elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2012 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            /* GKM FIXME: Fix trampoline to pass bounds so we can do
  66               without the `__unbounded' qualifier.  */
  67            struct link_map *__unbounded l, ElfW(Word) reloc_arg)
  68 {
  69   const ElfW(Sym) *const symtab
  70     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  71   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  72
  73   const PLTREL *const reloc
  74     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  75   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  76   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  77   lookup_t result;
  78   DL_FIXUP_VALUE_TYPE value;
  79
  80   /* Sanity check that we're really looking at a PLT relocation.  */
  81   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  82
  83    /* Look up the target symbol.  If the normal lookup rules are not
  84       used don't look in the global scope.  */
  85   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  86     {
  87       const struct r_found_version *version = NULL;
  88
  89       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  90         {
  91           const ElfW(Half) *vernum =
  92             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  93           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  94           version = &l->l_versions[ndx];
  95           if (version->hash == 0)
  96             version = NULL;
  97         }
  98
  99       /* We need to keep the scope around so do some locking.  This is
 100          not necessary for objects which cannot be unloaded or when
 101          we are not using any threads (yet).  */
 102       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 103       if (!RTLD_SINGLE_THREAD_P)
 104         {
 105           THREAD_GSCOPE_SET_FLAG ();
 106           flags |= DL_LOOKUP_GSCOPE_LOCK;
 107         }
 108
 109 #ifdef RTLD_ENABLE_FOREIGN_CALL
 110       RTLD_ENABLE_FOREIGN_CALL;
 111 #endif
 112
 113       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 114                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 115
 116       /* We are done with the global scope.  */
 117       if (!RTLD_SINGLE_THREAD_P)
 118         THREAD_GSCOPE_RESET_FLAG ();
 119
 120 #ifdef RTLD_FINALIZE_FOREIGN_CALL
 121       RTLD_FINALIZE_FOREIGN_CALL;
 122 #endif
 123
 124       /* Currently result contains the base load address (or link map)
 125          of the object that defines sym.  Now add in the symbol
 126          offset.  */
 127       value = DL_FIXUP_MAKE_VALUE (result,
 128                                    sym ? (LOOKUP_VALUE_ADDRESS (result)
 129                                           + sym->st_value) : 0);
 130     }
 131   else
 132     {
 133       /* We already found the symbol.  The module (and therefore its load
 134          address) is also known.  */
 135       value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + sym->st_value);
 136       result = l;
 137     }
 138
 139   /* And now perhaps the relocation addend.  */
 140   value = elf_machine_plt_value (l, reloc, value);
 141
 142   if (sym != NULL
 143       && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 144     value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 145
 146   /* Finally, fix up the plt itself.  */
 147   if (__builtin_expect (GLRO(dl_bind_not), 0))
 148     return value;
 149
 150   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 151 }
 152
 153 #if !defined PROF && !__BOUNDED_POINTERS__
 154 DL_FIXUP_VALUE_TYPE
 155 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 156 _dl_profile_fixup (
 157 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 158                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 159 #endif
 160                    struct link_map *l, ElfW(Word) reloc_arg,
 161                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 162 {
 163   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 164
 165   if (l->l_reloc_result == NULL)
 166     {
 167       /* BZ #14843: ELF_DYNAMIC_RELOCATE is called before l_reloc_result
 168          is allocated.  We will get here if ELF_DYNAMIC_RELOCATE calls a
 169          resolver function to resolve an IRELATIVE relocation and that
 170          resolver calls a function that is not yet resolved (lazy).  For
 171          example, the resolver in x86-64 libm.so calls __get_cpu_features
 172          defined in libc.so.  Skip audit and resolve the external function
 173          in this case.  */
 174       *framesizep = -1;
 175       return _dl_fixup (
 176 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 177 #  ifndef ELF_MACHINE_RUNTIME_FIXUP_PARAMS
 178 #   error Please define ELF_MACHINE_RUNTIME_FIXUP_PARAMS.
