elf/dl-runtime.c

   1 /* On-demand PLT fixup for shared objects.
   2    Copyright (C) 1995-2017 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                                    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   if (sym != NULL
 142       && __builtin_expect (ELFW(ST_TYPE) (sym->st_info) == STT_GNU_IFUNC, 0))
 143     value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 144
 145   /* Finally, fix up the plt itself.  */
 146   if (__glibc_unlikely (GLRO(dl_bind_not)))
 147     return value;
 148
 149   return elf_machine_fixup_plt (l, result, refsym, sym, reloc, rel_addr, value);
 150 }
 151
 152 #ifndef PROF
 153 DL_FIXUP_VALUE_TYPE
 154 __attribute ((noinline)) ARCH_FIXUP_ATTRIBUTE
 155 _dl_profile_fixup (
 156 #ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 157                    ELF_MACHINE_RUNTIME_FIXUP_ARGS,
 158 #endif
 159                    struct link_map *l, ElfW(Word) reloc_arg,
 160                    ElfW(Addr) retaddr, void *regs, long int *framesizep)
 161 {
 162   void (*mcount_fct) (ElfW(Addr), ElfW(Addr)) = _dl_mcount;
 163
 164   if (l->l_reloc_result == NULL)
 165     {
 166       /* BZ #14843: ELF_DYNAMIC_RELOCATE is called before l_reloc_result
 167          is allocated.  We will get here if ELF_DYNAMIC_RELOCATE calls a
 168          resolver function to resolve an IRELATIVE relocation and that
 169          resolver calls a function that is not yet resolved (lazy).  For
 170          example, the resolver in x86-64 libm.so calls __get_cpu_features
 171          defined in libc.so.  Skip audit and resolve the external function
 172          in this case.  */
 173       *framesizep = -1;
 174       return _dl_fixup (
 175 # ifdef ELF_MACHINE_RUNTIME_FIXUP_ARGS
 176 #  ifndef ELF_MACHINE_RUNTIME_FIXUP_PARAMS
 177 #   error Please define ELF_MACHINE_RUNTIME_FIXUP_PARAMS.
 178 #  endif
 179                         ELF_MACHINE_RUNTIME_FIXUP_PARAMS,
 180 # endif
 181                         l, reloc_arg);
 182     }
 183
 184   /* This is the address in the array where we store the result of previous
 185      relocations.  */
 186   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 187   DL_FIXUP_VALUE_TYPE *resultp = &reloc_result->addr;
 188
 189   DL_FIXUP_VALUE_TYPE value = *resultp;
 190   if (DL_FIXUP_VALUE_CODE_ADDR (value) == 0)
 191     {
 192       /* This is the first time we have to relocate this object.  */
 193       const ElfW(Sym) *const symtab
 194         = (const void *) D_PTR (l, l_info[DT_SYMTAB]);
 195       const char *strtab = (const char *) D_PTR (l, l_info[DT_STRTAB]);
 196
 197       const PLTREL *const reloc
 198         = (const void *) (D_PTR (l, l_info[DT_JMPREL]) + reloc_offset);
 199       const ElfW(Sym) *refsym = &symtab[ELFW(R_SYM) (reloc->r_info)];
 200       const ElfW(Sym) *defsym = refsym;
 201       lookup_t result;
 202
 203       /* Sanity check that we're really looking at a PLT relocation.  */
 204       assert (ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT);
 205
 206       /* Look up the target symbol.  If the symbol is marked STV_PROTECTED
 207          don't look in the global scope.  */
 208       if (__builtin_expect (ELFW(ST_VISIBILITY) (refsym->st_other), 0) == 0)
 209         {
 210           const struct r_found_version *version = NULL;
 211
 212           if (l->l_info[VERSYMIDX (DT_VERSYM)] != NULL)
 213             {
 214               const ElfW(Half) *vernum =
 215                 (const void *) D_PTR (l, l_info[VERSYMIDX (DT_VERSYM)]);
 216               ElfW(Half) ndx = vernum[ELFW(R_SYM) (reloc->r_info)] & 0x7fff;
 217               version = &l->l_versions[ndx];
 218               if (version->hash == 0)
 219                 version = NULL;
 220             }
 221
 222           /* We need to keep the scope around so do some locking.  This is
 223              not necessary for objects which cannot be unloaded or when
 224              we are not using any threads (yet).  */
 225           int flags = DL_LOOKUP_ADD_DEPENDENCY;
 226           if (!RTLD_SINGLE_THREAD_P)
 227             {
 228               THREAD_GSCOPE_SET_FLAG ();
 229               flags |= DL_LOOKUP_GSCOPE_LOCK;
 230             }
 231
 232           result = _dl_lookup_symbol_x (strtab + refsym->st_name, l,
 233                                         &defsym, l->l_scope, version,
 234                                         ELF_RTYPE_CLASS_PLT, flags, NULL);
 235
 236           /* We are done with the global scope.  */
 237           if (!RTLD_SINGLE_THREAD_P)
 238             THREAD_GSCOPE_RESET_FLAG ();
 239
 240           /* Currently result contains the base load address (or link map)
 241              of the object that defines sym.  Now add in the symbol
