elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2009, 2010, 2011 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 #define IN_DL_RUNTIME 1         /* This can be tested in dl-machine.h.  */
  20
  21 #include <alloca.h>
  22 #include <stdlib.h>
  23 #include <unistd.h>
  24 #include <sys/param.h>
  25 #include <ldsodefs.h>
  26 #include <sysdep-cancel.h>
  27 #include "dynamic-link.h"
  28 #include <tls.h>
  29 #include <dl-irel.h>
  30
  31
  32 #if (!defined ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
  33     || ELF_MACHINE_NO_REL
  34 # define PLTREL  ElfW(Rela)
  35 #else
  36 # define PLTREL  ElfW(Rel)
  37 #endif
  38
  39 #ifndef VERSYMIDX
  40 # define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym))
  41 #endif
  42
  43 /* The fixup functions might have need special attributes.  If none
  44    are provided define the macro as empty.  */
  45 #ifndef ARCH_FIXUP_ATTRIBUTE
  46 # define ARCH_FIXUP_ATTRIBUTE
  47 #endif
  48
  49 #ifndef reloc_offset
  50 # define reloc_offset reloc_arg
  51 # define reloc_index  reloc_arg / sizeof (PLTREL)
  52 #endif
  53
  54
  55
  56 /* This function is called through a special trampoline from the PLT the
  57    first time each PLT entry is called.  We must perform the relocation
  58    specified in the PLT of the given shared object, and return the resolved
  59    function address to the trampoline, which will restart the original call
  60    to that address.  Future calls will bounce directly from the PLT to the
  61    function.  */
  62
  63 #ifndef ELF_MACHINE_NO_PLT
  64 DL_FIXUP_VALUE_TYPE
  65 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
  66 _dl_fixup (
  67 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  68            ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  69 # endif
  70            /* GKM FIXME: Fix trampoline to pass bounds so we can do
  71               without the `__unbounded' qualifier.  */
  72            struct link_map *__unbounded l, ElfW(Word) reloc_arg)
  73 {
  74   const ElfW(Sym) *const symtab
  75     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  76   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  77
  78   const PLTREL *const reloc
  79     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  80   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  81   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  82   lookup_t result;
  83   DL_FIXUP_VALUE_TYPE value;
  84
  85   /* Sanity check that we're really looking at a PLT relocation.  */
  86   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  87
  88    /* Look up the target symbol.  If the normal lookup rules are not
  89       used don't look in the global scope.  */
  90   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  91     {
  92       const struct r_found_version *version = NULL;
  93
  94       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  95         {
  96           const ElfW(Half) *vernum =
  97             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  98           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  99           version = &l->l_versions[ndx];
 100           if (version->hash == 0)
 101             version = NULL;
 102         }
 103
 104       /* We need to keep the scope around so do some locking.  This is
 105          not necessary for objects which cannot be unloaded or when
 106          we are not using any threads (yet).  */
 107       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 108       if (!RTLD_SINGLE_THREAD_P)
 109         {
 110           THREAD_GSCOPE_SET_FLAG ();
 111           flags |= DL_LOOKUP_GSCOPE_LOCK;
 112         }
 113
 114 #ifdef RTLD_ENABLE_FOREIGN_CALL
 115       RTLD_ENABLE_FOREIGN_CALL;
 116 #endif
 117
 118       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 119                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 120
 121       /* We are done with the global scope.  */
 122       if (!RTLD_SINGLE_THREAD_P)
 123         THREAD_GSCOPE_RESET_FLAG ();
 124
 125 #ifdef RTLD_FINALIZE_FOREIGN_CALL
 126       RTLD_FINALIZE_FOREIGN_CALL;
 127 #endif
 128
 129       /* Currently result contains the base load address (or link map)
 130          of the object that defines sym.  Now add in the symbol
 131          offset.  */
 132       value = DL_FIXUP_MAKE_VALUE (result,
 133                                    sym ? (LOOKUP_VALUE_ADDRESS (result)
 134                                           + sym->st_value) : 0);
 135     }
 136   else
 137     {
 138       /* We already found the symbol.  The module (and therefore its load
 139          address) is also known.  */
 140       value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + sym->st_value);
 141       result = l;
 142     }
 143
 144   /* And now perhaps the relocation addend.  */
 145   value = elf_machine_plt_value (l, reloc, value);
 146
 147   if (sym != NULL
 148       && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 149     value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 150
 151   /* Finally, fix up the plt itself.  */
 152   if (__builtin_expect (GLRO(dl_bind_not), 0))
 153     return value;
 154
 155   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 156 }
 157 #endif
 158
 159 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 160 DL_FIXUP_VALUE_TYPE
 161 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 162 _dl_profile_fixup (
 163 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 164                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 165 #endif
 166                    struct link_map *l, ElfW(Word) reloc_arg,
 167                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 168 {
 169   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 170
 171   /* This is the address in the array where we store the result of previous
 172      relocations.  */
 173   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 174   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 175
 176   DL_FIXUP_VALUE_TYPE value = *resultp;
 177   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 178     {
 179       /* This is the first time we have to relocate this object.  */
 180       const ElfW(Sym) *const symtab
 181         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 182       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 183
