elf/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996-2017 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    <http://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
  29 #ifndef _DL_PLATFORMS_COUNT
  30 # define _DL_PLATFORMS_COUNT 0
  31 #endif
  32
  33 /* This is the starting address and the size of the mmap()ed file.  */
  34 static struct cache_file *cache;
  35 static struct cache_file_new *cache_new;
  36 static size_t cachesize;
  37
  38 /* 1 if cache_data + PTR points into the cache.  */
  39 #define _dl_cache_verify_ptr(ptr) (ptr < cache_data_size)
  40
  41 #define SEARCH_CACHE(cache) \
  42 /* We use binary search since the table is sorted in the cache file.          \
  43    The first matching entry in the table is returned.                         \
  44    It is important to use the same algorithm as used while generating         \
  45    the cache file.  */                                                        \
  46 do                                                                            \
  47   {                                                                           \
  48     left = 0;                                                                 \
  49     right = cache->nlibs - 1;                                                 \
  50                                                                               \
  51     while (left <= right)                                                     \
  52       {                                                                       \
  53         __typeof__ (cache->libs[0].key) key;                                  \
  54                                                                               \
  55         middle = (left + right) / 2;                                          \
  56                                                                               \
  57         key = cache->libs[middle].key;                                        \
  58                                                                               \
  59         /* Make sure string table indices are not bogus before using          \
  60            them.  */                                                          \
  61         if (! _dl_cache_verify_ptr (key))                                     \
  62           {                                                                   \
  63             cmpres = 1;                                                       \
  64             break;                                                            \
  65           }                                                                   \
  66                                                                               \
  67         /* Actually compare the entry with the key.  */                       \
  68         cmpres = _dl_cache_libcmp (name, cache_data + key);                   \
  69         if (__glibc_unlikely (cmpres == 0))                                   \
  70           {                                                                   \
  71             /* Found it.  LEFT now marks the last entry for which we          \
  72                know the name is correct.  */                                  \
  73             left = middle;                                                    \
  74                                                                               \
  75             /* There might be entries with this name before the one we        \
  76                found.  So we have to find the beginning.  */                  \
  77             while (middle > 0)                                                \
  78               {                                                               \
  79                 __typeof__ (cache->libs[0].key) key;                          \
  80                                                                               \
  81                 key = cache->libs[middle - 1].key;                            \
  82                 /* Make sure string table indices are not bogus before        \
  83                    using them.  */                                            \
  84                 if (! _dl_cache_verify_ptr (key)                              \
  85                     /* Actually compare the entry.  */                        \
  86                     || _dl_cache_libcmp (name, cache_data + key) != 0)        \
  87                   break;                                                      \
  88                 --middle;                                                     \
  89               }                                                               \
  90                                                                               \
  91             do                                                                \
  92               {                                                               \
  93                 int flags;                                                    \
  94                 __typeof__ (cache->libs[0]) *lib = &cache->libs[middle];      \
  95                                                                               \
  96                 /* Only perform the name test if necessary.  */               \
  97                 if (middle > left                                             \
  98                     /* We haven't seen this string so far.  Test whether the  \
  99                        index is ok and whether the name matches.  Otherwise   \
 100                        we are done.  */                                       \
 101                     && (! _dl_cache_verify_ptr (lib->key)                     \
 102                         || (_dl_cache_libcmp (name, cache_data + lib->key)    \
 103                             != 0)))                                           \
 104                   break;                                                      \
 105                                                                               \
 106                 flags = lib->flags;                                           \
 107                 if (_dl_cache_check_flags (flags)                             \
 108                     && _dl_cache_verify_ptr (lib->value))                     \
 109                   {                                                           \
 110                     if (best == NULL || flags == GLRO(dl_correct_cache_id))   \
 111                       {                                                       \
 112                         HWCAP_CHECK;                                          \
 113                         best = cache_data + lib->value;                       \
 114                                                                               \
 115                         if (flags == GLRO(dl_correct_cache_id))               \
 116                           /* We've found an exact match for the shared        \
 117                              object and no general `ELF' release.  Stop       \
 118                              searching.  */                                   \
 119                           break;                                              \
 120                       }                                                       \
 121                   }                                                           \
 122               }                                                               \
 123             while (++middle <= right);                                        \
 124             break;                                                            \
 125         }                                                                     \
 126                                                                               \
 127         if (cmpres < 0)                                                       \
 128           left = middle + 1;                                                  \
 129         else                                                                  \
 130           right = middle - 1;                                                 \
 131       }                                                                       \
 132   }                                                                           \
 133 while (0)
 134
 135
 136 int
 137 _dl_cache_libcmp (const char *p1, const char *p2)
 138 {
 139   while (*p1 != '\0')
 140     {
 141       if (*p1 >= '0' && *p1 <= '9')
 142         {
 143           if (*p2 >= '0' && *p2 <= '9')
 144             {
 145               /* Must compare this numerically.  */
 146               int val1;
 147               int val2;
 148
 149               val1 = *p1++ - '0';
 150               val2 = *p2++ - '0';
 151               while (*p1 >= '0' && *p1 <= '9')
 152                 val1 = val1 * 10 + *p1++ - '0';
 153               while (*p2 >= '0' && *p2 <= '9')
 154                 val2 = val2 * 10 + *p2++ - '0';
 155               if (val1 != val2)
 156                 return val1 - val2;
 157             }
 158           else
 159             return 1;
 160         }
 161       else if (*p2 >= '0' && *p2 <= '9')
 162         return -1;
 163       else if (*p1 != *p2)
 164         return *p1 - *p2;
 165       else
 166         {
 167           ++p1;
 168           ++p2;
 169         }
 170     }
 171   return *p1 - *p2;
 172 }
 173
 174
 175 /* Look up NAME in ld.so.cache and return the file name stored there, or null
 176    if none is found.  The cache is loaded if it was not already.  If loading
 177    the cache previously failed there will be no more attempts to load it.
