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 #ifndef ELF_MACHINE_NO_PLT
  60 DL_FIXUP_VALUE_TYPE
  61 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
  62 _dl_fixup (
  63 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  64            ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  65 # endif
  66            /* GKM FIXME: Fix trampoline to pass bounds so we can do
  67               without the `__unbounded' qualifier.  */
  68            struct link_map *__unbounded l, ElfW(Word) reloc_arg)
  69 {
  70   const ElfW(Sym) *const symtab
  71     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  72   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  73
  74   const PLTREL *const reloc
  75     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  76   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  77   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  78   lookup_t result;
  79   DL_FIXUP_VALUE_TYPE value;
  80
  81   /* Sanity check that we're really looking at a PLT relocation.  */
  82   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  83
  84    /* Look up the target symbol.  If the normal lookup rules are not
  85       used don't look in the global scope.  */
  86   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  87     {
  88       const struct r_found_version *version = NULL;
  89
  90       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  91         {
  92           const ElfW(Half) *vernum =
  93             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  94           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  95           version = &l->l_versions[ndx];
  96           if (version->hash == 0)
  97             version = NULL;
  98         }
  99
 100       /* We need to keep the scope around so do some locking.  This is
 101          not necessary for objects which cannot be unloaded or when
 102          we are not using any threads (yet).  */
 103       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 104       if (!RTLD_SINGLE_THREAD_P)
 105         {
 106           THREAD_GSCOPE_SET_FLAG ();
 107           flags |= DL_LOOKUP_GSCOPE_LOCK;
 108         }
 109
 110 #ifdef RTLD_ENABLE_FOREIGN_CALL
 111       RTLD_ENABLE_FOREIGN_CALL;
 112 #endif
 113
 114       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 115                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 116
 117       /* We are done with the global scope.  */
 118       if (!RTLD_SINGLE_THREAD_P)
 119         THREAD_GSCOPE_RESET_FLAG ();
 120
 121 #ifdef RTLD_FINALIZE_FOREIGN_CALL
 122       RTLD_FINALIZE_FOREIGN_CALL;
 123 #endif
 124
 125       /* Currently result contains the base load address (or link map)
 126          of the object that defines sym.  Now add in the symbol
 127          offset.  */
 128       value = DL_FIXUP_MAKE_VALUE (result,
 129                                    sym ? (LOOKUP_VALUE_ADDRESS (result)
 130                                           + sym->st_value) : 0);
 131     }
 132   else
 133     {
 134       /* We already found the symbol.  The module (and therefore its load
 135          address) is also known.  */
 136       value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + sym->st_value);
 137       result = l;
 138     }
 139
 140   /* And now perhaps the relocation addend.  */
 141   value = elf_machine_plt_value (l, reloc, value);
 142
 143   if (sym != NULL
 144       && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 145     value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 146
 147   /* Finally, fix up the plt itself.  */
 148   if (__builtin_expect (GLRO(dl_bind_not), 0))
 149     return value;
 150
 151   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 152 }
 153 #endif
 154
 155 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 156 DL_FIXUP_VALUE_TYPE
 157 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 158 _dl_profile_fixup (
 159 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 160                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 161 #endif
 162                    struct link_map *l, ElfW(Word) reloc_arg,
 163                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 164 {
 165   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 166
 167   if (l->l_reloc_result == NULL)
 168     {
 169       /* BZ #14843: ELF_DYNAMIC_RELOCATE is called before l_reloc_result
 170          is allocated.  We will get here if ELF_DYNAMIC_RELOCATE calls a
 171          resolver function to resolve an IRELATIVE relocation and that
 172          resolver calls a function that is not yet resolved (lazy).  For
 173          example, the resolver in x86-64 libm.so calls __get_cpu_features
 174          defined in libc.so.  Skip audit and resolve the external function
 175          in this case.  */
 176       *framesizep = -1;
 177       return _dl_fixup (
 178 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 179 #  ifndef ELF_MACHINE_RUNTIME_FIXUP_PARAMS
 180 #   error Please define ELF_MACHINE_RUNTIME_FIXUP_PARAMS.
