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Linux/kernel/kallsyms.c

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  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/compiler.h>
 28 
 29 /*
 30  * These will be re-linked against their real values
 31  * during the second link stage.
 32  */
 33 extern const unsigned long kallsyms_addresses[] __weak;
 34 extern const int kallsyms_offsets[] __weak;
 35 extern const u8 kallsyms_names[] __weak;
 36 
 37 /*
 38  * Tell the compiler that the count isn't in the small data section if the arch
 39  * has one (eg: FRV).
 40  */
 41 extern const unsigned int kallsyms_num_syms
 42 __attribute__((weak, section(".rodata")));
 43 
 44 extern const unsigned long kallsyms_relative_base
 45 __attribute__((weak, section(".rodata")));
 46 
 47 extern const u8 kallsyms_token_table[] __weak;
 48 extern const u16 kallsyms_token_index[] __weak;
 49 
 50 extern const unsigned int kallsyms_markers[] __weak;
 51 
 52 /*
 53  * Expand a compressed symbol data into the resulting uncompressed string,
 54  * if uncompressed string is too long (>= maxlen), it will be truncated,
 55  * given the offset to where the symbol is in the compressed stream.
 56  */
 57 static unsigned int kallsyms_expand_symbol(unsigned int off,
 58                                            char *result, size_t maxlen)
 59 {
 60         int len, skipped_first = 0;
 61         const u8 *tptr, *data;
 62 
 63         /* Get the compressed symbol length from the first symbol byte. */
 64         data = &kallsyms_names[off];
 65         len = *data;
 66         data++;
 67 
 68         /*
 69          * Update the offset to return the offset for the next symbol on
 70          * the compressed stream.
 71          */
 72         off += len + 1;
 73 
 74         /*
 75          * For every byte on the compressed symbol data, copy the table
 76          * entry for that byte.
 77          */
 78         while (len) {
 79                 tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
 80                 data++;
 81                 len--;
 82 
 83                 while (*tptr) {
 84                         if (skipped_first) {
 85                                 if (maxlen <= 1)
 86                                         goto tail;
 87                                 *result = *tptr;
 88                                 result++;
 89                                 maxlen--;
 90                         } else
 91                                 skipped_first = 1;
 92                         tptr++;
 93                 }
 94         }
 95 
 96 tail:
 97         if (maxlen)
 98                 *result = '\0';
 99 
100         /* Return to offset to the next symbol. */
101         return off;
102 }
103 
104 /*
105  * Get symbol type information. This is encoded as a single char at the
106  * beginning of the symbol name.
107  */
108 static char kallsyms_get_symbol_type(unsigned int off)
109 {
110         /*
111          * Get just the first code, look it up in the token table,
112          * and return the first char from this token.
113          */
114         return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
115 }
116 
117 
118 /*
119  * Find the offset on the compressed stream given and index in the
120  * kallsyms array.
121  */
122 static unsigned int get_symbol_offset(unsigned long pos)
123 {
124         const u8 *name;
125         int i;
126 
127         /*
128          * Use the closest marker we have. We have markers every 256 positions,
129          * so that should be close enough.
130          */
131         name = &kallsyms_names[kallsyms_markers[pos >> 8]];
132 
133         /*
134          * Sequentially scan all the symbols up to the point we're searching
135          * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
136          * so we just need to add the len to the current pointer for every
137          * symbol we wish to skip.
