elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2006, 2007, 2008, 2009 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 (__builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 148     value = ((DL_FIXUP_VALUE_TYPE (*) (void)) DL_FIXUP_VALUE_ADDR (value)) ();
 149
 150   /* Finally, fix up the plt itself.  */
 151   if (__builtin_expect (GLRO(dl_bind_not), 0))
 152     return value;
 153
 154   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 155 }
 156 #endif
 157
 158 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 159 DL_FIXUP_VALUE_TYPE
 160 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 161 _dl_profile_fixup (
 162 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 163                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 164 #endif
 165                    struct link_map *l, ElfW(Word) reloc_arg,
 166                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 167 {
 168   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 169
 170   /* This is the address in the array where we store the result of previous
 171      relocations.  */
 172   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 173   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 174
 175   DL_FIXUP_VALUE_TYPE value = *resultp;
 176   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 177     {
 178       /* This is the first time we have to relocate this object.  */
 179       const ElfW(Sym) *const symtab
 180         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 181       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 182
 183       const PLTREL *const reloc
 184         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 185       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 186       const ElfW(Sym) *defsym = refsym;
 187       lookup_t result;
 188
 189       /* Sanity check that we're really looking at a PLT relocation.  */
 190       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 191
 192       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 193          don't look in the global scope.  */
 194       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 195         {
 196           const struct r_found_version *version = NULL;
 197
 198           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 199             {
 200               const ElfW(Half) *vernum =
 201                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 202               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 203               version = &l->l_versions[ndx];
 204               if (version->hash == 0)
 205                 version = NULL;
 206             }
 207
 208           /* We need to keep the scope around so do some locking.  This is
 209              not necessary for objects which cannot be unloaded or when
 210              we are not using any threads (yet).  */
 211           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 212           if (!RTLD_SINGLE_THREAD_P)
 213             {
 214               THREAD_GSCOPE_SET_FLAG ();
 215               flags |= DL_LOOKUP_GSCOPE_LOCK;
 216             }
 217
 218           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 219                                         &defsym, l->l_scope, version,
 220                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 221
 222           /* We are done with the global scope.  */
 223           if (!RTLD_SINGLE_THREAD_P)
 224             THREAD_GSCOPE_RESET_FLAG ();
 225
 226           /* Currently result contains the base load address (or link map)
 227              of the object that defines sym.  Now add in the symbol
 228              offset.  */
 229           value = DL_FIXUP_MAKE_VALUE (result,
 230                                        defsym != NULL
 231                                        ? LOOKUP_VALUE_ADDRESS (result)
 232                                          + defsym->st_value : 0);
 233
 234           if (__builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 235                                 == STT_GNU_IFUNC, 0))
 236             value = ((DL_FIXUP_VALUE_TYPE (*) (void))
 237                      DL_FIXUP_VALUE_ADDR (value)) ();
 238         }
 239       else
 240         {
 241           /* We already found the symbol.  The module (and therefore its load
 242              address) is also known.  */
 243           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 244
 245           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 246                                 == STT_GNU_IFUNC, 0))
 247             value = ((DL_FIXUP_VALUE_TYPE (*) (void))
 248                      DL_FIXUP_VALUE_ADDR (value)) ();
 249
 250           result = l;
 251         }
 252       /* And now perhaps the relocation addend.  */
 253       value = elf_machine_plt_value (l, reloc, value);
 254
 255 #ifdef SHARED
 256       /* Auditing checkpoint: we have a new binding.  Provide the
 257          auditing libraries the possibility to change the value and
 258          tell us whether further auditing is wanted.  */
 259       if (defsym != NULL && GLRO(dl_naudit) > 0)
 260         {
 261           reloc_result->bound = result;
 262           /* Compute index of the symbol entry in the symbol table of
 263              the DSO with the definition.  */
 264           reloc_result->boundndx = (defsym
 265                                     - (ElfW(Sym) *) D_PTR (result,
 266                                                            l_info[DT_SYMTAB]));
 267
 268           /* Determine whether any of the two participating DSOs is
 269              interested in auditing.  */
 270           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 271             {
 272               unsigned int altvalue = 0;
 273               struct audit_ifaces *afct = GLRO(dl_audit);
 274               /* Synthesize a symbol record where the st_value field is
 275                  the result.  */
 276               ElfW(Sym) sym = *defsym;
 277               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 278
 279               /* Keep track whether there is any interest in tracing
 280                  the call in the lower two bits.  */
 281               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 282               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 283               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 284
 285               const char *strtab2 = (const void *) D_PTR (result,
 286                                                           l_info[DT_STRTAB]);
 287
 288               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 289                 {
 290                   /* XXX Check whether both DSOs must request action or
 291                      only one */
 292                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 293                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 294                     {
 295                       unsigned int flags = altvalue;
 296                       if (afct->symbind != NULL)
 297                         {
 298                           uintptr_t new_value
 299                             = afct->symbind (&sym, reloc_result->boundndx,
