elf/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <unistd.h>
  21 #include <ldsodefs.h>
  22 #include <sys/mman.h>
  23 #include <dl-cache.h>
  24 #include <dl-procinfo.h>
  25 #include <stdint.h>
  26 #include <_itoa.h>
  27 #include <dl-hwcaps.h>
  28 #include <dl-isa-level.h>
  29
  30 #ifndef _DL_PLATFORMS_COUNT
  31 # define _DL_PLATFORMS_COUNT 0
  32 #endif
  33
  34 /* This is the starting address and the size of the mmap()ed file.  */
  35 static struct cache_file *cache;
  36 static struct cache_file_new *cache_new;
  37 static size_t cachesize;
  38
  39 #ifdef SHARED
  40 /* This is used to cache the priorities of glibc-hwcaps
  41    subdirectories.  The elements of _dl_cache_priorities correspond to
  42    the strings in the cache_extension_tag_glibc_hwcaps section.  */
  43 static uint32_t *glibc_hwcaps_priorities;
  44 static uint32_t glibc_hwcaps_priorities_length;
  45 static uint32_t glibc_hwcaps_priorities_allocated;
  46
  47 /* True if the full malloc was used to allocated the array.  */
  48 static bool glibc_hwcaps_priorities_malloced;
  49
  50 /* Deallocate the glibc_hwcaps_priorities array.  */
  51 static void
  52 glibc_hwcaps_priorities_free (void)
  53 {
  54   /* When the minimal malloc is in use, free does not do anything,
  55      so it does not make sense to call it.  */
  56   if (glibc_hwcaps_priorities_malloced)
  57     free (glibc_hwcaps_priorities);
  58   glibc_hwcaps_priorities = NULL;
  59   glibc_hwcaps_priorities_allocated = 0;
  60 }
  61
  62 /* Ordered comparison of a hwcaps string from the cache on the left
  63    (identified by its string table index) and a _dl_hwcaps_priorities
  64    element on the right.  */
  65 static int
  66 glibc_hwcaps_compare (uint32_t left_index, struct dl_hwcaps_priority *right)
  67 {
  68   const char *left_name = (const char *) cache + left_index;
  69   uint32_t left_name_length = strlen (left_name);
  70   uint32_t to_compare;
  71   if (left_name_length < right->name_length)
  72     to_compare = left_name_length;
  73   else
  74     to_compare = right->name_length;
  75   int cmp = memcmp (left_name, right->name, to_compare);
  76   if (cmp != 0)
  77     return cmp;
  78   if (left_name_length < right->name_length)
  79     return -1;
  80   else if (left_name_length > right->name_length)
  81     return 1;
  82   else
  83     return 0;
  84 }
  85
  86 /* Initialize the glibc_hwcaps_priorities array and its length,
  87    glibc_hwcaps_priorities_length.  */
  88 static void
  89 glibc_hwcaps_priorities_init (void)
  90 {
  91   struct cache_extension_all_loaded ext;
  92   if (!cache_extension_load (cache_new, cache, cachesize, &ext))
  93     return;
  94
  95   uint32_t length = (ext.sections[cache_extension_tag_glibc_hwcaps].size
  96                      / sizeof (uint32_t));
  97   if (length > glibc_hwcaps_priorities_allocated)
  98     {
  99       glibc_hwcaps_priorities_free ();
 100
 101       uint32_t *new_allocation = malloc (length * sizeof (uint32_t));
 102       if (new_allocation == NULL)
 103         /* This effectively disables hwcaps on memory allocation
 104            errors.  */
 105         return;
 106
 107       glibc_hwcaps_priorities = new_allocation;
 108       glibc_hwcaps_priorities_allocated = length;
 109       glibc_hwcaps_priorities_malloced = __rtld_malloc_is_complete ();
 110     }
 111
 112   /* Compute the priorities for the subdirectories by merging the
 113      array in the cache with the dl_hwcaps_priorities array.  */
 114   const uint32_t *left = ext.sections[cache_extension_tag_glibc_hwcaps].base;
 115   const uint32_t *left_end = left + length;
 116   struct dl_hwcaps_priority *right = _dl_hwcaps_priorities;
 117   struct dl_hwcaps_priority *right_end = right + _dl_hwcaps_priorities_length;
 118   uint32_t *result = glibc_hwcaps_priorities;
 119
 120   while (left < left_end && right < right_end)
 121     {
 122       if (*left < cachesize)
 123         {
 124           int cmp = glibc_hwcaps_compare (*left, right);
 125           if (cmp == 0)
 126             {
 127               *result = right->priority;
 128               ++result;
 129               ++left;
 130               ++right;
 131             }
 132           else if (cmp < 0)
 133             {
 134               *result = 0;
 135               ++result;
 136               ++left;
 137             }
 138           else
 139             ++right;
 140         }
 141       else
 142         {
 143           *result = 0;
 144           ++result;
 145         }
 146     }
 147   while (left < left_end)
 148     {
 149       *result = 0;
 150       ++result;
 151       ++left;
 152     }
 153
 154   glibc_hwcaps_priorities_length = length;
 155 }
 156
 157 /* Return the priority of the cache_extension_tag_glibc_hwcaps section
 158    entry at INDEX.  Zero means do not use.  Otherwise, lower values
