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/compiler.h>
31 * These will be re-linked against their real values
32 * during the second link stage.
34 extern const unsigned long kallsyms_addresses
[] __weak
;
35 extern const int kallsyms_offsets
[] __weak
;
36 extern const u8 kallsyms_names
[] __weak
;
39 * Tell the compiler that the count isn't in the small data section if the arch
42 extern const unsigned int kallsyms_num_syms
43 __section(".rodata") __attribute__((weak
));
45 extern const unsigned long kallsyms_relative_base
46 __section(".rodata") __attribute__((weak
));
48 extern const char kallsyms_token_table
[] __weak
;
49 extern const u16 kallsyms_token_index
[] __weak
;
51 extern const unsigned int kallsyms_markers
[] __weak
;
54 * Expand a compressed symbol data into the resulting uncompressed string,
55 * if uncompressed string is too long (>= maxlen), it will be truncated,
56 * given the offset to where the symbol is in the compressed stream.
58 static unsigned int kallsyms_expand_symbol(unsigned int off
,
59 char *result
, size_t maxlen
)
61 int len
, skipped_first
= 0;
65 /* Get the compressed symbol length from the first symbol byte. */
66 data
= &kallsyms_names
[off
];
71 * Update the offset to return the offset for the next symbol on
72 * the compressed stream.
77 * For every byte on the compressed symbol data, copy the table
78 * entry for that byte.
81 tptr
= &kallsyms_token_table
[kallsyms_token_index
[*data
]];
102 /* Return to offset to the next symbol. */
107 * Get symbol type information. This is encoded as a single char at the
108 * beginning of the symbol name.
110 static char kallsyms_get_symbol_type(unsigned int off
)
113 * Get just the first code, look it up in the token table,
114 * and return the first char from this token.
116 return kallsyms_token_table
[kallsyms_token_index
[kallsyms_names
[off
+ 1]]];
121 * Find the offset on the compressed stream given and index in the
124 static unsigned int get_symbol_offset(unsigned long pos
)
130 * Use the closest marker we have. We have markers every 256 positions,
131 * so that should be close enough.
133 name
= &kallsyms_names
[kallsyms_markers
[pos
>> 8]];
136 * Sequentially scan all the symbols up to the point we're searching
137 * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
138 * so we just need to add the len to the current pointer for every
139 * symbol we wish to skip.
141 for (i
= 0; i
< (pos
& 0xFF); i
++)
142 name
= name
+ (*name
) + 1;
144 return name
- kallsyms_names
;
147 static unsigned long kallsyms_sym_address(int idx
)
149 if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE
))
150 return kallsyms_addresses
[idx
];
152 /* values are unsigned offsets if --absolute-percpu is not in effect */
153 if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU
))
154 return kallsyms_relative_base
+ (u32
)kallsyms_offsets
[idx
];
156 /* ...otherwise, positive offsets are absolute values */
157 if (kallsyms_offsets
[idx
] >= 0)
158 return kallsyms_offsets
[idx
];
160 /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
161 return kallsyms_relative_base
- 1 - kallsyms_offsets
[idx
];
164 #if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
166 * LLVM appends a hash to static function names when ThinLTO and CFI are
167 * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
168 * This causes confusion and potentially breaks user space tools, so we
169 * strip the suffix from expanded symbol names.
171 static inline bool cleanup_symbol_name(char *s
)
175 res
= strrchr(s
, '$');
182 static inline bool cleanup_symbol_name(char *s
) { return false; }
185 /* Lookup the address for this symbol. Returns 0 if not found. */
186 unsigned long kallsyms_lookup_name(const char *name
)
188 char namebuf
[KSYM_NAME_LEN
];
192 for (i
= 0, off
= 0; i
< kallsyms_num_syms
; i
++) {
193 off
= kallsyms_expand_symbol(off
, namebuf
, ARRAY_SIZE(namebuf
));
195 if (strcmp(namebuf
, name
) == 0)
196 return kallsyms_sym_address(i
);
198 if (cleanup_symbol_name(namebuf
) && strcmp(namebuf
, name
) == 0)
199 return kallsyms_sym_address(i
);
201 return module_kallsyms_lookup_name(name
);
204 #ifdef CONFIG_LIVEPATCH
206 * Iterate over all symbols in vmlinux. For symbols from modules use
207 * module_kallsyms_on_each_symbol instead.