 300                                              &l->l_audit[cnt].cookie,
 301                                              &result->l_audit[cnt].cookie,
 302                                              &flags,
 303                                              strtab2 + defsym->st_name);
 304                           if (new_value != (uintptr_t) sym.st_value)
 305                             {
 306                               altvalue = LA_SYMB_ALTVALUE;
 307                               sym.st_value = new_value;
 308                             }
 309                         }
 310
 311                       /* Remember the results for every audit library and
 312                          store a summary in the first two bits.  */
 313                       reloc_result->enterexit
 314                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 315                       reloc_result->enterexit
 316                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 317                             << ((cnt + 1) * 2));
 318                     }
 319                   else
 320                     /* If the bind flags say this auditor is not interested,
 321                        set the bits manually.  */
 322                     reloc_result->enterexit
 323                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 324                           << ((cnt + 1) * 2));
 325
 326                   afct = afct->next;
 327                 }
 328
 329               reloc_result->flags = altvalue;
 330               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 331             }
 332           else
 333             /* Set all bits since this symbol binding is not interesting.  */
 334             reloc_result->enterexit = (1u << DL_NNS) - 1;
 335         }
 336 #endif
 337
 338       /* Store the result for later runs.  */
 339       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 340         *resultp = value;
 341     }
 342
 343   /* By default we do not call the pltexit function.  */
 344   long int framesize = -1;
 345
 346 #ifdef SHARED
 347   /* Auditing checkpoint: report the PLT entering and allow the
 348      auditors to change the value.  */
 349   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 350       /* Don't do anything if no auditor wants to intercept this call.  */
 351       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 352     {
 353       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 354                                                 l_info[DT_SYMTAB])
 355                            + reloc_result->boundndx);
 356
 357       /* Set up the sym parameter.  */
 358       ElfW(Sym) sym = *defsym;
 359       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 360
 361       /* Get the symbol name.  */
 362       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 363                                                  l_info[DT_STRTAB]);
 364       const char *symname = strtab + sym.st_name;
 365
 366       /* Keep track of overwritten addresses.  */
 367       unsigned int altvalue = reloc_result->flags;
 368
 369       struct audit_ifaces *afct = GLRO(dl_audit);
 370       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 371         {
 372           if (afct->ARCH_LA_PLTENTER != NULL
 373               && (reloc_result->enterexit
 374                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 375             {
 376               unsigned int flags = altvalue;
 377               long int new_framesize = -1;
 378               uintptr_t new_value
 379                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 380                                           &l->l_audit[cnt].cookie,
 381                                           &reloc_result->bound->l_audit[cnt].cookie,
 382                                           regs, &flags, symname,
 383                                           &new_framesize);
 384               if (new_value != (uintptr_t) sym.st_value)
 385                 {
 386                   altvalue = LA_SYMB_ALTVALUE;
 387                   sym.st_value = new_value;
 388                 }
 389
 390               /* Remember the results for every audit library and
 391                  store a summary in the first two bits.  */
 392               reloc_result->enterexit
 393                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 394                     << (2 * (cnt + 1)));
 395
 396               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 397                                               << (2 * (cnt + 1))))
 398                   == 0 && new_framesize != -1 && framesize != -2)
 399                 {
 400                   /* If this is the first call providing information,
 401                      use it.  */
 402                   if (framesize == -1)
 403                     framesize = new_framesize;
 404                   /* If two pltenter calls provide conflicting information,
 405                      use the larger value.  */
 406                   else if (new_framesize != framesize)
 407                     framesize = MAX (new_framesize, framesize);
 408                 }
 409             }
 410
 411           afct = afct->next;
 412         }
 413
 414       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 415     }
 416 #endif
 417
 418   /* Store the frame size information.  */
 419   *framesizep = framesize;
 420
 421   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 422
 423   return value;
 424 }
 425
 426 #endif /* PROF && ELF_MACHINE_NO_PLT */
 427
 428
 429 #include <stdio.h>
 430 void
 431 ARCH_FIXUP_ATTRIBUTE
 432 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 433                   const void *inregs, void *outregs)
 434 {
 435 #ifdef SHARED
 436   /* This is the address in the array where we store the result of previous
 437      relocations.  */
 438   // XXX Maybe the bound information must be stored on the stack since
 439   // XXX with bind_not a new value could have been stored in the meantime.
 440   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 441   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 442                                             l_info[DT_SYMTAB])
 443                        + reloc_result->boundndx);
 444
 445   /* Set up the sym parameter.  */
 446   ElfW(Sym) sym = *defsym;
 447
 448   /* Get the symbol name.  */
 449   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 450                                              l_info[DT_STRTAB]);
 451   const char *symname = strtab + sym.st_name;
 452
 453   struct audit_ifaces *afct = GLRO(dl_audit);
 454   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 455     {
 456       if (afct->ARCH_LA_PLTEXIT != NULL
 457           && (reloc_result->enterexit
 458               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 459         {
 460           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 461                                  &l->l_audit[cnt].cookie,
 462                                  &reloc_result->bound->l_audit[cnt].cookie,
 463                                  inregs, outregs, symname);
 464         }
 465
 466       afct = afct->next;
 467     }
 468 #endif
 469 }