 159    indicate greater preference.  */
 160 static uint32_t
 161 glibc_hwcaps_priority (uint32_t index)
 162 {
 163   /* This does not need to repeated initialization attempts because
 164      this function is only called if there is glibc-hwcaps data in the
 165      cache, so the first call initializes the glibc_hwcaps_priorities
 166      array.  */
 167   if (glibc_hwcaps_priorities_length == 0)
 168     glibc_hwcaps_priorities_init ();
 169
 170   if (index < glibc_hwcaps_priorities_length)
 171     return glibc_hwcaps_priorities[index];
 172   else
 173     return 0;
 174 }
 175 #endif /* SHARED */
 176
 177 /* True if PTR is a valid string table index.  */
 178 static inline bool
 179 _dl_cache_verify_ptr (uint32_t ptr, size_t string_table_size)
 180 {
 181   return ptr < string_table_size;
 182 }
 183
 184 /* Compute the address of the element INDEX of the array at LIBS.
 185    Conceptually, this is &LIBS[INDEX], but use ENTRY_SIZE for the size
 186    of *LIBS.  */
 187 static inline const struct file_entry *
 188 _dl_cache_file_entry (const struct file_entry *libs, size_t entry_size,
 189                       size_t index)
 190 {
 191   return (const void *) libs + index * entry_size;
 192 }
 193
 194 /* We use binary search since the table is sorted in the cache file.
 195    The first matching entry in the table is returned.  It is important
 196    to use the same algorithm as used while generating the cache file.
 197    STRING_TABLE_SIZE indicates the maximum offset in STRING_TABLE at
 198    which data is mapped; it is not exact.  */
 199 static const char *
 200 search_cache (const char *string_table, uint32_t string_table_size,
 201               struct file_entry *libs, uint32_t nlibs, uint32_t entry_size,
 202               const char *name)
 203 {
 204   /* Used by the HWCAP check in the struct file_entry_new case.  */
 205   uint64_t platform = _dl_string_platform (GLRO (dl_platform));
 206   if (platform != (uint64_t) -1)
 207     platform = 1ULL << platform;
 208   uint64_t hwcap_mask = TUNABLE_GET (glibc, cpu, hwcap_mask, uint64_t, NULL);
 209 #define _DL_HWCAP_TLS_MASK (1LL << 63)
 210   uint64_t hwcap_exclude = ~((GLRO (dl_hwcap) & hwcap_mask)
 211                              | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
 212
 213   int left = 0;
 214   int right = nlibs - 1;
 215   const char *best = NULL;
 216 #ifdef SHARED
 217   uint32_t best_priority = 0;
 218 #endif
 219
 220   while (left <= right)
 221     {
 222       int middle = (left + right) / 2;
 223       uint32_t key = _dl_cache_file_entry (libs, entry_size, middle)->key;
 224
 225       /* Make sure string table indices are not bogus before using
 226          them.  */
 227       if (!_dl_cache_verify_ptr (key, string_table_size))
 228         return NULL;
 229
 230       /* Actually compare the entry with the key.  */
 231       int cmpres = _dl_cache_libcmp (name, string_table + key);
 232       if (__glibc_unlikely (cmpres == 0))
 233         {
 234           /* Found it.  LEFT now marks the last entry for which we
 235              know the name is correct.  */
 236           left = middle;
 237
 238           /* There might be entries with this name before the one we
 239              found.  So we have to find the beginning.  */
 240           while (middle > 0)
 241             {
 242               key = _dl_cache_file_entry (libs, entry_size, middle - 1)->key;
 243               /* Make sure string table indices are not bogus before
 244                  using them.  */
 245               if (!_dl_cache_verify_ptr (key, string_table_size)
 246                   /* Actually compare the entry.  */
 247                   || _dl_cache_libcmp (name, string_table + key) != 0)
 248                 break;
 249               --middle;
 250             }
 251
 252           do
 253             {
 254               int flags;
 255               const struct file_entry *lib
 256                 = _dl_cache_file_entry (libs, entry_size, middle);
 257
 258               /* Only perform the name test if necessary.  */
 259               if (middle > left
 260                   /* We haven't seen this string so far.  Test whether the
 261                      index is ok and whether the name matches.  Otherwise
 262                      we are done.  */
 263                   && (! _dl_cache_verify_ptr (lib->key, string_table_size)
 264                       || (_dl_cache_libcmp (name, string_table + lib->key)
 265                           != 0)))
 266                 break;
 267
 268               flags = lib->flags;
 269               if (_dl_cache_check_flags (flags)
 270                   && _dl_cache_verify_ptr (lib->value, string_table_size))
 271                 {
 272                   /* Named/extension hwcaps get slightly different
 273                      treatment: We keep searching for a better