209 int kallsyms_on_each_symbol(int (*fn
)(void *, const char *, struct module
*,
213 char namebuf
[KSYM_NAME_LEN
];
218 for (i
= 0, off
= 0; i
< kallsyms_num_syms
; i
++) {
219 off
= kallsyms_expand_symbol(off
, namebuf
, ARRAY_SIZE(namebuf
));
220 ret
= fn(data
, namebuf
, NULL
, kallsyms_sym_address(i
));
226 #endif /* CONFIG_LIVEPATCH */
228 static unsigned long get_symbol_pos(unsigned long addr
,
229 unsigned long *symbolsize
,
230 unsigned long *offset
)
232 unsigned long symbol_start
= 0, symbol_end
= 0;
233 unsigned long i
, low
, high
, mid
;
235 /* This kernel should never had been booted. */
236 if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE
))
237 BUG_ON(!kallsyms_addresses
);
239 BUG_ON(!kallsyms_offsets
);
241 /* Do a binary search on the sorted kallsyms_addresses array. */
243 high
= kallsyms_num_syms
;
245 while (high
- low
> 1) {
246 mid
= low
+ (high
- low
) / 2;
247 if (kallsyms_sym_address(mid
) <= addr
)
254 * Search for the first aliased symbol. Aliased
255 * symbols are symbols with the same address.
257 while (low
&& kallsyms_sym_address(low
-1) == kallsyms_sym_address(low
))
260 symbol_start
= kallsyms_sym_address(low
);
262 /* Search for next non-aliased symbol. */
263 for (i
= low
+ 1; i
< kallsyms_num_syms
; i
++) {
264 if (kallsyms_sym_address(i
) > symbol_start
) {
265 symbol_end
= kallsyms_sym_address(i
);
270 /* If we found no next symbol, we use the end of the section. */
272 if (is_kernel_inittext(addr
))
273 symbol_end
= (unsigned long)_einittext
;
274 else if (IS_ENABLED(CONFIG_KALLSYMS_ALL
))
275 symbol_end
= (unsigned long)_end
;
277 symbol_end
= (unsigned long)_etext
;
281 *symbolsize
= symbol_end
- symbol_start
;
283 *offset
= addr
- symbol_start
;
289 * Lookup an address but don't bother to find any names.
291 int kallsyms_lookup_size_offset(unsigned long addr
, unsigned long *symbolsize
,
292 unsigned long *offset
)
294 char namebuf
[KSYM_NAME_LEN
];
296 if (is_ksym_addr(addr
)) {
297 get_symbol_pos(addr
, symbolsize
, offset
);
300 return !!module_address_lookup(addr
, symbolsize
, offset
, NULL
, namebuf
) ||
301 !!__bpf_address_lookup(addr
, symbolsize
, offset
, namebuf
);
306 * - modname is set to NULL if it's in the kernel.
307 * - We guarantee that the returned name is valid until we reschedule even if.
308 * It resides in a module.
309 * - We also guarantee that modname will be valid until rescheduled.
