kernel/kallsyms.c

   1 /*
   2  * kallsyms.c: in-kernel printing of symbolic oopses and stack traces.
   3  *
   4  * Rewritten and vastly simplified by Rusty Russell for in-kernel
   5  * module loader:
   6  *   Copyright 2002 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
   7  *
   8  * ChangeLog:
   9  *
  10  * (25/Aug/2004) Paulo Marques <pmarques@grupopie.com>
  11  *      Changed the compression method from stem compression to "table lookup"
  12  *      compression (see scripts/kallsyms.c for a more complete description)
  13  */
  14 #include <linux/kallsyms.h>
  15 #include <linux/init.h>
  16 #include <linux/seq_file.h>
  17 #include <linux/fs.h>
  18 #include <linux/kdb.h>
  19 #include <linux/err.h>
  20 #include <linux/proc_fs.h>
  21 #include <linux/sched.h>        /* for cond_resched */
  22 #include <linux/ctype.h>
  23 #include <linux/slab.h>
  24 #include <linux/filter.h>
  25 #include <linux/ftrace.h>
  26 #include <linux/compiler.h>
  27
  28 /*
  29  * These will be re-linked against their real values
  30  * during the second link stage.
  31  */
  32 extern const unsigned long kallsyms_addresses[] __weak;
  33 extern const int kallsyms_offsets[] __weak;
  34 extern const u8 kallsyms_names[] __weak;
  35
  36 /*
  37  * Tell the compiler that the count isn't in the small data section if the arch
  38  * has one (eg: FRV).
  39  */
  40 extern const unsigned long kallsyms_num_syms
  41 __attribute__((weak, section(".rodata")));
  42
  43 extern const unsigned long kallsyms_relative_base
  44 __attribute__((weak, section(".rodata")));
  45
  46 extern const u8 kallsyms_token_table[] __weak;
  47 extern const u16 kallsyms_token_index[] __weak;
  48
  49 extern const unsigned long kallsyms_markers[] __weak;
  50
  51 /*
  52  * Expand a compressed symbol data into the resulting uncompressed string,
  53  * if uncompressed string is too long (>= maxlen), it will be truncated,
  54  * given the offset to where the symbol is in the compressed stream.
  55  */
  56 static unsigned int kallsyms_expand_symbol(unsigned int off,
  57                                            char *result, size_t maxlen)
  58 {
  59         int len, skipped_first = 0;
  60         const u8 *tptr, *data;
  61
  62         /* Get the compressed symbol length from the first symbol byte. */
  63         data = &kallsyms_names[off];
  64         len = *data;
  65         data++;
  66
  67         /*
  68          * Update the offset to return the offset for the next symbol on
  69          * the compressed stream.
  70          */
  71         off += len + 1;
  72
  73         /*
  74          * For every byte on the compressed symbol data, copy the table
  75          * entry for that byte.
  76          */
  77         while (len) {
  78                 tptr = &kallsyms_token_table[kallsyms_token_index[*data]];
  79                 data++;
  80                 len--;
  81
  82                 while (*tptr) {
  83                         if (skipped_first) {
  84                                 if (maxlen <= 1)
  85                                         goto tail;
  86                                 *result = *tptr;
  87                                 result++;
  88                                 maxlen--;
  89                         } else
  90                                 skipped_first = 1;
  91                         tptr++;
  92                 }
  93         }
  94
  95 tail:
  96         if (maxlen)
  97                 *result = '\0';
  98
  99         /* Return to offset to the next symbol. */
 100         return off;
 101 }
 102
 103 /*
 104  * Get symbol type information. This is encoded as a single char at the
 105  * beginning of the symbol name.
 106  */
 107 static char kallsyms_get_symbol_type(unsigned int off)
 108 {
 109         /*
 110          * Get just the first code, look it up in the token table,
 111          * and return the first char from this token.
 112          */
 113         return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]];
 114 }
 115
 116
 117 /*
 118  * Find the offset on the compressed stream given and index in the
 119  * kallsyms array.