138          */
139         for (i = 0; i < (pos & 0xFF); i++)
140                 name = name + (*name) + 1;
141 
142         return name - kallsyms_names;
143 }
144 
145 static unsigned long kallsyms_sym_address(int idx)
146 {
147         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
148                 return kallsyms_addresses[idx];
149 
150         /* values are unsigned offsets if --absolute-percpu is not in effect */
151         if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
152                 return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
153 
154         /* ...otherwise, positive offsets are absolute values */
155         if (kallsyms_offsets[idx] >= 0)
156                 return kallsyms_offsets[idx];
157 
158         /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
159         return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
160 }
161 
162 /* Lookup the address for this symbol. Returns 0 if not found. */
163 unsigned long kallsyms_lookup_name(const char *name)
164 {
165         char namebuf[KSYM_NAME_LEN];
166         unsigned long i;
167         unsigned int off;
168 
169         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
170                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
171 
172                 if (strcmp(namebuf, name) == 0)
173                         return kallsyms_sym_address(i);
174         }
175         return module_kallsyms_lookup_name(name);
176 }
177 EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
178 
179 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
180                                       unsigned long),
181                             void *data)
182 {
183         char namebuf[KSYM_NAME_LEN];
184         unsigned long i;
185         unsigned int off;
186         int ret;
187 
188         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
189                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
190                 ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
191                 if (ret != 0)
192                         return ret;
193         }
194         return module_kallsyms_on_each_symbol(fn, data);
195 }
196 EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol);
197 
198 static unsigned long get_symbol_pos(unsigned long addr,
199                                     unsigned long *symbolsize,
200                                     unsigned long *offset)
201 {
202         unsigned long symbol_start = 0, symbol_end = 0;
203         unsigned long i, low, high, mid;
204 
205         /* This kernel should never had been booted. */
206         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
207                 BUG_ON(!kallsyms_addresses);
208         else
209                 BUG_ON(!kallsyms_offsets);
210 
211         /* Do a binary search on the sorted kallsyms_addresses array. */
212         low = 0;
213         high = kallsyms_num_syms;
214 
215         while (high - low > 1) {
216                 mid = low + (high - low) / 2;
217                 if (kallsyms_sym_address(mid) <= addr)
218                         low = mid;
219                 else
220                         high = mid;
221         }
222 
223         /*
224          * Search for the first aliased symbol. Aliased
225          * symbols are symbols with the same address.
226          */
227         while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
228                 --low;
229 
230         symbol_start = kallsyms_sym_address(low);
231 
232         /* Search for next non-aliased symbol. */
233         for (i = low + 1; i < kallsyms_num_syms; i++) {
234                 if (kallsyms_sym_address(i) > symbol_start) {
235                         symbol_end = kallsyms_sym_address(i);
236                         break;
237                 }
238         }
239 
240         /* If we found no next symbol, we use the end of the section. */
241         if (!symbol_end) {
242                 if (is_kernel_inittext(addr))
243                         symbol_end = (unsigned long)_einittext;
244                 else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
245                         symbol_end = (unsigned long)_end;
246                 else
247                         symbol_end = (unsigned long)_etext;
248         }
249 
250         if (symbolsize)
251                 *symbolsize = symbol_end - symbol_start;
252         if (offset)
253                 *offset = addr - symbol_start;
254 
255         return low;
256 }
257 
258 /*
259  * Lookup an address but don't bother to find any names.
260  */
261 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
262                                 unsigned long *offset)
263 {
264         char namebuf[KSYM_NAME_LEN];
265 
266         if (is_ksym_addr(addr)) {
267                 get_symbol_pos(addr, symbolsize, offset);
268                 return 1;
269         }
270         return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
271                !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
272 }
273 
274 /*
275  * Lookup an address
276  * - modname is set to NULL if it's in the kernel.
277  * - We guarantee that the returned name is valid until we reschedule even if.
278  *   It resides in a module.
279  * - We also guarantee that modname will be valid until rescheduled.
