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 /* Lookup the address for this symbol. Returns 0 if not found. */
 165 unsigned long kallsyms_lookup_name(const char *name)
 166 {
 167         char namebuf[KSYM_NAME_LEN];
 168         unsigned long i;
 169         unsigned int off;
 170
 171         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 172                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 173
 174                 if (strcmp(namebuf, name) == 0)
 175                         return kallsyms_sym_address(i);
 176         }
 177         return module_kallsyms_lookup_name(name);
 178 }
 179
 180 #ifdef CONFIG_LIVEPATCH
 181 /*
 182  * Iterate over all symbols in vmlinux.  For symbols from modules use
 183  * module_kallsyms_on_each_symbol instead.
 184  */
 185 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 186                                       unsigned long),
 187                             void *data)
 188 {
 189         char namebuf[KSYM_NAME_LEN];
 190         unsigned long i;
 191         unsigned int off;
 192         int ret;
 193
 194         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 195                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 196                 ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
 197                 if (ret != 0)
 198                         return ret;
 199         }
 200         return 0;
 201 }
 202 #endif /* CONFIG_LIVEPATCH */
 203
 204 static unsigned long get_symbol_pos(unsigned long addr,
 205                                     unsigned long *symbolsize,
 206                                     unsigned long *offset)
 207 {
 208         unsigned long symbol_start = 0, symbol_end = 0;
 209         unsigned long i, low, high, mid;
 210
 211         /* This kernel should never had been booted. */
 212         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 213                 BUG_ON(!kallsyms_addresses);
 214         else
 215                 BUG_ON(!kallsyms_offsets);
 216
 217         /* Do a binary search on the sorted kallsyms_addresses array. */
 218         low = 0;
 219         high = kallsyms_num_syms;
 220
 221         while (high - low > 1) {
 222                 mid = low + (high - low) / 2;
 223                 if (kallsyms_sym_address(mid) <= addr)
 224                         low = mid;
 225                 else
 226                         high = mid;
 227         }
 228
 229         /*
 230          * Search for the first aliased symbol. Aliased
 231          * symbols are symbols with the same address.
 232          */
 233         while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
 234                 --low;
 235
 236         symbol_start = kallsyms_sym_address(low);
 237
 238         /* Search for next non-aliased symbol. */
 239         for (i = low + 1; i < kallsyms_num_syms; i++) {
 240                 if (kallsyms_sym_address(i) > symbol_start) {
 241                         symbol_end = kallsyms_sym_address(i);
 242                         break;
 243                 }
 244         }
 245
 246         /* If we found no next symbol, we use the end of the section. */
 247         if (!symbol_end) {
 248                 if (is_kernel_inittext(addr))
 249                         symbol_end = (unsigned long)_einittext;
 250                 else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
 251                         symbol_end = (unsigned long)_end;
 252                 else
 253                         symbol_end = (unsigned long)_etext;
 254         }
 255
 256         if (symbolsize)
 257                 *symbolsize = symbol_end - symbol_start;
 258         if (offset)
 259                 *offset = addr - symbol_start;
 260
 261         return low;
 262 }
 263
 264 /*
 265  * Lookup an address but don't bother to find any names.
 266  */
 267 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
 268                                 unsigned long *offset)
 269 {
 270         char namebuf[KSYM_NAME_LEN];
 271
 272         if (is_ksym_addr(addr)) {
 273                 get_symbol_pos(addr, symbolsize, offset);
 274                 return 1;
 275         }
 276         return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
 277                !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
 278 }
 279
 280 /*
 281  * Lookup an address
 282  * - modname is set to NULL if it's in the kernel.
 283  * - We guarantee that the returned name is valid until we reschedule even if.
 284  *   It resides in a module.
 285  * - We also guarantee that modname will be valid until rescheduled.
