summaryrefslogtreecommitdiffstats
path: root/kernel/module/kallsyms.c
blob: ef73ae7c89094bdad10f851489d98330bd40dc57 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Module kallsyms support
 *
 * Copyright (C) 2010 Rusty Russell
 */

#include <linux/module.h>
#include <linux/module_symbol.h>
#include <linux/kallsyms.h>
#include <linux/buildid.h>
#include <linux/bsearch.h>
#include "internal.h"

/* Lookup exported symbol in given range of kernel_symbols */
static const struct kernel_symbol *lookup_exported_symbol(const char *name,
							  const struct kernel_symbol *start,
							  const struct kernel_symbol *stop)
{
	return bsearch(name, start, stop - start,
			sizeof(struct kernel_symbol), cmp_name);
}

static int is_exported(const char *name, unsigned long value,
		       const struct module *mod)
{
	const struct kernel_symbol *ks;

	if (!mod)
		ks = lookup_exported_symbol(name, __start___ksymtab, __stop___ksymtab);
	else
		ks = lookup_exported_symbol(name, mod->syms, mod->syms + mod->num_syms);

	return ks && kernel_symbol_value(ks) == value;
}

/* As per nm */
static char elf_type(const Elf_Sym *sym, const struct load_info *info)
{
	const Elf_Shdr *sechdrs = info->sechdrs;

	if (ELF_ST_BIND(sym->st_info) == STB_WEAK) {
		if (ELF_ST_TYPE(sym->st_info) == STT_OBJECT)
			return 'v';
		else
			return 'w';
	}
	if (sym->st_shndx == SHN_UNDEF)
		return 'U';
	if (sym->st_shndx == SHN_ABS || sym->st_shndx == info->index.pcpu)
		return 'a';
	if (sym->st_shndx >= SHN_LORESERVE)
		return '?';
	if (sechdrs[sym->st_shndx].sh_flags & SHF_EXECINSTR)
		return 't';
	if (sechdrs[sym->st_shndx].sh_flags & SHF_ALLOC &&
	    sechdrs[sym->st_shndx].sh_type != SHT_NOBITS) {
		if (!(sechdrs[sym->st_shndx].sh_flags & SHF_WRITE))
			return 'r';
		else if (sechdrs[sym->st_shndx].sh_flags & ARCH_SHF_SMALL)
			return 'g';
		else
			return 'd';
	}
	if (sechdrs[sym->st_shndx].sh_type == SHT_NOBITS) {
		if (sechdrs[sym->st_shndx].sh_flags & ARCH_SHF_SMALL)
			return 's';
		else
			return 'b';
	}
	if (strstarts(info->secstrings + sechdrs[sym->st_shndx].sh_name,
		      ".debug")) {
		return 'n';
	}
	return '?';
}

static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
			   unsigned int shnum, unsigned int pcpundx)
{
	const Elf_Shdr *sec;
	enum mod_mem_type type;

	if (src->st_shndx == SHN_UNDEF ||
	    src->st_shndx >= shnum ||
	    !src->st_name)
		return false;

#ifdef CONFIG_KALLSYMS_ALL
	if (src->st_shndx == pcpundx)
		return true;
#endif

	sec = sechdrs + src->st_shndx;
	type = sec->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT;
	if (!(sec->sh_flags & SHF_ALLOC)
#ifndef CONFIG_KALLSYMS_ALL
	    || !(sec->sh_flags & SHF_EXECINSTR)
#endif
	    || mod_mem_type_is_init(type))
		return false;

	return true;
}

/*
 * We only allocate and copy the strings needed by the parts of symtab
 * we keep.  This is simple, but has the effect of making multiple
 * copies of duplicates.  We could be more sophisticated, see
 * linux-kernel thread starting with
 * <73defb5e4bca04a6431392cc341112b1@localhost>.
 */
void layout_symtab(struct module *mod, struct load_info *info)
{
	Elf_Shdr *symsect = info->sechdrs + info->index.sym;
	Elf_Shdr *strsect = info->sechdrs + info->index.str;
	const Elf_Sym *src;
	unsigned int i, nsrc, ndst, strtab_size = 0;
	struct module_memory *mod_mem_data = &mod->mem[MOD_DATA];
	struct module_memory *mod_mem_init_data = &mod->mem[MOD_INIT_DATA];

