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