kernel/kallsyms.c

   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/kprobes.h>
  28 #include <linux/compiler.h>
  29
  30 /*
  31  * These will be re-linked against their real values
  32  * during the second link stage.
  33  */
  34 extern const unsigned long kallsyms_addresses[] __weak;
  35 extern const int kallsyms_offsets[] __weak;
  36 extern const u8 kallsyms_names[] __weak;
  37
  38 /*
  39  * Tell the compiler that the count isn't in the small data section if the arch
  40  * has one (eg: FRV).
  41  */
  42 extern const unsigned int kallsyms_num_syms
  43 __section(".rodata") __attribute__((weak));
  44
  45 extern const unsigned long kallsyms_relative_base
  46 __section(".rodata") __attribute__((weak));
  47
  48 extern const char kallsyms_token_table[] __weak;
  49 extern const u16 kallsyms_token_index[] __weak;
  50
  51 extern const unsigned int kallsyms_markers[] __weak;
  52
  53 /*
  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.
  57  */
  58 static unsigned int kallsyms_expand_symbol(unsigned int off,
  59                                            char *result, size_t maxlen)
  60 {
  61         int len, skipped_first = 0;
  62         const char *tptr;
  63         const u8 *data;
  64
  65         /* Get the compressed symbol length from the first symbol byte. */
  66         data = &kallsyms_names[off];
  67         len = *data;
  68         data++;
  69
  70         /*
  71          * Update the offset to return the offset for the next symbol on
  72          * the compressed stream.
  73          */
  74         off += len + 1;
  75
  76         /*
  77          * For every byte on the compressed symbol data, copy the table
  78          * entry for that byte.
  79          */
  80         while (len) {
  81                 tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
  82                 data++;
  83                 len--;
  84
  85                 while (*tptr) {
  86                         if (skipped_first) {
  87                                 if (maxlen <= 1)
  88                                         goto tail;
  89                                 *result = *tptr;
  90                                 result++;
  91                                 maxlen--;
  92                         } else
  93                                 skipped_first = 1;
  94                         tptr++;
  95                 }
  96         }
  97
  98 tail:
  99         if (maxlen)
 100                 *result = '\0';
 101
 102         /* Return to offset to the next symbol. */
 103         return off;
 104 }
 105
 106 /*
 107  * Get symbol type information. This is encoded as a single char at the
 108  * beginning of the symbol name.
 109  */
 110 static char kallsyms_get_symbol_type(unsigned int off)
 111 {
 112         /*
 113          * Get just the first code, look it up in the token table,
 114          * and return the first char from this token.
 115          */
 116         return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
 117 }
 118
 119
 120 /*
 121  * Find the offset on the compressed stream given and index in the
 122  * kallsyms array.
 123  */
 124 static unsigned int get_symbol_offset(unsigned long pos)
 125 {
 126         const u8 *name;
 127         int i;
 128
 129         /*
 130          * Use the closest marker we have. We have markers every 256 positions,
 131          * so that should be close enough.
 132          */
 133         name = &kallsyms_names[kallsyms_markers[pos >> 8]];
 134
 135         /*
 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.
 140          */
 141         for (i = 0; i < (pos & 0xFF); i++)
 142                 name = name + (*name) + 1;
 143
 144         return name - kallsyms_names;
 145 }
 146
 147 static unsigned long kallsyms_sym_address(int idx)
 148 {
 149         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 150                 return kallsyms_addresses[idx];
 151
 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];
 155
 156         /* ...otherwise, positive offsets are absolute values */
 157         if (kallsyms_offsets[idx] >= 0)
 158                 return kallsyms_offsets[idx];
 159
 160         /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
 161         return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
 162 }
 163
 164 #if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
 165 /*
 166  * LLVM appends a hash to static function names when ThinLTO and CFI are
 167  * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.
 168  * This causes confusion and potentially breaks user space tools, so we
 169  * strip the suffix from expanded symbol names.
