1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Module kallsyms support
4 *
5 * Copyright (C) 2010 Rusty Russell
6 */
7
8 #include <linux/module.h>
9 #include <linux/module_symbol.h>
10 #include <linux/kallsyms.h>
11 #include <linux/buildid.h>
12 #include <linux/bsearch.h>
13 #include "internal.h"
14
15 /* Lookup exported symbol in given range of kernel_symbols */
16 static const struct kernel_symbol *lookup_exported_symbol(const char *name,
17 const struct kernel_symbol *start,
18 const struct kernel_symbol *stop)
19 {
20 return bsearch(name, start, stop - start,
21 sizeof(struct kernel_symbol), cmp_name);
22 }
23
24 static int is_exported(const char *name, unsigned long value,
25 const struct module *mod)
26 {
27 const struct kernel_symbol *ks;
28
29 if (!mod)
30 ks = lookup_exported_symbol(name, __start___ksymtab, __stop___ksymtab);
31 else
32 ks = lookup_exported_symbol(name, mod->syms, mod->syms + mod->num_syms);
33
34 return ks && kernel_symbol_value(ks) == value;
35 }
36
37 /* As per nm */
38 static char elf_type(const Elf_Sym *sym, const struct load_info *info)
39 {
40 const Elf_Shdr *sechdrs = info->sechdrs;
41
42 if (ELF_ST_BIND(sym->st_info) == STB_WEAK) {
43 if (ELF_ST_TYPE(sym->st_info) == STT_OBJECT)
44 return 'v';
45 else
46 return 'w';
47 }
48 if (sym->st_shndx == SHN_UNDEF)
49 return 'U';
50 if (sym->st_shndx == SHN_ABS || sym->st_shndx == info->index.pcpu)
51 return 'a';
52 if (sym->st_shndx >= SHN_LORESERVE)
53 return '?';
54 if (sechdrs[sym->st_shndx].sh_flags & SHF_EXECINSTR)
55 return 't';
56 if (sechdrs[sym->st_shndx].sh_flags & SHF_ALLOC &&
57 sechdrs[sym->st_shndx].sh_type != SHT_NOBITS) {
58 if (!(sechdrs[sym->st_shndx].sh_flags & SHF_WRITE))
59 return 'r';
60 else if (sechdrs[sym->st_shndx].sh_flags & ARCH_SHF_SMALL)
61 return 'g';
62 else
63 return 'd';
64 }
65 if (sechdrs[sym->st_shndx].sh_type == SHT_NOBITS) {
66 if (sechdrs[sym->st_shndx].sh_flags & ARCH_SHF_SMALL)
67 return 's';
68 else
69 return 'b';
70 }
71 if (strstarts(info->secstrings + sechdrs[sym->st_shndx].sh_name,
72 ".debug")) {
73 return 'n';
74 }
75 return '?';
76 }
77
78 static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
79 unsigned int shnum, unsigned int pcpundx)
80 {
81 const Elf_Shdr *sec;
82 enum mod_mem_type type;
83
84 if (src->st_shndx == SHN_UNDEF ||
85 src->st_shndx >= shnum ||
86 !src->st_name)
87 return false;
88
89 #ifdef CONFIG_KALLSYMS_ALL
90 if (src->st_shndx == pcpundx)
91 return true;
92 #endif
93
94 sec = sechdrs + src->st_shndx;
95 type = sec->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT;
96 if (!(sec->sh_flags & SHF_ALLOC)
97 #ifndef CONFIG_KALLSYMS_ALL
98 || !(sec->sh_flags & SHF_EXECINSTR)
99 #endif
100 || mod_mem_type_is_init(type))
101 return false;
102
103 return true;
104 }
105
106 /*
107 * We only allocate and copy the strings needed by the parts of symtab
108 * we keep. This is simple, but has the effect of making multiple
109 * copies of duplicates. We could be more sophisticated, see
110 * linux-kernel thread starting with
111 * <73defb5e4bca04a6431392cc341112b1@localhost>.