 120  */
 121 static unsigned int get_symbol_offset(unsigned long pos)
 122 {
 123         const u8 *name;
 124         int i;
 125
 126         /*
 127          * Use the closest marker we have. We have markers every 256 positions,
 128          * so that should be close enough.
 129          */
 130         name = &kallsyms_names[kallsyms_markers[pos >> 8]];
 131
 132         /*
 133          * Sequentially scan all the symbols up to the point we're searching
 134          * for. Every symbol is stored in a [<len>][<len> bytes of data] format,
 135          * so we just need to add the len to the current pointer for every
 136          * symbol we wish to skip.
 137          */
 138         for (i = 0; i < (pos & 0xFF); i++)
 139                 name = name + (*name) + 1;
 140
 141         return name - kallsyms_names;
 142 }
 143
 144 static unsigned long kallsyms_sym_address(int idx)
 145 {
 146         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 147                 return kallsyms_addresses[idx];
 148
 149         /* values are unsigned offsets if --absolute-percpu is not in effect */
 150         if (!IS_ENABLED(CONFIG_KALLSYMS_ABSOLUTE_PERCPU))
 151                 return kallsyms_relative_base + (u32)kallsyms_offsets[idx];
 152
 153         /* ...otherwise, positive offsets are absolute values */
 154         if (kallsyms_offsets[idx] >= 0)
 155                 return kallsyms_offsets[idx];
 156
 157         /* ...and negative offsets are relative to kallsyms_relative_base - 1 */
 158         return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
 159 }
 160
 161 /* Lookup the address for this symbol. Returns 0 if not found. */
 162 unsigned long kallsyms_lookup_name(const char *name)
 163 {
 164         char namebuf[KSYM_NAME_LEN];
 165         unsigned long i;
 166         unsigned int off;
 167
 168         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 169                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 170
 171                 if (strcmp(namebuf, name) == 0)
 172                         return kallsyms_sym_address(i);
 173         }
 174         return module_kallsyms_lookup_name(name);
 175 }
 176 EXPORT_SYMBOL_GPL(kallsyms_lookup_name);
 177
 178 int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *,
 179                                       unsigned long),
 180                             void *data)
 181 {
 182         char namebuf[KSYM_NAME_LEN];
 183         unsigned long i;
 184         unsigned int off;
 185         int ret;
 186
 187         for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 188                 off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 189                 ret = fn(data, namebuf, NULL, kallsyms_sym_address(i));
 190                 if (ret != 0)
 191                         return ret;
 192         }
 193         return module_kallsyms_on_each_symbol(fn, data);
 194 }
 195 EXPORT_SYMBOL_GPL(kallsyms_on_each_symbol);
 196
 197 static unsigned long get_symbol_pos(unsigned long addr,
 198                                     unsigned long *symbolsize,
 199                                     unsigned long *offset)
 200 {
 201         unsigned long symbol_start = 0, symbol_end = 0;
 202         unsigned long i, low, high, mid;
 203
 204         /* This kernel should never had been booted. */
 205         if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE))
 206                 BUG_ON(!kallsyms_addresses);
 207         else
 208                 BUG_ON(!kallsyms_offsets);
 209
 210         /* Do a binary search on the sorted kallsyms_addresses array. */
 211         low = 0;
 212         high = kallsyms_num_syms;
 213
 214         while (high - low > 1) {
 215                 mid = low + (high - low) / 2;
 216                 if (kallsyms_sym_address(mid) <= addr)
 217                         low = mid;
 218                 else
 219                         high = mid;
 220         }
 221
 222         /*
 223          * Search for the first aliased symbol. Aliased
 224          * symbols are symbols with the same address.
