elf/dl-reloc.c

   1 /* Relocate a shared object and resolve its references to other loaded objects.
   2    Copyright (C) 1995-2018 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 <errno.h>
  20 #include <libintl.h>
  21 #include <stdlib.h>
  22 #include <unistd.h>
  23 #include <ldsodefs.h>
  24 #include <sys/mman.h>
  25 #include <sys/param.h>
  26 #include <sys/types.h>
  27 #include <_itoa.h>
  28 #include <libc-pointer-arith.h>
  29 #include "dynamic-link.h"
  30
  31 /* Statistics function.  */
  32 #ifdef SHARED
  33 # define bump_num_cache_relocations() ++GL(dl_num_cache_relocations)
  34 #else
  35 # define bump_num_cache_relocations() ((void) 0)
  36 #endif
  37
  38
  39 /* We are trying to perform a static TLS relocation in MAP, but it was
  40    dynamically loaded.  This can only work if there is enough surplus in
  41    the static TLS area already allocated for each running thread.  If this
  42    object's TLS segment is too big to fit, we fail.  If it fits,
  43    we set MAP->l_tls_offset and return.
  44    This function intentionally does not return any value but signals error
  45    directly, as static TLS should be rare and code handling it should
  46    not be inlined as much as possible.  */
  47 int
  48 _dl_try_allocate_static_tls (struct link_map *map)
  49 {
  50   /* If we've already used the variable with dynamic access, or if the
  51      alignment requirements are too high, fail.  */
  52   if (map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET
  53       || map->l_tls_align > GL(dl_tls_static_align))
  54     {
  55     fail:
  56       return -1;
  57     }
  58
  59 #if TLS_TCB_AT_TP
  60   size_t freebytes = GL(dl_tls_static_size) - GL(dl_tls_static_used);
  61   if (freebytes < TLS_TCB_SIZE)
  62     goto fail;
  63   freebytes -= TLS_TCB_SIZE;
  64
  65   size_t blsize = map->l_tls_blocksize + map->l_tls_firstbyte_offset;
  66   if (freebytes < blsize)
  67     goto fail;
  68
  69   size_t n = (freebytes - blsize) / map->l_tls_align;
  70
  71   size_t offset = GL(dl_tls_static_used) + (freebytes - n * map->l_tls_align
  72                                             - map->l_tls_firstbyte_offset);
  73
  74   map->l_tls_offset = GL(dl_tls_static_used) = offset;
  75 #elif TLS_DTV_AT_TP
  76   /* dl_tls_static_used includes the TCB at the beginning.  */
  77   size_t offset = (ALIGN_UP(GL(dl_tls_static_used)
  78                             - map->l_tls_firstbyte_offset,
  79                             map->l_tls_align)
  80                    + map->l_tls_firstbyte_offset);
  81   size_t used = offset + map->l_tls_blocksize;
  82
  83   if (used > GL(dl_tls_static_size))
  84     goto fail;
  85
  86   map->l_tls_offset = offset;
  87   map->l_tls_firstbyte_offset = GL(dl_tls_static_used);
  88   GL(dl_tls_static_used) = used;
  89 #else
  90 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
  91 #endif
  92
  93   /* If the object is not yet relocated we cannot initialize the
  94      static TLS region.  Delay it.  */
  95   if (map->l_real->l_relocated)
  96     {
  97 #ifdef SHARED
  98       if (__builtin_expect (THREAD_DTV()[0].counter != GL(dl_tls_generation),
  99                             0))
 100         /* Update the slot information data for at least the generation of
 101            the DSO we are allocating data for.  */
 102         (void) _dl_update_slotinfo (map->l_tls_modid);
 103 #endif
 104
 105       GL(dl_init_static_tls) (map);
 106     }
 107   else
 108     map->l_need_tls_init = 1;
 109
 110   return 0;
 111 }
 112
 113 void
 114 __attribute_noinline__
 115 _dl_allocate_static_tls (struct link_map *map)
 116 {
 117   if (map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET
 118       || _dl_try_allocate_static_tls (map))
 119     {
 120       _dl_signal_error (0, map->l_name, NULL, N_("\
 121 cannot allocate memory in static TLS block"));
 122     }
 123 }
 124
 125 /* Initialize static TLS area and DTV for current (only) thread.