 184       const PLTREL *const reloc
 185         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 186       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 187       const ElfW(Sym) *defsym = refsym;
 188       lookup_t result;
 189
 190       /* Sanity check that we're really looking at a PLT relocation.  */
 191       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 192
 193       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 194          don't look in the global scope.  */
 195       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 196         {
 197           const struct r_found_version *version = NULL;
 198
 199           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 200             {
 201               const ElfW(Half) *vernum =
 202                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 203               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 204               version = &l->l_versions[ndx];
 205               if (version->hash == 0)
 206                 version = NULL;
 207             }
 208
 209           /* We need to keep the scope around so do some locking.  This is
 210              not necessary for objects which cannot be unloaded or when
 211              we are not using any threads (yet).  */
 212           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 213           if (!RTLD_SINGLE_THREAD_P)
 214             {
 215               THREAD_GSCOPE_SET_FLAG ();
 216               flags |= DL_LOOKUP_GSCOPE_LOCK;
 217             }
 218
 219           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 220                                         &defsym, l->l_scope, version,
 221                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 222
 223           /* We are done with the global scope.  */
 224           if (!RTLD_SINGLE_THREAD_P)
 225             THREAD_GSCOPE_RESET_FLAG ();
 226
 227           /* Currently result contains the base load address (or link map)
 228              of the object that defines sym.  Now add in the symbol
 229              offset.  */
 230           value = DL_FIXUP_MAKE_VALUE (result,
 231                                        defsym != NULL
 232                                        ? LOOKUP_VALUE_ADDRESS (result)
 233                                          + defsym->st_value : 0);
 234
 235           if (defsym != NULL
 236               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 237                                    == STT_GNU_IFUNC, 0))
 238             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 239         }
 240       else
 241         {
 242           /* We already found the symbol.  The module (and therefore its load
 243              address) is also known.  */
 244           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 245
 246           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 247                                 == STT_GNU_IFUNC, 0))
 248             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 249
 250           result = l;
 251         }
 252       /* And now perhaps the relocation addend.  */
 253       value = elf_machine_plt_value (l, reloc, value);
 254
 255 #ifdef SHARED
 256       /* Auditing checkpoint: we have a new binding.  Provide the
 257          auditing libraries the possibility to change the value and
 258          tell us whether further auditing is wanted.  */
 259       if (defsym != NULL && GLRO(dl_naudit) > 0)
 260         {
 261           reloc_result->bound = result;
 262           /* Compute index of the symbol entry in the symbol table of
 263              the DSO with the definition.  */
 264           reloc_result->boundndx = (defsym
 265                                     - (ElfW(Sym) *) D_PTR (result,
 266                                                            l_info[DT_SYMTAB]));
 267
 268           /* Determine whether any of the two participating DSOs is
 269              interested in auditing.  */
 270           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 271             {
 272               unsigned int flags = 0;
 273               struct audit_ifaces *afct = GLRO(dl_audit);
 274               /* Synthesize a symbol record where the st_value field is
 275                  the result.  */
 276               ElfW(Sym) sym = *defsym;
 277               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 278
 279               /* Keep track whether there is any interest in tracing
 280                  the call in the lower two bits.  */
 281               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 282               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 283               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 284
 285               const char *strtab2 = (const void *) D_PTR (result,
 286                                                           l_info[DT_STRTAB]);
 287
 288               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 289                 {
 290                   /* XXX Check whether both DSOs must request action or
 291                      only one */
 292                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 293                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 294                     {
 295                       if (afct->symbind != NULL)
 296                         {
 297                           uintptr_t new_value
 298                             = afct->symbind (&sym, reloc_result->boundndx,
 299                                              &l->l_audit[cnt].cookie,
 300                                              &result->l_audit[cnt].cookie,
 301                                              &flags,
 302                                              strtab2 + defsym->st_name);
 303                           if (new_value != (uintptr_t) sym.st_value)
 304                             {
 305                               flags |= LA_SYMB_ALTVALUE;
 306                               sym.st_value = new_value;
 307                             }
 308                         }
 309
 310                       /* Remember the results for every audit library and
 311                          store a summary in the first two bits.  */
 312                       reloc_result->enterexit
 313                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 314                       reloc_result->enterexit