 225          */
 226         while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low))
 227                 --low;
 228
 229         symbol_start = kallsyms_sym_address(low);
 230
 231         /* Search for next non-aliased symbol. */
 232         for (i = low + 1; i < kallsyms_num_syms; i++) {
 233                 if (kallsyms_sym_address(i) > symbol_start) {
 234                         symbol_end = kallsyms_sym_address(i);
 235                         break;
 236                 }
 237         }
 238
 239         /* If we found no next symbol, we use the end of the section. */
 240         if (!symbol_end) {
 241                 if (is_kernel_inittext(addr))
 242                         symbol_end = (unsigned long)_einittext;
 243                 else if (IS_ENABLED(CONFIG_KALLSYMS_ALL))
 244                         symbol_end = (unsigned long)_end;
 245                 else
 246                         symbol_end = (unsigned long)_etext;
 247         }
 248
 249         if (symbolsize)
 250                 *symbolsize = symbol_end - symbol_start;
 251         if (offset)
 252                 *offset = addr - symbol_start;
 253
 254         return low;
 255 }
 256
 257 /*
 258  * Lookup an address but don't bother to find any names.
 259  */
 260 int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
 261                                 unsigned long *offset)
 262 {
 263         char namebuf[KSYM_NAME_LEN];
 264
 265         if (is_ksym_addr(addr))
 266                 return !!get_symbol_pos(addr, symbolsize, offset);
 267         return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
 268                !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
 269 }
 270
 271 /*
 272  * Lookup an address
 273  * - modname is set to NULL if it's in the kernel.
 274  * - We guarantee that the returned name is valid until we reschedule even if.
 275  *   It resides in a module.
 276  * - We also guarantee that modname will be valid until rescheduled.
 277  */
 278 const char *kallsyms_lookup(unsigned long addr,
 279                             unsigned long *symbolsize,
 280                             unsigned long *offset,
 281                             char **modname, char *namebuf)
 282 {
 283         const char *ret;
 284
 285         namebuf[KSYM_NAME_LEN - 1] = 0;
 286         namebuf[0] = 0;
 287
 288         if (is_ksym_addr(addr)) {
 289                 unsigned long pos;
 290
 291                 pos = get_symbol_pos(addr, symbolsize, offset);
 292                 /* Grab name */
 293                 kallsyms_expand_symbol(get_symbol_offset(pos),
 294                                        namebuf, KSYM_NAME_LEN);
 295                 if (modname)
 296                         *modname = NULL;
 297                 return namebuf;
 298         }
 299
 300         /* See if it's in a module or a BPF JITed image. */
 301         ret = module_address_lookup(addr, symbolsize, offset,
 302                                     modname, namebuf);
 303         if (!ret)
 304                 ret = bpf_address_lookup(addr, symbolsize,
 305                                          offset, modname, namebuf);
 306
 307         if (!ret)
 308                 ret = ftrace_mod_address_lookup(addr, symbolsize,
 309                                                 offset, modname, namebuf);
 310         return ret;
 311 }
 312
 313 int lookup_symbol_name(unsigned long addr, char *symname)
 314 {
 315         symname[0] = '\0';
 316         symname[KSYM_NAME_LEN - 1] = '\0';
 317
 318         if (is_ksym_addr(addr)) {
 319                 unsigned long pos;
 320
 321                 pos = get_symbol_pos(addr, NULL, NULL);
 322                 /* Grab name */
 323                 kallsyms_expand_symbol(get_symbol_offset(pos),
 324                                        symname, KSYM_NAME_LEN);
 325                 return 0;
 326         }
 327         /* See if it's in a module. */
 328         return lookup_module_symbol_name(addr, symname);
 329 }
 330
 331 int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
 332                         unsigned long *offset, char *modname, char *name)
 333 {
 334         name[0] = '\0';
 335         name[KSYM_NAME_LEN - 1] = '\0';
 336
 337         if (is_ksym_addr(addr)) {
