elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2013 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 /* The fixup functions might have need special attributes.  If none
  40    are provided define the macro as empty.  */
  41 #ifndef ARCH_FIXUP_ATTRIBUTE
  42 # define ARCH_FIXUP_ATTRIBUTE
  43 #endif
  44
  45 #ifndef reloc_offset
  46 # define reloc_offset reloc_arg
  47 # define reloc_index  reloc_arg / sizeof (PLTREL)
  48 #endif
  49
  50
  51
  52 /* This function is called through a special trampoline from the PLT the
  53    first time each PLT entry is called.  We must perform the relocation
  54    specified in the PLT of the given shared object, and return the resolved
  55    function address to the trampoline, which will restart the original call
  56    to that address.  Future calls will bounce directly from the PLT to the
  57    function.  */
  58
  59 DL_FIXUP_VALUE_TYPE
  60 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
  61 _dl_fixup (
  62 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  63            ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  64 # endif
  65            struct link_map *l, ElfW(Word) reloc_arg)
  66 {
  67   const ElfW(Sym) *const symtab
  68     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  69   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  70
  71   const PLTREL *const reloc
  72     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  73   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  74   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  75   lookup_t result;
  76   DL_FIXUP_VALUE_TYPE value;
  77
  78   /* Sanity check that we're really looking at a PLT relocation.  */
  79   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  80
  81    /* Look up the target symbol.  If the normal lookup rules are not
  82       used don't look in the global scope.  */
  83   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  84     {
  85       const struct r_found_version *version = NULL;
  86
  87       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  88         {
  89           const ElfW(Half) *vernum =
  90             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  91           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  92           version = &l->l_versions[ndx];
  93           if (version->hash == 0)
  94             version = NULL;
  95         }
  96
  97       /* We need to keep the scope around so do some locking.  This is
  98          not necessary for objects which cannot be unloaded or when
  99          we are not using any threads (yet).  */
 100       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 101       if (!RTLD_SINGLE_THREAD_P)
 102         {
 103           THREAD_GSCOPE_SET_FLAG ();
 104           flags |= DL_LOOKUP_GSCOPE_LOCK;
 105         }
 106
 107 #ifdef RTLD_ENABLE_FOREIGN_CALL
 108       RTLD_ENABLE_FOREIGN_CALL;
 109 #endif
 110
 111       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 112                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 113
 114       /* We are done with the global scope.  */
 115       if (!RTLD_SINGLE_THREAD_P)
 116         THREAD_GSCOPE_RESET_FLAG ();
 117
 118 #ifdef RTLD_FINALIZE_FOREIGN_CALL
 119       RTLD_FINALIZE_FOREIGN_CALL;
 120 #endif
 121
 122       /* Currently result contains the base load address (or link map)
 123          of the object that defines sym.  Now add in the symbol
 124          offset.  */
 125       value = DL_FIXUP_MAKE_VALUE (result,
 126                                    sym ? (LOOKUP_VALUE_ADDRESS (result)
 127                                           + sym->st_value) : 0);
 128     }
 129   else
 130     {
 131       /* We already found the symbol.  The module (and therefore its load
 132          address) is also known.  */
 133       value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + sym->st_value);
 134       result = l;
 135     }
 136
 137   /* And now perhaps the relocation addend.  */
 138   value = elf_machine_plt_value (l, reloc, value);
 139
 140   if (sym != NULL
 141       && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 142     value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 143
 144   /* Finally, fix up the plt itself.  */
 145   if (__builtin_expect (GLRO(dl_bind_not), 0))
 146     return value;
 147
 148   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 149 }
 150
 151 #ifndef PROF
 152 DL_FIXUP_VALUE_TYPE
 153 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 154 _dl_profile_fixup (
 155 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 156                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 157 #endif
 158                    struct link_map *l, ElfW(Word) reloc_arg,
 159                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 160 {
 161   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 162
 163   if (l->l_reloc_result == NULL)
 164     {
 165       /* BZ #14843: ELF_DYNAMIC_RELOCATE is called before l_reloc_result
 166          is allocated.  We will get here if ELF_DYNAMIC_RELOCATE calls a
 167          resolver function to resolve an IRELATIVE relocation and that
 168          resolver calls a function that is not yet resolved (lazy).  For
 169          example, the resolver in x86-64 libm.so calls __get_cpu_features
 170          defined in libc.so.  Skip audit and resolve the external function
 171          in this case.  */
 172       *framesizep = -1;
 173       return _dl_fixup (
 174 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 175 #  ifndef ELF_MACHINE_RUNTIME_FIXUP_PARAMS
 176 #   error Please define ELF_MACHINE_RUNTIME_FIXUP_PARAMS.
