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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #define IN_DL_RUNTIME 1         /* This can be tested in dl-machine.h.  */
  21
  22 #include <alloca.h>
  23 #include <stdlib.h>
  24 #include <unistd.h>
  25 #include <sys/param.h>
  26 #include <ldsodefs.h>
  27 #include <sysdep-cancel.h>
  28 #include "dynamic-link.h"
  29 #include <tls.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 = ((DL_FIXUP_VALUE_TYPE (*) (void)) 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 = ((DL_FIXUP_VALUE_TYPE (*) (void))
 239                      DL_FIXUP_VALUE_ADDR (value)) ();
 240         }
 241       else
 242         {
 243           /* We already found the symbol.  The module (and therefore its load
 244              address) is also known.  */
 245           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 246
 247           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 248                                 == STT_GNU_IFUNC, 0))
 249             value = ((DL_FIXUP_VALUE_TYPE (*) (void))
 250                      DL_FIXUP_VALUE_ADDR (value)) ();
 251
 252           result = l;
 253         }
 254       /* And now perhaps the relocation addend.  */
 255       value = elf_machine_plt_value (l, reloc, value);
 256
 257 #ifdef SHARED
 258       /* Auditing checkpoint: we have a new binding.  Provide the
 259          auditing libraries the possibility to change the value and
 260          tell us whether further auditing is wanted.  */
 261       if (defsym != NULL && GLRO(dl_naudit) > 0)
 262         {
 263           reloc_result->bound = result;
 264           /* Compute index of the symbol entry in the symbol table of
 265              the DSO with the definition.  */
 266           reloc_result->boundndx = (defsym
 267                                     - (ElfW(Sym) *) D_PTR (result,
 268                                                            l_info[DT_SYMTAB]));
 269
 270           /* Determine whether any of the two participating DSOs is
 271              interested in auditing.  */
 272           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 273             {
 274               unsigned int altvalue = 0;
 275               struct audit_ifaces *afct = GLRO(dl_audit);
 276               /* Synthesize a symbol record where the st_value field is
 277                  the result.  */
 278               ElfW(Sym) sym = *defsym;
 279               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 280
 281               /* Keep track whether there is any interest in tracing
 282                  the call in the lower two bits.  */
 283               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 284               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 285               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 286
 287               const char *strtab2 = (const void *) D_PTR (result,
 288                                                           l_info[DT_STRTAB]);
 289
 290               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 291                 {
 292                   /* XXX Check whether both DSOs must request action or
 293                      only one */
 294                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 295                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 296                     {
 297                       unsigned int flags = altvalue;
 298                       if (afct->symbind != NULL)
 299                         {
 300                           uintptr_t new_value
 301                             = afct->symbind (&sym, reloc_result->boundndx,
 302                                              &l->l_audit[cnt].cookie,
 303                                              &result->l_audit[cnt].cookie,
 304                                              &flags,
 305                                              strtab2 + defsym->st_name);
 306                           if (new_value != (uintptr_t) sym.st_value)
 307                             {
 308                               altvalue = LA_SYMB_ALTVALUE;
 309                               sym.st_value = new_value;
 310                             }
 311                         }
 312
 313                       /* Remember the results for every audit library and
 314                          store a summary in the first two bits.  */
 315                       reloc_result->enterexit
 316                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 317                       reloc_result->enterexit
 318                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 319                             << ((cnt + 1) * 2));
 320                     }
 321                   else
 322                     /* If the bind flags say this auditor is not interested,
 323                        set the bits manually.  */
 324                     reloc_result->enterexit
 325                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 326                           << ((cnt + 1) * 2));
 327
 328                   afct = afct->next;
 329                 }
 330
 331               reloc_result->flags = altvalue;
 332               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 333             }
 334           else
 335             /* Set all bits since this symbol binding is not interesting.  */
 336             reloc_result->enterexit = (1u << DL_NNS) - 1;
 337         }
 338 #endif
 339