 338                 unsigned long pos;
 339
 340                 pos = get_symbol_pos(addr, size, offset);
 341                 /* Grab name */
 342                 kallsyms_expand_symbol(get_symbol_offset(pos),
 343                                        name, KSYM_NAME_LEN);
 344                 modname[0] = '\0';
 345                 return 0;
 346         }
 347         /* See if it's in a module. */
 348         return lookup_module_symbol_attrs(addr, size, offset, modname, name);
 349 }
 350
 351 /* Look up a kernel symbol and return it in a text buffer. */
 352 static int __sprint_symbol(char *buffer, unsigned long address,
 353                            int symbol_offset, int add_offset)
 354 {
 355         char *modname;
 356         const char *name;
 357         unsigned long offset, size;
 358         int len;
 359
 360         address += symbol_offset;
 361         name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
 362         if (!name)
 363                 return sprintf(buffer, "0x%lx", address - symbol_offset);
 364
 365         if (name != buffer)
 366                 strcpy(buffer, name);
 367         len = strlen(buffer);
 368         offset -= symbol_offset;
 369
 370         if (add_offset)
 371                 len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
 372
 373         if (modname)
 374                 len += sprintf(buffer + len, " [%s]", modname);
 375
 376         return len;
 377 }
 378
 379 /**
 380  * sprint_symbol - Look up a kernel symbol and return it in a text buffer
 381  * @buffer: buffer to be stored
 382  * @address: address to lookup
 383  *
 384  * This function looks up a kernel symbol with @address and stores its name,
 385  * offset, size and module name to @buffer if possible. If no symbol was found,
 386  * just saves its @address as is.
 387  *
 388  * This function returns the number of bytes stored in @buffer.
 389  */
 390 int sprint_symbol(char *buffer, unsigned long address)
 391 {
 392         return __sprint_symbol(buffer, address, 0, 1);
 393 }
 394 EXPORT_SYMBOL_GPL(sprint_symbol);
 395
 396 /**
 397  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
 398  * @buffer: buffer to be stored
 399  * @address: address to lookup
 400  *
 401  * This function looks up a kernel symbol with @address and stores its name
 402  * and module name to @buffer if possible. If no symbol was found, just saves
 403  * its @address as is.
 404  *
 405  * This function returns the number of bytes stored in @buffer.
 406  */
 407 int sprint_symbol_no_offset(char *buffer, unsigned long address)
 408 {
 409         return __sprint_symbol(buffer, address, 0, 0);
 410 }
 411 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
 412
 413 /**
 414  * sprint_backtrace - Look up a backtrace symbol and return it in a text buffer
 415  * @buffer: buffer to be stored
 416  * @address: address to lookup
 417  *
 418  * This function is for stack backtrace and does the same thing as
 419  * sprint_symbol() but with modified/decreased @address. If there is a
 420  * tail-call to the function marked "noreturn", gcc optimized out code after
 421  * the call so that the stack-saved return address could point outside of the
 422  * caller. This function ensures that kallsyms will find the original caller
 423  * by decreasing @address.
 424  *
 425  * This function returns the number of bytes stored in @buffer.
 426  */
 427 int sprint_backtrace(char *buffer, unsigned long address)
 428 {
 429         return __sprint_symbol(buffer, address, -1, 1);
 430 }
 431
 432 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
 433 struct kallsym_iter {
 434         loff_t pos;
 435         loff_t pos_mod_end;
 436         loff_t pos_ftrace_mod_end;
 437         unsigned long value;
 438         unsigned int nameoff; /* If iterating in core kernel symbols. */
 439         char type;
 440         char name[KSYM_NAME_LEN];
 441         char module_name[MODULE_NAME_LEN];
 442         int exported;
 443         int show_value;
 444 };
 445
 446 static int get_ksymbol_mod(struct kallsym_iter *iter)
 447 {
 448         int ret = module_get_kallsym(iter->pos - kallsyms_num_syms,
 449                                      &iter->value, &iter->type,
 450                                      iter->name, iter->module_name,
