elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2006, 2007 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
  30 #if (!defined ELF_MACHINE_NO_RELA && !defined ELF_MACHINE_PLT_REL) \
  31     || ELF_MACHINE_NO_REL
  32 # define PLTREL  ElfW(Rela)
  33 #else
  34 # define PLTREL  ElfW(Rel)
  35 #endif
  36
  37 #ifndef VERSYMIDX
  38 # define VERSYMIDX(sym) (DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (sym))
  39 #endif
  40
  41 /* The fixup functions might have need special attributes.  If none
  42    are provided define the macro as empty.  */
  43 #ifndef ARCH_FIXUP_ATTRIBUTE
  44 # define ARCH_FIXUP_ATTRIBUTE
  45 #endif
  46
  47
  48 /* This function is called through a special trampoline from the PLT the
  49    first time each PLT entry is called.  We must perform the relocation
  50    specified in the PLT of the given shared object, and return the resolved
  51    function address to the trampoline, which will restart the original call
  52    to that address.  Future calls will bounce directly from the PLT to the
  53    function.  */
  54
  55 #ifndef ELF_MACHINE_NO_PLT
  56 DL_FIXUP_VALUE_TYPE
  57 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
  58 _dl_fixup (
  59 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  60            ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  61 # endif
  62            /* GKM FIXME: Fix trampoline to pass bounds so we can do
  63               without the `__unbounded' qualifier.  */
  64            struct link_map *__unbounded l, ElfW(Word) reloc_offset)
  65 {
  66   const ElfW(Sym) *const symtab
  67     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  68   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  69
  70   const PLTREL *const reloc
  71     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  72   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  73   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  74   lookup_t result;
  75   DL_FIXUP_VALUE_TYPE value;
  76
  77   /* Sanity check that we're really looking at a PLT relocation.  */
  78   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  79
  80    /* Look up the target symbol.  If the normal lookup rules are not
  81       used don't look in the global scope.  */
  82   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  83     {
  84       const struct r_found_version *version = NULL;
  85
  86       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  87         {
  88           const ElfW(Half) *vernum =
  89             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  90           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  91           version = &l->l_versions[ndx];
  92           if (version->hash == 0)
  93             version = NULL;
  94         }
  95
  96       /* We need to keep the scope around so do some locking.  This is
  97          not necessary for objects which cannot be unloaded or when
  98          we are not using any threads (yet).  */
  99       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 100       if (l->l_type == lt_loaded && !RTLD_SINGLE_THREAD_P)
 101         {
 102           __rtld_mrlock_lock (l->l_scope_lock);
 103           flags |= DL_LOOKUP_SCOPE_LOCK;
 104         }
 105
 106       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 107                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 108
 109       if ((flags & DL_LOOKUP_SCOPE_LOCK) != 0)
 110         __rtld_mrlock_unlock (l->l_scope_lock);
 111
 112       /* Currently result contains the base load address (or link map)
 113          of the object that defines sym.  Now add in the symbol
 114          offset.  */
 115       value = DL_FIXUP_MAKE_VALUE (result,
 116                                    sym ? (LOOKUP_VALUE_ADDRESS (result)
 117                                           + sym->st_value) : 0);
 118     }
 119   else
 120     {
 121       /* We already found the symbol.  The module (and therefore its load
 122          address) is also known.  */
 123       value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + sym->st_value);
 124       result = l;
 125     }
 126
 127   /* And now perhaps the relocation addend.  */
 128   value = elf_machine_plt_value (l, reloc, value);
 129
 130   /* Finally, fix up the plt itself.  */
 131   if (__builtin_expect (GLRO(dl_bind_not), 0))
 132     return value;
 133
 134   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 135 }
 136 #endif
 137
 138 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 139
 140 DL_FIXUP_VALUE_TYPE
 141 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 142 _dl_profile_fixup (
 143 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 144                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 145 #endif
 146                    struct link_map *l, ElfW(Word) reloc_offset,
 147                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 148 {
 149   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = INTUSE(_dl_mcount);
 150
 151   /* This is the address in the array where we store the result of previous
 152      relocations.  */
 153   struct reloc_result *reloc_result
 154     = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 155   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 156
 157   DL_FIXUP_VALUE_TYPE value = *resultp;
 158   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 159     {
 160       /* This is the first time we have to relocate this object.  */
 161       const ElfW(Sym) *const symtab
 162         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 163       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 164
 165       const PLTREL *const reloc
 166         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 167       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 168       const ElfW(Sym) *defsym = refsym;
 169       lookup_t result;
 170
 171       /* Sanity check that we're really looking at a PLT relocation.  */
 172       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 173