 181 #  endif
 182                         ELF_MACHINE_RUNTIME_FIXUP_PARAMS,
 183 # endif
 184                         l, reloc_arg);
 185     }
 186
 187   /* This is the address in the array where we store the result of previous
 188      relocations.  */
 189   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 190   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 191
 192   DL_FIXUP_VALUE_TYPE value = *resultp;
 193   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 194     {
 195       /* This is the first time we have to relocate this object.  */
 196       const ElfW(Sym) *const symtab
 197         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 198       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 199
 200       const PLTREL *const reloc
 201         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 202       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 203       const ElfW(Sym) *defsym = refsym;
 204       lookup_t result;
 205
 206       /* Sanity check that we're really looking at a PLT relocation.  */
 207       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 208
 209       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 210          don't look in the global scope.  */
 211       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 212         {
 213           const struct r_found_version *version = NULL;
 214
 215           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 216             {
 217               const ElfW(Half) *vernum =
 218                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 219               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 220               version = &l->l_versions[ndx];
 221               if (version->hash == 0)
 222                 version = NULL;
 223             }
 224
 225           /* We need to keep the scope around so do some locking.  This is
 226              not necessary for objects which cannot be unloaded or when
 227              we are not using any threads (yet).  */
 228           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 229           if (!RTLD_SINGLE_THREAD_P)
 230             {
 231               THREAD_GSCOPE_SET_FLAG ();
 232               flags |= DL_LOOKUP_GSCOPE_LOCK;
 233             }
 234
 235           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 236                                         &defsym, l->l_scope, version,
 237                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 238
 239           /* We are done with the global scope.  */
 240           if (!RTLD_SINGLE_THREAD_P)
 241             THREAD_GSCOPE_RESET_FLAG ();
 242
 243           /* Currently result contains the base load address (or link map)
 244              of the object that defines sym.  Now add in the symbol
 245              offset.  */
 246           value = DL_FIXUP_MAKE_VALUE (result,
 247                                        defsym != NULL
 248                                        ? LOOKUP_VALUE_ADDRESS (result)
 249                                          + defsym->st_value : 0);
 250
 251           if (defsym != NULL
 252               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 253                                    == STT_GNU_IFUNC, 0))
 254             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 255         }
 256       else
 257         {
 258           /* We already found the symbol.  The module (and therefore its load
 259              address) is also known.  */
 260           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 261
 262           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 263                                 == STT_GNU_IFUNC, 0))
 264             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 265
 266           result = l;
 267         }
 268       /* And now perhaps the relocation addend.  */
 269       value = elf_machine_plt_value (l, reloc, value);
 270
 271 #ifdef SHARED
 272       /* Auditing checkpoint: we have a new binding.  Provide the
 273          auditing libraries the possibility to change the value and
 274          tell us whether further auditing is wanted.  */
 275       if (defsym != NULL && GLRO(dl_naudit) > 0)
 276         {
 277           reloc_result->bound = result;
 278           /* Compute index of the symbol entry in the symbol table of
 279              the DSO with the definition.  */
 280           reloc_result->boundndx = (defsym
 281                                     - (ElfW(Sym) *) D_PTR (result,
 282                                                            l_info[DT_SYMTAB]));
 283
 284           /* Determine whether any of the two participating DSOs is
 285              interested in auditing.  */
 286           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 287             {
 288               unsigned int flags = 0;
 289               struct audit_ifaces *afct = GLRO(dl_audit);
 290               /* Synthesize a symbol record where the st_value field is
 291                  the result.  */
 292               ElfW(Sym) sym = *defsym;
 293               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 294
 295               /* Keep track whether there is any interest in tracing
 296                  the call in the lower two bits.  */
 297               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 298               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 299               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 300
 301               const char *strtab2 = (const void *) D_PTR (result,
 302                                                           l_info[DT_STRTAB]);
 303
 304               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 305                 {
 306                   /* XXX Check whether both DSOs must request action or
 307                      only one */
 308                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 309                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 310                     {
 311                       if (afct->symbind != NULL)
 312                         {
 313                           uintptr_t new_value
 314                             = afct->symbind (&sym, reloc_result->boundndx,
 315                                              &l->l_audit[cnt].cookie,
 316                                              &result->l_audit[cnt].cookie,
 317                                              &flags,
 318                                              strtab2 + defsym->st_name);
 319                           if (new_value != (uintptr_t) sym.st_value)
 320                             {
 321                               flags |= LA_SYMB_ALTVALUE;
 322                               sym.st_value = new_value;