 274                      match.  */
 275                   bool named_hwcap = false;
 276
 277                   if (entry_size >= sizeof (struct file_entry_new))
 278                     {
 279                       /* The entry is large enough to include
 280                          HWCAP data.  Check it.  */
 281                       struct file_entry_new *libnew
 282                         = (struct file_entry_new *) lib;
 283
 284 #ifdef SHARED
 285                       named_hwcap = dl_cache_hwcap_extension (libnew);
 286                       if (named_hwcap
 287                           && !dl_cache_hwcap_isa_level_compatible (libnew))
 288                         continue;
 289 #endif
 290
 291                       /* The entries with named/extension hwcaps have
 292                          been exhausted (they are listed before all
 293                          other entries).  Return the best match
 294                          encountered so far if there is one.  */
 295                       if (!named_hwcap && best != NULL)
 296                         break;
 297
 298                       if ((libnew->hwcap & hwcap_exclude) && !named_hwcap)
 299                         continue;
 300                       if (_DL_PLATFORMS_COUNT
 301                           && (libnew->hwcap & _DL_HWCAP_PLATFORM) != 0
 302                           && ((libnew->hwcap & _DL_HWCAP_PLATFORM)
 303                               != platform))
 304                         continue;
 305
 306 #ifdef SHARED
 307                       /* For named hwcaps, determine the priority and
 308                          see if beats what has been found so far.  */
 309                       if (named_hwcap)
 310                         {
 311                           uint32_t entry_priority
 312                             = glibc_hwcaps_priority (libnew->hwcap);
 313                           if (entry_priority == 0)
 314                             /* Not usable at all.  Skip.  */
 315                             continue;
 316                           else if (best == NULL
 317                                    || entry_priority < best_priority)
 318                             /* This entry is of higher priority
 319                                than the previous one, or it is the
 320                                first entry.  */
 321                             best_priority = entry_priority;
 322                           else
 323                             /* An entry has already been found,
 324                                but it is a better match.  */
 325                             continue;
 326                         }
 327 #endif /* SHARED */
 328                     }
 329
 330                   best = string_table + lib->value;
 331
 332                   if (!named_hwcap && flags == _DL_CACHE_DEFAULT_ID)
 333                     /* With named hwcaps, we need to keep searching to
 334                        see if we find a better match.  A better match
 335                        is also possible if the flags of the current
 336                        entry do not match the expected cache flags.
 337                        But if the flags match, no better entry will be
 338                        found.  */
 339                     break;
 340                 }
 341             }
 342           while (++middle <= right);
 343           break;
 344         }
 345
 346       if (cmpres < 0)
 347         left = middle + 1;
 348       else
 349         right = middle - 1;
 350     }
 351
 352   return best;
 353 }
 354
 355 int
 356 _dl_cache_libcmp (const char *p1, const char *p2)
 357 {
 358   while (*p1 != '\0')
 359     {
 360       if (*p1 >= '0' && *p1 <= '9')
 361         {
 362           if (*p2 >= '0' && *p2 <= '9')
 363             {
 364               /* Must compare this numerically.  */
 365               int val1;
 366               int val2;
 367
 368               val1 = *p1++ - '0';
 369               val2 = *p2++ - '0';
 370               while (*p1 >= '0' && *p1 <= '9')
 371                 val1 = val1 * 10 + *p1++ - '0';
 372               while (*p2 >= '0' && *p2 <= '9')
 373                 val2 = val2 * 10 + *p2++ - '0';
 374               if (val1 != val2)
 375                 return val1 - val2;
 376             }
 377           else
 378             return 1;
 379         }
 380       else if (*p2 >= '0' && *p2 <= '9')
 381         return -1;
 382       else if (*p1 != *p2)
 383         return *p1 - *p2;
 384       else
 385         {
 386           ++p1;
 387           ++p2;
 388         }
 389     }
 390   return *p1 - *p2;
 391 }
 392
 393
 394 /* Look up NAME in ld.so.cache and return the file name stored there, or null
 395    if none is found.  The cache is loaded if it was not already.  If loading
 396    the cache previously failed there will be no more attempts to load it.
