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