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 #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
  50 /* This function is called through a special trampoline from the PLT the
  51    first time each PLT entry is called.  We must perform the relocation
  52    specified in the PLT of the given shared object, and return the resolved
  53    function address to the trampoline, which will restart the original call
  54    to that address.  Future calls will bounce directly from the PLT to the
  55    function.  */
  56
  57 #ifndef ELF_MACHINE_NO_PLT
  58 DL_FIXUP_VALUE_TYPE
  59 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
  60 _dl_fixup (
  61 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  62            ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  63 # endif
  64            /* GKM FIXME: Fix trampoline to pass bounds so we can do
  65               without the `__unbounded' qualifier.  */
  66            struct link_map *__unbounded l, ElfW(Word) reloc_offset)
  67 {
  68   const ElfW(Sym) *const symtab
  69     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  70   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  71
  72   const PLTREL *const reloc
  73     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  74   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  75   void *const rel_addr = (void *)(l->l_addr + reloc->r_offset);
  76   lookup_t result;
  77   DL_FIXUP_VALUE_TYPE value;
  78
  79   /* Sanity check that we're really looking at a PLT relocation.  */
  80   assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
  81
  82    /* Look up the target symbol.  If the normal lookup rules are not
  83       used don't look in the global scope.  */
  84   if (__builtin_expect (ELFW(ST_VISIBILITY) (sym->st_other), 0) == 0)
  85     {
  86       const struct r_found_version *version = NULL;
  87
  88       if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
  89         {
  90           const ElfW(Half) *vernum =
  91             (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
  92           ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
  93           version = &l->l_versions[ndx];
  94           if (version->hash == 0)
  95             version = NULL;
  96         }
  97
  98       /* We need to keep the scope around so do some locking.  This is
  99          not necessary for objects which cannot be unloaded or when
 100          we are not using any threads (yet).  */
 101       int flags = DL_LOOKUP_ADD_DEPENDENCY;
 102       if (!RTLD_SINGLE_THREAD_P)
 103         {
 104           THREAD_GSCOPE_SET_FLAG ();
 105
 106           if (l->l_type == lt_loaded)
 107             {
 108               __rtld_mrlock_lock (l->l_scope_lock);
 109               flags |= DL_LOOKUP_SCOPE_LOCK;
 110             }
 111         }
 112
 113       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 114                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 115
 116       if ((flags & DL_LOOKUP_SCOPE_LOCK) != 0)
 117         __rtld_mrlock_unlock (l->l_scope_lock);
 118
 119       /* We are done with the global scope.  */
 120       if (!RTLD_SINGLE_THREAD_P)
 121         THREAD_GSCOPE_RESET_FLAG ();
 122
 123       /* Currently result contains the base load address (or link map)
 124          of the object that defines sym.  Now add in the symbol
 125          offset.  */
 126       value = DL_FIXUP_MAKE_VALUE (result,
 127                                    sym ? (LOOKUP_VALUE_ADDRESS (result)
 128                                           + sym->st_value) : 0);
 129     }
 130   else
 131     {
 132       /* We already found the symbol.  The module (and therefore its load
 133          address) is also known.  */
 134       value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + sym->st_value);
 135       result = l;
 136     }
 137
 138   /* And now perhaps the relocation addend.  */
 139   value = elf_machine_plt_value (l, reloc, value);
 140
 141   /* Finally, fix up the plt itself.  */
 142   if (__builtin_expect (GLRO(dl_bind_not), 0))
 143     return value;
 144
 145   return elf_machine_fixup_plt (l, result, reloc, rel_addr, value);
 146 }
 147 #endif
 148
 149 #if !defined PROF && !defined ELF_MACHINE_NO_PLT && !__BOUNDED_POINTERS__
 150
 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_offset,
 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
 165     = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 166   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 167
 168   DL_FIXUP_VALUE_TYPE value = *resultp;
 169   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 170     {
 171       /* This is the first time we have to relocate this object.  */
 172       const ElfW(Sym) *const symtab
 173         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 174       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 175
 176       const PLTREL *const reloc
 177         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 178       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 179       const ElfW(Sym) *defsym = refsym;
 180       lookup_t result;
 181
 182       /* Sanity check that we're really looking at a PLT relocation.  */
 183       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 184
 185       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 186          don't look in the global scope.  */
 187       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 188         {
 189           const struct r_found_version *version = NULL;
 190
 191           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 192             {
 193               const ElfW(Half) *vernum =
 194                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 195               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 196               version = &l->l_versions[ndx];
 197               if (version->hash == 0)
 198                 version = NULL;
 199             }
 200
 201           /* We need to keep the scope around so do some locking.  This is
 202              not necessary for objects which cannot be unloaded or when
 203              we are not using any threads (yet).  */
 204           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 205           if (!RTLD_SINGLE_THREAD_P)
 206             {
 207               THREAD_GSCOPE_SET_FLAG ();
 208
 209               if (l->l_type == lt_loaded)
 210                 {
 211                   __rtld_mrlock_lock (l->l_scope_lock);
 212                   flags |= DL_LOOKUP_SCOPE_LOCK;
 213                 }
 214             }
 215
 216           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 217                                         &defsym, l->l_scope, version,
 218                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 219
 220           if ((flags & DL_LOOKUP_SCOPE_LOCK) != 0)
 221             __rtld_mrlock_unlock (l->l_scope_lock);
 222
 223           /* We are done with the global scope.  */
 224           if (!RTLD_SINGLE_THREAD_P)
 225             THREAD_GSCOPE_RESET_FLAG ();
 226
 227           /* Currently result contains the base load address (or link map)
 228              of the object that defines sym.  Now add in the symbol
 229              offset.  */
 230           value = DL_FIXUP_MAKE_VALUE (result,
 231                                        defsym != NULL
 232                                        ? LOOKUP_VALUE_ADDRESS (result)
 233                                          + defsym->st_value : 0);
 234         }
 235       else
 236         {
 237           /* We already found the symbol.  The module (and therefore its load
 238              address) is also known.  */
 239           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 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_offset,
 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
 431     = &l->l_reloc_result[reloc_offset / sizeof (PLTREL)];
 432   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 433                                             l_info[DT_SYMTAB])
 434                        + reloc_result->boundndx);
 435
 436   /* Set up the sym parameter.  */
 437   ElfW(Sym) sym = *defsym;
 438
 439   /* Get the symbol name.  */
 440   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 441                                              l_info[DT_STRTAB]);
 442   const char *symname = strtab + sym.st_name;
 443
 444   struct audit_ifaces *afct = GLRO(dl_audit);
 445   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 446     {
 447       if (afct->ARCH_LA_PLTEXIT != NULL
 448           && (reloc_result->enterexit
 449               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 450         {
 451           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 452                                  &l->l_audit[cnt].cookie,
 453                                  &reloc_result->bound->l_audit[cnt].cookie,
 454                                  inregs, outregs, symname);
 455         }
 456
 457       afct = afct->next;
 458     }
 459 #endif
 460 }