 397    The caller is responsible for freeing the returned string.  The ld.so.cache
 398    may be unmapped at any time by a completing recursive dlopen and
 399    this function must take care that it does not return references to
 400    any data in the mapping.  */
 401 char *
 402 _dl_load_cache_lookup (const char *name)
 403 {
 404   /* Print a message if the loading of libs is traced.  */
 405   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
 406     _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
 407
 408   if (cache == NULL)
 409     {
 410       /* Read the contents of the file.  */
 411       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 412                                                PROT_READ);
 413
 414       /* We can handle three different cache file formats here:
 415          - only the new format
 416          - the old libc5/glibc2.0/2.1 format
 417          - the old format with the new format in it
 418          The following checks if the cache contains any of these formats.  */
 419       if (file != MAP_FAILED && cachesize > sizeof *cache_new
 420           && memcmp (file, CACHEMAGIC_VERSION_NEW,
 421                      sizeof CACHEMAGIC_VERSION_NEW - 1) == 0
 422           /* Check for corruption, avoiding overflow.  */
 423           && ((cachesize - sizeof *cache_new) / sizeof (struct file_entry_new)
 424               >= ((struct cache_file_new *) file)->nlibs))
 425         {
 426           if (! cache_file_new_matches_endian (file))
 427             {
 428               __munmap (file, cachesize);
 429               file = (void *) -1;
 430             }
 431           cache_new = file;
 432           cache = file;
 433         }
 434       else if (file != MAP_FAILED && cachesize > sizeof *cache
 435                && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0
 436                /* Check for corruption, avoiding overflow.  */
 437                && ((cachesize - sizeof *cache) / sizeof (struct file_entry)
 438                    >= ((struct cache_file *) file)->nlibs))
 439         {
 440           size_t offset;
 441           /* Looks ok.  */
 442           cache = file;
 443
 444           /* Check for new version.  */
 445           offset = ALIGN_CACHE (sizeof (struct cache_file)
 446                                 + cache->nlibs * sizeof (struct file_entry));
 447
 448           cache_new = (struct cache_file_new *) ((void *) cache + offset);
 449           if (cachesize < (offset + sizeof (struct cache_file_new))
 450               || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
 451                          sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
 452               cache_new = (void *) -1;
 453           else
 454             {
 455               if (! cache_file_new_matches_endian (cache_new))
 456                 {
 457                   /* The old-format part of the cache is bogus as well
 458                      if the endianness does not match.  (But it is
 459                      unclear how the new header can be located if the
 460                      endianess does not match.)  */
 461                   cache = (void *) -1;
 462                   cache_new = (void *) -1;
 463                   __munmap (file, cachesize);
 464                 }
 465             }
 466         }
 467       else
 468         {
 469           if (file != MAP_FAILED)
 470             __munmap (file, cachesize);
 471           cache = (void *) -1;
 472         }
 473
 474       assert (cache != NULL);
 475     }
 476
 477   if (cache == (void *) -1)
 478     /* Previously looked for the cache file and didn't find it.  */
 479     return NULL;
 480
 481   const char *best;
 482   if (cache_new != (void *) -1)
 483     {
 484       const char *string_table = (const char *) cache_new;
 485       best = search_cache (string_table, cachesize,
 486                            &cache_new->libs[0].entry, cache_new->nlibs,
 487                            sizeof (cache_new->libs[0]), name);
 488     }
 489   else
 490     {
 491       const char *string_table = (const char *) &cache->libs[cache->nlibs];
 492       uint32_t string_table_size
 493         = (const char *) cache + cachesize - string_table;
 494       best = search_cache (string_table, string_table_size,
 495                            &cache->libs[0], cache->nlibs,
 496                            sizeof (cache->libs[0]), name);
 497     }
 498
 499   /* Print our result if wanted.  */
 500   if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
 501       && best != NULL)
 502     _dl_debug_printf ("  trying file=%s\n", best);
 503
 504   if (best == NULL)
 505     return NULL;
 506
 507   /* The double copy is *required* since malloc may be interposed
 508      and call dlopen itself whose completion would unmap the data
 509      we are accessing. Therefore we must make the copy of the
 510      mapping data without using malloc.  */
 511   char *temp;
 512   size_t best_len = strlen (best) + 1;
 513   temp = alloca (best_len);
 514   memcpy (temp, best, best_len);
 515   return __strdup (temp);
 516 }
 517
 518 #ifndef MAP_COPY
 519 /* If the system does not support MAP_COPY we cannot leave the file open
 520    all the time since this would create problems when the file is replaced.
 521    Therefore we provide this function to close the file and open it again
 522    once needed.  */
 523 void
 524 _dl_unload_cache (void)
 525 {
 526   if (cache != NULL && cache != (struct cache_file *) -1)
 527     {
 528       __munmap (cache, cachesize);
 529       cache = NULL;
 530     }
 531 #ifdef SHARED
 532   /* This marks the glibc_hwcaps_priorities array as out-of-date.  */
 533   glibc_hwcaps_priorities_length = 0;
 534 #endif
 535 }
 536 #endif