 177 #  endif
 178                         ELF_MACHINE_RUNTIME_FIXUP_PARAMS,
 179 # endif
 180                         l, reloc_arg);
 181     }
 182
 183   /* This is the address in the array where we store the result of previous
 184      relocations.  */
 185   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 186   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 187
 188   DL_FIXUP_VALUE_TYPE value = *resultp;
 189   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 190     {
 191       /* This is the first time we have to relocate this object.  */
 192       const ElfW(Sym) *const symtab
 193         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 194       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 195
 196       const PLTREL *const reloc
 197         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 198       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 199       const ElfW(Sym) *defsym = refsym;
 200       lookup_t result;
 201
 202       /* Sanity check that we're really looking at a PLT relocation.  */
 203       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 204
 205       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 206          don't look in the global scope.  */
 207       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 208         {
 209           const struct r_found_version *version = NULL;
 210
 211           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 212             {
 213               const ElfW(Half) *vernum =
 214                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 215               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 216               version = &l->l_versions[ndx];
 217               if (version->hash == 0)
 218                 version = NULL;
 219             }
 220
 221           /* We need to keep the scope around so do some locking.  This is
 222              not necessary for objects which cannot be unloaded or when
 223              we are not using any threads (yet).  */
 224           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 225           if (!RTLD_SINGLE_THREAD_P)
 226             {
 227               THREAD_GSCOPE_SET_FLAG ();
 228               flags |= DL_LOOKUP_GSCOPE_LOCK;
 229             }
 230
 231           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 232                                         &defsym, l->l_scope, version,
 233                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 234
 235           /* We are done with the global scope.  */
 236           if (!RTLD_SINGLE_THREAD_P)
 237             THREAD_GSCOPE_RESET_FLAG ();
 238
 239           /* Currently result contains the base load address (or link map)
 240              of the object that defines sym.  Now add in the symbol
 241              offset.  */
 242           value = DL_FIXUP_MAKE_VALUE (result,
 243                                        defsym != NULL
 244                                        ? LOOKUP_VALUE_ADDRESS (result)
 245                                          + defsym->st_value : 0);
 246
 247           if (defsym != NULL
 248               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 249                                    == STT_GNU_IFUNC, 0))
 250             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 251         }
 252       else
 253         {
 254           /* We already found the symbol.  The module (and therefore its load
 255              address) is also known.  */
 256           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 257
 258           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 259                                 == STT_GNU_IFUNC, 0))
 260             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 261
 262           result = l;
 263         }
 264       /* And now perhaps the relocation addend.  */
 265       value = elf_machine_plt_value (l, reloc, value);
 266
 267 #ifdef SHARED
 268       /* Auditing checkpoint: we have a new binding.  Provide the
 269          auditing libraries the possibility to change the value and
 270          tell us whether further auditing is wanted.  */
 271       if (defsym != NULL && GLRO(dl_naudit) > 0)
 272         {
 273           reloc_result->bound = result;
 274           /* Compute index of the symbol entry in the symbol table of
 275              the DSO with the definition.  */
 276           reloc_result->boundndx = (defsym
 277                                     - (ElfW(Sym) *) D_PTR (result,
 278                                                            l_info[DT_SYMTAB]));
 279
 280           /* Determine whether any of the two participating DSOs is
 281              interested in auditing.  */
 282           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 283             {
 284               unsigned int flags = 0;
 285               struct audit_ifaces *afct = GLRO(dl_audit);
 286               /* Synthesize a symbol record where the st_value field is
 287                  the result.  */
 288               ElfW(Sym) sym = *defsym;
 289               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 290
 291               /* Keep track whether there is any interest in tracing
 292                  the call in the lower two bits.  */
 293               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 294               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 295               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 296
 297               const char *strtab2 = (const void *) D_PTR (result,
 298                                                           l_info[DT_STRTAB]);
 299
 300               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 301                 {
 302                   /* XXX Check whether both DSOs must request action or
 303                      only one */
 304                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 305                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 306                     {
 307                       if (afct->symbind != NULL)
 308                         {
 309                           uintptr_t new_value
 310                             = afct->symbind (&sym, reloc_result->boundndx,
 311                                              &l->l_audit[cnt].cookie,
 312                                              &result->l_audit[cnt].cookie,
 313                                              &flags,
 314                                              strtab2 + defsym->st_name);
 315                           if (new_value != (uintptr_t) sym.st_value)
 316                             {
 317                               flags |= LA_SYMB_ALTVALUE;