280  */
281 const char *kallsyms_lookup(unsigned long addr,
282                             unsigned long *symbolsize,
283                             unsigned long *offset,
284                             char **modname, char *namebuf)
285 {
286         const char *ret;
287 
288         namebuf[KSYM_NAME_LEN - 1] = 0;
289         namebuf[0] = 0;
290 
291         if (is_ksym_addr(addr)) {
292                 unsigned long pos;
293 
294                 pos = get_symbol_pos(addr, symbolsize, offset);
295                 /* Grab name */
296                 kallsyms_expand_symbol(get_symbol_offset(pos),
297                                        namebuf, KSYM_NAME_LEN);
298                 if (modname)
299                         *modname = NULL;
300                 return namebuf;
301         }
302 
303         /* See if it's in a module or a BPF JITed image. */
304         ret = module_address_lookup(addr, symbolsize, offset,
305                                     modname, namebuf);
306         if (!ret)
307                 ret = bpf_address_lookup(addr, symbolsize,
308                                          offset, modname, namebuf);
309 
310         if (!ret)
311                 ret = ftrace_mod_address_lookup(addr, symbolsize,
312                                                 offset, modname, namebuf);
313         return ret;
314 }
315 
316 int lookup_symbol_name(unsigned long addr, char *symname)
317 {
318         symname[0] = '\0';
319         symname[KSYM_NAME_LEN - 1] = '\0';
320 
321         if (is_ksym_addr(addr)) {
322                 unsigned long pos;
323 
324                 pos = get_symbol_pos(addr, NULL, NULL);
325                 /* Grab name */
326                 kallsyms_expand_symbol(get_symbol_offset(pos),
327                                        symname, KSYM_NAME_LEN);
328                 return 0;
329         }
330         /* See if it's in a module. */
331         return lookup_module_symbol_name(addr, symname);
332 }
333 
334 int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
335                         unsigned long *offset, char *modname, char *name)
336 {
337         name[0] = '\0';
338         name[KSYM_NAME_LEN - 1] = '\0';
339 
340         if (is_ksym_addr(addr)) {
341                 unsigned long pos;
342 
343                 pos = get_symbol_pos(addr, size, offset);
344                 /* Grab name */
345                 kallsyms_expand_symbol(get_symbol_offset(pos),
346                                        name, KSYM_NAME_LEN);
347                 modname[0] = '\0';
348                 return 0;
349         }
350         /* See if it's in a module. */
351         return lookup_module_symbol_attrs(addr, size, offset, modname, name);
352 }
353 
354 /* Look up a kernel symbol and return it in a text buffer. */
355 static int __sprint_symbol(char *buffer, unsigned long address,
356                            int symbol_offset, int add_offset)
357 {
358         char *modname;
359         const char *name;
360         unsigned long offset, size;
361         int len;
362 
363         address += symbol_offset;
364         name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
365         if (!name)
366                 return sprintf(buffer, "0x%lx", address - symbol_offset);
367 
368         if (name != buffer)
369                 strcpy(buffer, name);
370         len = strlen(buffer);
371         offset -= symbol_offset;
372 
373         if (add_offset)
374                 len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
375 
376         if (modname)
377                 len += sprintf(buffer + len, " [%s]", modname);
378 
379         return len;
380 }
381 
382 /**
383  * sprint_symbol - Look up a kernel symbol and return it in a text buffer
384  * @buffer: buffer to be stored
385  * @address: address to lookup
386  *
387  * This function looks up a kernel symbol with @address and stores its name,
388  * offset, size and module name to @buffer if possible. If no symbol was found,
389  * just saves its @address as is.
390  *
391  * This function returns the number of bytes stored in @buffer.
392  */
393 int sprint_symbol(char *buffer, unsigned long address)
394 {
395         return __sprint_symbol(buffer, address, 0, 1);
396 }
397 EXPORT_SYMBOL_GPL(sprint_symbol);
398 
399 /**
400  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
401  * @buffer: buffer to be stored
402  * @address: address to lookup
403  *
404  * This function looks up a kernel symbol with @address and stores its name
405  * and module name to @buffer if possible. If no symbol was found, just saves
406  * its @address as is.
407  *
408  * This function returns the number of bytes stored in @buffer.
409  */
410 int sprint_symbol_no_offset(char *buffer, unsigned long address)
411 {
412         return __sprint_symbol(buffer, address, 0, 0);
413 }
414 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
415 
416 /**
417  * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
418  * @buffer: buffer to be stored
419  * @address: address to lookup
420  *
421  * This function is for stack backtrace and does the same thing as
422  * sprint_symbol() but with modified/decreased @address. If there is a
423  * tail-call to the function marked "noreturn", gcc optimized out code after
424  * the call so that the stack-saved return address could point outside of the
425  * caller. This function ensures that kallsyms will find the original caller
426  * by decreasing @address.