311 const char *kallsyms_lookup(unsigned long addr
,
312 unsigned long *symbolsize
,
313 unsigned long *offset
,
314 char **modname
, char *namebuf
)
318 namebuf
[KSYM_NAME_LEN
- 1] = 0;
321 if (is_ksym_addr(addr
)) {
324 pos
= get_symbol_pos(addr
, symbolsize
, offset
);
326 kallsyms_expand_symbol(get_symbol_offset(pos
),
327 namebuf
, KSYM_NAME_LEN
);
335 /* See if it's in a module or a BPF JITed image. */
336 ret
= module_address_lookup(addr
, symbolsize
, offset
,
339 ret
= bpf_address_lookup(addr
, symbolsize
,
340 offset
, modname
, namebuf
);
343 ret
= ftrace_mod_address_lookup(addr
, symbolsize
,
344 offset
, modname
, namebuf
);
347 cleanup_symbol_name(namebuf
);
351 int lookup_symbol_name(unsigned long addr
, char *symname
)
356 symname
[KSYM_NAME_LEN
- 1] = '\0';
358 if (is_ksym_addr(addr
)) {
361 pos
= get_symbol_pos(addr
, NULL
, NULL
);
363 kallsyms_expand_symbol(get_symbol_offset(pos
),
364 symname
, KSYM_NAME_LEN
);
367 /* See if it's in a module. */
368 res
= lookup_module_symbol_name(addr
, symname
);
373 cleanup_symbol_name(symname
);
377 int lookup_symbol_attrs(unsigned long addr
, unsigned long *size
,
378 unsigned long *offset
, char *modname
, char *name
)
383 name
[KSYM_NAME_LEN
- 1] = '\0';
385 if (is_ksym_addr(addr
)) {
388 pos
= get_symbol_pos(addr
, size
, offset
);
390 kallsyms_expand_symbol(get_symbol_offset(pos
),
391 name
, KSYM_NAME_LEN
);
395 /* See if it's in a module. */
396 res
= lookup_module_symbol_attrs(addr
, size
, offset
, modname
, name
);
401 cleanup_symbol_name(name
);
405 /* Look up a kernel symbol and return it in a text buffer. */
406 static int __sprint_symbol(char *buffer
, unsigned long address
,
407 int symbol_offset
, int add_offset
)
411 unsigned long offset
, size
;
414 address
+= symbol_offset
;
415 name
= kallsyms_lookup(address
, &size
, &offset
, &modname
, buffer
);
417 return sprintf(buffer
, "0x%lx", address
- symbol_offset
);
420 strcpy(buffer
, name
);
421 len
= strlen(buffer
);
422 offset
-= symbol_offset
;
425 len
+= sprintf(buffer
+ len
, "+%#lx/%#lx", offset
, size
);
428 len
+= sprintf(buffer
+ len
, " [%s]", modname
);
434 * sprint_symbol - Look up a kernel symbol and return it in a text buffer
435 * @buffer: buffer to be stored
436 * @address: address to lookup
438 * This function looks up a kernel symbol with @address and stores its name,
439 * offset, size and module name to @buffer if possible. If no symbol was found,
440 * just saves its @address as is.
442 * This function returns the number of bytes stored in @buffer.
444 int sprint_symbol(char *buffer
, unsigned long address
)
446 return __sprint_symbol(buffer
, address
, 0, 1);
448 EXPORT_SYMBOL_GPL(sprint_symbol
);
451 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
452 * @buffer: buffer to be stored
453 * @address: address to lookup
455 * This function looks up a kernel symbol with @address and stores its name
456 * and module name to @buffer if possible. If no symbol was found, just saves
457 * its @address as is.
459 * This function returns the number of bytes stored in @buffer.
461 int sprint_symbol_no_offset(char *buffer
, unsigned long address
)
463 return __sprint_symbol(buffer
, address
, 0, 0);
465 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset
);
468 * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
469 * @buffer: buffer to be stored
470 * @address: address to lookup
472 * This function is for stack backtrace and does the same thing as
473 * sprint_symbol() but with modified/decreased @address. If there is a
474 * tail-call to the function marked "noreturn", gcc optimized out code after
475 * the call so that the stack-saved return address could point outside of the
476 * caller. This function ensures that kallsyms will find the original caller
477 * by decreasing @address.
479 * This function returns the number of bytes stored in @buffer.