 318                               sym.st_value = new_value;
 319                             }
 320                         }
 321
 322                       /* Remember the results for every audit library and
 323                          store a summary in the first two bits.  */
 324                       reloc_result->enterexit
 325                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 326                       reloc_result->enterexit
 327                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 328                             << ((cnt + 1) * 2));
 329                     }
 330                   else
 331                     /* If the bind flags say this auditor is not interested,
 332                        set the bits manually.  */
 333                     reloc_result->enterexit
 334                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 335                           << ((cnt + 1) * 2));
 336
 337                   afct = afct->next;
 338                 }
 339
 340               reloc_result->flags = flags;
 341               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 342             }
 343           else
 344             /* Set all bits since this symbol binding is not interesting.  */
 345             reloc_result->enterexit = (1u << DL_NNS) - 1;
 346         }
 347 #endif
 348
 349       /* Store the result for later runs.  */
 350       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 351         *resultp = value;
 352     }
 353
 354   /* By default we do not call the pltexit function.  */
 355   long int framesize = -1;
 356
 357 #ifdef SHARED
 358   /* Auditing checkpoint: report the PLT entering and allow the
 359      auditors to change the value.  */
 360   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 361       /* Don't do anything if no auditor wants to intercept this call.  */
 362       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 363     {
 364       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 365                                                 l_info[DT_SYMTAB])
 366                            + reloc_result->boundndx);
 367
 368       /* Set up the sym parameter.  */
 369       ElfW(Sym) sym = *defsym;
 370       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 371
 372       /* Get the symbol name.  */
 373       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 374                                                  l_info[DT_STRTAB]);
 375       const char *symname = strtab + sym.st_name;
 376
 377       /* Keep track of overwritten addresses.  */
 378       unsigned int flags = reloc_result->flags;
 379
 380       struct audit_ifaces *afct = GLRO(dl_audit);
 381       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 382         {
 383           if (afct->ARCH_LA_PLTENTER != NULL
 384               && (reloc_result->enterexit
 385                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 386             {
 387               long int new_framesize = -1;
 388               uintptr_t new_value
 389                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 390                                           &l->l_audit[cnt].cookie,
 391                                           &reloc_result->bound->l_audit[cnt].cookie,
 392                                           regs, &flags, symname,
 393                                           &new_framesize);
 394               if (new_value != (uintptr_t) sym.st_value)
 395                 {
 396                   flags |= LA_SYMB_ALTVALUE;
 397                   sym.st_value = new_value;
 398                 }
 399
 400               /* Remember the results for every audit library and
 401                  store a summary in the first two bits.  */
 402               reloc_result->enterexit
 403                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 404                     << (2 * (cnt + 1)));
 405
 406               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 407                                               << (2 * (cnt + 1))))
 408                   == 0 && new_framesize != -1 && framesize != -2)
 409                 {
 410                   /* If this is the first call providing information,
 411                      use it.  */
 412                   if (framesize == -1)
 413                     framesize = new_framesize;
 414                   /* If two pltenter calls provide conflicting information,
 415                      use the larger value.  */
 416                   else if (new_framesize != framesize)
 417                     framesize = MAX (new_framesize, framesize);
 418                 }
 419             }
 420
 421           afct = afct->next;
 422         }
 423
 424       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 425     }
 426 #endif
 427
 428   /* Store the frame size information.  */
 429   *framesizep = framesize;
 430
 431   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 432
 433   return value;
 434 }
 435
 436 #endif /* PROF */
 437
 438
 439 #include <stdio.h>
 440 void
 441 ARCH_FIXUP_ATTRIBUTE
 442 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 443                   const void *inregs, void *outregs)
 444 {
 445 #ifdef SHARED
 446   /* This is the address in the array where we store the result of previous
 447      relocations.  */
 448   // XXX Maybe the bound information must be stored on the stack since
 449   // XXX with bind_not a new value could have been stored in the meantime.
 450   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 451   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 452                                             l_info[DT_SYMTAB])
 453                        + reloc_result->boundndx);
 454
 455   /* Set up the sym parameter.  */
 456   ElfW(Sym) sym = *defsym;
 457   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 458
 459   /* Get the symbol name.  */
 460   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 461                                              l_info[DT_STRTAB]);
 462   const char *symname = strtab + sym.st_name;
 463
 464   struct audit_ifaces *afct = GLRO(dl_audit);
 465   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 466     {
 467       if (afct->ARCH_LA_PLTEXIT != NULL
 468           && (reloc_result->enterexit
 469               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 470         {
 471           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 472                                  &l->l_audit[cnt].cookie,
 473                                  &reloc_result->bound->l_audit[cnt].cookie,
 474                                  inregs, outregs, symname);
 475         }
 476
 477       afct = afct->next;
 478     }
 479 #endif
 480 }