 286  */
 287 const char *kallsyms_lookup(unsigned long addr,
 288                             unsigned long *symbolsize,
 289                             unsigned long *offset,
 290                             char **modname, char *namebuf)
 291 {
 292         const char *ret;
 293
 294         namebuf[KSYM_NAME_LEN - 1] = 0;
 295         namebuf[0] = 0;
 296
 297         if (is_ksym_addr(addr)) {
 298                 unsigned long pos;
 299
 300                 pos = get_symbol_pos(addr, symbolsize, offset);
 301                 /* Grab name */
 302                 kallsyms_expand_symbol(get_symbol_offset(pos),
 303                                        namebuf, KSYM_NAME_LEN);
 304                 if (modname)
 305                         *modname = NULL;
 306                 return namebuf;
 307         }
 308
 309         /* See if it's in a module or a BPF JITed image. */
 310         ret = module_address_lookup(addr, symbolsize, offset,
 311                                     modname, namebuf);
 312         if (!ret)
 313                 ret = bpf_address_lookup(addr, symbolsize,
 314                                          offset, modname, namebuf);
 315
 316         if (!ret)
 317                 ret = ftrace_mod_address_lookup(addr, symbolsize,
 318                                                 offset, modname, namebuf);
 319         return ret;
 320 }
 321
 322 int lookup_symbol_name(unsigned long addr, char *symname)
 323 {
 324         symname[0] = '\0';
 325         symname[KSYM_NAME_LEN - 1] = '\0';
 326
 327         if (is_ksym_addr(addr)) {
 328                 unsigned long pos;
 329
 330                 pos = get_symbol_pos(addr, NULL, NULL);
 331                 /* Grab name */
 332                 kallsyms_expand_symbol(get_symbol_offset(pos),
 333                                        symname, KSYM_NAME_LEN);
 334                 return 0;
 335         }
 336         /* See if it's in a module. */
 337         return lookup_module_symbol_name(addr, symname);
 338 }
 339
 340 int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
 341                         unsigned long *offset, char *modname, char *name)
 342 {
 343         name[0] = '\0';
 344         name[KSYM_NAME_LEN - 1] = '\0';
 345
 346         if (is_ksym_addr(addr)) {
 347                 unsigned long pos;
 348
 349                 pos = get_symbol_pos(addr, size, offset);
 350                 /* Grab name */
 351                 kallsyms_expand_symbol(get_symbol_offset(pos),
 352                                        name, KSYM_NAME_LEN);
 353                 modname[0] = '\0';
 354                 return 0;
 355         }
 356         /* See if it's in a module. */
 357         return lookup_module_symbol_attrs(addr, size, offset, modname, name);
 358 }
 359
 360 /* Look up a kernel symbol and return it in a text buffer. */
 361 static int __sprint_symbol(char *buffer, unsigned long address,
 362                            int symbol_offset, int add_offset)
 363 {
 364         char *modname;
 365         const char *name;
 366         unsigned long offset, size;
 367         int len;
 368
 369         address += symbol_offset;
 370         name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
 371         if (!name)
 372                 return sprintf(buffer, "0x%lx", address - symbol_offset);
 373
 374         if (name != buffer)
 375                 strcpy(buffer, name);
 376         len = strlen(buffer);
 377         offset -= symbol_offset;
 378
 379         if (add_offset)
 380                 len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
 381
 382         if (modname)
 383                 len += sprintf(buffer + len, " [%s]", modname);
 384
 385         return len;
 386 }
 387
 388 /**
 389  * sprint_symbol - Look up a kernel symbol and return it in a text buffer
 390  * @buffer: buffer to be stored
 391  * @address: address to lookup
 392  *
 393  * This function looks up a kernel symbol with @address and stores its name,
 394  * offset, size and module name to @buffer if possible. If no symbol was found,
 395  * just saves its @address as is.
 396  *
 397  * This function returns the number of bytes stored in @buffer.
