elf/dl-reloc.c

   1 /* Relocate a shared object and resolve its references to other loaded objects.
   2    Copyright (C) 1995-2022 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 <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 with -1.  If it fits,
  43    we set MAP->l_tls_offset and return 0.
  44    A portion of the surplus static TLS can be optionally used to optimize
  45    dynamic TLS access (with TLSDESC or powerpc TLS optimizations).
  46    If OPTIONAL is true then TLS is allocated for such optimization and
  47    the caller must have a fallback in case the optional portion of surplus
  48    TLS runs out.  If OPTIONAL is false then the entire surplus TLS area is
  49    considered and the allocation only fails if that runs out.  */
  50 int
  51 _dl_try_allocate_static_tls (struct link_map *map, bool optional)
  52 {
  53   /* If we've already used the variable with dynamic access, or if the
  54      alignment requirements are too high, fail.  */
  55   if (map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET
  56       || map->l_tls_align > GLRO (dl_tls_static_align))
  57     {
  58     fail:
  59       return -1;
  60     }
  61
  62 #if TLS_TCB_AT_TP
  63   size_t freebytes = GLRO (dl_tls_static_size) - GL(dl_tls_static_used);
  64   if (freebytes < TLS_TCB_SIZE)
  65     goto fail;
  66   freebytes -= TLS_TCB_SIZE;
  67
  68   size_t blsize = map->l_tls_blocksize + map->l_tls_firstbyte_offset;
  69   if (freebytes < blsize)
  70     goto fail;
  71
  72   size_t n = (freebytes - blsize) / map->l_tls_align;
  73
  74   /* Account optional static TLS surplus usage.  */
  75   size_t use = freebytes - n * map->l_tls_align - map->l_tls_firstbyte_offset;
  76   if (optional && use > GL(dl_tls_static_optional))
  77     goto fail;
  78   else if (optional)
  79     GL(dl_tls_static_optional) -= use;
  80
  81   size_t offset = GL(dl_tls_static_used) + use;
  82
  83   map->l_tls_offset = GL(dl_tls_static_used) = offset;
  84 #elif TLS_DTV_AT_TP
  85   /* dl_tls_static_used includes the TCB at the beginning.  */
  86   size_t offset = (ALIGN_UP(GL(dl_tls_static_used)
  87                             - map->l_tls_firstbyte_offset,
  88                             map->l_tls_align)
  89                    + map->l_tls_firstbyte_offset);
  90   size_t used = offset + map->l_tls_blocksize;
  91
  92   if (used > GLRO (dl_tls_static_size))
  93     goto fail;
  94
  95   /* Account optional static TLS surplus usage.  */
  96   size_t use = used - GL(dl_tls_static_used);
  97   if (optional && use > GL(dl_tls_static_optional))
  98     goto fail;
  99   else if (optional)
 100     GL(dl_tls_static_optional) -= use;
 101
 102   map->l_tls_offset = offset;
 103   map->l_tls_firstbyte_offset = GL(dl_tls_static_used);
 104   GL(dl_tls_static_used) = used;
 105 #else
 106 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 107 #endif
 108
 109   /* If the object is not yet relocated we cannot initialize the
 110      static TLS region.  Delay it.  */
 111   if (map->l_real->l_relocated)
 112     {
 113 #ifdef SHARED
 114       if (__builtin_expect (THREAD_DTV()[0].counter != GL(dl_tls_generation),
 115                             0))
 116         /* Update the slot information data for at least the generation of
 117            the DSO we are allocating data for.  */
 118         (void) _dl_update_slotinfo (map->l_tls_modid);
 119 #endif
 120
 121       dl_init_static_tls (map);
 122     }
 123   else
 124     map->l_need_tls_init = 1;
 125
 126   return 0;
 127 }
 128
 129 /* This function intentionally does not return any value but signals error
 130    directly, as static TLS should be rare and code handling it should
 131    not be inlined as much as possible.  */
 132 void
 133 __attribute_noinline__
 134 _dl_allocate_static_tls (struct link_map *map)
 135 {
 136   if (map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET
 137       || _dl_try_allocate_static_tls (map, false))
 138     {
 139       _dl_signal_error (0, map->l_name, NULL, N_("\
 140 cannot allocate memory in static TLS block"));
 141     }
 142 }
 143
 144 #if !PTHREAD_IN_LIBC
 145 /* Initialize static TLS area and DTV for current (only) thread.