 178    The caller is responsible for freeing the returned string.  The ld.so.cache
 179    may be unmapped at any time by a completing recursive dlopen and
 180    this function must take care that it does not return references to
 181    any data in the mapping.  */
 182 char *
 183 _dl_load_cache_lookup (const char *name)
 184 {
 185   int left, right, middle;
 186   int cmpres;
 187   const char *cache_data;
 188   uint32_t cache_data_size;
 189   const char *best;
 190
 191   /* Print a message if the loading of libs is traced.  */
 192   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
 193     _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
 194
 195   if (cache == NULL)
 196     {
 197       /* Read the contents of the file.  */
 198       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 199                                                PROT_READ);
 200
 201       /* We can handle three different cache file formats here:
 202          - the old libc5/glibc2.0/2.1 format
 203          - the old format with the new format in it
 204          - only the new format
 205          The following checks if the cache contains any of these formats.  */
 206       if (file != MAP_FAILED && cachesize > sizeof *cache
 207           && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
 208         {
 209           size_t offset;
 210           /* Looks ok.  */
 211           cache = file;
 212
 213           /* Check for new version.  */
 214           offset = ALIGN_CACHE (sizeof (struct cache_file)
 215                                 + cache->nlibs * sizeof (struct file_entry));
 216
 217           cache_new = (struct cache_file_new *) ((void *) cache + offset);
 218           if (cachesize < (offset + sizeof (struct cache_file_new))
 219               || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
 220                          sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
 221             cache_new = (void *) -1;
 222         }
 223       else if (file != MAP_FAILED && cachesize > sizeof *cache_new
 224                && memcmp (file, CACHEMAGIC_VERSION_NEW,
 225                           sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
 226         {
 227           cache_new = file;
 228           cache = file;
 229         }
 230       else
 231         {
 232           if (file != MAP_FAILED)
 233             __munmap (file, cachesize);
 234           cache = (void *) -1;
 235         }
 236
 237       assert (cache != NULL);
 238     }
 239
 240   if (cache == (void *) -1)
 241     /* Previously looked for the cache file and didn't find it.  */
 242     return NULL;
 243
 244   best = NULL;
 245
 246   if (cache_new != (void *) -1)
 247     {
 248       uint64_t platform;
 249
 250       /* This is where the strings start.  */
 251       cache_data = (const char *) cache_new;
 252
 253       /* Now we can compute how large the string table is.  */
 254       cache_data_size = (const char *) cache + cachesize - cache_data;
 255
 256       platform = _dl_string_platform (GLRO(dl_platform));
 257       if (platform != (uint64_t) -1)
 258         platform = 1ULL << platform;
 259
 260       uint64_t hwcap_mask = GET_HWCAP_MASK();
 261
 262 #define _DL_HWCAP_TLS_MASK (1LL << 63)
 263       uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & hwcap_mask)
 264                                  | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
 265
 266       /* Only accept hwcap if it's for the right platform.  */
 267 #define HWCAP_CHECK \
 268       if (lib->hwcap & hwcap_exclude)                                         \
 269         continue;                                                             \
 270       if (GLRO(dl_osversion) && lib->osversion > GLRO(dl_osversion))          \
 271         continue;                                                             \
 272       if (_DL_PLATFORMS_COUNT                                                 \
 273           && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0                           \
 274           && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform)                   \
 275         continue
 276       SEARCH_CACHE (cache_new);
 277     }
 278   else
 279     {
 280       /* This is where the strings start.  */
 281       cache_data = (const char *) &cache->libs[cache->nlibs];
 282
 283       /* Now we can compute how large the string table is.  */
 284       cache_data_size = (const char *) cache + cachesize - cache_data;
 285
 286 #undef HWCAP_CHECK
 287 #define HWCAP_CHECK do {} while (0)
 288       SEARCH_CACHE (cache);
 289     }
 290
 291   /* Print our result if wanted.  */
 292   if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
 293       && best != NULL)
 294     _dl_debug_printf ("  trying file=%s\n", best);
 295
 296   if (best == NULL)
 297     return NULL;
 298
 299   /* The double copy is *required* since malloc may be interposed
 300      and call dlopen itself whose completion would unmap the data
 301      we are accessing. Therefore we must make the copy of the
 302      mapping data without using malloc.  */
 303   char *temp;
 304   temp = alloca (strlen (best) + 1);
 305   strcpy (temp, best);
 306   return __strdup (temp);
 307 }
 308
 309 #ifndef MAP_COPY
 310 /* If the system does not support MAP_COPY we cannot leave the file open
 311    all the time since this would create problems when the file is replaced.
 312    Therefore we provide this function to close the file and open it again
 313    once needed.  */
 314 void
 315 _dl_unload_cache (void)
 316 {
 317   if (cache != NULL && cache != (struct cache_file *) -1)
 318     {
 319       __munmap (cache, cachesize);
 320       cache = NULL;
 321     }
 322 }
 323 #endif