elf/dl-reloc.c

   1 /* Relocate a shared object and resolve its references to other loaded objects.
   2    Copyright (C) 1995-2016 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 "dynamic-link.h"
  29 #include <libc-internal.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 internal_function
  49 _dl_try_allocate_static_tls (struct link_map *map)
  50 {
  51   /* If we've already used the variable with dynamic access, or if the
  52      alignment requirements are too high, fail.  */
  53   if (map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET
  54       || map->l_tls_align > GL(dl_tls_static_align))
  55     {
  56     fail:
  57       return -1;
  58     }
  59
  60 #if TLS_TCB_AT_TP
  61   size_t freebytes = GL(dl_tls_static_size) - GL(dl_tls_static_used);
  62   if (freebytes < TLS_TCB_SIZE)
  63     goto fail;
  64   freebytes -= TLS_TCB_SIZE;
  65
  66   size_t blsize = map->l_tls_blocksize + map->l_tls_firstbyte_offset;
  67   if (freebytes < blsize)
  68     goto fail;
  69
  70   size_t n = (freebytes - blsize) / map->l_tls_align;
  71
  72   size_t offset = GL(dl_tls_static_used) + (freebytes - n * map->l_tls_align
  73                                             - map->l_tls_firstbyte_offset);
  74
  75   map->l_tls_offset = GL(dl_tls_static_used) = offset;
  76 #elif TLS_DTV_AT_TP
  77   /* dl_tls_static_used includes the TCB at the beginning.  */
  78   size_t offset = (ALIGN_UP(GL(dl_tls_static_used)
  79                             - map->l_tls_firstbyte_offset,
  80                             map->l_tls_align)
  81                    + map->l_tls_firstbyte_offset);
  82   size_t used = offset + map->l_tls_blocksize;
  83
  84   if (used > GL(dl_tls_static_size))
  85     goto fail;
  86
  87   map->l_tls_offset = offset;
  88   map->l_tls_firstbyte_offset = GL(dl_tls_static_used);
  89   GL(dl_tls_static_used) = used;
  90 #else
  91 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
  92 #endif
  93
  94   /* If the object is not yet relocated we cannot initialize the
  95      static TLS region.  Delay it.  */
  96   if (map->l_real->l_relocated)
  97     {
  98 #ifdef SHARED
  99       if (__builtin_expect (THREAD_DTV()[0].counter != GL(dl_tls_generation),
 100                             0))
 101         /* Update the slot information data for at least the generation of
 102            the DSO we are allocating data for.  */
 103         (void) _dl_update_slotinfo (map->l_tls_modid);
 104 #endif
 105
 106       GL(dl_init_static_tls) (map);
 107     }
 108   else
 109     map->l_need_tls_init = 1;
 110
 111   return 0;
 112 }
 113
 114 void
 115 internal_function __attribute_noinline__
 116 _dl_allocate_static_tls (struct link_map *map)
 117 {
 118   if (map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET
 119       || _dl_try_allocate_static_tls (map))
 120     {
 121       _dl_signal_error (0, map->l_name, NULL, N_("\
 122 cannot allocate memory in static TLS block"));
 123     }
 124 }
 125
 126 /* Initialize static TLS area and DTV for current (only) thread.
