;
640 static int get_ksymbol_bpf(struct kallsym_iter *iter)
644 strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
646 ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
647 &iter->value, &iter->type,
650 iter->pos_bpf_end = iter->pos;
658 * This uses "__builtin__kprobes" as a module name for symbols for pages
659 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
662 static int get_ksymbol_kprobe(struct kallsym_iter *iter)
664 strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
666 return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
667 &iter->value, &iter->type,
668 iter->name) < 0 ? 0 : 1;
671 /* Returns space to next name. */
672 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
674 unsigned off = iter->nameoff;
676 iter->module_name[0] = '\0';
677 iter->value = kallsyms_sym_address(iter->pos);
679 iter->type = kallsyms_get_symbol_type(off);
681 off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
683 return off - iter->nameoff;
686 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
688 iter->name[0] = '\0';
689 iter->nameoff = get_symbol_offset(new_pos);
692 iter->pos_arch_end = 0;
693 iter->pos_mod_end = 0;
694 iter->pos_ftrace_mod_end = 0;
695 iter->pos_bpf_end = 0;
700 * The end position (last + 1) of each additional kallsyms section is recorded
701 * in iter->pos_..._end as each section is added, and so can be used to
702 * determine which get_ksymbol_...() function to call next.
704 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
708 if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
709 get_ksymbol_arch(iter))
712 if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
713 get_ksymbol_mod(iter))
716 if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
717 get_ksymbol_ftrace_mod(iter))
720 if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
721 get_ksymbol_bpf(iter))
724 return get_ksymbol_kprobe(iter);
727 /* Returns false if pos at or past end of file. */
728 static int update_iter(struct kallsym_iter *iter, loff_t pos)
730 /* Module symbols can be accessed randomly. */
731 if (pos >= kallsyms_num_syms)
732 return update_iter_mod(iter, pos);
734 /* If we're not on the desired position, reset to new position. */
735 if (pos != iter->pos)
736 reset_iter(iter, pos);
738 iter->nameoff += get_ksymbol_core(iter);
744 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
748 if (!update_iter(m->private, *pos))
753 static void *s_start(struct seq_file *m, loff_t *pos)
755 if (!update_iter(m->private, *pos))
760 static void s_stop(struct seq_file *m, void *p)
764 static int s_show(struct seq_file *m, void *p)
767 struct kallsym_iter *iter = m->private;
769 /* Some debugging symbols have no name. Ignore them. */
773 value = iter->show_value ? (void *)iter->value : NULL;
775 if (iter->module_name[0]) {
779 * Label it "global" if it is exported,
780 * "local" if not exported.
782 type = iter->exported ? toupper(iter->type) :
784 seq_printf(m, "%px %c %s\t[%s]\n", value,
785 type, iter->name, iter->module_name);
787 seq_printf(m, "%px %c %s\n", value,
788 iter->type, iter->name);
792 static const struct seq_operations kallsyms_op = {
799 static inline int kallsyms_for_perf(void)
801 #ifdef CONFIG_PERF_EVENTS
802 extern int sysctl_perf_event_paranoid;
803 if (sysctl_perf_event_paranoid <= 1)
810 * We show kallsyms information even to normal users if we've enabled
811 * kernel profiling and are explicitly not paranoid (so kptr_restrict
812 * is clear, and sysctl_perf_event_paranoid isn't set).
814 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
817 bool kallsyms_show_value(const struct cred *cred)
819 switch (kptr_restrict) {
821 if (kallsyms_for_perf())
825 if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
826 CAP_OPT_NOAUDIT) == 0)
834 static int kallsyms_open(struct inode *inode, struct file *file)
837 * We keep iterator in m->private, since normal case is to
838 * s_start from where we left off, so we avoid doing
839 * using get_symbol_offset for every symbol.
841 struct kallsym_iter *iter;
842 iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
848 * Instead of checking this on every s_show() call, cache
849 * the result here at open time.
851 iter->show_value = kallsyms_show_value(file->f_cred);
855 #ifdef CONFIG_KGDB_KDB
856 const char *kdb_walk_kallsyms(loff_t *pos)
858 static struct kallsym_iter kdb_walk_kallsyms_iter;
860 memset(&kdb_walk_kallsyms_iter, 0,
861 sizeof(kdb_walk_kallsyms_iter));
862 reset_iter(&kdb_walk_kallsyms_iter, 0);
865 if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
868 /* Some debugging symbols have no name. Ignore them. */
869 if (kdb_walk_kallsyms_iter.name[0])
870 return kdb_walk_kallsyms_iter.name;
873 #endif /* CONFIG_KGDB_KDB */
875 static const struct proc_ops kallsyms_proc_ops = {
876 .proc_open = kallsyms_open,
877 .proc_read = seq_read,
878 .proc_lseek = seq_lseek,
879 .proc_release = seq_release_private,
882 static int __init kallsyms_init(void)
884 proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
887 device_initcall(kallsyms_init);