 146    libpthread implementations should provide their own hook
 147    to handle all threads.  */
 148 void
 149 _dl_nothread_init_static_tls (struct link_map *map)
 150 {
 151 #if TLS_TCB_AT_TP
 152   void *dest = (char *) THREAD_SELF - map->l_tls_offset;
 153 #elif TLS_DTV_AT_TP
 154   void *dest = (char *) THREAD_SELF + map->l_tls_offset + TLS_PRE_TCB_SIZE;
 155 #else
 156 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 157 #endif
 158
 159   /* Initialize the memory.  */
 160   memset (__mempcpy (dest, map->l_tls_initimage, map->l_tls_initimage_size),
 161           '\0', map->l_tls_blocksize - map->l_tls_initimage_size);
 162 }
 163 #endif /* !PTHREAD_IN_LIBC */
 164
 165 /* This macro is used as a callback from the ELF_DYNAMIC_RELOCATE code.  */
 166 #define RESOLVE_MAP(l, scope, ref, version, r_type)                           \
 167     ((ELFW(ST_BIND) ((*ref)->st_info) != STB_LOCAL                            \
 168       && __glibc_likely (!dl_symbol_visibility_binds_local_p (*ref)))         \
 169      ? ((__glibc_unlikely ((*ref) == l->l_lookup_cache.sym)                   \
 170          && elf_machine_type_class (r_type) == l->l_lookup_cache.type_class)  \
 171         ? (bump_num_cache_relocations (),                                     \
 172            (*ref) = l->l_lookup_cache.ret,                                    \
 173            l->l_lookup_cache.value)                                           \
 174         : ({ lookup_t _lr;                                                    \
 175              int _tc = elf_machine_type_class (r_type);                       \
 176              l->l_lookup_cache.type_class = _tc;                              \
 177              l->l_lookup_cache.sym = (*ref);                                  \
 178              const struct r_found_version *v = NULL;                          \
 179              if ((version) != NULL && (version)->hash != 0)                   \
 180                v = (version);                                                 \
 181              _lr = _dl_lookup_symbol_x ((const char *) D_PTR (l, l_info[DT_STRTAB]) + (*ref)->st_name, \
 182                                         l, (ref), scope, v, _tc,              \
 183                                         DL_LOOKUP_ADD_DEPENDENCY              \
 184                                         | DL_LOOKUP_FOR_RELOCATE, NULL);      \
 185              l->l_lookup_cache.ret = (*ref);                                  \
 186              l->l_lookup_cache.value = _lr; }))                               \
 187      : l)
 188
 189 #include "dynamic-link.h"
 190
 191 void
 192 _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[],
 193                      int reloc_mode, int consider_profiling)
 194 {
 195   struct textrels
 196   {
 197     caddr_t start;
 198     size_t len;
 199     int prot;
 200     struct textrels *next;
 201   } *textrels = NULL;
 202   /* Initialize it to make the compiler happy.  */
 203   const char *errstring = NULL;
 204   int lazy = reloc_mode & RTLD_LAZY;
 205   int skip_ifunc = reloc_mode & __RTLD_NOIFUNC;
 206
 207 #ifdef SHARED
 208   bool consider_symbind = false;
 209   /* If we are auditing, install the same handlers we need for profiling.  */
 210   if ((reloc_mode & __RTLD_AUDIT) == 0)
 211     {
 212       struct audit_ifaces *afct = GLRO(dl_audit);
 213       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 214         {
 215           /* Profiling is needed only if PLT hooks are provided.  */
 216           if (afct->ARCH_LA_PLTENTER != NULL
 217               || afct->ARCH_LA_PLTEXIT != NULL)
 218             consider_profiling = 1;
 219           if (afct->symbind != NULL)
 220             consider_symbind = true;
 221
 222           afct = afct->next;
 223         }
 224     }
 225 #elif defined PROF
 226   /* Never use dynamic linker profiling for gprof profiling code.  */
 227 # define consider_profiling 0
 228 #else
 229 # define consider_symbind 0
 230 #endif
 231
 232   if (l->l_relocated)
 233     return;
 234
 235   /* If DT_BIND_NOW is set relocate all references in this object.  We
 236      do not do this if we are profiling, of course.  */
 237   // XXX Correct for auditing?
 238   if (!consider_profiling
 239       && __builtin_expect (l->l_info[DT_BIND_NOW] != NULL, 0))
 240     lazy = 0;
 241
 242   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_RELOC))
 243     _dl_debug_printf ("\nrelocation processing: %s%s\n",
 244                       DSO_FILENAME (l->l_name), lazy ? " (lazy)" : "");
 245
 246   /* DT_TEXTREL is now in level 2 and might phase out at some time.
