elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2020 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 #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 (!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_hidden __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   const ElfW(Sym) *refsym = sym;
  75   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  76   lookup_t result;
  77   DL_FIXUP_VALUE_TYPE value;
  78
  79   /* Sanity check that we're really looking at a PLT relocation.  */
  80   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  81
  82    /* Look up the target symbol.  If the normal lookup rules are not
  83       used don't look in the global scope.  */
  84   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  85     {
  86       const struct r_found_version *version = NULL;
  87
  88       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  89         {
  90           const ElfW(Half) *vernum =
  91             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  92           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  93           version = &l->l_versions[ndx];
  94           if (version->hash == 0)
  95             version = NULL;
  96         }
  97
  98       /* We need to keep the scope around so do some locking.  This is
  99          not necessary for objects which cannot be unloaded or when
 100          we are not using any threads (yet).  */
 101       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 102       if (!RTLD_SINGLE_THREAD_P)
 103         {
 104           THREAD_GSCOPE_SET_FLAG ();
 105           flags |= DL_LOOKUP_GSCOPE_LOCK;
 106         }
 107
 108 #ifdef RTLD_ENABLE_FOREIGN_CALL
 109       RTLD_ENABLE_FOREIGN_CALL;
 110 #endif
 111
 112       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 113                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 114
 115       /* We are done with the global scope.  */
 116       if (!RTLD_SINGLE_THREAD_P)
 117         THREAD_GSCOPE_RESET_FLAG ();
 118
 119 #ifdef RTLD_FINALIZE_FOREIGN_CALL
 120       RTLD_FINALIZE_FOREIGN_CALL;
 121 #endif
 122
 123       /* Currently result contains the base load address (or link map)
 124          of the object that defines sym.  Now add in the symbol
 125          offset.  */
 126       value = DL_FIXUP_MAKE_VALUE (result,
 127                                    SYMBOL_ADDRESS (result, sym, false));
 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, SYMBOL_ADDRESS (l, sym, true));
 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 (__glibc_unlikely (GLRO(dl_bind_not)))
 146     return value;
 147
 148   return elf_machine_fixup_plt (l, result, refsym, sym, 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)) = _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
 187  /* CONCURRENCY NOTES:
 188
 189   Multiple threads may be calling the same PLT sequence and with
 190   LD_AUDIT enabled they will be calling into _dl_profile_fixup to
 191   update the reloc_result with the result of the lazy resolution.
 192   The reloc_result guard variable is reloc_init, and we use
 193   acquire/release loads and store to it to ensure that the results of
 194   the structure are consistent with the loaded value of the guard.
 195   This does not fix all of the data races that occur when two or more
 196   threads read reloc_result->reloc_init with a value of zero and read
 197   and write to that reloc_result concurrently.  The expectation is
 198   generally that while this is a data race it works because the
 199   threads write the same values.  Until the data races are fixed
 200   there is a potential for problems to arise from these data races.
 201   The reloc result updates should happen in parallel but there should
 202   be an atomic RMW which does the final update to the real result
 203   entry (see bug 23790).
 204
 205   The following code uses reloc_result->init set to 0 to indicate if it is
 206   the first time this object is being relocated, otherwise 1 which
 207   indicates the object has already been relocated.