 126    libpthread implementations should provide their own hook
 127    to handle all threads.  */
 128 void
 129 _dl_nothread_init_static_tls (struct link_map *map)
 130 {
 131 #if TLS_TCB_AT_TP
 132   void *dest = (char *) THREAD_SELF - map->l_tls_offset;
 133 #elif TLS_DTV_AT_TP
 134   void *dest = (char *) THREAD_SELF + map->l_tls_offset + TLS_PRE_TCB_SIZE;
 135 #else
 136 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 137 #endif
 138
 139   /* Initialize the memory.  */
 140   memset (__mempcpy (dest, map->l_tls_initimage, map->l_tls_initimage_size),
 141           '\0', map->l_tls_blocksize - map->l_tls_initimage_size);
 142 }
 143
 144
 145 void
 146 _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[],
 147                      int reloc_mode, int consider_profiling)
 148 {
 149   struct textrels
 150   {
 151     caddr_t start;
 152     size_t len;
 153     int prot;
 154     struct textrels *next;
 155   } *textrels = NULL;
 156   /* Initialize it to make the compiler happy.  */
 157   const char *errstring = NULL;
 158   int lazy = reloc_mode & RTLD_LAZY;
 159   int skip_ifunc = reloc_mode & __RTLD_NOIFUNC;
 160
 161 #ifdef SHARED
 162   /* If we are auditing, install the same handlers we need for profiling.  */
 163   if ((reloc_mode & __RTLD_AUDIT) == 0)
 164     consider_profiling |= GLRO(dl_audit) != NULL;
 165 #elif defined PROF
 166   /* Never use dynamic linker profiling for gprof profiling code.  */
 167 # define consider_profiling 0
 168 #endif
 169
 170   if (l->l_relocated)
 171     return;
 172
 173   /* If DT_BIND_NOW is set relocate all references in this object.  We
 174      do not do this if we are profiling, of course.  */
 175   // XXX Correct for auditing?
 176   if (!consider_profiling
 177       && __builtin_expect (l->l_info[DT_BIND_NOW] != NULL, 0))
 178     lazy = 0;
 179
 180   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_RELOC))
 181     _dl_debug_printf ("\nrelocation processing: %s%s\n",
 182                       DSO_FILENAME (l->l_name), lazy ? " (lazy)" : "");
 183
 184   /* DT_TEXTREL is now in level 2 and might phase out at some time.
 185      But we rewrite the DT_FLAGS entry to a DT_TEXTREL entry to make
 186      testing easier and therefore it will be available at all time.  */
 187   if (__glibc_unlikely (l->l_info[DT_TEXTREL] != NULL))
 188     {
 189       /* Bletch.  We must make read-only segments writable
 190          long enough to relocate them.  */
 191       const ElfW(Phdr) *ph;
 192       for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
 193         if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
 194           {
 195             struct textrels *newp;
 196
 197             newp = (struct textrels *) alloca (sizeof (*newp));
 198             newp->len = ALIGN_UP (ph->p_vaddr + ph->p_memsz, GLRO(dl_pagesize))
 199                         - ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
 200             newp->start = PTR_ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize))
 201                           + (caddr_t) l->l_addr;
 202
 203             if (__mprotect (newp->start, newp->len, PROT_READ|PROT_WRITE) < 0)
 204               {
 205                 errstring = N_("cannot make segment writable for relocation");
 206               call_error:
 207                 _dl_signal_error (errno, l->l_name, NULL, errstring);
 208               }
 209
 210 #if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7
 211             newp->prot = (PF_TO_PROT
 212                           >> ((ph->p_flags & (PF_R | PF_W | PF_X)) * 4)) & 0xf;
 213 #else
 214             newp->prot = 0;
 215             if (ph->p_flags & PF_R)
 216               newp->prot |= PROT_READ;
 217             if (ph->p_flags & PF_W)
 218               newp->prot |= PROT_WRITE;
 219             if (ph->p_flags & PF_X)
 220               newp->prot |= PROT_EXEC;
 221 #endif
 222             newp->next = textrels;
 223             textrels = newp;
 224           }
 225     }
 226
 227   {
 228     /* Do the actual relocation of the object's GOT and other data.  */
 229
 230     /* String table object symbols.  */
 231     const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 232
 233     /* This macro is used as a callback from the ELF_DYNAMIC_RELOCATE code.  */
 234 #define RESOLVE_MAP(ref, version, r_type) \
 235     ((ELFW(ST_BIND) ((*ref)->st_info) != STB_LOCAL                            \
 236       && __glibc_likely (!dl_symbol_visibility_binds_local_p (*ref)))         \
 237      ? ((__builtin_expect ((*ref) == l->l_lookup_cache.sym, 0)                \
 238          && elf_machine_type_class (r_type) == l->l_lookup_cache.type_class)  \
 239         ? (bump_num_cache_relocations (),                                     \
 240            (*ref) = l->l_lookup_cache.ret,                                    \