 398  */
 399 int sprint_symbol(char *buffer, unsigned long address)
 400 {
 401         return __sprint_symbol(buffer, address, 0, 1);
 402 }
 403 EXPORT_SYMBOL_GPL(sprint_symbol);
 404
 405 /**
 406  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
 407  * @buffer: buffer to be stored
 408  * @address: address to lookup
 409  *
 410  * This function looks up a kernel symbol with @address and stores its name
 411  * and module name to @buffer if possible. If no symbol was found, just saves
 412  * its @address as is.
 413  *
 414  * This function returns the number of bytes stored in @buffer.
 415  */
 416 int sprint_symbol_no_offset(char *buffer, unsigned long address)
 417 {
 418         return __sprint_symbol(buffer, address, 0, 0);
 419 }
 420 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
 421
 422 /**
 423  * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
 424  * @buffer: buffer to be stored
 425  * @address: address to lookup
 426  *
 427  * This function is for stack backtrace and does the same thing as
 428  * sprint_symbol() but with modified/decreased @address. If there is a
 429  * tail-call to the function marked "noreturn", gcc optimized out code after
 430  * the call so that the stack-saved return address could point outside of the
 431  * caller. This function ensures that kallsyms will find the original caller
 432  * by decreasing @address.
 433  *
 434  * This function returns the number of bytes stored in @buffer.
 435  */
 436 int sprint_backtrace(char *buffer, unsigned long address)
 437 {
 438         return __sprint_symbol(buffer, address, -1, 1);
 439 }
 440
 441 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 442 struct kallsym_iter {
 443         loff_t pos;
 444         loff_t pos_arch_end;
 445         loff_t pos_mod_end;
 446         loff_t pos_ftrace_mod_end;
 447         loff_t pos_bpf_end;
 448         unsigned long value;
 449         unsigned int nameoff; /* If iterating in core kernel symbols. */
 450         char type;
 451         char name[KSYM_NAME_LEN];
 452         char module_name[MODULE_NAME_LEN];
 453         int exported;
 454         int show_value;
 455 };
 456
 457 int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
 458                             char *type, char *name)
 459 {
 460         return -EINVAL;
 461 }
 462
 463 static int get_ksymbol_arch(struct kallsym_iter *iter)
 464 {
 465         int ret = arch_get_kallsym(iter->pos - kallsyms_num_syms,
 466                                    &iter->value, &iter->type,
 467                                    iter->name);
 468
 469         if (ret < 0) {
 470                 iter->pos_arch_end = iter->pos;
 471                 return 0;
 472         }
 473
 474         return 1;
 475 }
 476
 477 static int get_ksymbol_mod(struct kallsym_iter *iter)
 478 {
 479         int ret = module_get_kallsym(iter->pos - iter->pos_arch_end,
 480                                      &iter->value, &iter->type,
 481                                      iter->name, iter->module_name,
 482                                      &iter->exported);
 483         if (ret < 0) {
 484                 iter->pos_mod_end = iter->pos;
 485                 return 0;
 486         }
 487
 488         return 1;
 489 }
 490
 491 /*
 492  * ftrace_mod_get_kallsym() may also get symbols for pages allocated for ftrace
 493  * purposes. In that case "__builtin__ftrace" is used as a module name, even
 494  * though "__builtin__ftrace" is not a module.
 495  */
 496 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
 497 {
 498         int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
 499                                          &iter->value, &iter->type,
 500                                          iter->name, iter->module_name,
 501                                          &iter->exported);
 502         if (ret < 0) {
 503                 iter->pos_ftrace_mod_end = iter->pos;
 504                 return 0;
 505         }
 506
 507         return 1;
 508 }
 509
 510 static int get_ksymbol_bpf(struct kallsym_iter *iter)
 511 {
 512         int ret;
 513
 514         strlcpy(iter->module_name, "bpf", MODULE_NAME_LEN);
 515         iter->exported = 0;
 516         ret = bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
 517                               &iter->value, &iter->type,
 518                               iter->name);
 519         if (ret < 0) {
 520                 iter->pos_bpf_end = iter->pos;
 521                 return 0;
 522         }
 523
 524         return 1;
 525 }
 526
 527 /*
 528  * This uses "__builtin__kprobes" as a module name for symbols for pages
 529  * allocated for kprobes' purposes, even though "__builtin__kprobes" is not a
 530  * module.