 179 #  endif
 180                         ELF_MACHINE_RUNTIME_FIXUP_PARAMS,
 181 # endif
 182                         l, reloc_arg);
 183     }
 184
 185   /* This is the address in the array where we store the result of previous
 186      relocations.  */
 187   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 188   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 189
 190   DL_FIXUP_VALUE_TYPE value = *resultp;
 191   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 192     {
 193       /* This is the first time we have to relocate this object.  */
 194       const ElfW(Sym) *const symtab
 195         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 196       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 197
 198       const PLTREL *const reloc
 199         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 200       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 201       const ElfW(Sym) *defsym = refsym;
 202       lookup_t result;
 203
 204       /* Sanity check that we're really looking at a PLT relocation.  */
 205       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 206
 207       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 208          don't look in the global scope.  */
 209       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 210         {
 211           const struct r_found_version *version = NULL;
 212
 213           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 214             {
 215               const ElfW(Half) *vernum =
 216                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 217               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 218               version = &l->l_versions[ndx];
 219               if (version->hash == 0)
 220                 version = NULL;
 221             }
 222
 223           /* We need to keep the scope around so do some locking.  This is
 224              not necessary for objects which cannot be unloaded or when
 225              we are not using any threads (yet).  */
 226           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 227           if (!RTLD_SINGLE_THREAD_P)
 228             {
 229               THREAD_GSCOPE_SET_FLAG ();
 230               flags |= DL_LOOKUP_GSCOPE_LOCK;
 231             }
 232
 233           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 234                                         &defsym, l->l_scope, version,
 235                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 236
 237           /* We are done with the global scope.  */
 238           if (!RTLD_SINGLE_THREAD_P)
 239             THREAD_GSCOPE_RESET_FLAG ();
 240
 241           /* Currently result contains the base load address (or link map)
 242              of the object that defines sym.  Now add in the symbol
 243              offset.  */
 244           value = DL_FIXUP_MAKE_VALUE (result,
 245                                        defsym != NULL
 246                                        ? LOOKUP_VALUE_ADDRESS (result)
 247                                          + defsym->st_value : 0);
 248
 249           if (defsym != NULL
 250               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 251                                    == STT_GNU_IFUNC, 0))
 252             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 253         }
 254       else
 255         {
 256           /* We already found the symbol.  The module (and therefore its load
 257              address) is also known.  */
 258           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 259
 260           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 261                                 == STT_GNU_IFUNC, 0))
 262             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 263
 264           result = l;
 265         }
 266       /* And now perhaps the relocation addend.  */
 267       value = elf_machine_plt_value (l, reloc, value);
 268
 269 #ifdef SHARED
 270       /* Auditing checkpoint: we have a new binding.  Provide the
 271          auditing libraries the possibility to change the value and
 272          tell us whether further auditing is wanted.  */
 273       if (defsym != NULL && GLRO(dl_naudit) > 0)
 274         {
 275           reloc_result->bound = result;
 276           /* Compute index of the symbol entry in the symbol table of
 277              the DSO with the definition.  */
 278           reloc_result->boundndx = (defsym
 279                                     - (ElfW(Sym) *) D_PTR (result,
 280                                                            l_info[DT_SYMTAB]));
 281
 282           /* Determine whether any of the two participating DSOs is
 283              interested in auditing.  */
 284           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 285             {
 286               unsigned int flags = 0;
 287               struct audit_ifaces *afct = GLRO(dl_audit);
 288               /* Synthesize a symbol record where the st_value field is
 289                  the result.  */
 290               ElfW(Sym) sym = *defsym;
 291               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 292
 293               /* Keep track whether there is any interest in tracing
 294                  the call in the lower two bits.  */
 295               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 296               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 297               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 298
 299               const char *strtab2 = (const void *) D_PTR (result,
 300                                                           l_info[DT_STRTAB]);
 301
 302               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 303                 {
 304                   /* XXX Check whether both DSOs must request action or
 305                      only one */
 306                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 307                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 308                     {
 309                       if (afct->symbind != NULL)
 310                         {
 311                           uintptr_t new_value
 312                             = afct->symbind (&sym, reloc_result->boundndx,
 313                                              &l->l_audit[cnt].cookie,
 314                                              &result->l_audit[cnt].cookie,
 315                                              &flags,
 316                                              strtab2 + defsym->st_name);
 317                           if (new_value != (uintptr_t) sym.st_value)
 318                             {
 319                               flags |= LA_SYMB_ALTVALUE;