 247      But we rewrite the DT_FLAGS entry to a DT_TEXTREL entry to make
 248      testing easier and therefore it will be available at all time.  */
 249   if (__glibc_unlikely (l->l_info[DT_TEXTREL] != NULL))
 250     {
 251       /* Bletch.  We must make read-only segments writable
 252          long enough to relocate them.  */
 253       const ElfW(Phdr) *ph;
 254       for (ph = l->l_phdr; ph < &l->l_phdr[l->l_phnum]; ++ph)
 255         if (ph->p_type == PT_LOAD && (ph->p_flags & PF_W) == 0)
 256           {
 257             struct textrels *newp;
 258
 259             newp = (struct textrels *) alloca (sizeof (*newp));
 260             newp->len = ALIGN_UP (ph->p_vaddr + ph->p_memsz, GLRO(dl_pagesize))
 261                         - ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize));
 262             newp->start = PTR_ALIGN_DOWN (ph->p_vaddr, GLRO(dl_pagesize))
 263                           + (caddr_t) l->l_addr;
 264
 265             newp->prot = 0;
 266             if (ph->p_flags & PF_R)
 267               newp->prot |= PROT_READ;
 268             if (ph->p_flags & PF_W)
 269               newp->prot |= PROT_WRITE;
 270             if (ph->p_flags & PF_X)
 271               newp->prot |= PROT_EXEC;
 272
 273             if (__mprotect (newp->start, newp->len, newp->prot|PROT_WRITE) < 0)
 274               {
 275                 errstring = N_("cannot make segment writable for relocation");
 276               call_error:
 277                 _dl_signal_error (errno, l->l_name, NULL, errstring);
 278               }
 279
 280             newp->next = textrels;
 281             textrels = newp;
 282           }
 283     }
 284
 285   {
 286     /* Do the actual relocation of the object's GOT and other data.  */
 287
 288     ELF_DYNAMIC_RELOCATE (l, scope, lazy, consider_profiling, skip_ifunc);
 289
 290 #ifndef PROF
 291     if ((consider_profiling || consider_symbind)
 292         && l->l_info[DT_PLTRELSZ] != NULL)
 293       {
 294         /* Allocate the array which will contain the already found
 295            relocations.  If the shared object lacks a PLT (for example
 296            if it only contains lead function) the l_info[DT_PLTRELSZ]
 297            will be NULL.  */
 298         size_t sizeofrel = l->l_info[DT_PLTREL]->d_un.d_val == DT_RELA
 299                            ? sizeof (ElfW(Rela))
 300                            : sizeof (ElfW(Rel));
 301         size_t relcount = l->l_info[DT_PLTRELSZ]->d_un.d_val / sizeofrel;
 302         l->l_reloc_result = calloc (sizeof (l->l_reloc_result[0]), relcount);
 303
 304         if (l->l_reloc_result == NULL)
 305           {
 306             errstring = N_("\
 307 %s: out of memory to store relocation results for %s\n");
 308             _dl_fatal_printf (errstring, RTLD_PROGNAME, l->l_name);
 309           }
 310       }
 311 #endif
 312   }
 313
 314   /* Mark the object so we know this work has been done.  */
 315   l->l_relocated = 1;
 316
 317   /* Undo the segment protection changes.  */
 318   while (__builtin_expect (textrels != NULL, 0))
 319     {
 320       if (__mprotect (textrels->start, textrels->len, textrels->prot) < 0)
 321         {
 322           errstring = N_("cannot restore segment prot after reloc");
 323           goto call_error;
 324         }
 325
 326 #ifdef CLEAR_CACHE
 327       CLEAR_CACHE (textrels->start, textrels->start + textrels->len);
 328 #endif
 329
 330       textrels = textrels->next;
 331     }
 332
 333   /* In case we can protect the data now that the relocations are
 334      done, do it.  */
 335   if (l->l_relro_size != 0)
 336     _dl_protect_relro (l);
 337 }
 338
 339
 340 void
 341 _dl_protect_relro (struct link_map *l)
 342 {
 343   ElfW(Addr) start = ALIGN_DOWN((l->l_addr
 344                                  + l->l_relro_addr),
 345                                 GLRO(dl_pagesize));
 346   ElfW(Addr) end = ALIGN_DOWN((l->l_addr
 347                                + l->l_relro_addr
 348                                + l->l_relro_size),
 349                               GLRO(dl_pagesize));
 350   if (start != end
 351       && __mprotect ((void *) start, end - start, PROT_READ) < 0)
 352     {
 353       static const char errstring[] = N_("\
 354 cannot apply additional memory protection after relocation");
 355       _dl_signal_error (errno, l->l_name, NULL, errstring);
 356     }
 357 }
 358
 359 void
 360 __attribute_noinline__
 361 _dl_reloc_bad_type (struct link_map *map, unsigned int type, int plt)
 362 {
 363 #define DIGIT(b)        _itoa_lower_digits[(b) & 0xf];
 364
 365   /* XXX We cannot translate these messages.  */
 366   static const char msg[2][32
 367 #if __ELF_NATIVE_CLASS == 64
 368                            + 6
 369 #endif
 370   ] = { "unexpected reloc type 0x",
 371         "unexpected PLT reloc type 0x" };
 372   char msgbuf[sizeof (msg[0])];
 373   char *cp;
 374
 375   cp = __stpcpy (msgbuf, msg[plt]);
 376 #if __ELF_NATIVE_CLASS == 64
 377   if (__builtin_expect(type > 0xff, 0))
 378     {
 379       *cp++ = DIGIT (type >> 28);
 380       *cp++ = DIGIT (type >> 24);
 381       *cp++ = DIGIT (type >> 20);
 382       *cp++ = DIGIT (type >> 16);
 383       *cp++ = DIGIT (type >> 12);
 384       *cp++ = DIGIT (type >> 8);
 385     }
 386 #endif
 387   *cp++ = DIGIT (type >> 4);
 388   *cp++ = DIGIT (type);
 389   *cp = '\0';
 390
 391   _dl_signal_error (0, map->l_name, NULL, msgbuf);
 392 }