elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2018 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 (!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 DL_FIXUP_VALUE_TYPE
  60 attribute_hidden __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
  61 _dl_fixup (
  62 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
  63            ELF_MACHINE_RUNTIME_FIXUP_ARGS,
  64 # endif
  65            struct link_map *l, ElfW(Word) reloc_arg)
  66 {
  67   const ElfW(Sym) *const symtab
  68     = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
  69   const char *strtab = (const void *) D_PTR (l, l_info[DT_STRTAB]);
  70
  71   const PLTREL *const reloc
  72     = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
  73   const ElfW(Sym) *sym = &symtab[ELFW(R_SYM) (reloc->r_info)];
  74   const ElfW(Sym) *refsym = sym;
  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           flags |= DL_LOOKUP_GSCOPE_LOCK;
 106         }
 107
 108 #ifdef RTLD_ENABLE_FOREIGN_CALL
 109       RTLD_ENABLE_FOREIGN_CALL;
 110 #endif
 111
 112       result = _dl_lookup_symbol_x (strtab + sym->st_name, l, &sym, l->l_scope,
 113                                     version, ELF_RTYPE_CLASS_PLT, flags, NULL);
 114
 115       /* We are done with the global scope.  */
 116       if (!RTLD_SINGLE_THREAD_P)
 117         THREAD_GSCOPE_RESET_FLAG ();
 118
 119 #ifdef RTLD_FINALIZE_FOREIGN_CALL
 120       RTLD_FINALIZE_FOREIGN_CALL;
 121 #endif
 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                                    SYMBOL_ADDRESS (result, sym, false));
 128     }
 129   else
 130     {
 131       /* We already found the symbol.  The module (and therefore its load
 132          address) is also known.  */
 133       value = DL_FIXUP_MAKE_VALUE (l, SYMBOL_ADDRESS (l, sym, true));
 134       result = l;
 135     }
 136
 137   /* And now perhaps the relocation addend.  */
 138   value = elf_machine_plt_value (l, reloc, value);
 139
 140   if (sym != NULL
 141       && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 142     value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 143
 144   /* Finally, fix up the plt itself.  */
 145   if (__glibc_unlikely (GLRO(dl_bind_not)))
 146     return value;
 147
 148   return elf_machine_fixup_plt (l, result, refsym, sym, reloc, rel_addr, value);
 149 }
 150
 151 #ifndef PROF
 152 DL_FIXUP_VALUE_TYPE
 153 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 154 _dl_profile_fixup (
 155 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 156                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 157 #endif
 158                    struct link_map *l, ElfW(Word) reloc_arg,
 159                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 160 {
 161   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
 162
 163   if (l->l_reloc_result == NULL)
 164     {
 165       /* BZ #14843: ELF_DYNAMIC_RELOCATE is called before l_reloc_result
 166          is allocated.  We will get here if ELF_DYNAMIC_RELOCATE calls a
 167          resolver function to resolve an IRELATIVE relocation and that
 168          resolver calls a function that is not yet resolved (lazy).  For
 169          example, the resolver in x86-64 libm.so calls __get_cpu_features
 170          defined in libc.so.  Skip audit and resolve the external function
 171          in this case.  */
 172       *framesizep = -1;
 173       return _dl_fixup (
 174 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 175 #  ifndef ELF_MACHINE_RUNTIME_FIXUP_PARAMS
 176 #   error Please define ELF_MACHINE_RUNTIME_FIXUP_PARAMS.