481 int sprint_backtrace(char *buffer
, unsigned long address
)
483 return __sprint_symbol(buffer
, address
, -1, 1);
486 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
487 struct kallsym_iter
{
491 loff_t pos_ftrace_mod_end
;
494 unsigned int nameoff
; /* If iterating in core kernel symbols. */
496 char name
[KSYM_NAME_LEN
];
497 char module_name
[MODULE_NAME_LEN
];
502 int __weak
arch_get_kallsym(unsigned int symnum
, unsigned long *value
,
503 char *type
, char *name
)
508 static int get_ksymbol_arch(struct kallsym_iter
*iter
)
510 int ret
= arch_get_kallsym(iter
->pos
- kallsyms_num_syms
,
511 &iter
->value
, &iter
->type
,
515 iter
->pos_arch_end
= iter
->pos
;
522 static int get_ksymbol_mod(struct kallsym_iter
*iter
)
524 int ret
= module_get_kallsym(iter
->pos
- iter
->pos_arch_end
,
525 &iter
->value
, &iter
->type
,
526 iter
->name
, iter
->module_name
,
529 iter
->pos_mod_end
= iter
->pos
;
537 * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
538 * purposes. In that case "__builtin__ftrace" is used as a module name, even
539 * though "__builtin__ftrace" is not a module.
541 static int get_ksymbol_ftrace_mod(struct kallsym_iter
*iter
)
543 int ret
= ftrace_mod_get_kallsym(iter
->pos
- iter
->pos_mod_end
,
544 &iter
->value
, &iter
->type
,
545 iter
->name
, iter
->module_name
,
548 iter
->pos_ftrace_mod_end
= iter
->pos
;
555 static int get_ksymbol_bpf(struct kallsym_iter
*iter
)
559 strlcpy(iter
->module_name
, "bpf", MODULE_NAME_LEN
);
561 ret
= bpf_get_kallsym(iter
->pos
- iter
->pos_ftrace_mod_end
,
562 &iter
->value
, &iter
->type
,
565 iter
->pos_bpf_end
= iter
->pos
;
573 * This uses "__builtin__kprobes" as a module name for symbols for pages
574 * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
577 static int get_ksymbol_kprobe(struct kallsym_iter
*iter
)
579 strlcpy(iter
->module_name
, "__builtin__kprobes", MODULE_NAME_LEN
);
581 return kprobe_get_kallsym(iter
->pos
- iter
->pos_bpf_end
,
582 &iter
->value
, &iter
->type
,
583 iter
->name
) < 0 ? 0 : 1;
586 /* Returns space to next name. */
587 static unsigned long get_ksymbol_core(struct kallsym_iter
*iter
)
589 unsigned off
= iter
->nameoff
;
591 iter
->module_name
[0] = '\0';
592 iter
->value
= kallsyms_sym_address(iter
->pos
);
594 iter
->type
= kallsyms_get_symbol_type(off
);
596 off
= kallsyms_expand_symbol(off
, iter
->name
, ARRAY_SIZE(iter
->name
));
598 return off
- iter
->nameoff
;
601 static void reset_iter(struct kallsym_iter
*iter
, loff_t new_pos
)
603 iter
->name
[0] = '\0';
604 iter
->nameoff
= get_symbol_offset(new_pos
);
607 iter
->pos_arch_end
= 0;
608 iter
->pos_mod_end
= 0;
609 iter
->pos_ftrace_mod_end
= 0;
610 iter
->pos_bpf_end
= 0;
615 * The end position (last + 1) of each additional kallsyms section is recorded
616 * in iter->pos_..._end as each section is added, and so can be used to
617 * determine which get_ksymbol_...() function to call next.