 531  */
 532 static int get_ksymbol_kprobe(struct kallsym_iter *iter)
 533 {
 534         strlcpy(iter->module_name, "__builtin__kprobes", MODULE_NAME_LEN);
 535         iter->exported = 0;
 536         return kprobe_get_kallsym(iter->pos - iter->pos_bpf_end,
 537                                   &iter->value, &iter->type,
 538                                   iter->name) < 0 ? 0 : 1;
 539 }
 540
 541 /* Returns space to next name. */
 542 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 543 {
 544         unsigned off = iter->nameoff;
 545
 546         iter->module_name[0] = '\0';
 547         iter->value = kallsyms_sym_address(iter->pos);
 548
 549         iter->type = kallsyms_get_symbol_type(off);
 550
 551         off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
 552
 553         return off - iter->nameoff;
 554 }
 555
 556 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 557 {
 558         iter->name[0] = '\0';
 559         iter->nameoff = get_symbol_offset(new_pos);
 560         iter->pos = new_pos;
 561         if (new_pos == 0) {
 562                 iter->pos_arch_end = 0;
 563                 iter->pos_mod_end = 0;
 564                 iter->pos_ftrace_mod_end = 0;
 565                 iter->pos_bpf_end = 0;
 566         }
 567 }
 568
 569 /*
 570  * The end position (last + 1) of each additional kallsyms section is recorded
 571  * in iter->pos_..._end as each section is added, and so can be used to
 572  * determine which get_ksymbol_...() function to call next.
 573  */
 574 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 575 {
 576         iter->pos = pos;
 577
 578         if ((!iter->pos_arch_end || iter->pos_arch_end > pos) &&
 579             get_ksymbol_arch(iter))
 580                 return 1;
 581
 582         if ((!iter->pos_mod_end || iter->pos_mod_end > pos) &&
 583             get_ksymbol_mod(iter))
 584                 return 1;
 585
 586         if ((!iter->pos_ftrace_mod_end || iter->pos_ftrace_mod_end > pos) &&
 587             get_ksymbol_ftrace_mod(iter))
 588                 return 1;
 589
 590         if ((!iter->pos_bpf_end || iter->pos_bpf_end > pos) &&
 591             get_ksymbol_bpf(iter))
 592                 return 1;
 593
 594         return get_ksymbol_kprobe(iter);
 595 }
 596
 597 /* Returns false if pos at or past end of file. */
 598 static int update_iter(struct kallsym_iter *iter, loff_t pos)
 599 {
 600         /* Module symbols can be accessed randomly. */
 601         if (pos >= kallsyms_num_syms)
 602                 return update_iter_mod(iter, pos);
 603
 604         /* If we're not on the desired position, reset to new position. */
 605         if (pos != iter->pos)
 606                 reset_iter(iter, pos);
 607
 608         iter->nameoff += get_ksymbol_core(iter);
 609         iter->pos++;
 610
 611         return 1;
 612 }
 613
 614 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
 615 {
 616         (*pos)++;
 617
 618         if (!update_iter(m->private, *pos))
 619                 return NULL;
 620         return p;
 621 }
 622
 623 static void *s_start(struct seq_file *m, loff_t *pos)
 624 {
 625         if (!update_iter(m->private, *pos))
 626                 return NULL;
 627         return m->private;
 628 }
 629
 630 static void s_stop(struct seq_file *m, void *p)
 631 {
 632 }
 633
 634 static int s_show(struct seq_file *m, void *p)
 635 {
 636         void *value;
 637         struct kallsym_iter *iter = m->private;
 638
 639         /* Some debugging symbols have no name.  Ignore them. */
 640         if (!iter->name[0])
 641                 return 0;
 642
 643         value = iter->show_value ? (void *)iter->value : NULL;
 644
 645         if (iter->module_name[0]) {
 646                 char type;
 647
 648                 /*
 649                  * Label it "global" if it is exported,
 650                  * "local" if not exported.