112 */
113 void layout_symtab(struct module *mod, struct load_info *info)
114 {
115 Elf_Shdr *symsect = info->sechdrs + info->index.sym;
116 Elf_Shdr *strsect = info->sechdrs + info->index.str;
117 const Elf_Sym *src;
118 unsigned int i, nsrc, ndst, strtab_size = 0;
119 struct module_memory *mod_mem_data = &mod->mem[MOD_DATA];
120 struct module_memory *mod_mem_init_data = &mod->mem[MOD_INIT_DATA];
121
122 /* Put symbol section at end of init part of module. */
123 symsect->sh_flags |= SHF_ALLOC;
124 symsect->sh_entsize = module_get_offset_and_type(mod, MOD_INIT_DATA,
125 symsect, info->index.sym);
126 pr_debug("\t%s\n", info->secstrings + symsect->sh_name);
127
128 src = (void *)info->hdr + symsect->sh_offset;
129 nsrc = symsect->sh_size / sizeof(*src);
130
131 /* Compute total space required for the core symbols' strtab. */
132 for (ndst = i = 0; i < nsrc; i++) {
133 if (i == 0 || is_livepatch_module(mod) ||
134 is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
135 info->index.pcpu)) {
136 strtab_size += strlen(&info->strtab[src[i].st_name]) + 1;
137 ndst++;
138 }
139 }
140
141 /* Append room for core symbols at end of core part. */
142 info->symoffs = ALIGN(mod_mem_data->size, symsect->sh_addralign ?: 1);
143 info->stroffs = mod_mem_data->size = info->symoffs + ndst * sizeof(Elf_Sym);
144 mod_mem_data->size += strtab_size;
145 /* Note add_kallsyms() computes strtab_size as core_typeoffs - stroffs */
146 info->core_typeoffs = mod_mem_data->size;
147 mod_mem_data->size += ndst * sizeof(char);
148
149 /* Put string table section at end of init part of module. */
150 strsect->sh_flags |= SHF_ALLOC;
151 strsect->sh_entsize = module_get_offset_and_type(mod, MOD_INIT_DATA,
152 strsect, info->index.str);
153 pr_debug("\t%s\n", info->secstrings + strsect->sh_name);
154
155 /* We'll tack temporary mod_kallsyms on the end. */
156 mod_mem_init_data->size = ALIGN(mod_mem_init_data->size,
157 __alignof__(struct mod_kallsyms));
158 info->mod_kallsyms_init_off = mod_mem_init_data->size;
159
160 mod_mem_init_data->size += sizeof(struct mod_kallsyms);
161 info->init_typeoffs = mod_mem_init_data->size;
162 mod_mem_init_data->size += nsrc * sizeof(char);
163 }
164
165 /*
166 * We use the full symtab and strtab which layout_symtab arranged to
167 * be appended to the init section. Later we switch to the cut-down
168 * core-only ones.
169 */
170 void add_kallsyms(struct module *mod, const struct load_info *info)
171 {
172 unsigned int i, ndst;
173 const Elf_Sym *src;
174 Elf_Sym *dst;
175 char *s;
176 Elf_Shdr *symsec = &info->sechdrs[info->index.sym];
177 unsigned long strtab_size;
178 void *data_base = mod->mem[MOD_DATA].base;
179 void *init_data_base = mod->mem[MOD_INIT_DATA].base;
180
181 /* Set up to point into init section. */
182 mod->kallsyms = (void __rcu *)init_data_base +
183 info->mod_kallsyms_init_off;
184
185 rcu_read_lock();
186 /* The following is safe since this pointer cannot change */
187 rcu_dereference(mod->kallsyms)->symtab = (void *)symsec->sh_addr;
188 rcu_dereference(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym);
189 /* Make sure we get permanent strtab: don't use info->strtab. */
190 rcu_dereference(mod->kallsyms)->strtab =
191 (void *)info->sechdrs[info->index.str].sh_addr;
192 rcu_dereference(mod->kallsyms)->typetab = init_data_base + info->init_typeoffs;
193
194 /*
195 * Now populate the cut down core kallsyms for after init
196 * and set types up while we still have access to sections.