 127    libpthread implementations should provide their own hook
 128    to handle all threads.  */
 129 void
 130 _dl_nothread_init_static_tls (struct link_map *map)
 131 {
 132 #if TLS_TCB_AT_TP
 133   void *dest = (char *) THREAD_SELF - map->l_tls_offset;
 134 #elif TLS_DTV_AT_TP
 135   void *dest = (char *) THREAD_SELF + map->l_tls_offset + TLS_PRE_TCB_SIZE;
 136 #else
 137 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 138 #endif
 139
 140   /* Initialize the memory.  */
 141   memset (__mempcpy (dest, map->l_tls_initimage, map->l_tls_initimage_size),
 142           '\0', map->l_tls_blocksize - map->l_tls_initimage_size);
 143 }
 144
 145
 146 void
 147 _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[],
 148                      int reloc_mode, int consider_profiling)
 149 {
 150   struct textrels
 151   {
 152     caddr_t start;
 153     size_t len;
 154     int prot;
 155     struct textrels *next;
 156   } *textrels = NULL;
 157   /* Initialize it to make the compiler happy.  */
 158   const char *errstring = NULL;
 159   int lazy = reloc_mode & RTLD_LAZY;
 160   int skip_ifunc = reloc_mode & __RTLD_NOIFUNC;
 161
 162 #ifdef SHARED
 163   /* If we are auditing, install the same handlers we need for profiling.  */
 164   if ((reloc_mode & __RTLD_AUDIT) == 0)
 165     consider_profiling |= GLRO(dl_audit) != NULL;
 166 #elif defined PROF
 167   /* Never use dynamic linker profiling for gprof profiling code.  */
 168 # define consider_profiling 0
 169 #endif
 170
 171   if (l->l_relocated)
 172     return;
 173
 174   /* If DT_BIND_NOW is set relocate all references in this object.  We
 175      do not do this if we are profiling, of course.  */
 176   // XXX Correct for auditing?
 177   if (!consider_profiling
 178       && __builtin_expect (l->l_info[DT_BIND_NOW] != NULL, 0))
 179     lazy = 0;
 180
 181   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_RELOC))
 182     _dl_debug_printf ("\nrelocation processing: %s%s\n",
 183                       DSO_FILENAME (l->l_name), lazy ? " (lazy)" : "");
 184
 185   /* DT_TEXTREL is now in level 2 and might phase out at some time.
 186      But we rewrite the DT_FLAGS entry to a DT_TEXTREL entry to make
 187      testing easier and therefore it will be available at all time.  */
 188   if (__glibc_unlikely (l->l_info[DT_TEXTREL] != NULL))
 189     {
 190       /* Bletch.  We must make read-only segments writable
 191          long enough to relocate them.  */
 192       const ElfW(Phdr) *ph;
 193       for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
 194         if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
 195           {
 196             struct textrels *newp;
 197
 198             newp = (struct textrels *) alloca (sizeof (*newp));
 199             newp->len = ALIGN_UP (ph->p_vaddr + ph->p_memsz, GLRO(dl_pagesize))
 200                         - ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
 201             newp->start = PTR_ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize))
 202                           + (caddr_t) l->l_addr;
 203
 204             if (__mprotect (newp->start, newp->len, PROT_READ|PROT_WRITE) < 0)
 205               {
 206                 errstring = N_("cannot make segment writable for relocation");
 207               call_error:
 208                 _dl_signal_error (errno, l->l_name, NULL, errstring);
 209               }
 210
 211 #if (PF_R | PF_W | PF_X) == 7 && (PROT_READ | PROT_WRITE | PROT_EXEC) == 7
 212             newp->prot = (PF_TO_PROT
 213                           >> ((ph->p_flags & (PF_R | PF_W | PF_X)) * 4)) & 0xf;
 214 #else
 215             newp->prot = 0;
 216             if (ph->p_flags & PF_R)
 217               newp->prot |= PROT_READ;
 218             if (ph->p_flags & PF_W)
 219               newp->prot |= PROT_WRITE;
 220             if (ph->p_flags & PF_X)
 221               newp->prot |= PROT_EXEC;
 222 #endif
 223             newp->next = textrels;
 224             textrels = newp;
 225           }
 226     }
 227
 228   {
 229     /* Do the actual relocation of the object's GOT and other data.  */
 230
 231     /* String table object symbols.  */
 232     const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
 233
 234     /* This macro is used as a callback from the ELF_DYNAMIC_RELOCATE code.  */
 235 #define RESOLVE_MAP(ref, version, r_type) \
 236     (ELFW(ST_BIND) ((*ref)->st_info) != STB_LOCAL                             \
 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 internal_function
 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 internal_function __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 }