427  *
428  * This function returns the number of bytes stored in @buffer.
429  */
430 int sprint_backtrace(char *buffer, unsigned long address)
431 {
432         return __sprint_symbol(buffer, address, -1, 1);
433 }
434 
435 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
436 struct kallsym_iter {
437         loff_t pos;
438         loff_t pos_arch_end;
439         loff_t pos_mod_end;
440         loff_t pos_ftrace_mod_end;
441         unsigned long value;
442         unsigned int nameoff; /* If iterating in core kernel symbols. */
443         char type;
444         char name[KSYM_NAME_LEN];
445         char module_name[MODULE_NAME_LEN];
446         int exported;
447         int show_value;
448 };
449 
450 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
451                             char *type, char *name)
452 {
453         return -EINVAL;
454 }
455 
456 static int get_ksymbol_arch(struct kallsym_iter *iter)
457 {
458         int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
459                                    &iter->value, &iter->type,
460                                    iter->name);
461 
462         if (ret < 0) {
463                 iter->pos_arch_end = iter->pos;
464                 return 0;
465         }
466 
467         return 1;
468 }
469 
470 static int get_ksymbol_mod(struct kallsym_iter *iter)
471 {
472         int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
473                                      &iter->value, &iter->type,
474                                      iter->name, iter->module_name,
475                                      &iter->exported);
476         if (ret < 0) {
477                 iter->pos_mod_end = iter->pos;
478                 return 0;
479         }
480 
481         return 1;
482 }
483 
484 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
485 {
486         int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
487                                          &iter->value, &iter->type,
488                                          iter->name, iter->module_name,
489                                          &iter->exported);
490         if (ret < 0) {
491                 iter->pos_ftrace_mod_end = iter->pos;
492                 return 0;
493         }
494 
495         return 1;
496 }
497 
498 static int get_ksymbol_bpf(struct kallsym_iter *iter)
499 {
500         strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
501         iter->exported = 0;
502         return bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
503                                &iter->value, &iter->type,
504                                iter->name) < 0 ? 0 : 1;
505 }
506 
507 /* Returns space to next name. */
508 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
509 {
510         unsigned off = iter->nameoff;
511 
512         iter->module_name[0] = '\0';
513         iter->value = kallsyms_sym_address(iter->pos);
514 
515         iter->type = kallsyms_get_symbol_type(off);
516 
517         off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
518 
519         return off - iter->nameoff;
520 }
521 
522 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
523 {
524         iter->name[0] = '\0';
525         iter->nameoff = get_symbol_offset(new_pos);
526         iter->pos = new_pos;
527         if (new_pos == 0) {
528                 iter->pos_arch_end = 0;
529                 iter->pos_mod_end = 0;
530                 iter->pos_ftrace_mod_end = 0;
531         }
532 }
533 
534 /*
535  * The end position (last + 1) of each additional kallsyms section is recorded
536  * in iter->pos_..._end as each section is added, and so can be used to
537  * determine which get_ksymbol_...() function to call next.
538  */
539 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
540 {
541         iter->pos = pos;
542 
543         if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
544             get_ksymbol_arch(iter))
545                 return 1;
546 
547         if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
548             get_ksymbol_mod(iter))
549                 return 1;
550 
551         if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
552             get_ksymbol_ftrace_mod(iter))
553                 return 1;
554 
555         return get_ksymbol_bpf(iter);
556 }
557 
558 /* Returns false if pos at or past end of file. */
559 static int update_iter(struct kallsym_iter *iter, loff_t pos)
560 {
561         /* Module symbols can be accessed randomly. */
562         if (pos >= kallsyms_num_syms)
563                 return update_iter_mod(iter, pos);
564 
565         /* If we're not on the desired position, reset to new position. */
566         if (pos != iter->pos)
567                 reset_iter(iter, pos);
568 
569         iter->nameoff += get_ksymbol_core(iter);
570         iter->pos++;
571 
572         return 1;
573 }
574 
575 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
576 {
577         (*pos)++;
578 
579         if (!update_iter(m->private, *pos))
580                 return NULL;
581         return p;
582 }
583 
584 static void *s_start(struct seq_file *m, loff_t *pos)
585 {
586         if (!update_iter(m->private, *pos))
587                 return NULL;
588         return m->private;
589 }
590 
591 static void s_stop(struct seq_file *m, void *p)
592 {
593 }
594 
595 static int s_show(struct seq_file *m, void *p)
596 {
597         void *value;
598         struct kallsym_iter *iter = m->private;
599 
600         /* Some debugging symbols have no name.  Ignore them. */
601         if (!iter->name[0])
602                 return 0;
603 
604         value = iter->show_value ? (void *)iter->value : NULL;
605 
606         if (iter->module_name[0]) {
607                 char type;
608 
609                 /*
610                  * Label it "global" if it is exported,
611                  * "local" if not exported.