 170  */
 171 static inline bool cleanup_symbol_name(char *s)
 172 {
 173         char *res;
 174
 175         res = strrchr(s, '$');
 176         if (res)
 177                 *res = '\0';
 178
 179         return res != NULL;
 180 }
 181 #else
 182 static inline bool cleanup_symbol_name(char *s) { return false; }
 183 #endif
 184
 185 /* Lookup the address for this symbol. Returns 0 if not found. */
 186 unsigned long kallsyms_lookup_name(const char *name)
 187 {
 188         char namebuf[KSYM_NAME_LEN];
 189         unsigned long i;
 190         unsigned int off;
 191
 192         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 193                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 194
 195                 if (strcmp(namebuf, name) == 0)
 196                         return kallsyms_sym_address(i);
 197
 198                 if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
 199                         return kallsyms_sym_address(i);
 200         }
 201         return module_kallsyms_lookup_name(name);
 202 }
 203
 204 #ifdef CONFIG_LIVEPATCH
 205 /*
 206  * Iterate over all symbols in vmlinux.  For symbols from modules use
 207  * module_kallsyms_on_each_symbol instead.
 208  */
 209 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 210                                       unsigned long),
 211                             void *data)
 212 {
 213         char namebuf[KSYM_NAME_LEN];
 214         unsigned long i;
 215         unsigned int off;
 216         int ret;
 217
 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));
 221                 if (ret != 0)
 222                         return ret;
 223         }
 224         return 0;
 225 }
 226 #endif /* CONFIG_LIVEPATCH */
 227
 228 static unsigned long get_symbol_pos(unsigned long addr,
 229                                     unsigned long *symbolsize,
 230                                     unsigned long *offset)
 231 {
 232         unsigned long symbol_start = 0, symbol_end = 0;
 233         unsigned long i, low, high, mid;
 234
 235         /* This kernel should never had been booted. */
 236         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 237                 BUG_ON(!kallsyms_addresses);
 238         else
 239                 BUG_ON(!kallsyms_offsets);
 240
 241         /* Do a binary search on the sorted kallsyms_addresses array. */
 242         low = 0;
 243         high = kallsyms_num_syms;
 244
 245         while (high - low > 1) {
 246                 mid = low + (high - low) / 2;
 247                 if (kallsyms_sym_address(mid) <= addr)
 248                         low = mid;
 249                 else
 250                         high = mid;
 251         }
 252
 253         /*
 254          * Search for the first aliased symbol. Aliased
 255          * symbols are symbols with the same address.
 256          */
 257         while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
 258                 --low;
 259
 260         symbol_start = kallsyms_sym_address(low);
 261
 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);
 266                         break;
 267                 }
 268         }
 269
 270         /* If we found no next symbol, we use the end of the section. */
 271         if (!symbol_end) {
 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;
 276                 else
 277                         symbol_end = (unsigned long)_etext;
 278         }
 279
 280         if (symbolsize)
 281                 *symbolsize = symbol_end - symbol_start;
 282         if (offset)
 283                 *offset = addr - symbol_start;
 284
 285         return low;
 286 }
 287
 288 /*
 289  * Lookup an address but don't bother to find any names.
 290  */
 291 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
 292                                 unsigned long *offset)
 293 {
 294         char namebuf[KSYM_NAME_LEN];
 295
 296         if (is_ksym_addr(addr)) {
 297                 get_symbol_pos(addr, symbolsize, offset);
 298                 return 1;
 299         }
 300         return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
 301                !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
 302 }
 303
 304 /*
 305  * Lookup an address
 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.
