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 #include <dl-irel.h>
  31
  32
  33 #if (!defined ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
  34     || ELF_MACHINE_NO_REL
  35 # define PLTREL  ElfW(Rela)
  36 #else
  37 # define PLTREL  ElfW(Rel)
  38 #endif
  39
  40 #ifndef VERSYMIDX
  41 # define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym))
  42 #endif
  43
  44 /* The fixup functions might have need special attributes.  If none
  45    are provided define the macro as empty.  */
  46 #ifndef ARCH_FIXUP_ATTRIBUTE
  47 # define ARCH_FIXUP_ATTRIBUTE
  48 #endif
  49
  50 #ifndef reloc_offset
  51 # define reloc_offset reloc_arg
  52 # define reloc_index  reloc_arg / sizeof (PLTREL)
  53 #endif
  54
  55
  56
  57 /* This function is called through a special trampoline from the PLT the
  58    first time each PLT entry is called.  We must perform the relocation
  59    specified in the PLT of the given shared object, and return the resolved
  60    function address to the trampoline, which will restart the original call
  61    to that address.  Future calls will bounce directly from the PLT to the
  62    function.  */
  63
  64 #ifndef ELF_MACHINE_NO_PLT
  65 DL_FIXUP_VALUE_TYPE
  66 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
  67 _dl_fixup (
  68 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  69            ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  70 # endif
  71            /* GKM FIXME: Fix trampoline to pass bounds so we can do
  72               without the `__unbounded' qualifier.  */
  73            struct link_map *__unbounded l, ElfW(Word) reloc_arg)
  74 {
  75   const ElfW(Sym) *const symtab
  76     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  77   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  78
  79   const PLTREL *const reloc
  80     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  81   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  82   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  83   lookup_t result;
  84   DL_FIXUP_VALUE_TYPE value;
  85
  86   /* Sanity check that we're really looking at a PLT relocation.  */
  87   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  88
  89    /* Look up the target symbol.  If the normal lookup rules are not
  90       used don't look in the global scope.  */
  91   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  92     {
  93       const struct r_found_version *version = NULL;
  94
  95       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  96         {
  97           const ElfW(Half) *vernum =
  98             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  99           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 100           version = &l->l_versions[ndx];
 101           if (version->hash == 0)
 102             version = NULL;
 103         }
 104
 105       /* We need to keep the scope around so do some locking.  This is
 106          not necessary for objects which cannot be unloaded or when
 107          we are not using any threads (yet).  */
 108       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 109       if (!RTLD_SINGLE_THREAD_P)
 110         {
 111           THREAD_GSCOPE_SET_FLAG ();
 112           flags |= DL_LOOKUP_GSCOPE_LOCK;
 113         }
 114
 115 #ifdef RTLD_ENABLE_FOREIGN_CALL
 116       RTLD_ENABLE_FOREIGN_CALL;
 117 #endif
 118
 119       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 120                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 121
 122       /* We are done with the global scope.  */
 123       if (!RTLD_SINGLE_THREAD_P)
 124         THREAD_GSCOPE_RESET_FLAG ();
 125
 126 #ifdef RTLD_FINALIZE_FOREIGN_CALL
 127       RTLD_FINALIZE_FOREIGN_CALL;
 128 #endif
 129
 130       /* Currently result contains the base load address (or link map)
 131          of the object that defines sym.  Now add in the symbol
 132          offset.  */
 133       value = DL_FIXUP_MAKE_VALUE (result,
 134                                    sym ? (LOOKUP_VALUE_ADDRESS (result)
 135                                           + sym->st_value) : 0);
 136     }
 137   else
 138     {
 139       /* We already found the symbol.  The module (and therefore its load
 140          address) is also known.  */
 141       value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + sym->st_value);
 142       result = l;
 143     }
 144
 145   /* And now perhaps the relocation addend.  */
 146   value = elf_machine_plt_value (l, reloc, value);
 147
 148   if (sym != NULL
 149       && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 150     value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 151
 152   /* Finally, fix up the plt itself.  */
 153   if (__builtin_expect (GLRO(dl_bind_not), 0))
 154     return value;
 155
 156   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 157 }
 158 #endif
 159
 160 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 161 DL_FIXUP_VALUE_TYPE
 162 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 163 _dl_profile_fixup (
 164 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 165                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 166 #endif
 167                    struct link_map *l, ElfW(Word) reloc_arg,
 168                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 169 {
 170   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 171
 172   /* This is the address in the array where we store the result of previous
 173      relocations.  */
 174   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 175   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 176
 177   DL_FIXUP_VALUE_TYPE value = *resultp;
 178   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 179     {
 180       /* This is the first time we have to relocate this object.  */
 181       const ElfW(Sym) *const symtab
 182         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 183       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 184
 185       const PLTREL *const reloc
 186         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 187       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 188       const ElfW(Sym) *defsym = refsym;
 189       lookup_t result;
 190
 191       /* Sanity check that we're really looking at a PLT relocation.  */
 192       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 193
 194       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 195          don't look in the global scope.  */
 196       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 197         {
 198           const struct r_found_version *version = NULL;
 199
 200           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 201             {
 202               const ElfW(Half) *vernum =
 203                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 204               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 205               version = &l->l_versions[ndx];
 206               if (version->hash == 0)
 207                 version = NULL;
 208             }
 209