	/* Put symbol section at end of init part of module. */
	symsect->sh_flags |= SHF_ALLOC;
	symsect->sh_entsize = module_get_offset_and_type(mod, MOD_INIT_DATA,
							 symsect, info->index.sym);
	pr_debug("\t%s\n", info->secstrings + symsect->sh_name);

	src = (void *)info->hdr + symsect->sh_offset;
	nsrc = symsect->sh_size / sizeof(*src);

	/* Compute total space required for the core symbols' strtab. */
	for (ndst = i = 0; i < nsrc; i++) {
		if (i == 0 || is_livepatch_module(mod) ||
		    is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
				   info->index.pcpu)) {
			strtab_size += strlen(&info->strtab[src[i].st_name]) + 1;
			ndst++;
		}
	}

	/* Append room for core symbols at end of core part. */
	info->symoffs = ALIGN(mod_mem_data->size, symsect->sh_addralign ?: 1);
	info->stroffs = mod_mem_data->size = info->symoffs + ndst * sizeof(Elf_Sym);
	mod_mem_data->size += strtab_size;
	/* Note add_kallsyms() computes strtab_size as core_typeoffs - stroffs */
	info->core_typeoffs = mod_mem_data->size;
	mod_mem_data->size += ndst * sizeof(char);

	/* Put string table section at end of init part of module. */
	strsect->sh_flags |= SHF_ALLOC;
	strsect->sh_entsize = module_get_offset_and_type(mod, MOD_INIT_DATA,
							 strsect, info->index.str);
	pr_debug("\t%s\n", info->secstrings + strsect->sh_name);

	/* We'll tack temporary mod_kallsyms on the end. */
	mod_mem_init_data->size = ALIGN(mod_mem_init_data->size,
					__alignof__(struct mod_kallsyms));
	info->mod_kallsyms_init_off = mod_mem_init_data->size;

	mod_mem_init_data->size += sizeof(struct mod_kallsyms);
	info->init_typeoffs = mod_mem_init_data->size;
	mod_mem_init_data->size += nsrc * sizeof(char);
}

/*
 * We use the full symtab and strtab which layout_symtab arranged to
 * be appended to the init section.  Later we switch to the cut-down
 * core-only ones.
 */
void add_kallsyms(struct module *mod, const struct load_info *info)
{
	unsigned int i, ndst;
	const Elf_Sym *src;
	Elf_Sym *dst;
	char *s;
	Elf_Shdr *symsec = &info->sechdrs[info->index.sym];
	unsigned long strtab_size;
	void *data_base = mod->mem[MOD_DATA].base;
	void *init_data_base = mod->mem[MOD_INIT_DATA].base;

	/* Set up to point into init section. */
	mod->kallsyms = (void __rcu *)init_data_base +
		info->mod_kallsyms_init_off;

	rcu_read_lock();
	/* The following is safe since this pointer cannot change */
	rcu_dereference(mod->kallsyms)->symtab = (void *)symsec->sh_addr;
	rcu_dereference(mod->kallsyms)->num_symtab = symsec->sh_size / sizeof(Elf_Sym);
	/* Make sure we get permanent strtab: don't use info->strtab. */
	rcu_dereference(mod->kallsyms)->strtab =
		(void *)info->sechdrs[info->index.str].sh_addr;
	rcu_dereference(mod->kallsyms)->typetab = init_data_base + info->init_typeoffs;

	/*
	 * Now populate the cut down core kallsyms for after init
	 * and set types up while we still have access to sections.
	 */
	mod->core_kallsyms.symtab = dst = data_base + info->symoffs;
	mod->core_kallsyms.strtab = s = data_base + info->stroffs;
	mod->core_kallsyms.typetab = data_base + info->core_typeoffs;
	strtab_size = info->core_typeoffs - info->stroffs;
	src = rcu_dereference(mod->kallsyms)->symtab;
	for (ndst = i = 0; i < rcu_dereference(mod->kallsyms)->num_symtab; i++) {
		rcu_dereference(mod->kallsyms)->typetab[i] = elf_type(src + i, info);
		if (i == 0 || is_livepatch_module(mod) ||
		    is_core_symbol(src + i, info->sechdrs, info->hdr->e_shnum,
				   info->index.pcpu)) {
			ssize_t ret;

			mod->core_kallsyms.typetab[ndst] =
			    rcu_dereference(mod->kallsyms)->typetab[i];
			dst[ndst] = src[i];
			dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
			ret = strscpy(s,
				      &rcu_dereference(mod->kallsyms)->strtab[src[i].st_name],
				      strtab_size);
			if (ret < 0)
				break;
			s += ret + 1;
			strtab_size -= ret + 1;
		}
	}
	rcu_read_unlock();
	mod->core_kallsyms.num_symtab = ndst;
}