 323                             }
 324                         }
 325
 326                       /* Remember the results for every audit library and
 327                          store a summary in the first two bits.  */
 328                       reloc_result->enterexit
 329                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 330                       reloc_result->enterexit
 331                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 332                             << ((cnt + 1) * 2));
 333                     }
 334                   else
 335                     /* If the bind flags say this auditor is not interested,
 336                        set the bits manually.  */
 337                     reloc_result->enterexit
 338                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 339                           << ((cnt + 1) * 2));
 340
 341                   afct = afct->next;
 342                 }
 343
 344               reloc_result->flags = flags;
 345               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 346             }
 347           else
 348             /* Set all bits since this symbol binding is not interesting.  */
 349             reloc_result->enterexit = (1u << DL_NNS) - 1;
 350         }
 351 #endif
 352
 353       /* Store the result for later runs.  */
 354       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 355         *resultp = value;
 356     }
 357
 358   /* By default we do not call the pltexit function.  */
 359   long int framesize = -1;
 360
 361 #ifdef SHARED
 362   /* Auditing checkpoint: report the PLT entering and allow the
 363      auditors to change the value.  */
 364   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 365       /* Don't do anything if no auditor wants to intercept this call.  */
 366       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 367     {
 368       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 369                                                 l_info[DT_SYMTAB])
 370                            + reloc_result->boundndx);
 371
 372       /* Set up the sym parameter.  */
 373       ElfW(Sym) sym = *defsym;
 374       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 375
 376       /* Get the symbol name.  */
 377       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 378                                                  l_info[DT_STRTAB]);
 379       const char *symname = strtab + sym.st_name;
 380
 381       /* Keep track of overwritten addresses.  */
 382       unsigned int flags = reloc_result->flags;
 383
 384       struct audit_ifaces *afct = GLRO(dl_audit);
 385       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 386         {
 387           if (afct->ARCH_LA_PLTENTER != NULL
 388               && (reloc_result->enterexit
 389                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 390             {
 391               long int new_framesize = -1;
 392               uintptr_t new_value
 393                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 394                                           &l->l_audit[cnt].cookie,
 395                                           &reloc_result->bound->l_audit[cnt].cookie,
 396                                           regs, &flags, symname,
 397                                           &new_framesize);
 398               if (new_value != (uintptr_t) sym.st_value)
 399                 {
 400                   flags |= LA_SYMB_ALTVALUE;
 401                   sym.st_value = new_value;
 402                 }
 403
 404               /* Remember the results for every audit library and
 405                  store a summary in the first two bits.  */
 406               reloc_result->enterexit
 407                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 408                     << (2 * (cnt + 1)));
 409
 410               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 411                                               << (2 * (cnt + 1))))
 412                   == 0 && new_framesize != -1 && framesize != -2)
 413                 {
 414                   /* If this is the first call providing information,
 415                      use it.  */
 416                   if (framesize == -1)
 417                     framesize = new_framesize;
 418                   /* If two pltenter calls provide conflicting information,
 419                      use the larger value.  */
 420                   else if (new_framesize != framesize)
 421                     framesize = MAX (new_framesize, framesize);
 422                 }
 423             }
 424
 425           afct = afct->next;
 426         }
 427
 428       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 429     }
 430 #endif
 431
 432   /* Store the frame size information.  */
 433   *framesizep = framesize;
 434
 435   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 436
 437   return value;
 438 }
 439
 440 #endif /* PROF && ELF_MACHINE_NO_PLT */
 441
 442
 443 #include <stdio.h>
 444 void
 445 ARCH_FIXUP_ATTRIBUTE
 446 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 447                   const void *inregs, void *outregs)
 448 {
 449 #ifdef SHARED
 450   /* This is the address in the array where we store the result of previous
 451      relocations.  */
 452   // XXX Maybe the bound information must be stored on the stack since
 453   // XXX with bind_not a new value could have been stored in the meantime.
 454   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 455   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 456                                             l_info[DT_SYMTAB])
 457                        + reloc_result->boundndx);
 458
 459   /* Set up the sym parameter.  */
 460   ElfW(Sym) sym = *defsym;
 461   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 462
 463   /* Get the symbol name.  */
 464   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 465                                              l_info[DT_STRTAB]);
 466   const char *symname = strtab + sym.st_name;
 467
 468   struct audit_ifaces *afct = GLRO(dl_audit);
 469   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 470     {
 471       if (afct->ARCH_LA_PLTEXIT != NULL
 472           && (reloc_result->enterexit
 473               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 474         {
 475           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 476                                  &l->l_audit[cnt].cookie,
 477                                  &reloc_result->bound->l_audit[cnt].cookie,
 478                                  inregs, outregs, symname);
 479         }
 480
 481       afct = afct->next;
 482     }
 483 #endif
 484 }