 310  */
 311 const char *kallsyms_lookup(unsigned long addr,
 312                             unsigned long *symbolsize,
 313                             unsigned long *offset,
 314                             char **modname, char *namebuf)
 315 {
 316         const char *ret;
 317
 318         namebuf[KSYM_NAME_LEN - 1] = 0;
 319         namebuf[0] = 0;
 320
 321         if (is_ksym_addr(addr)) {
 322                 unsigned long pos;
 323
 324                 pos = get_symbol_pos(addr, symbolsize, offset);
 325                 /* Grab name */
 326                 kallsyms_expand_symbol(get_symbol_offset(pos),
 327                                        namebuf, KSYM_NAME_LEN);
 328                 if (modname)
 329                         *modname = NULL;
 330
 331                 ret = namebuf;
 332                 goto found;
 333         }
 334
 335         /* See if it's in a module or a BPF JITed image. */
 336         ret = module_address_lookup(addr, symbolsize, offset,
 337                                     modname, namebuf);
 338         if (!ret)
 339                 ret = bpf_address_lookup(addr, symbolsize,
 340                                          offset, modname, namebuf);
 341
 342         if (!ret)
 343                 ret = ftrace_mod_address_lookup(addr, symbolsize,
 344                                                 offset, modname, namebuf);
 345
 346 found:
 347         cleanup_symbol_name(namebuf);
 348         return ret;
 349 }
 350
 351 int lookup_symbol_name(unsigned long addr, char *symname)
 352 {
 353         int res;
 354
 355         symname[0] = '\0';
 356         symname[KSYM_NAME_LEN - 1] = '\0';
 357
 358         if (is_ksym_addr(addr)) {
 359                 unsigned long pos;
 360
 361                 pos = get_symbol_pos(addr, NULL, NULL);
 362                 /* Grab name */
 363                 kallsyms_expand_symbol(get_symbol_offset(pos),
 364                                        symname, KSYM_NAME_LEN);
 365                 goto found;
 366         }
 367         /* See if it's in a module. */
 368         res = lookup_module_symbol_name(addr, symname);
 369         if (res)
 370                 return res;
 371
 372 found:
 373         cleanup_symbol_name(symname);
 374         return 0;
 375 }
 376
 377 int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
 378                         unsigned long *offset, char *modname, char *name)
 379 {
 380         int res;
 381
 382         name[0] = '\0';
 383         name[KSYM_NAME_LEN - 1] = '\0';
 384
 385         if (is_ksym_addr(addr)) {
 386                 unsigned long pos;
 387
 388                 pos = get_symbol_pos(addr, size, offset);
 389                 /* Grab name */
 390                 kallsyms_expand_symbol(get_symbol_offset(pos),
 391                                        name, KSYM_NAME_LEN);
 392                 modname[0] = '\0';
 393                 goto found;
 394         }
 395         /* See if it's in a module. */
 396         res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
 397         if (res)
 398                 return res;
 399
 400 found:
 401         cleanup_symbol_name(name);
 402         return 0;
 403 }
 404
 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)
 408 {
 409         char *modname;
 410         const char *name;
 411         unsigned long offset, size;
 412         int len;
 413
 414         address += symbol_offset;
 415         name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
 416         if (!name)
 417                 return sprintf(buffer, "0x%lx", address - symbol_offset);
 418
 419         if (name != buffer)
 420                 strcpy(buffer, name);
 421         len = strlen(buffer);
 422         offset -= symbol_offset;
 423
 424         if (add_offset)
 425                 len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
 426
 427         if (modname)
 428                 len += sprintf(buffer + len, " [%s]", modname);
 429
 430         return len;
 431 }
 432
 433 /**
 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
 437  *
 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.
 441  *
 442  * This function returns the number of bytes stored in @buffer.
 443  */
 444 int sprint_symbol(char *buffer, unsigned long address)
 445 {
 446         return __sprint_symbol(buffer, address, 0, 1);
 447 }
 448 EXPORT_SYMBOL_GPL(sprint_symbol);
 449
 450 /**
 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
 454  *
 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.
 458  *
 459  * This function returns the number of bytes stored in @buffer.
 460  */
 461 int sprint_symbol_no_offset(char *buffer, unsigned long address)
 462 {
 463         return __sprint_symbol(buffer, address, 0, 0);
 464 }
 465 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
 466
 467 /**
 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
 471  *
 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.
 478  *
 479  * This function returns the number of bytes stored in @buffer.