 174       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 175          don't look in the global scope.  */
 176       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 177         {
 178           const struct r_found_version *version = NULL;
 179
 180           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 181             {
 182               const ElfW(Half) *vernum =
 183                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 184               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 185               version = &l->l_versions[ndx];
 186               if (version->hash == 0)
 187                 version = NULL;
 188             }
 189
 190           /* We need to keep the scope around so do some locking.  This is
 191              not necessary for objects which cannot be unloaded or when
 192              we are not using any threads (yet).  */
 193           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 194           if (l->l_type == lt_loaded && !RTLD_SINGLE_THREAD_P)
 195             {
 196               __rtld_mrlock_lock (l->l_scope_lock);
 197               flags |= DL_LOOKUP_SCOPE_LOCK;
 198             }
 199
 200           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 201                                         &defsym, l->l_scope, version,
 202                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 203
 204           if ((flags & DL_LOOKUP_SCOPE_LOCK) != 0)
 205             __rtld_mrlock_unlock (l->l_scope_lock);
 206
 207           /* Currently result contains the base load address (or link map)
 208              of the object that defines sym.  Now add in the symbol
 209              offset.  */
 210           value = DL_FIXUP_MAKE_VALUE (result,
 211                                        defsym != NULL
 212                                        ? LOOKUP_VALUE_ADDRESS (result)
 213                                          + defsym->st_value : 0);
 214         }
 215       else
 216         {
 217           /* We already found the symbol.  The module (and therefore its load
 218              address) is also known.  */
 219           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 220           result = l;
 221         }
 222       /* And now perhaps the relocation addend.  */
 223       value = elf_machine_plt_value (l, reloc, value);
 224
 225 #ifdef SHARED
 226       /* Auditing checkpoint: we have a new binding.  Provide the
 227          auditing libraries the possibility to change the value and
 228          tell us whether further auditing is wanted.  */
 229       if (defsym != NULL && GLRO(dl_naudit) > 0)
 230         {
 231           reloc_result->bound = result;
 232           /* Compute index of the symbol entry in the symbol table of
 233              the DSO with the definition.  */
 234           reloc_result->boundndx = (defsym
 235                                     - (ElfW(Sym) *) D_PTR (result,
 236                                                            l_info[DT_SYMTAB]));
 237
 238           /* Determine whether any of the two participating DSOs is
 239              interested in auditing.  */
 240           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 241             {
 242               unsigned int altvalue = 0;
 243               struct audit_ifaces *afct = GLRO(dl_audit);
 244               /* Synthesize a symbol record where the st_value field is
 245                  the result.  */
 246               ElfW(Sym) sym = *defsym;
 247               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 248
 249               /* Keep track whether there is any interest in tracing
 250                  the call in the lower two bits.  */
 251               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 252               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 253               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 254
 255               const char *strtab2 = (const void *) D_PTR (result,
 256                                                           l_info[DT_STRTAB]);
 257
 258               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 259                 {
 260                   /* XXX Check whether both DSOs must request action or
 261                      only one */
 262                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 263                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 264                     {
 265                       unsigned int flags = altvalue;
 266                       if (afct->symbind != NULL)
 267                         {
 268                           uintptr_t new_value
 269                             = afct->symbind (&sym, reloc_result->boundndx,
 270                                              &l->l_audit[cnt].cookie,
 271                                              &result->l_audit[cnt].cookie,
 272                                              &flags,
 273                                              strtab2 + defsym->st_name);
 274                           if (new_value != (uintptr_t) sym.st_value)
 275                             {
 276                               altvalue = LA_SYMB_ALTVALUE;
 277                               sym.st_value = new_value;
 278                             }
 279                         }
 280
 281                       /* Remember the results for every audit library and
 282                          store a summary in the first two bits.  */
 283                       reloc_result->enterexit
 284                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 285                       reloc_result->enterexit
 286                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 287                             << ((cnt + 1) * 2));
 288                     }
 289                   else
 290                     /* If the bind flags say this auditor is not interested,
 291                        set the bits manually.  */
 292                     reloc_result->enterexit