#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
void init_build_id(struct module *mod, const struct load_info *info)
{
	const Elf_Shdr *sechdr;
	unsigned int i;

	for (i = 0; i < info->hdr->e_shnum; i++) {
		sechdr = &info->sechdrs[i];
		if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE &&
		    !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id,
					sechdr->sh_size))
			break;
	}
}
#else
void init_build_id(struct module *mod, const struct load_info *info)
{
}
#endif

static const char *kallsyms_symbol_name(struct mod_kallsyms *kallsyms, unsigned int symnum)
{
	return kallsyms->strtab + kallsyms->symtab[symnum].st_name;
}

/*
 * Given a module and address, find the corresponding symbol and return its name
 * while providing its size and offset if needed.
 */
static const char *find_kallsyms_symbol(struct module *mod,
					unsigned long addr,
					unsigned long *size,
					unsigned long *offset)
{
	unsigned int i, best = 0;
	unsigned long nextval, bestval;
	struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
	struct module_memory *mod_mem;

	/* At worse, next value is at end of module */
	if (within_module_init(addr, mod))
		mod_mem = &mod->mem[MOD_INIT_TEXT];
	else
		mod_mem = &mod->mem[MOD_TEXT];

	nextval = (unsigned long)mod_mem->base + mod_mem->size;

	bestval = kallsyms_symbol_value(&kallsyms->symtab[best]);

	/*
	 * Scan for closest preceding symbol, and next symbol. (ELF
	 * starts real symbols at 1).
	 */
	for (i = 1; i < kallsyms->num_symtab; i++) {
		const Elf_Sym *sym = &kallsyms->symtab[i];
		unsigned long thisval = kallsyms_symbol_value(sym);

		if (sym->st_shndx == SHN_UNDEF)
			continue;

		/*
		 * We ignore unnamed symbols: they're uninformative
		 * and inserted at a whim.
		 */
		if (*kallsyms_symbol_name(kallsyms, i) == '\0' ||
		    is_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
			continue;

		if (thisval <= addr && thisval > bestval) {
			best = i;
			bestval = thisval;
		}
		if (thisval > addr && thisval < nextval)
			nextval = thisval;
	}

	if (!best)
		return NULL;

	if (size)
		*size = nextval - bestval;
	if (offset)
		*offset = addr - bestval;

	return kallsyms_symbol_name(kallsyms, best);
}

void * __weak dereference_module_function_descriptor(struct module *mod,
						     void *ptr)
{
	return ptr;
}

/*
 * For kallsyms to ask for address resolution.  NULL means not found.  Careful
 * not to lock to avoid deadlock on oopses, simply disable preemption.
 */
const char *module_address_lookup(unsigned long addr,
				  unsigned long *size,
			    unsigned long *offset,
			    char **modname,
			    const unsigned char **modbuildid,
			    char *namebuf)
{
	const char *ret = NULL;
	struct module *mod;

	preempt_disable();
	mod = __module_address(addr);
	if (mod) {
		if (modname)
			*modname = mod->name;
		if (modbuildid) {
#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
			*modbuildid = mod->build_id;
#else
			*modbuildid = NULL;
#endif
		}

		ret = find_kallsyms_symbol(mod, addr, size, offset);
	}
	/* Make a copy in here where it's safe */
	if (ret) {
		strncpy(namebuf, ret, KSYM_NAME_LEN - 1);
		ret = namebuf;
	}
	preempt_enable();

	return ret;
}

int lookup_module_symbol_name(unsigned long addr, char *symname)
{
	struct module *mod;