 320                               sym.st_value = new_value;
 321                             }
 322                         }
 323
 324                       /* Remember the results for every audit library and
 325                          store a summary in the first two bits.  */
 326                       reloc_result->enterexit
 327                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 328                       reloc_result->enterexit
 329                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 330                             << ((cnt + 1) * 2));
 331                     }
 332                   else
 333                     /* If the bind flags say this auditor is not interested,
 334                        set the bits manually.  */
 335                     reloc_result->enterexit
 336                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 337                           << ((cnt + 1) * 2));
 338
 339                   afct = afct->next;
 340                 }
 341
 342               reloc_result->flags = flags;
 343               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 344             }
 345           else
 346             /* Set all bits since this symbol binding is not interesting.  */
 347             reloc_result->enterexit = (1u << DL_NNS) - 1;
 348         }
 349 #endif
 350
 351       /* Store the result for later runs.  */
 352       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 353         *resultp = value;
 354     }
 355
 356   /* By default we do not call the pltexit function.  */
 357   long int framesize = -1;
 358
 359 #ifdef SHARED
 360   /* Auditing checkpoint: report the PLT entering and allow the
 361      auditors to change the value.  */
 362   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 363       /* Don't do anything if no auditor wants to intercept this call.  */
 364       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 365     {
 366       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 367                                                 l_info[DT_SYMTAB])
 368                            + reloc_result->boundndx);
 369
 370       /* Set up the sym parameter.  */
 371       ElfW(Sym) sym = *defsym;
 372       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 373
 374       /* Get the symbol name.  */
 375       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 376                                                  l_info[DT_STRTAB]);
 377       const char *symname = strtab + sym.st_name;
 378
 379       /* Keep track of overwritten addresses.  */
 380       unsigned int flags = reloc_result->flags;
 381
 382       struct audit_ifaces *afct = GLRO(dl_audit);
 383       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 384         {
 385           if (afct->ARCH_LA_PLTENTER != NULL
 386               && (reloc_result->enterexit
 387                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 388             {
 389               long int new_framesize = -1;
 390               uintptr_t new_value
 391                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 392                                           &l->l_audit[cnt].cookie,
 393                                           &reloc_result->bound->l_audit[cnt].cookie,
 394                                           regs, &flags, symname,
 395                                           &new_framesize);
 396               if (new_value != (uintptr_t) sym.st_value)
 397                 {
 398                   flags |= LA_SYMB_ALTVALUE;
 399                   sym.st_value = new_value;
 400                 }
 401
 402               /* Remember the results for every audit library and
 403                  store a summary in the first two bits.  */
 404               reloc_result->enterexit
 405                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 406                     << (2 * (cnt + 1)));
 407
 408               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 409                                               << (2 * (cnt + 1))))
 410                   == 0 && new_framesize != -1 && framesize != -2)
 411                 {
 412                   /* If this is the first call providing information,
 413                      use it.  */
 414                   if (framesize == -1)
 415                     framesize = new_framesize;
 416                   /* If two pltenter calls provide conflicting information,
 417                      use the larger value.  */
 418                   else if (new_framesize != framesize)
 419                     framesize = MAX (new_framesize, framesize);
 420                 }
 421             }
 422
 423           afct = afct->next;
 424         }
 425
 426       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 427     }
 428 #endif
 429
 430   /* Store the frame size information.  */
 431   *framesizep = framesize;
 432
 433   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 434
 435   return value;
 436 }
 437
 438 #endif /* PROF */
 439
 440
 441 #include <stdio.h>
 442 void
 443 ARCH_FIXUP_ATTRIBUTE
 444 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 445                   const void *inregs, void *outregs)
 446 {
 447 #ifdef SHARED
 448   /* This is the address in the array where we store the result of previous
 449      relocations.  */
 450   // XXX Maybe the bound information must be stored on the stack since
 451   // XXX with bind_not a new value could have been stored in the meantime.
 452   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 453   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 454                                             l_info[DT_SYMTAB])
 455                        + reloc_result->boundndx);
 456
 457   /* Set up the sym parameter.  */
 458   ElfW(Sym) sym = *defsym;
 459   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 460
 461   /* Get the symbol name.  */
 462   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 463                                              l_info[DT_STRTAB]);
 464   const char *symname = strtab + sym.st_name;
 465
 466   struct audit_ifaces *afct = GLRO(dl_audit);
 467   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 468     {
 469       if (afct->ARCH_LA_PLTEXIT != NULL
 470           && (reloc_result->enterexit
 471               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 472         {
 473           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 474                                  &l->l_audit[cnt].cookie,
 475                                  &reloc_result->bound->l_audit[cnt].cookie,
 476                                  inregs, outregs, symname);
 477         }
 478
 479       afct = afct->next;
 480     }
 481 #endif
 482 }