 480  */
 481 int sprint_backtrace(char *buffer, unsigned long address)
 482 {
 483         return __sprint_symbol(buffer, address, -1, 1);
 484 }
 485
 486 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 487 struct kallsym_iter {
 488         loff_t pos;
 489         loff_t pos_arch_end;
 490         loff_t pos_mod_end;
 491         loff_t pos_ftrace_mod_end;
 492         loff_t pos_bpf_end;
 493         unsigned long value;
 494         unsigned int nameoff; /* If iterating in core kernel symbols. */
 495         char type;
 496         char name[KSYM_NAME_LEN];
 497         char module_name[MODULE_NAME_LEN];
 498         int exported;
 499         int show_value;
 500 };
 501
 502 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
 503                             char *type, char *name)
 504 {
 505         return -EINVAL;
 506 }
 507
 508 static int get_ksymbol_arch(struct kallsym_iter *iter)
 509 {
 510         int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
 511                                    &iter->value, &iter->type,
 512                                    iter->name);
 513
 514         if (ret < 0) {
 515                 iter->pos_arch_end = iter->pos;
 516                 return 0;
 517         }
 518
 519         return 1;
 520 }
 521
 522 static int get_ksymbol_mod(struct kallsym_iter *iter)
 523 {
 524         int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
 525                                      &iter->value, &iter->type,
 526                                      iter->name, iter->module_name,
 527                                      &iter->exported);
 528         if (ret < 0) {
 529                 iter->pos_mod_end = iter->pos;
 530                 return 0;
 531         }
 532
 533         return 1;
 534 }
 535
 536 /*
 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.
 540  */
 541 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
 542 {
 543         int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
 544                                          &iter->value, &iter->type,
 545                                          iter->name, iter->module_name,
 546                                          &iter->exported);
 547         if (ret < 0) {
 548                 iter->pos_ftrace_mod_end = iter->pos;
 549                 return 0;
 550         }
 551
 552         return 1;
 553 }
 554
 555 static int get_ksymbol_bpf(struct kallsym_iter *iter)
 556 {
 557         int ret;
 558
 559         strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
 560         iter->exported = 0;
 561         ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
 562                               &iter->value, &iter->type,
 563                               iter->name);
 564         if (ret < 0) {
 565                 iter->pos_bpf_end = iter->pos;
 566                 return 0;
 567         }
 568
 569         return 1;
 570 }
 571
 572 /*
 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
 575  * module.
 576  */
 577 static int get_ksymbol_kprobe(struct kallsym_iter *iter)
 578 {
 579         strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
 580         iter->exported = 0;
 581         return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
 582                                   &iter->value, &iter->type,
 583                                   iter->name) < 0 ? 0 : 1;
 584 }
 585
 586 /* Returns space to next name. */
 587 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 588 {
 589         unsigned off = iter->nameoff;
 590
 591         iter->module_name[0] = '\0';
 592         iter->value = kallsyms_sym_address(iter->pos);
 593
 594         iter->type = kallsyms_get_symbol_type(off);
 595
 596         off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
 597
 598         return off - iter->nameoff;
 599 }
 600
 601 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 602 {
 603         iter->name[0] = '\0';
 604         iter->nameoff = get_symbol_offset(new_pos);
 605         iter->pos = new_pos;
 606         if (new_pos == 0) {
 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;
 611         }
 612 }
 613
 614 /*
 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.