197 */
198 mod->core_kallsyms.symtab = dst = data_base + info->symoffs;
199 mod->core_kallsyms.strtab = s = data_base + info->stroffs;
200 mod->core_kallsyms.typetab = data_base + info->core_typeoffs;
201 strtab_size = info->core_typeoffs - info->stroffs;
202 src = rcu_dereference(mod->kallsyms)->symtab;
203 for (ndst = i = 0; i < rcu_dereference(mod->kallsyms)->num_symtab; i++) {
204 rcu_dereference(mod->kallsyms)->typetab[i] = elf_type(src + i, info);
205 if (i == 0 || is_livepatch_module(mod) ||
206 is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
207 info->index.pcpu)) {
208 ssize_t ret;
209
210 mod->core_kallsyms.typetab[ndst] =
211 rcu_dereference(mod->kallsyms)->typetab[i];
212 dst[ndst] = src[i];
213 dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
214 ret = strscpy(s,
215 &rcu_dereference(mod->kallsyms)->strtab[src[i].st_name],
216 strtab_size);
217 if (ret < 0)
218 break;
219 s += ret + 1;
220 strtab_size -= ret + 1;
221 }
222 }
223 rcu_read_unlock();
224 mod->core_kallsyms.num_symtab = ndst;
225 }
226
227 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
228 void init_build_id(struct module *mod, const struct load_info *info)
229 {
230 const Elf_Shdr *sechdr;
231 unsigned int i;
232
233 for (i = 0; i < info->hdr->e_shnum; i++) {
234 sechdr = &info->sechdrs[i];
235 if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE &&
236 !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id,
237 sechdr->sh_size))
238 break;
239 }
240 }
241 #else
242 void init_build_id(struct module *mod, const struct load_info *info)
243 {
244 }
245 #endif
246
247 static const char *kallsyms_symbol_name(struct mod_kallsyms *kallsyms, unsigned int symnum)
248 {
249 return kallsyms->strtab + kallsyms->symtab[symnum].st_name;
250 }
251
252 /*
253 * Given a module and address, find the corresponding symbol and return its name
254 * while providing its size and offset if needed.
255 */
256 static const char *find_kallsyms_symbol(struct module *mod,
257 unsigned long addr,
258 unsigned long *size,
259 unsigned long *offset)
260 {
261 unsigned int i, best = 0;
262 unsigned long nextval, bestval;
263 struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
264 struct module_memory *mod_mem;
265
266 /* At worse, next value is at end of module */
267 if (within_module_init(addr, mod))
268 mod_mem = &mod->mem[MOD_INIT_TEXT];
269 else
270 mod_mem = &mod->mem[MOD_TEXT];
271
272 nextval = (unsigned long)mod_mem->base + mod_mem->size;
273
274 bestval = kallsyms_symbol_value(&kallsyms->symtab[best]);
275
276 /*
277 * Scan for closest preceding symbol, and next symbol. (ELF
278 * starts real symbols at 1).
279 */
280 for (i = 1; i < kallsyms->num_symtab; i++) {
281 const Elf_Sym *sym = &kallsyms->symtab[i];
282 unsigned long thisval = kallsyms_symbol_value(sym);
283
284 if (sym->st_shndx == SHN_UNDEF)
285 continue;
286
287 /*
288 * We ignore unnamed symbols: they're uninformative
289 * and inserted at a whim.
290 */
291 if (*kallsyms_symbol_name(kallsyms, i) == '\0' ||
292 is_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
293 continue;
294
295 if (thisval <= addr && thisval > bestval) {
296 best = i;
297 bestval = thisval;
298 }
299 if (thisval > addr && thisval < nextval)
300 nextval = thisval;
301 }
302
303 if (!best)
304 return NULL;
305
306 if (size)
307 *size = nextval - bestval;
308 if (offset)
309 *offset = addr - bestval;
310
311 return kallsyms_symbol_name(kallsyms, best);
312 }
313
314 void * __weak dereference_module_function_descriptor(struct module *mod,
315 void *ptr)
316 {
317 return ptr;
318 }
319
320 /*
321 * For kallsyms to ask for address resolution. NULL means not found. Careful
322 * not to lock to avoid deadlock on oopses, simply disable preemption.