612                  */
613                 type = iter->exported ? toupper(iter->type) :
614                                         tolower(iter->type);
615                 seq_printf(m, "%px %c %s\t[%s]\n", value,
616                            type, iter->name, iter->module_name);
617         } else
618                 seq_printf(m, "%px %c %s\n", value,
619                            iter->type, iter->name);
620         return 0;
621 }
622 
623 static const struct seq_operations kallsyms_op = {
624         .start = s_start,
625         .next = s_next,
626         .stop = s_stop,
627         .show = s_show
628 };
629 
630 static inline int kallsyms_for_perf(void)
631 {
632 #ifdef CONFIG_PERF_EVENTS
633         extern int sysctl_perf_event_paranoid;
634         if (sysctl_perf_event_paranoid <= 1)
635                 return 1;
636 #endif
637         return 0;
638 }
639 
640 /*
641  * We show kallsyms information even to normal users if we've enabled
642  * kernel profiling and are explicitly not paranoid (so kptr_restrict
643  * is clear, and sysctl_perf_event_paranoid isn't set).
644  *
645  * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
646  * block even that).
647  */
648 int kallsyms_show_value(void)
649 {
650         switch (kptr_restrict) {
651         case 0:
652                 if (kallsyms_for_perf())
653                         return 1;
654         /* fallthrough */
655         case 1:
656                 if (has_capability_noaudit(current, CAP_SYSLOG))
657                         return 1;
658         /* fallthrough */
659         default:
660                 return 0;
661         }
662 }
663 
664 static int kallsyms_open(struct inode *inode, struct file *file)
665 {
666         /*
667          * We keep iterator in m->private, since normal case is to
668          * s_start from where we left off, so we avoid doing
669          * using get_symbol_offset for every symbol.
670          */
671         struct kallsym_iter *iter;
672         iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
673         if (!iter)
674                 return -ENOMEM;
675         reset_iter(iter, 0);
676 
677         iter->show_value = kallsyms_show_value();
678         return 0;
679 }
680 
681 #ifdef  CONFIG_KGDB_KDB
682 const char *kdb_walk_kallsyms(loff_t *pos)
683 {
684         static struct kallsym_iter kdb_walk_kallsyms_iter;
685         if (*pos == 0) {
686                 memset(&kdb_walk_kallsyms_iter, 0,
687                        sizeof(kdb_walk_kallsyms_iter));
688                 reset_iter(&kdb_walk_kallsyms_iter, 0);
689         }
690         while (1) {
691                 if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
692                         return NULL;
693                 ++*pos;
694                 /* Some debugging symbols have no name.  Ignore them. */
695                 if (kdb_walk_kallsyms_iter.name[0])
696                         return kdb_walk_kallsyms_iter.name;
697         }
698 }
699 #endif  /* CONFIG_KGDB_KDB */
700 
701 static const struct file_operations kallsyms_operations = {
702         .open = kallsyms_open,
703         .read = seq_read,
704         .llseek = seq_lseek,
705         .release = seq_release_private,
706 };
707 
708 static int __init kallsyms_init(void)
709 {
710         proc_create("kallsyms", 0444, NULL, &kallsyms_operations);
711         return 0;
712 }
713 device_initcall(kallsyms_init);
714 

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