kernel/module/kallsyms.c

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