 293                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 294                           << ((cnt + 1) * 2));
 295
 296                   afct = afct->next;
 297                 }
 298
 299               reloc_result->flags = altvalue;
 300               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 301             }
 302           else
 303             /* Set all bits since this symbol binding is not interesting.  */
 304             reloc_result->enterexit = (1u << DL_NNS) - 1;
 305         }
 306 #endif
 307
 308       /* Store the result for later runs.  */
 309       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 310         *resultp = value;
 311     }
 312
 313   /* By default we do not call the pltexit function.  */
 314   long int framesize = -1;
 315
 316 #ifdef SHARED
 317   /* Auditing checkpoint: report the PLT entering and allow the
 318      auditors to change the value.  */
 319   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 320       /* Don't do anything if no auditor wants to intercept this call.  */
 321       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 322     {
 323       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 324                                                 l_info[DT_SYMTAB])
 325                            + reloc_result->boundndx);
 326
 327       /* Set up the sym parameter.  */
 328       ElfW(Sym) sym = *defsym;
 329       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 330
 331       /* Get the symbol name.  */
 332       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 333                                                  l_info[DT_STRTAB]);
 334       const char *symname = strtab + sym.st_name;
 335
 336       /* Keep track of overwritten addresses.  */
 337       unsigned int altvalue = reloc_result->flags;
 338
 339       struct audit_ifaces *afct = GLRO(dl_audit);
 340       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 341         {
 342           if (afct->ARCH_LA_PLTENTER != NULL
 343               && (reloc_result->enterexit
 344                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 345             {
 346               unsigned int flags = altvalue;
 347               long int new_framesize = -1;
 348               uintptr_t new_value
 349                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 350                                           &l->l_audit[cnt].cookie,
 351                                           &reloc_result->bound->l_audit[cnt].cookie,
 352                                           regs, &flags, symname,
 353                                           &new_framesize);
 354               if (new_value != (uintptr_t) sym.st_value)
 355                 {
 356                   altvalue = LA_SYMB_ALTVALUE;
 357                   sym.st_value = new_value;
 358                 }
 359
 360               /* Remember the results for every audit library and
 361                  store a summary in the first two bits.  */
 362               reloc_result->enterexit
 363                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 364                     << (2 * (cnt + 1)));
 365
 366               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 367                                               << (2 * (cnt + 1))))
 368                   == 0 && new_framesize != -1 && framesize != -2)
 369                 {
 370                   /* If this is the first call providing information,
 371                      use it.  */
 372                   if (framesize == -1)
 373                     framesize = new_framesize;
 374                   /* If two pltenter calls provide conflicting information,
 375                      use the larger value.  */
 376                   else if (new_framesize != framesize)
 377                     framesize = MAX (new_framesize, framesize);
 378                 }
 379             }
 380
 381           afct = afct->next;
 382         }
 383
 384       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 385     }
 386 #endif
 387
 388   /* Store the frame size information.  */
 389   *framesizep = framesize;
 390
 391   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 392
 393   return value;
 394 }
 395
 396 #endif /* PROF && ELF_MACHINE_NO_PLT */
 397
 398
 399 #include <stdio.h>
 400 void
 401 ARCH_FIXUP_ATTRIBUTE
 402 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_offset,
 403                   const void *inregs, void *outregs)
 404 {
 405 #ifdef SHARED
 406   /* This is the address in the array where we store the result of previous
 407      relocations.  */
 408   // XXX Maybe the bound information must be stored on the stack since
 409   // XXX with bind_not a new value could have been stored in the meantime.
 410   struct reloc_result *reloc_result
 411     = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 412   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 413                                             l_info[DT_SYMTAB])
 414                        + reloc_result->boundndx);
 415
 416   /* Set up the sym parameter.  */
 417   ElfW(Sym) sym = *defsym;
 418
 419   /* Get the symbol name.  */
 420   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 421                                              l_info[DT_STRTAB]);
 422   const char *symname = strtab + sym.st_name;
 423
 424   struct audit_ifaces *afct = GLRO(dl_audit);
 425   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 426     {
 427       if (afct->ARCH_LA_PLTEXIT != NULL
 428           && (reloc_result->enterexit
 429               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 430         {
 431           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 432                                  &l->l_audit[cnt].cookie,
 433                                  &reloc_result->bound->l_audit[cnt].cookie,
 434                                  inregs, outregs, symname);
 435         }
 436
 437       afct = afct->next;
 438     }
 439 #endif
 440 }