 210           /* We need to keep the scope around so do some locking.  This is
 211              not necessary for objects which cannot be unloaded or when
 212              we are not using any threads (yet).  */
 213           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 214           if (!RTLD_SINGLE_THREAD_P)
 215             {
 216               THREAD_GSCOPE_SET_FLAG ();
 217               flags |= DL_LOOKUP_GSCOPE_LOCK;
 218             }
 219
 220           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 221                                         &defsym, l->l_scope, version,
 222                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 223
 224           /* We are done with the global scope.  */
 225           if (!RTLD_SINGLE_THREAD_P)
 226             THREAD_GSCOPE_RESET_FLAG ();
 227
 228           /* Currently result contains the base load address (or link map)
 229              of the object that defines sym.  Now add in the symbol
 230              offset.  */
 231           value = DL_FIXUP_MAKE_VALUE (result,
 232                                        defsym != NULL
 233                                        ? LOOKUP_VALUE_ADDRESS (result)
 234                                          + defsym->st_value : 0);
 235
 236           if (defsym != NULL
 237               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 238                                    == STT_GNU_IFUNC, 0))
 239             value = elf_ifunc_invoke (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 = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 250
 251           result = l;
 252         }
 253       /* And now perhaps the relocation addend.  */
 254       value = elf_machine_plt_value (l, reloc, value);
 255
 256 #ifdef SHARED
 257       /* Auditing checkpoint: we have a new binding.  Provide the
 258          auditing libraries the possibility to change the value and
 259          tell us whether further auditing is wanted.  */
 260       if (defsym != NULL && GLRO(dl_naudit) > 0)
 261         {
 262           reloc_result->bound = result;
 263           /* Compute index of the symbol entry in the symbol table of
 264              the DSO with the definition.  */
 265           reloc_result->boundndx = (defsym
 266                                     - (ElfW(Sym) *) D_PTR (result,
 267                                                            l_info[DT_SYMTAB]));
 268
 269           /* Determine whether any of the two participating DSOs is
 270              interested in auditing.  */
 271           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 272             {
 273               unsigned int flags = 0;
 274               struct audit_ifaces *afct = GLRO(dl_audit);
 275               /* Synthesize a symbol record where the st_value field is
 276                  the result.  */
 277               ElfW(Sym) sym = *defsym;
 278               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 279
 280               /* Keep track whether there is any interest in tracing
 281                  the call in the lower two bits.  */
 282               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 283               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 284               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 285
 286               const char *strtab2 = (const void *) D_PTR (result,
 287                                                           l_info[DT_STRTAB]);
 288
 289               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 290                 {
 291                   /* XXX Check whether both DSOs must request action or
 292                      only one */
 293                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 294                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 295                     {
 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                               flags |= 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 = flags;
 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 flags = 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               long int new_framesize = -1;
 377               uintptr_t new_value
 378                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 379                                           &l->l_audit[cnt].cookie,
 380                                           &reloc_result->bound->l_audit[cnt].cookie,
 381                                           regs, &flags, symname,
 382                                           &new_framesize);
 383               if (new_value != (uintptr_t) sym.st_value)
 384                 {
 385                   flags |= LA_SYMB_ALTVALUE;
 386                   sym.st_value = new_value;
 387                 }
 388
 389               /* Remember the results for every audit library and
 390                  store a summary in the first two bits.  */
 391               reloc_result->enterexit
 392                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 393                     << (2 * (cnt + 1)));
 394
 395               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 396                                               << (2 * (cnt + 1))))
 397                   == 0 && new_framesize != -1 && framesize != -2)
 398                 {
 399                   /* If this is the first call providing information,
 400                      use it.  */
 401                   if (framesize == -1)
 402                     framesize = new_framesize;
 403                   /* If two pltenter calls provide conflicting information,
 404                      use the larger value.  */
 405                   else if (new_framesize != framesize)
 406                     framesize = MAX (new_framesize, framesize);
 407                 }
 408             }
 409
 410           afct = afct->next;
 411         }
 412
 413       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 414     }
 415 #endif
 416
 417   /* Store the frame size information.  */
 418   *framesizep = framesize;
 419
 420   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 421
 422   return value;
 423 }
 424
 425 #endif /* PROF && ELF_MACHINE_NO_PLT */
 426
 427
 428 #include <stdio.h>
 429 void
 430 ARCH_FIXUP_ATTRIBUTE
 431 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 432                   const void *inregs, void *outregs)
 433 {
 434 #ifdef SHARED
 435   /* This is the address in the array where we store the result of previous
 436      relocations.  */
 437   // XXX Maybe the bound information must be stored on the stack since
 438   // XXX with bind_not a new value could have been stored in the meantime.
 439   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 440   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 441                                             l_info[DT_SYMTAB])
 442                        + reloc_result->boundndx);
 443
 444   /* Set up the sym parameter.  */
 445   ElfW(Sym) sym = *defsym;
 446   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 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 }