 208
 209   Reading/Writing from/to reloc_result->reloc_init must not happen
 210   before previous writes to reloc_result complete as they could
 211   end-up with an incomplete struct.  */
 212   DL_FIXUP_VALUE_TYPE value;
 213   unsigned int init = atomic_load_acquire (&reloc_result->init);
 214
 215   if (init == 0)
 216     {
 217       /* This is the first time we have to relocate this object.  */
 218       const ElfW(Sym) *const symtab
 219         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 220       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 221
 222       const PLTREL *const reloc
 223         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 224       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 225       const ElfW(Sym) *defsym = refsym;
 226       lookup_t result;
 227
 228       /* Sanity check that we're really looking at a PLT relocation.  */
 229       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 230
 231       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 232          don't look in the global scope.  */
 233       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 234         {
 235           const struct r_found_version *version = NULL;
 236
 237           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 238             {
 239               const ElfW(Half) *vernum =
 240                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 241               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 242               version = &l->l_versions[ndx];
 243               if (version->hash == 0)
 244                 version = NULL;
 245             }
 246
 247           /* We need to keep the scope around so do some locking.  This is
 248              not necessary for objects which cannot be unloaded or when
 249              we are not using any threads (yet).  */
 250           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 251           if (!RTLD_SINGLE_THREAD_P)
 252             {
 253               THREAD_GSCOPE_SET_FLAG ();
 254               flags |= DL_LOOKUP_GSCOPE_LOCK;
 255             }
 256
 257           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 258                                         &defsym, l->l_scope, version,
 259                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 260
 261           /* We are done with the global scope.  */
 262           if (!RTLD_SINGLE_THREAD_P)
 263             THREAD_GSCOPE_RESET_FLAG ();
 264
 265           /* Currently result contains the base load address (or link map)
 266              of the object that defines sym.  Now add in the symbol
 267              offset.  */
 268           value = DL_FIXUP_MAKE_VALUE (result,
 269                                        SYMBOL_ADDRESS (result, defsym, false));
 270
 271           if (defsym != NULL
 272               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 273                                    == STT_GNU_IFUNC, 0))
 274             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 275         }
 276       else
 277         {
 278           /* We already found the symbol.  The module (and therefore its load
 279              address) is also known.  */
 280           value = DL_FIXUP_MAKE_VALUE (l, SYMBOL_ADDRESS (l, refsym, true));
 281
 282           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 283                                 == STT_GNU_IFUNC, 0))
 284             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 285
 286           result = l;
 287         }
 288       /* And now perhaps the relocation addend.  */
 289       value = elf_machine_plt_value (l, reloc, value);
 290
 291 #ifdef SHARED
 292       /* Auditing checkpoint: we have a new binding.  Provide the
 293          auditing libraries the possibility to change the value and
 294          tell us whether further auditing is wanted.  */
 295       if (defsym != NULL && GLRO(dl_naudit) > 0)
 296         {
 297           reloc_result->bound = result;
 298           /* Compute index of the symbol entry in the symbol table of
 299              the DSO with the definition.  */
 300           reloc_result->boundndx = (defsym
 301                                     - (ElfW(Sym) *) D_PTR (result,
 302                                                            l_info[DT_SYMTAB]));
 303
 304           /* Determine whether any of the two participating DSOs is
 305              interested in auditing.  */
 306           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 307             {
 308               unsigned int flags = 0;
 309               struct audit_ifaces *afct = GLRO(dl_audit);
 310               /* Synthesize a symbol record where the st_value field is
 311                  the result.  */
 312               ElfW(Sym) sym = *defsym;
 313               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 314
 315               /* Keep track whether there is any interest in tracing
 316                  the call in the lower two bits.  */
 317               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 318               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 319               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 320
 321               const char *strtab2 = (const void *) D_PTR (result,
 322                                                           l_info[DT_STRTAB]);
 323
 324               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 325                 {
 326                   /* XXX Check whether both DSOs must request action or
 327                      only one */
 328                   struct auditstate *l_state = link_map_audit_state (l, cnt);
 329                   struct auditstate *result_state
 330                     = link_map_audit_state (result, cnt);
 331                   if ((l_state->bindflags & LA_FLG_BINDFROM) != 0
 332                       && (result_state->bindflags & LA_FLG_BINDTO) != 0)
 333                     {
 334                       if (afct->symbind != NULL)
 335                         {
 336                           uintptr_t new_value
 337                             = afct->symbind (&sym, reloc_result->boundndx,
 338                                              &l_state->cookie,
 339                                              &result_state->cookie,
 340                                              &flags,
 341                                              strtab2 + defsym->st_name);
 342                           if (new_value != (uintptr_t) sym.st_value)
 343                             {
 344                               flags |= LA_SYMB_ALTVALUE;
 345                               sym.st_value = new_value;
 346                             }
 347                         }
 348
 349                       /* Remember the results for every audit library and
 350                          store a summary in the first two bits.  */
 351                       reloc_result->enterexit
 352                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 353                       reloc_result->enterexit