 315                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 316                             << ((cnt + 1) * 2));
 317                     }
 318                   else
 319                     /* If the bind flags say this auditor is not interested,
 320                        set the bits manually.  */
 321                     reloc_result->enterexit
 322                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 323                           << ((cnt + 1) * 2));
 324
 325                   afct = afct->next;
 326                 }
 327
 328               reloc_result->flags = flags;
 329               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 330             }
 331           else
 332             /* Set all bits since this symbol binding is not interesting.  */
 333             reloc_result->enterexit = (1u << DL_NNS) - 1;
 334         }
 335 #endif
 336
 337       /* Store the result for later runs.  */
 338       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 339         *resultp = value;
 340     }
 341
 342   /* By default we do not call the pltexit function.  */
 343   long int framesize = -1;
 344
 345 #ifdef SHARED
 346   /* Auditing checkpoint: report the PLT entering and allow the
 347      auditors to change the value.  */
 348   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 349       /* Don't do anything if no auditor wants to intercept this call.  */
 350       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 351     {
 352       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 353                                                 l_info[DT_SYMTAB])
 354                            + reloc_result->boundndx);
 355
 356       /* Set up the sym parameter.  */
 357       ElfW(Sym) sym = *defsym;
 358       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 359
 360       /* Get the symbol name.  */
 361       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 362                                                  l_info[DT_STRTAB]);
 363       const char *symname = strtab + sym.st_name;
 364
 365       /* Keep track of overwritten addresses.  */
 366       unsigned int flags = reloc_result->flags;
 367
 368       struct audit_ifaces *afct = GLRO(dl_audit);
 369       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 370         {
 371           if (afct->ARCH_LA_PLTENTER != NULL
 372               && (reloc_result->enterexit
 373                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 374             {
 375               long int new_framesize = -1;
 376               uintptr_t new_value
 377                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 378                                           &l->l_audit[cnt].cookie,
 379                                           &reloc_result->bound->l_audit[cnt].cookie,
 380                                           regs, &flags, symname,
 381                                           &new_framesize);
 382               if (new_value != (uintptr_t) sym.st_value)
 383                 {
 384                   flags |= LA_SYMB_ALTVALUE;
 385                   sym.st_value = new_value;
 386                 }
 387
 388               /* Remember the results for every audit library and
 389                  store a summary in the first two bits.  */
 390               reloc_result->enterexit
 391                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 392                     << (2 * (cnt + 1)));
 393
 394               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 395                                               << (2 * (cnt + 1))))
 396                   == 0 && new_framesize != -1 && framesize != -2)
 397                 {
 398                   /* If this is the first call providing information,
 399                      use it.  */
 400                   if (framesize == -1)
 401                     framesize = new_framesize;
 402                   /* If two pltenter calls provide conflicting information,
 403                      use the larger value.  */
 404                   else if (new_framesize != framesize)
 405                     framesize = MAX (new_framesize, framesize);
 406                 }
 407             }
 408
 409           afct = afct->next;
 410         }
 411
 412       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 413     }
 414 #endif
 415
 416   /* Store the frame size information.  */
 417   *framesizep = framesize;
 418
 419   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 420
 421   return value;
 422 }
 423
 424 #endif /* PROF && ELF_MACHINE_NO_PLT */
 425
 426
 427 #include <stdio.h>
 428 void
 429 ARCH_FIXUP_ATTRIBUTE
 430 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 431                   const void *inregs, void *outregs)
 432 {
 433 #ifdef SHARED
 434   /* This is the address in the array where we store the result of previous
 435      relocations.  */
 436   // XXX Maybe the bound information must be stored on the stack since
 437   // XXX with bind_not a new value could have been stored in the meantime.
 438   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 439   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 440                                             l_info[DT_SYMTAB])
 441                        + reloc_result->boundndx);
 442
 443   /* Set up the sym parameter.  */
 444   ElfW(Sym) sym = *defsym;
 445   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 446
 447   /* Get the symbol name.  */
 448   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 449                                              l_info[DT_STRTAB]);
 450   const char *symname = strtab + sym.st_name;
 451
 452   struct audit_ifaces *afct = GLRO(dl_audit);
 453   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 454     {
 455       if (afct->ARCH_LA_PLTEXIT != NULL
 456           && (reloc_result->enterexit
 457               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 458         {
 459           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 460                                  &l->l_audit[cnt].cookie,
 461                                  &reloc_result->bound->l_audit[cnt].cookie,
 462                                  inregs, outregs, symname);
 463         }
 464
 465       afct = afct->next;
 466     }
 467 #endif
 468 }