 177 #  endif
 178                         ELF_MACHINE_RUNTIME_FIXUP_PARAMS,
 179 # endif
 180                         l, reloc_arg);
 181     }
 182
 183   /* This is the address in the array where we store the result of previous
 184      relocations.  */
 185   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 186   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 187
 188   DL_FIXUP_VALUE_TYPE value = *resultp;
 189   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 190     {
 191       /* This is the first time we have to relocate this object.  */
 192       const ElfW(Sym) *const symtab
 193         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 194       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 195
 196       const PLTREL *const reloc
 197         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 198       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 199       const ElfW(Sym) *defsym = refsym;
 200       lookup_t result;
 201
 202       /* Sanity check that we're really looking at a PLT relocation.  */
 203       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 204
 205       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 206          don't look in the global scope.  */
 207       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 208         {
 209           const struct r_found_version *version = NULL;
 210
 211           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 212             {
 213               const ElfW(Half) *vernum =
 214                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 215               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 216               version = &l->l_versions[ndx];
 217               if (version->hash == 0)
 218                 version = NULL;
 219             }
 220
 221           /* We need to keep the scope around so do some locking.  This is
 222              not necessary for objects which cannot be unloaded or when
 223              we are not using any threads (yet).  */
 224           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 225           if (!RTLD_SINGLE_THREAD_P)
 226             {
 227               THREAD_GSCOPE_SET_FLAG ();
 228               flags |= DL_LOOKUP_GSCOPE_LOCK;
 229             }
 230
 231           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 232                                         &defsym, l->l_scope, version,
 233                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 234
 235           /* We are done with the global scope.  */
 236           if (!RTLD_SINGLE_THREAD_P)
 237             THREAD_GSCOPE_RESET_FLAG ();
 238
 239           /* Currently result contains the base load address (or link map)
 240              of the object that defines sym.  Now add in the symbol
 241              offset.  */
 242           value = DL_FIXUP_MAKE_VALUE (result,
 243                                        SYMBOL_ADDRESS (result, defsym, false));
 244
 245           if (defsym != NULL
 246               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 247                                    == STT_GNU_IFUNC, 0))
 248             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 249         }
 250       else
 251         {
 252           /* We already found the symbol.  The module (and therefore its load
 253              address) is also known.  */
 254           value = DL_FIXUP_MAKE_VALUE (l, SYMBOL_ADDRESS (l, refsym, true));
 255
 256           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 257                                 == STT_GNU_IFUNC, 0))
 258             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 259
 260           result = l;
 261         }
 262       /* And now perhaps the relocation addend.  */
 263       value = elf_machine_plt_value (l, reloc, value);
 264
 265 #ifdef SHARED
 266       /* Auditing checkpoint: we have a new binding.  Provide the
 267          auditing libraries the possibility to change the value and
 268          tell us whether further auditing is wanted.  */
 269       if (defsym != NULL && GLRO(dl_naudit) > 0)
 270         {
 271           reloc_result->bound = result;
 272           /* Compute index of the symbol entry in the symbol table of
 273              the DSO with the definition.  */
 274           reloc_result->boundndx = (defsym
 275                                     - (ElfW(Sym) *) D_PTR (result,
 276                                                            l_info[DT_SYMTAB]));
 277
 278           /* Determine whether any of the two participating DSOs is
 279              interested in auditing.  */
 280           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 281             {
 282               unsigned int flags = 0;
 283               struct audit_ifaces *afct = GLRO(dl_audit);
 284               /* Synthesize a symbol record where the st_value field is
 285                  the result.  */
 286               ElfW(Sym) sym = *defsym;
 287               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 288
 289               /* Keep track whether there is any interest in tracing
 290                  the call in the lower two bits.  */
 291               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 292               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 293               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 294
 295               const char *strtab2 = (const void *) D_PTR (result,
 296                                                           l_info[DT_STRTAB]);
 297
 298               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 299                 {
 300                   /* XXX Check whether both DSOs must request action or
 301                      only one */
 302                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 303                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 304                     {
 305                       if (afct->symbind != NULL)
 306                         {
 307                           uintptr_t new_value
 308                             = afct->symbind (&sym, reloc_result->boundndx,
 309                                              &l->l_audit[cnt].cookie,
 310                                              &result->l_audit[cnt].cookie,
 311                                              &flags,
 312                                              strtab2 + defsym->st_name);
 313                           if (new_value != (uintptr_t) sym.st_value)
 314                             {
 315                               flags |= LA_SYMB_ALTVALUE;
 316                               sym.st_value = new_value;