 241            l->l_lookup_cache.value)                                           \
 242         : ({ lookup_t _lr;                                                    \
 243              int _tc = elf_machine_type_class (r_type);                       \
 244              l->l_lookup_cache.type_class = _tc;                              \
 245              l->l_lookup_cache.sym = (*ref);                                  \
 246              const struct r_found_version *v = NULL;                          \
 247              if ((version) != NULL && (version)->hash != 0)                   \
 248                v = (version);                                                 \
 249              _lr = _dl_lookup_symbol_x (strtab + (*ref)->st_name, l, (ref),   \
 250                                         scope, v, _tc,                        \
 251                                         DL_LOOKUP_ADD_DEPENDENCY, NULL);      \
 252              l->l_lookup_cache.ret = (*ref);                                  \
 253              l->l_lookup_cache.value = _lr; }))                               \
 254      : l)
 255
 256 #include "dynamic-link.h"
 257
 258     ELF_DYNAMIC_RELOCATE (l, lazy, consider_profiling, skip_ifunc);
 259
 260 #ifndef PROF
 261     if (__glibc_unlikely (consider_profiling)
 262         && l->l_info[DT_PLTRELSZ] != NULL)
 263       {
 264         /* Allocate the array which will contain the already found
 265            relocations.  If the shared object lacks a PLT (for example
 266            if it only contains lead function) the l_info[DT_PLTRELSZ]
 267            will be NULL.  */
 268         size_t sizeofrel = l->l_info[DT_PLTREL]->d_un.d_val == DT_RELA
 269                            ? sizeof (ElfW(Rela))
 270                            : sizeof (ElfW(Rel));
 271         size_t relcount = l->l_info[DT_PLTRELSZ]->d_un.d_val / sizeofrel;
 272         l->l_reloc_result = calloc (sizeof (l->l_reloc_result[0]), relcount);
 273
 274         if (l->l_reloc_result == NULL)
 275           {
 276             errstring = N_("\
 277 %s: out of memory to store relocation results for %s\n");
 278             _dl_fatal_printf (errstring, RTLD_PROGNAME, l->l_name);
 279           }
 280       }
 281 #endif
 282   }
 283
 284   /* Mark the object so we know this work has been done.  */
 285   l->l_relocated = 1;
 286
 287   /* Undo the segment protection changes.  */
 288   while (__builtin_expect (textrels != NULL, 0))
 289     {
 290       if (__mprotect (textrels->start, textrels->len, textrels->prot) < 0)
 291         {
 292           errstring = N_("cannot restore segment prot after reloc");
 293           goto call_error;
 294         }
 295
 296 #ifdef CLEAR_CACHE
 297       CLEAR_CACHE (textrels->start, textrels->start + textrels->len);
 298 #endif
 299
 300       textrels = textrels->next;
 301     }
 302
 303   /* In case we can protect the data now that the relocations are
 304      done, do it.  */
 305   if (l->l_relro_size != 0)
 306     _dl_protect_relro (l);
 307 }
 308
 309
 310 void
 311 _dl_protect_relro (struct link_map *l)
 312 {
 313   ElfW(Addr) start = ALIGN_DOWN((l->l_addr
 314                                  + l->l_relro_addr),
 315                                 GLRO(dl_pagesize));
 316   ElfW(Addr) end = ALIGN_DOWN((l->l_addr
 317                                + l->l_relro_addr
 318                                + l->l_relro_size),
 319                               GLRO(dl_pagesize));
 320   if (start != end
 321       && __mprotect ((void *) start, end - start, PROT_READ) < 0)
 322     {
 323       static const char errstring[] = N_("\
 324 cannot apply additional memory protection after relocation");
 325       _dl_signal_error (errno, l->l_name, NULL, errstring);
 326     }
 327 }
 328
 329 void
 330 __attribute_noinline__
 331 _dl_reloc_bad_type (struct link_map *map, unsigned int type, int plt)
 332 {
 333 #define DIGIT(b)        _itoa_lower_digits[(b) & 0xf];
 334
 335   /* XXX We cannot translate these messages.  */
 336   static const char msg[2][32
 337 #if __ELF_NATIVE_CLASS == 64
 338                            + 6
 339 #endif
 340   ] = { "unexpected reloc type 0x",
 341         "unexpected PLT reloc type 0x" };
 342   char msgbuf[sizeof (msg[0])];
 343   char *cp;
 344
 345   cp = __stpcpy (msgbuf, msg[plt]);
 346 #if __ELF_NATIVE_CLASS == 64
 347   if (__builtin_expect(type > 0xff, 0))
 348     {
 349       *cp++ = DIGIT (type >> 28);
 350       *cp++ = DIGIT (type >> 24);
 351       *cp++ = DIGIT (type >> 20);
 352       *cp++ = DIGIT (type >> 16);
 353       *cp++ = DIGIT (type >> 12);
 354       *cp++ = DIGIT (type >> 8);
 355     }
 356 #endif
 357   *cp++ = DIGIT (type >> 4);
 358   *cp++ = DIGIT (type);
 359   *cp = '\0';
 360
 361   _dl_signal_error (0, map->l_name, NULL, msgbuf);
 362 }