 354                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 355                             << ((cnt + 1) * 2));
 356                     }
 357                   else
 358                     /* If the bind flags say this auditor is not interested,
 359                        set the bits manually.  */
 360                     reloc_result->enterexit
 361                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 362                           << ((cnt + 1) * 2));
 363
 364                   afct = afct->next;
 365                 }
 366
 367               reloc_result->flags = flags;
 368               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 369             }
 370           else
 371             /* Set all bits since this symbol binding is not interesting.  */
 372             reloc_result->enterexit = (1u << DL_NNS) - 1;
 373         }
 374 #endif
 375
 376       /* Store the result for later runs.  */
 377       if (__glibc_likely (! GLRO(dl_bind_not)))
 378         {
 379           reloc_result->addr = value;
 380           /* Guarantee all previous writes complete before
 381              init is updated.  See CONCURRENCY NOTES earlier  */
 382           atomic_store_release (&reloc_result->init, 1);
 383         }
 384       init = 1;
 385     }
 386   else
 387     value = reloc_result->addr;
 388
 389   /* By default we do not call the pltexit function.  */
 390   long int framesize = -1;
 391
 392
 393 #ifdef SHARED
 394   /* Auditing checkpoint: report the PLT entering and allow the
 395      auditors to change the value.  */
 396   if (GLRO(dl_naudit) > 0
 397       /* Don't do anything if no auditor wants to intercept this call.  */
 398       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 399     {
 400       /* Sanity check:  DL_FIXUP_VALUE_CODE_ADDR (value) should have been
 401          initialized earlier in this function or in another thread.  */
 402       assert (DL_FIXUP_VALUE_CODE_ADDR (value) != 0);
 403       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 404                                                 l_info[DT_SYMTAB])
 405                            + reloc_result->boundndx);
 406
 407       /* Set up the sym parameter.  */
 408       ElfW(Sym) sym = *defsym;
 409       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 410
 411       /* Get the symbol name.  */
 412       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 413                                                  l_info[DT_STRTAB]);
 414       const char *symname = strtab + sym.st_name;
 415
 416       /* Keep track of overwritten addresses.  */
 417       unsigned int flags = reloc_result->flags;
 418
 419       struct audit_ifaces *afct = GLRO(dl_audit);
 420       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 421         {
 422           if (afct->ARCH_LA_PLTENTER != NULL
 423               && (reloc_result->enterexit
 424                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 425             {
 426               long int new_framesize = -1;
 427               struct auditstate *l_state = link_map_audit_state (l, cnt);
 428               struct auditstate *bound_state
 429                 = link_map_audit_state (reloc_result->bound, cnt);
 430               uintptr_t new_value
 431                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 432                                           &l_state->cookie,
 433                                           &bound_state->cookie,
 434                                           regs, &flags, symname,
 435                                           &new_framesize);
 436               if (new_value != (uintptr_t) sym.st_value)
 437                 {
 438                   flags |= LA_SYMB_ALTVALUE;
 439                   sym.st_value = new_value;
 440                 }
 441
 442               /* Remember the results for every audit library and
 443                  store a summary in the first two bits.  */
 444               reloc_result->enterexit
 445                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 446                     << (2 * (cnt + 1)));
 447
 448               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 449                                               << (2 * (cnt + 1))))
 450                   == 0 && new_framesize != -1 && framesize != -2)
 451                 {
 452                   /* If this is the first call providing information,
 453                      use it.  */
 454                   if (framesize == -1)
 455                     framesize = new_framesize;
 456                   /* If two pltenter calls provide conflicting information,
 457                      use the larger value.  */
 458                   else if (new_framesize != framesize)
 459                     framesize = MAX (new_framesize, framesize);
 460                 }
 461             }
 462
 463           afct = afct->next;
 464         }
 465
 466       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 467     }
 468 #endif
 469
 470   /* Store the frame size information.  */
 471   *framesizep = framesize;
 472
 473   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 474
 475   return value;
 476 }
 477
 478 #endif /* PROF */
 479
 480
 481 #include <stdio.h>
 482 void
 483 ARCH_FIXUP_ATTRIBUTE
 484 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 485                   const void *inregs, void *outregs)
 486 {
 487 #ifdef SHARED
 488   /* This is the address in the array where we store the result of previous
 489      relocations.  */
 490   // XXX Maybe the bound information must be stored on the stack since
 491   // XXX with bind_not a new value could have been stored in the meantime.
 492   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 493   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 494                                             l_info[DT_SYMTAB])
 495                        + reloc_result->boundndx);
 496
 497   /* Set up the sym parameter.  */
 498   ElfW(Sym) sym = *defsym;
 499   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 500
 501   /* Get the symbol name.  */
 502   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 503                                              l_info[DT_STRTAB]);
 504   const char *symname = strtab + sym.st_name;
 505
 506   struct audit_ifaces *afct = GLRO(dl_audit);
 507   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 508     {
 509       if (afct->ARCH_LA_PLTEXIT != NULL
 510           && (reloc_result->enterexit
 511               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 512         {
 513           struct auditstate *l_state = link_map_audit_state (l, cnt);
 514           struct auditstate *bound_state
 515             = link_map_audit_state (reloc_result->bound, cnt);
 516           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 517                                  &l_state->cookie, &bound_state->cookie,
 518                                  inregs, outregs, symname);
 519         }
 520
 521       afct = afct->next;
 522     }
 523 #endif
 524 }