 618  */
 619 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 620 {
 621         iter->pos = pos;
 622
 623         if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
 624             get_ksymbol_arch(iter))
 625                 return 1;
 626
 627         if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
 628             get_ksymbol_mod(iter))
 629                 return 1;
 630
 631         if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
 632             get_ksymbol_ftrace_mod(iter))
 633                 return 1;
 634
 635         if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
 636             get_ksymbol_bpf(iter))
 637                 return 1;
 638
 639         return get_ksymbol_kprobe(iter);
 640 }
 641
 642 /* Returns false if pos at or past end of file. */
 643 static int update_iter(struct kallsym_iter *iter, loff_t pos)
 644 {
 645         /* Module symbols can be accessed randomly. */
 646         if (pos >= kallsyms_num_syms)
 647                 return update_iter_mod(iter, pos);
 648
 649         /* If we're not on the desired position, reset to new position. */
 650         if (pos != iter->pos)
 651                 reset_iter(iter, pos);
 652
 653         iter->nameoff += get_ksymbol_core(iter);
 654         iter->pos++;
 655
 656         return 1;
 657 }
 658
 659 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
 660 {
 661         (*pos)++;
 662
 663         if (!update_iter(m->private, *pos))
 664                 return NULL;
 665         return p;
 666 }
 667
 668 static void *s_start(struct seq_file *m, loff_t *pos)
 669 {
 670         if (!update_iter(m->private, *pos))
 671                 return NULL;
 672         return m->private;
 673 }
 674
 675 static void s_stop(struct seq_file *m, void *p)
 676 {
 677 }
 678
 679 static int s_show(struct seq_file *m, void *p)
 680 {
 681         void *value;
 682         struct kallsym_iter *iter = m->private;
 683
 684         /* Some debugging symbols have no name.  Ignore them. */
 685         if (!iter->name[0])
 686                 return 0;
 687
 688         value = iter->show_value ? (void *)iter->value : NULL;
 689
 690         if (iter->module_name[0]) {
 691                 char type;
 692
 693                 /*
 694                  * Label it "global" if it is exported,
 695                  * "local" if not exported.
 696                  */
 697                 type = iter->exported ? toupper(iter->type) :
 698                                         tolower(iter->type);
 699                 seq_printf(m, "%px %c %s\t[%s]\n", value,
 700                            type, iter->name, iter->module_name);
 701         } else
 702                 seq_printf(m, "%px %c %s\n", value,
 703                            iter->type, iter->name);
 704         return 0;
 705 }
 706
 707 static const struct seq_operations kallsyms_op = {
 708         .start = s_start,
 709         .next = s_next,
 710         .stop = s_stop,
 711         .show = s_show
 712 };
 713
 714 static inline int kallsyms_for_perf(void)
 715 {
 716 #ifdef CONFIG_PERF_EVENTS
 717         extern int sysctl_perf_event_paranoid;
 718         if (sysctl_perf_event_paranoid <= 1)
 719                 return 1;
 720 #endif
 721         return 0;
 722 }
 723
 724 /*
 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).
 728  *
 729  * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 730  * block even that).
 731  */
 732 bool kallsyms_show_value(const struct cred *cred)
 733 {
 734         switch (kptr_restrict) {
 735         case 0:
 736                 if (kallsyms_for_perf())
 737                         return true;
 738                 fallthrough;
 739         case 1:
 740                 if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
 741                                      CAP_OPT_NOAUDIT) == 0)
 742                         return true;
 743                 fallthrough;
 744         default:
 745                 return false;
 746         }
 747 }
 748
 749 static int kallsyms_open(struct inode *inode, struct file *file)
 750 {
 751         /*
 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.
 755          */
 756         struct kallsym_iter *iter;
 757         iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
 758         if (!iter)
 759                 return -ENOMEM;
 760         reset_iter(iter, 0);
 761
 762         /*
 763          * Instead of checking this on every s_show() call, cache
 764          * the result here at open time.
 765          */
 766         iter->show_value = kallsyms_show_value(file->f_cred);
 767         return 0;
 768 }
 769
 770 #ifdef  CONFIG_KGDB_KDB
 771 const char *kdb_walk_kallsyms(loff_t *pos)
 772 {
 773         static struct kallsym_iter kdb_walk_kallsyms_iter;
 774         if (*pos == 0) {
 775                 memset(&kdb_walk_kallsyms_iter, 0,
 776                        sizeof(kdb_walk_kallsyms_iter));
 777                 reset_iter(&kdb_walk_kallsyms_iter, 0);
 778         }
 779         while (1) {
 780                 if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
 781                         return NULL;
 782                 ++*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;
 786         }
 787 }
 788 #endif  /* CONFIG_KGDB_KDB */
 789
 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,
 795 };
 796
 797 static int __init kallsyms_init(void)
 798 {
 799         proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
 800         return 0;
 801 }
 802 device_initcall(kallsyms_init);