 340       /* Store the result for later runs.  */
 341       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 342         *resultp = value;
 343     }
 344
 345   /* By default we do not call the pltexit function.  */
 346   long int framesize = -1;
 347
 348 #ifdef SHARED
 349   /* Auditing checkpoint: report the PLT entering and allow the
 350      auditors to change the value.  */
 351   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 352       /* Don't do anything if no auditor wants to intercept this call.  */
 353       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 354     {
 355       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 356                                                 l_info[DT_SYMTAB])
 357                            + reloc_result->boundndx);
 358
 359       /* Set up the sym parameter.  */
 360       ElfW(Sym) sym = *defsym;
 361       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 362
 363       /* Get the symbol name.  */
 364       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 365                                                  l_info[DT_STRTAB]);
 366       const char *symname = strtab + sym.st_name;
 367
 368       /* Keep track of overwritten addresses.  */
 369       unsigned int altvalue = reloc_result->flags;
 370
 371       struct audit_ifaces *afct = GLRO(dl_audit);
 372       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 373         {
 374           if (afct->ARCH_LA_PLTENTER != NULL
 375               && (reloc_result->enterexit
 376                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 377             {
 378               unsigned int flags = altvalue;
 379               long int new_framesize = -1;
 380               uintptr_t new_value
 381                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 382                                           &l->l_audit[cnt].cookie,
 383                                           &reloc_result->bound->l_audit[cnt].cookie,
 384                                           regs, &flags, symname,
 385                                           &new_framesize);
 386               if (new_value != (uintptr_t) sym.st_value)
 387                 {
 388                   altvalue = LA_SYMB_ALTVALUE;
 389                   sym.st_value = new_value;
 390                 }
 391
 392               /* Remember the results for every audit library and
 393                  store a summary in the first two bits.  */
 394               reloc_result->enterexit
 395                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 396                     << (2 * (cnt + 1)));
 397
 398               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 399                                               << (2 * (cnt + 1))))
 400                   == 0 && new_framesize != -1 && framesize != -2)
 401                 {
 402                   /* If this is the first call providing information,
 403                      use it.  */
 404                   if (framesize == -1)
 405                     framesize = new_framesize;
 406                   /* If two pltenter calls provide conflicting information,
 407                      use the larger value.  */
 408                   else if (new_framesize != framesize)
 409                     framesize = MAX (new_framesize, framesize);
 410                 }
 411             }
 412
 413           afct = afct->next;
 414         }
 415
 416       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 417     }
 418 #endif
 419
 420   /* Store the frame size information.  */
 421   *framesizep = framesize;
 422
 423   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 424
 425   return value;
 426 }
 427
 428 #endif /* PROF && ELF_MACHINE_NO_PLT */
 429
 430
 431 #include <stdio.h>
 432 void
 433 ARCH_FIXUP_ATTRIBUTE
 434 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 435                   const void *inregs, void *outregs)
 436 {
 437 #ifdef SHARED
 438   /* This is the address in the array where we store the result of previous
 439      relocations.  */
 440   // XXX Maybe the bound information must be stored on the stack since
 441   // XXX with bind_not a new value could have been stored in the meantime.
 442   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 443   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 444                                             l_info[DT_SYMTAB])
 445                        + reloc_result->boundndx);
 446
 447   /* Set up the sym parameter.  */
 448   ElfW(Sym) sym = *defsym;
 449   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 450
 451   /* Get the symbol name.  */
 452   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 453                                              l_info[DT_STRTAB]);
 454   const char *symname = strtab + sym.st_name;
 455
 456   struct audit_ifaces *afct = GLRO(dl_audit);
 457   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 458     {
 459       if (afct->ARCH_LA_PLTEXIT != NULL
 460           && (reloc_result->enterexit
 461               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 462         {
 463           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 464                                  &l->l_audit[cnt].cookie,
 465                                  &reloc_result->bound->l_audit[cnt].cookie,
 466                                  inregs, outregs, symname);
 467         }
 468
 469       afct = afct->next;
 470     }
 471 #endif
 472 }