	preempt_disable();
	list_for_each_entry_rcu(mod, &modules, list) {
		if (mod->state == MODULE_STATE_UNFORMED)
			continue;
		if (within_module(addr, mod)) {
			const char *sym;

			sym = find_kallsyms_symbol(mod, addr, NULL, NULL);
			if (!sym)
				goto out;

			strscpy(symname, sym, KSYM_NAME_LEN);
			preempt_enable();
			return 0;
		}
	}
out:
	preempt_enable();
	return -ERANGE;
}

int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
		       char *name, char *module_name, int *exported)
{
	struct module *mod;

	preempt_disable();
	list_for_each_entry_rcu(mod, &modules, list) {
		struct mod_kallsyms *kallsyms;

		if (mod->state == MODULE_STATE_UNFORMED)
			continue;
		kallsyms = rcu_dereference_sched(mod->kallsyms);
		if (symnum < kallsyms->num_symtab) {
			const Elf_Sym *sym = &kallsyms->symtab[symnum];

			*value = kallsyms_symbol_value(sym);
			*type = kallsyms->typetab[symnum];
			strscpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN);
			strscpy(module_name, mod->name, MODULE_NAME_LEN);
			*exported = is_exported(name, *value, mod);
			preempt_enable();
			return 0;
		}
		symnum -= kallsyms->num_symtab;
	}
	preempt_enable();
	return -ERANGE;
}

/* Given a module and name of symbol, find and return the symbol's value */
static unsigned long __find_kallsyms_symbol_value(struct module *mod, const char *name)
{
	unsigned int i;
	struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);

	for (i = 0; i < kallsyms->num_symtab; i++) {
		const Elf_Sym *sym = &kallsyms->symtab[i];

		if (strcmp(name, kallsyms_symbol_name(kallsyms, i)) == 0 &&
		    sym->st_shndx != SHN_UNDEF)
			return kallsyms_symbol_value(sym);
	}
	return 0;
}

static unsigned long __module_kallsyms_lookup_name(const char *name)
{
	struct module *mod;
	char *colon;

	colon = strnchr(name, MODULE_NAME_LEN, ':');
	if (colon) {
		mod = find_module_all(name, colon - name, false);
		if (mod)
			return __find_kallsyms_symbol_value(mod, colon + 1);
		return 0;
	}

	list_for_each_entry_rcu(mod, &modules, list) {
		unsigned long ret;

		if (mod->state == MODULE_STATE_UNFORMED)
			continue;
		ret = __find_kallsyms_symbol_value(mod, name);
		if (ret)
			return ret;
	}
	return 0;
}

/* Look for this name: can be of form module:name. */
unsigned long module_kallsyms_lookup_name(const char *name)
{
	unsigned long ret;

	/* Don't lock: we're in enough trouble already. */
	preempt_disable();
	ret = __module_kallsyms_lookup_name(name);
	preempt_enable();
	return ret;
}

unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
{
	unsigned long ret;

	preempt_disable();
	ret = __find_kallsyms_symbol_value(mod, name);
	preempt_enable();
	return ret;
}

int module_kallsyms_on_each_symbol(const char *modname,
				   int (*fn)(void *, const char *, unsigned long),
				   void *data)
{
	struct module *mod;
	unsigned int i;
	int ret = 0;

	mutex_lock(&module_mutex);
	list_for_each_entry(mod, &modules, list) {
		struct mod_kallsyms *kallsyms;

		if (mod->state == MODULE_STATE_UNFORMED)
			continue;

		if (modname && strcmp(modname, mod->name))
			continue;

		/* Use rcu_dereference_sched() to remain compliant with the sparse tool */
		preempt_disable();
		kallsyms = rcu_dereference_sched(mod->kallsyms);
		preempt_enable();

		for (i = 0; i < kallsyms->num_symtab; i++) {
			const Elf_Sym *sym = &kallsyms->symtab[i];

			if (sym->st_shndx == SHN_UNDEF)
				continue;

			ret = fn(data, kallsyms_symbol_name(kallsyms, i),
				 kallsyms_symbol_value(sym));
			if (ret != 0)
				goto out;
		}

		/*
		 * The given module is found, the subsequent modules do not
		 * need to be compared.
		 */
		if (modname)
			break;
	}
out:
	mutex_unlock(&module_mutex);
	return ret;
}