323 */
324 int module_address_lookup(unsigned long addr,
325 unsigned long *size,
326 unsigned long *offset,
327 char **modname,
328 const unsigned char **modbuildid,
329 char *namebuf)
330 {
331 const char *sym;
332 int ret = 0;
333 struct module *mod;
334
335 preempt_disable();
336 mod = __module_address(addr);
337 if (mod) {
338 if (modname)
339 *modname = mod->name;
340 if (modbuildid) {
341 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
342 *modbuildid = mod->build_id;
343 #else
344 *modbuildid = NULL;
345 #endif
346 }
347
348 sym = find_kallsyms_symbol(mod, addr, size, offset);
349
350 if (sym)
351 ret = strscpy(namebuf, sym, KSYM_NAME_LEN);
352 }
353 preempt_enable();
354
355 return ret;
356 }
357
358 int lookup_module_symbol_name(unsigned long addr, char *symname)
359 {
360 struct module *mod;
361
362 preempt_disable();
363 list_for_each_entry_rcu(mod, &modules, list) {
364 if (mod->state == MODULE_STATE_UNFORMED)
365 continue;
366 if (within_module(addr, mod)) {
367 const char *sym;
368
369 sym = find_kallsyms_symbol(mod, addr, NULL, NULL);
370 if (!sym)
371 goto out;
372
373 strscpy(symname, sym, KSYM_NAME_LEN);
374 preempt_enable();
375 return 0;
376 }
377 }
378 out:
379 preempt_enable();
380 return -ERANGE;
381 }
382
383 int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
384 char *name, char *module_name, int *exported)
385 {
386 struct module *mod;
387
388 preempt_disable();
389 list_for_each_entry_rcu(mod, &modules, list) {
390 struct mod_kallsyms *kallsyms;
391
392 if (mod->state == MODULE_STATE_UNFORMED)
393 continue;
394 kallsyms = rcu_dereference_sched(mod->kallsyms);
395 if (symnum < kallsyms->num_symtab) {
396 const Elf_Sym *sym = &kallsyms->symtab[symnum];
397
398 *value = kallsyms_symbol_value(sym);
399 *type = kallsyms->typetab[symnum];
400 strscpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN);
401 strscpy(module_name, mod->name, MODULE_NAME_LEN);
402 *exported = is_exported(name, *value, mod);
403 preempt_enable();
404 return 0;
405 }
406 symnum -= kallsyms->num_symtab;
407 }
408 preempt_enable();
409 return -ERANGE;
410 }
411
412 /* Given a module and name of symbol, find and return the symbol's value */
413 static unsigned long __find_kallsyms_symbol_value(struct module *mod, const char *name)
414 {
415 unsigned int i;
416 struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
417
418 for (i = 0; i < kallsyms->num_symtab; i++) {
419 const Elf_Sym *sym = &kallsyms->symtab[i];
420
421 if (strcmp(name, kallsyms_symbol_name(kallsyms, i)) == 0 &&
422 sym->st_shndx != SHN_UNDEF)
423 return kallsyms_symbol_value(sym);
424 }
425 return 0;
426 }
427
428 static unsigned long __module_kallsyms_lookup_name(const char *name)
429 {
430 struct module *mod;
431 char *colon;
432
433 colon = strnchr(name, MODULE_NAME_LEN, ':');
434 if (colon) {
435 mod = find_module_all(name, colon - name, false);
436 if (mod)
437 return __find_kallsyms_symbol_value(mod, colon + 1);
438 return 0;
439 }
440
441 list_for_each_entry_rcu(mod, &modules, list) {
442 unsigned long ret;
443
444 if (mod->state == MODULE_STATE_UNFORMED)
445 continue;
446 ret = __find_kallsyms_symbol_value(mod, name);
447 if (ret)
448 return ret;
449 }
450 return 0;
451 }
452
453 /* Look for this name: can be of form module:name. */
454 unsigned long module_kallsyms_lookup_name(const char *name)
455 {
456 unsigned long ret;
457
458 /* Don't lock: we're in enough trouble already. */
459 preempt_disable();
460 ret = __module_kallsyms_lookup_name(name);
461 preempt_enable();
462 return ret;
463 }
464
465 unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
466 {
467 unsigned long ret;
468
469 preempt_disable();
470 ret = __find_kallsyms_symbol_value(mod, name);
471 preempt_enable();
472 return ret;
473 }
474
475 int module_kallsyms_on_each_symbol(const char *modname,
476 int (*fn)(void *, const char *, unsigned long),
477 void *data)
478 {
479 struct module *mod;
480 unsigned int i;
481 int ret = 0;
482
483 mutex_lock(&module_mutex);
484 list_for_each_entry(mod, &modules, list) {
485 struct mod_kallsyms *kallsyms;
486
487 if (mod->state == MODULE_STATE_UNFORMED)
488 continue;
489
490 if (modname && strcmp(modname, mod->name))
491 continue;
492
493 /* Use rcu_dereference_sched() to remain compliant with the sparse tool */
494 preempt_disable();
495 kallsyms = rcu_dereference_sched(mod->kallsyms);
496 preempt_enable();
497
498 for (i = 0; i < kallsyms->num_symtab; i++) {
499 const Elf_Sym *sym = &kallsyms->symtab[i];
500
501 if (sym->st_shndx == SHN_UNDEF)
502 continue;
503
504 ret = fn(data, kallsyms_symbol_name(kallsyms, i),
505 kallsyms_symbol_value(sym));
506 if (ret != 0)
507 goto out;
508 }
509
510 /*
511 * The given module is found, the subsequent modules do not
512 * need to be compared.
513 */
514 if (modname)
515 break;
516 }
517 out:
518 mutex_unlock(&module_mutex);
519 return ret;
520 }
521
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