 451                                      &iter->exported);
 452         if (ret < 0) {
 453                 iter->pos_mod_end = iter->pos;
 454                 return 0;
 455         }
 456
 457         return 1;
 458 }
 459
 460 static int get_ksymbol_ftrace_mod(struct kallsym_iter *iter)
 461 {
 462         int ret = ftrace_mod_get_kallsym(iter->pos - iter->pos_mod_end,
 463                                          &iter->value, &iter->type,
 464                                          iter->name, iter->module_name,
 465                                          &iter->exported);
 466         if (ret < 0) {
 467                 iter->pos_ftrace_mod_end = iter->pos;
 468                 return 0;
 469         }
 470
 471         return 1;
 472 }
 473
 474 static int get_ksymbol_bpf(struct kallsym_iter *iter)
 475 {
 476         iter->module_name[0] = '\0';
 477         iter->exported = 0;
 478         return bpf_get_kallsym(iter->pos - iter->pos_ftrace_mod_end,
 479                                &iter->value, &iter->type,
 480                                iter->name) < 0 ? 0 : 1;
 481 }
 482
 483 /* Returns space to next name. */
 484 static unsigned long get_ksymbol_core(struct kallsym_iter *iter)
 485 {
 486         unsigned off = iter->nameoff;
 487
 488         iter->module_name[0] = '\0';
 489         iter->value = kallsyms_sym_address(iter->pos);
 490
 491         iter->type = kallsyms_get_symbol_type(off);
 492
 493         off = kallsyms_expand_symbol(off, iter->name, ARRAY_SIZE(iter->name));
 494
 495         return off - iter->nameoff;
 496 }
 497
 498 static void reset_iter(struct kallsym_iter *iter, loff_t new_pos)
 499 {
 500         iter->name[0] = '\0';
 501         iter->nameoff = get_symbol_offset(new_pos);
 502         iter->pos = new_pos;
 503         if (new_pos == 0) {
 504                 iter->pos_mod_end = 0;
 505                 iter->pos_ftrace_mod_end = 0;
 506         }
 507 }
 508
 509 static int update_iter_mod(struct kallsym_iter *iter, loff_t pos)
 510 {
 511         iter->pos = pos;
 512
 513         if (iter->pos_ftrace_mod_end > 0 &&
 514             iter->pos_ftrace_mod_end < iter->pos)
 515                 return get_ksymbol_bpf(iter);
 516
 517         if (iter->pos_mod_end > 0 &&
 518             iter->pos_mod_end < iter->pos) {
 519                 if (!get_ksymbol_ftrace_mod(iter))
 520                         return get_ksymbol_bpf(iter);
 521                 return 1;
 522         }
 523
 524         if (!get_ksymbol_mod(iter)) {
 525                 if (!get_ksymbol_ftrace_mod(iter))
 526                         return get_ksymbol_bpf(iter);
 527         }
 528
 529         return 1;
 530 }
 531
 532 /* Returns false if pos at or past end of file. */
 533 static int update_iter(struct kallsym_iter *iter, loff_t pos)
 534 {
 535         /* Module symbols can be accessed randomly. */
 536         if (pos >= kallsyms_num_syms)
 537                 return update_iter_mod(iter, pos);
 538
 539         /* If we're not on the desired position, reset to new position. */
 540         if (pos != iter->pos)
 541                 reset_iter(iter, pos);
 542
 543         iter->nameoff += get_ksymbol_core(iter);
 544         iter->pos++;
 545
 546         return 1;
 547 }
 548
 549 static void *s_next(struct seq_file *m, void *p, loff_t *pos)
 550 {
 551         (*pos)++;
 552
 553         if (!update_iter(m->private, *pos))
 554                 return NULL;
 555         return p;
 556 }
 557
 558 static void *s_start(struct seq_file *m, loff_t *pos)
 559 {
 560         if (!update_iter(m->private, *pos))
 561                 return NULL;
 562         return m->private;
 563 }
 564
 565 static void s_stop(struct seq_file *m, void *p)
 566 {
 567 }
 568
 569 static int s_show(struct seq_file *m, void *p)
 570 {
 571         void *value;
 572         struct kallsym_iter *iter = m->private;
 573
 574         /* Some debugging symbols have no name.  Ignore them. */
 575         if (!iter->name[0])
 576                 return 0;
 577
 578         value = iter->show_value ? (void *)iter->value : NULL;
 579
 580         if (iter->module_name[0]) {
 581                 char type;
 582
 583                 /*
 584                  * Label it "global" if it is exported,
 585                  * "local" if not exported.