 317                             }
 318                         }
 319
 320                       /* Remember the results for every audit library and
 321                          store a summary in the first two bits.  */
 322                       reloc_result->enterexit
 323                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 324                       reloc_result->enterexit
 325                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 326                             << ((cnt + 1) * 2));
 327                     }
 328                   else
 329                     /* If the bind flags say this auditor is not interested,
 330                        set the bits manually.  */
 331                     reloc_result->enterexit
 332                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 333                           << ((cnt + 1) * 2));
 334
 335                   afct = afct->next;
 336                 }
 337
 338               reloc_result->flags = flags;
 339               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 340             }
 341           else
 342             /* Set all bits since this symbol binding is not interesting.  */
 343             reloc_result->enterexit = (1u << DL_NNS) - 1;
 344         }
 345 #endif
 346
 347       /* Store the result for later runs.  */
 348       if (__glibc_likely (! GLRO(dl_bind_not)))
 349         *resultp = value;
 350     }
 351
 352   /* By default we do not call the pltexit function.  */
 353   long int framesize = -1;
 354
 355 #ifdef SHARED
 356   /* Auditing checkpoint: report the PLT entering and allow the
 357      auditors to change the value.  */
 358   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 359       /* Don't do anything if no auditor wants to intercept this call.  */
 360       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 361     {
 362       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 363                                                 l_info[DT_SYMTAB])
 364                            + reloc_result->boundndx);
 365
 366       /* Set up the sym parameter.  */
 367       ElfW(Sym) sym = *defsym;
 368       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 369
 370       /* Get the symbol name.  */
 371       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 372                                                  l_info[DT_STRTAB]);
 373       const char *symname = strtab + sym.st_name;
 374
 375       /* Keep track of overwritten addresses.  */
 376       unsigned int flags = reloc_result->flags;
 377
 378       struct audit_ifaces *afct = GLRO(dl_audit);
 379       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 380         {
 381           if (afct->ARCH_LA_PLTENTER != NULL
 382               && (reloc_result->enterexit
 383                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 384             {
 385               long int new_framesize = -1;
 386               uintptr_t new_value
 387                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 388                                           &l->l_audit[cnt].cookie,
 389                                           &reloc_result->bound->l_audit[cnt].cookie,
 390                                           regs, &flags, symname,
 391                                           &new_framesize);
 392               if (new_value != (uintptr_t) sym.st_value)
 393                 {
 394                   flags |= LA_SYMB_ALTVALUE;
 395                   sym.st_value = new_value;
 396                 }
 397
 398               /* Remember the results for every audit library and
 399                  store a summary in the first two bits.  */
 400               reloc_result->enterexit
 401                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 402                     << (2 * (cnt + 1)));
 403
 404               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 405                                               << (2 * (cnt + 1))))
 406                   == 0 && new_framesize != -1 && framesize != -2)
 407                 {
 408                   /* If this is the first call providing information,
 409                      use it.  */
 410                   if (framesize == -1)
 411                     framesize = new_framesize;
 412                   /* If two pltenter calls provide conflicting information,
 413                      use the larger value.  */
 414                   else if (new_framesize != framesize)
 415                     framesize = MAX (new_framesize, framesize);
 416                 }
 417             }
 418
 419           afct = afct->next;
 420         }
 421
 422       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 423     }
 424 #endif
 425
 426   /* Store the frame size information.  */
 427   *framesizep = framesize;
 428
 429   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 430
 431   return value;
 432 }
 433
 434 #endif /* PROF */
 435
 436
 437 #include <stdio.h>
 438 void
 439 ARCH_FIXUP_ATTRIBUTE
 440 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 441                   const void *inregs, void *outregs)
 442 {
 443 #ifdef SHARED
 444   /* This is the address in the array where we store the result of previous
 445      relocations.  */
 446   // XXX Maybe the bound information must be stored on the stack since
 447   // XXX with bind_not a new value could have been stored in the meantime.
 448   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 449   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 450                                             l_info[DT_SYMTAB])
 451                        + reloc_result->boundndx);
 452
 453   /* Set up the sym parameter.  */
 454   ElfW(Sym) sym = *defsym;
 455   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 456
 457   /* Get the symbol name.  */
 458   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 459                                              l_info[DT_STRTAB]);
 460   const char *symname = strtab + sym.st_name;
 461
 462   struct audit_ifaces *afct = GLRO(dl_audit);
 463   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 464     {
 465       if (afct->ARCH_LA_PLTEXIT != NULL
 466           && (reloc_result->enterexit
 467               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 468         {
 469           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 470                                  &l->l_audit[cnt].cookie,
 471                                  &reloc_result->bound->l_audit[cnt].cookie,
 472                                  inregs, outregs, symname);
 473         }
 474
 475       afct = afct->next;
 476     }
 477 #endif
 478 }