619 static int update_iter_mod(struct kallsym_iter
*iter
, loff_t pos
)
623 if ((!iter
->pos_arch_end
|| iter
->pos_arch_end
> pos
) &&
624 get_ksymbol_arch(iter
))
627 if ((!iter
->pos_mod_end
|| iter
->pos_mod_end
> pos
) &&
628 get_ksymbol_mod(iter
))
631 if ((!iter
->pos_ftrace_mod_end
|| iter
->pos_ftrace_mod_end
> pos
) &&
632 get_ksymbol_ftrace_mod(iter
))
635 if ((!iter
->pos_bpf_end
|| iter
->pos_bpf_end
> pos
) &&
636 get_ksymbol_bpf(iter
))
639 return get_ksymbol_kprobe(iter
);
642 /* Returns false if pos at or past end of file. */
643 static int update_iter(struct kallsym_iter
*iter
, loff_t pos
)
645 /* Module symbols can be accessed randomly. */
646 if (pos
>= kallsyms_num_syms
)
647 return update_iter_mod(iter
, pos
);
649 /* If we're not on the desired position, reset to new position. */
650 if (pos
!= iter
->pos
)
651 reset_iter(iter
, pos
);
653 iter
->nameoff
+= get_ksymbol_core(iter
);
659 static void *s_next(struct seq_file
*m
, void *p
, loff_t
*pos
)
663 if (!update_iter(m
->private, *pos
))
668 static void *s_start(struct seq_file
*m
, loff_t
*pos
)
670 if (!update_iter(m
->private, *pos
))
675 static void s_stop(struct seq_file
*m
, void *p
)
679 static int s_show(struct seq_file
*m
, void *p
)
682 struct kallsym_iter
*iter
= m
->private;
684 /* Some debugging symbols have no name. Ignore them. */
688 value
= iter
->show_value
? (void *)iter
->value
: NULL
;
690 if (iter
->module_name
[0]) {
694 * Label it "global" if it is exported,
695 * "local" if not exported.
697 type
= iter
->exported
? toupper(iter
->type
) :
699 seq_printf(m
, "%px %c %s\t[%s]\n", value
,
700 type
, iter
->name
, iter
->module_name
);
702 seq_printf(m
, "%px %c %s\n", value
,
703 iter
->type
, iter
->name
);
707 static const struct seq_operations kallsyms_op
= {
714 static inline int kallsyms_for_perf(void)
716 #ifdef CONFIG_PERF_EVENTS
717 extern int sysctl_perf_event_paranoid
;
718 if (sysctl_perf_event_paranoid
<= 1)
725 * We show kallsyms information even to normal users if we've enabled
726 * kernel profiling and are explicitly not paranoid (so kptr_restrict
727 * is clear, and sysctl_perf_event_paranoid isn't set).
729 * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
732 bool kallsyms_show_value(const struct cred
*cred
)
734 switch (kptr_restrict
) {
736 if (kallsyms_for_perf())
740 if (security_capable(cred
, &init_user_ns
, CAP_SYSLOG
,
741 CAP_OPT_NOAUDIT
) == 0)
749 static int kallsyms_open(struct inode
*inode
, struct file
*file
)
752 * We keep iterator in m->private, since normal case is to
753 * s_start from where we left off, so we avoid doing
754 * using get_symbol_offset for every symbol.
756 struct kallsym_iter
*iter
;
757 iter
= __seq_open_private(file
, &kallsyms_op
, sizeof(*iter
));
763 * Instead of checking this on every s_show() call, cache
764 * the result here at open time.
766 iter
->show_value
= kallsyms_show_value(file
->f_cred
);
770 #ifdef CONFIG_KGDB_KDB
771 const char *kdb_walk_kallsyms(loff_t
*pos
)
773 static struct kallsym_iter kdb_walk_kallsyms_iter
;
775 memset(&kdb_walk_kallsyms_iter
, 0,
776 sizeof(kdb_walk_kallsyms_iter
));
777 reset_iter(&kdb_walk_kallsyms_iter
, 0);
780 if (!update_iter(&kdb_walk_kallsyms_iter
, *pos
))
783 /* Some debugging symbols have no name. Ignore them. */
784 if (kdb_walk_kallsyms_iter
.name
[0])
785 return kdb_walk_kallsyms_iter
.name
;
788 #endif /* CONFIG_KGDB_KDB */
790 static const struct proc_ops kallsyms_proc_ops
= {
791 .proc_open
= kallsyms_open
,
792 .proc_read
= seq_read
,
793 .proc_lseek
= seq_lseek
,
794 .proc_release
= seq_release_private
,
797 static int __init
kallsyms_init(void)
799 proc_create("kallsyms", 0444, NULL
, &kallsyms_proc_ops
);
802 device_initcall(kallsyms_init
);