 651                  */
 652                 type = iter->exported ? toupper(iter->type) :
 653                                         tolower(iter->type);
 654                 seq_printf(m, "%px %c %s\t[%s]\n", value,
 655                            type, iter->name, iter->module_name);
 656         } else
 657                 seq_printf(m, "%px %c %s\n", value,
 658                            iter->type, iter->name);
 659         return 0;
 660 }
 661
 662 static const struct seq_operations kallsyms_op = {
 663         .start = s_start,
 664         .next = s_next,
 665         .stop = s_stop,
 666         .show = s_show
 667 };
 668
 669 static inline int kallsyms_for_perf(void)
 670 {
 671 #ifdef CONFIG_PERF_EVENTS
 672         extern int sysctl_perf_event_paranoid;
 673         if (sysctl_perf_event_paranoid <= 1)
 674                 return 1;
 675 #endif
 676         return 0;
 677 }
 678
 679 /*
 680  * We show kallsyms information even to normal users if we've enabled
 681  * kernel profiling and are explicitly not paranoid (so kptr_restrict
 682  * is clear, and sysctl_perf_event_paranoid isn't set).
 683  *
 684  * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 685  * block even that).
 686  */
 687 bool kallsyms_show_value(const struct cred *cred)
 688 {
 689         switch (kptr_restrict) {
 690         case 0:
 691                 if (kallsyms_for_perf())
 692                         return true;
 693                 fallthrough;
 694         case 1:
 695                 if (security_capable(cred, &init_user_ns, CAP_SYSLOG,
 696                                      CAP_OPT_NOAUDIT) == 0)
 697                         return true;
 698                 fallthrough;
 699         default:
 700                 return false;
 701         }
 702 }
 703
 704 static int kallsyms_open(struct inode *inode, struct file *file)
 705 {
 706         /*
 707          * We keep iterator in m->private, since normal case is to
 708          * s_start from where we left off, so we avoid doing
 709          * using get_symbol_offset for every symbol.
 710          */
 711         struct kallsym_iter *iter;
 712         iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
 713         if (!iter)
 714                 return -ENOMEM;
 715         reset_iter(iter, 0);
 716
 717         /*
 718          * Instead of checking this on every s_show() call, cache
 719          * the result here at open time.
 720          */
 721         iter->show_value = kallsyms_show_value(file->f_cred);
 722         return 0;
 723 }
 724
 725 #ifdef  CONFIG_KGDB_KDB
 726 const char *kdb_walk_kallsyms(loff_t *pos)
 727 {
 728         static struct kallsym_iter kdb_walk_kallsyms_iter;
 729         if (*pos == 0) {
 730                 memset(&kdb_walk_kallsyms_iter, 0,
 731                        sizeof(kdb_walk_kallsyms_iter));
 732                 reset_iter(&kdb_walk_kallsyms_iter, 0);
 733         }
 734         while (1) {
 735                 if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
 736                         return NULL;
 737                 ++*pos;
 738                 /* Some debugging symbols have no name.  Ignore them. */
 739                 if (kdb_walk_kallsyms_iter.name[0])
 740                         return kdb_walk_kallsyms_iter.name;
 741         }
 742 }
 743 #endif  /* CONFIG_KGDB_KDB */
 744
 745 static const struct proc_ops kallsyms_proc_ops = {
 746         .proc_open      = kallsyms_open,
 747         .proc_read      = seq_read,
 748         .proc_lseek     = seq_lseek,
 749         .proc_release   = seq_release_private,
 750 };
 751
 752 static int __init kallsyms_init(void)
 753 {
 754         proc_create("kallsyms", 0444, NULL, &kallsyms_proc_ops);
 755         return 0;
 756 }
 757 device_initcall(kallsyms_init);