 586                  */
 587                 type = iter->exported ? toupper(iter->type) :
 588                                         tolower(iter->type);
 589                 seq_printf(m, "%px %c %s\t[%s]\n", value,
 590                            type, iter->name, iter->module_name);
 591         } else
 592                 seq_printf(m, "%px %c %s\n", value,
 593                            iter->type, iter->name);
 594         return 0;
 595 }
 596
 597 static const struct seq_operations kallsyms_op = {
 598         .start = s_start,
 599         .next = s_next,
 600         .stop = s_stop,
 601         .show = s_show
 602 };
 603
 604 static inline int kallsyms_for_perf(void)
 605 {
 606 #ifdef CONFIG_PERF_EVENTS
 607         extern int sysctl_perf_event_paranoid;
 608         if (sysctl_perf_event_paranoid <= 1)
 609                 return 1;
 610 #endif
 611         return 0;
 612 }
 613
 614 /*
 615  * We show kallsyms information even to normal users if we've enabled
 616  * kernel profiling and are explicitly not paranoid (so kptr_restrict
 617  * is clear, and sysctl_perf_event_paranoid isn't set).
 618  *
 619  * Otherwise, require CAP_SYSLOG (assuming kptr_restrict isn't set to
 620  * block even that).
 621  */
 622 int kallsyms_show_value(void)
 623 {
 624         switch (kptr_restrict) {
 625         case 0:
 626                 if (kallsyms_for_perf())
 627                         return 1;
 628         /* fallthrough */
 629         case 1:
 630                 if (has_capability_noaudit(current, CAP_SYSLOG))
 631                         return 1;
 632         /* fallthrough */
 633         default:
 634                 return 0;
 635         }
 636 }
 637
 638 static int kallsyms_open(struct inode *inode, struct file *file)
 639 {
 640         /*
 641          * We keep iterator in m->private, since normal case is to
 642          * s_start from where we left off, so we avoid doing
 643          * using get_symbol_offset for every symbol.
 644          */
 645         struct kallsym_iter *iter;
 646         iter = __seq_open_private(file, &kallsyms_op, sizeof(*iter));
 647         if (!iter)
 648                 return -ENOMEM;
 649         reset_iter(iter, 0);
 650
 651         iter->show_value = kallsyms_show_value();
 652         return 0;
 653 }
 654
 655 #ifdef  CONFIG_KGDB_KDB
 656 const char *kdb_walk_kallsyms(loff_t *pos)
 657 {
 658         static struct kallsym_iter kdb_walk_kallsyms_iter;
 659         if (*pos == 0) {
 660                 memset(&kdb_walk_kallsyms_iter, 0,
 661                        sizeof(kdb_walk_kallsyms_iter));
 662                 reset_iter(&kdb_walk_kallsyms_iter, 0);
 663         }
 664         while (1) {
 665                 if (!update_iter(&kdb_walk_kallsyms_iter, *pos))
 666                         return NULL;
 667                 ++*pos;
 668                 /* Some debugging symbols have no name.  Ignore them. */
 669                 if (kdb_walk_kallsyms_iter.name[0])
 670                         return kdb_walk_kallsyms_iter.name;
 671         }
 672 }
 673 #endif  /* CONFIG_KGDB_KDB */
 674
 675 static const struct file_operations kallsyms_operations = {
 676         .open = kallsyms_open,
 677         .read = seq_read,
 678         .llseek = seq_lseek,
 679         .release = seq_release_private,
 680 };
 681
 682 static int __init kallsyms_init(void)
 683 {
 684         proc_create("kallsyms", 0444, NULL, &kallsyms_operations);
 685         return 0;
 686 }
 687 device_initcall(kallsyms_init);