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)) 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)) value) ();
 229         }
 230       else
 231         {
 232           /* We already found the symbol.  The module (and therefore its load
 233              address) is also known.  */
 234           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 235
 236           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 237                                 == STT_GNU_IFUNC, 0))
 238             value = ((DL_FIXUP_VALUE_TYPE (*) (void)) value) ();
 239
 240           result = l;
 241         }
 242       /* And now perhaps the relocation addend.  */
 243       value = elf_machine_plt_value (l, reloc, value);
 244
 245 #ifdef SHARED
 246       /* Auditing checkpoint: we have a new binding.  Provide the
 247          auditing libraries the possibility to change the value and
 248          tell us whether further auditing is wanted.  */
 249       if (defsym != NULL && GLRO(dl_naudit) > 0)
 250         {
 251           reloc_result->bound = result;
 252           /* Compute index of the symbol entry in the symbol table of
 253              the DSO with the definition.  */
 254           reloc_result->boundndx = (defsym
 255                                     - (ElfW(Sym) *) D_PTR (result,
 256                                                            l_info[DT_SYMTAB]));
 257
 258           /* Determine whether any of the two participating DSOs is
 259              interested in auditing.  */
 260           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 261             {
 262               unsigned int altvalue = 0;
 263               struct audit_ifaces *afct = GLRO(dl_audit);
 264               /* Synthesize a symbol record where the st_value field is
 265                  the result.  */
 266               ElfW(Sym) sym = *defsym;
 267               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 268
 269               /* Keep track whether there is any interest in tracing
 270                  the call in the lower two bits.  */
 271               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 272               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 273               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 274
 275               const char *strtab2 = (const void *) D_PTR (result,
 276                                                           l_info[DT_STRTAB]);
 277
 278               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 279                 {
 280                   /* XXX Check whether both DSOs must request action or
 281                      only one */
 282                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 283                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 284                     {
 285                       unsigned int flags = altvalue;
 286                       if (afct->symbind != NULL)
 287                         {
 288                           uintptr_t new_value
 289                             = afct->symbind (&sym, reloc_result->boundndx,
 290                                              &l->l_audit[cnt].cookie,
 291                                              &result->l_audit[cnt].cookie,
 292                                              &flags,
 293                                              strtab2 + defsym->st_name);
 294                           if (new_value != (uintptr_t) sym.st_value)
 295                             {
 296                               altvalue = LA_SYMB_ALTVALUE;
 297                               sym.st_value = new_value;
 298                             }
 299                         }
 300
 301                       /* Remember the results for every audit library and
 302                          store a summary in the first two bits.  */
 303                       reloc_result->enterexit
 304                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 305                       reloc_result->enterexit
 306                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 307                             << ((cnt + 1) * 2));
 308                     }
 309                   else
 310                     /* If the bind flags say this auditor is not interested,
 311                        set the bits manually.  */
 312                     reloc_result->enterexit
 313                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 314                           << ((cnt + 1) * 2));
 315
 316                   afct = afct->next;
 317                 }
 318
 319               reloc_result->flags = altvalue;
 320               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 321             }
 322           else
 323             /* Set all bits since this symbol binding is not interesting.  */
 324             reloc_result->enterexit = (1u << DL_NNS) - 1;
 325         }
 326 #endif
 327
 328       /* Store the result for later runs.  */
 329       if (__builtin_expect (! GLRO(dl_bind_not), 1))
 330         *resultp = value;
 331     }
 332
 333   /* By default we do not call the pltexit function.  */
 334   long int framesize = -1;
 335
 336 #ifdef SHARED
 337   /* Auditing checkpoint: report the PLT entering and allow the
 338      auditors to change the value.  */
 339   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 340       /* Don't do anything if no auditor wants to intercept this call.  */
 341       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 342     {
 343       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 344                                                 l_info[DT_SYMTAB])
 345                            + reloc_result->boundndx);
 346
 347       /* Set up the sym parameter.  */
 348       ElfW(Sym) sym = *defsym;
 349       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 350
 351       /* Get the symbol name.  */
 352       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 353                                                  l_info[DT_STRTAB]);
 354       const char *symname = strtab + sym.st_name;
 355
 356       /* Keep track of overwritten addresses.  */
 357       unsigned int altvalue = reloc_result->flags;
 358
 359       struct audit_ifaces *afct = GLRO(dl_audit);
 360       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 361         {
 362           if (afct->ARCH_LA_PLTENTER != NULL
 363               && (reloc_result->enterexit
 364                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 365             {
 366               unsigned int flags = altvalue;
 367               long int new_framesize = -1;
 368               uintptr_t new_value
 369                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 370                                           &l->l_audit[cnt].cookie,
 371                                           &reloc_result->bound->l_audit[cnt].cookie,
 372                                           regs, &flags, symname,
 373                                           &new_framesize);
 374               if (new_value != (uintptr_t) sym.st_value)
 375                 {
 376                   altvalue = LA_SYMB_ALTVALUE;
 377                   sym.st_value = new_value;
 378                 }
 379
 380               /* Remember the results for every audit library and
 381                  store a summary in the first two bits.  */
 382               reloc_result->enterexit
 383                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 384                     << (2 * (cnt + 1)));
 385
 386               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 387                                               << (2 * (cnt + 1))))
 388                   == 0 && new_framesize != -1 && framesize != -2)
 389                 {
 390                   /* If this is the first call providing information,
 391                      use it.  */
 392                   if (framesize == -1)
 393                     framesize = new_framesize;
 394                   /* If two pltenter calls provide conflicting information,
 395                      use the larger value.  */
 396                   else if (new_framesize != framesize)
 397                     framesize = MAX (new_framesize, framesize);
 398                 }
 399             }
 400
 401           afct = afct->next;
 402         }
 403
 404       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 405     }
 406 #endif
 407
 408   /* Store the frame size information.  */
 409   *framesizep = framesize;
 410
 411   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 412
 413   return value;
 414 }
 415
 416 #endif /* PROF && ELF_MACHINE_NO_PLT */
 417
 418
 419 #include <stdio.h>
 420 void
 421 ARCH_FIXUP_ATTRIBUTE
 422 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 423                   const void *inregs, void *outregs)
 424 {
 425 #ifdef SHARED
 426   /* This is the address in the array where we store the result of previous
 427      relocations.  */
 428   // XXX Maybe the bound information must be stored on the stack since
 429   // XXX with bind_not a new value could have been stored in the meantime.
 430   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 431   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 432                                             l_info[DT_SYMTAB])
 433                        + reloc_result->boundndx);
 434
 435   /* Set up the sym parameter.  */
 436   ElfW(Sym) sym = *defsym;
 437
 438   /* Get the symbol name.  */
 439   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 440                                              l_info[DT_STRTAB]);
 441   const char *symname = strtab + sym.st_name;
 442
 443   struct audit_ifaces *afct = GLRO(dl_audit);
 444   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 445     {
 446       if (afct->ARCH_LA_PLTEXIT != NULL
 447           && (reloc_result->enterexit
 448               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 449         {
 450           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 451                                  &l->l_audit[cnt].cookie,
 452                                  &reloc_result->bound->l_audit[cnt].cookie,
 453                                  inregs, outregs, symname);
 454         }
 455
 456       afct = afct->next;
 457     }
 458 #endif
 459 }