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