 242              offset.  */
 243           value = DL_FIXUP_MAKE_VALUE (result,
 244                                        defsym != NULL
 245                                        ? LOOKUP_VALUE_ADDRESS (result)
 246                                          + defsym->st_value : 0);
 247
 248           if (defsym != NULL
 249               && __builtin_expect (ELFW(ST_TYPE) (defsym->st_info)
 250                                    == STT_GNU_IFUNC, 0))
 251             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 252         }
 253       else
 254         {
 255           /* We already found the symbol.  The module (and therefore its load
 256              address) is also known.  */
 257           value = DL_FIXUP_MAKE_VALUE (l, l->l_addr + refsym->st_value);
 258
 259           if (__builtin_expect (ELFW(ST_TYPE) (refsym->st_info)
 260                                 == STT_GNU_IFUNC, 0))
 261             value = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (value));
 262
 263           result = l;
 264         }
 265       /* And now perhaps the relocation addend.  */
 266       value = elf_machine_plt_value (l, reloc, value);
 267
 268 #ifdef SHARED
 269       /* Auditing checkpoint: we have a new binding.  Provide the
 270          auditing libraries the possibility to change the value and
 271          tell us whether further auditing is wanted.  */
 272       if (defsym != NULL && GLRO(dl_naudit) > 0)
 273         {
 274           reloc_result->bound = result;
 275           /* Compute index of the symbol entry in the symbol table of
 276              the DSO with the definition.  */
 277           reloc_result->boundndx = (defsym
 278                                     - (ElfW(Sym) *) D_PTR (result,
 279                                                            l_info[DT_SYMTAB]));
 280
 281           /* Determine whether any of the two participating DSOs is
 282              interested in auditing.  */
 283           if ((l->l_audit_any_plt | result->l_audit_any_plt) != 0)
 284             {
 285               unsigned int flags = 0;
 286               struct audit_ifaces *afct = GLRO(dl_audit);
 287               /* Synthesize a symbol record where the st_value field is
 288                  the result.  */
 289               ElfW(Sym) sym = *defsym;
 290               sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 291
 292               /* Keep track whether there is any interest in tracing
 293                  the call in the lower two bits.  */
 294               assert (DL_NNS * 2 <= sizeof (reloc_result->flags) * 8);
 295               assert ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT) == 3);
 296               reloc_result->enterexit = LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT;
 297
 298               const char *strtab2 = (const void *) D_PTR (result,
 299                                                           l_info[DT_STRTAB]);
 300
 301               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 302                 {
 303                   /* XXX Check whether both DSOs must request action or
 304                      only one */
 305                   if ((l->l_audit[cnt].bindflags & LA_FLG_BINDFROM) != 0
 306                       && (result->l_audit[cnt].bindflags & LA_FLG_BINDTO) != 0)
 307                     {
 308                       if (afct->symbind != NULL)
 309                         {
 310                           uintptr_t new_value
 311                             = afct->symbind (&sym, reloc_result->boundndx,
 312                                              &l->l_audit[cnt].cookie,
 313                                              &result->l_audit[cnt].cookie,
 314                                              &flags,
 315                                              strtab2 + defsym->st_name);
 316                           if (new_value != (uintptr_t) sym.st_value)
 317                             {
 318                               flags |= LA_SYMB_ALTVALUE;
 319                               sym.st_value = new_value;
 320                             }
 321                         }
 322
 323                       /* Remember the results for every audit library and
 324                          store a summary in the first two bits.  */
 325                       reloc_result->enterexit
 326                         &= flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT);
 327                       reloc_result->enterexit
 328                         |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 329                             << ((cnt + 1) * 2));
 330                     }
 331                   else
 332                     /* If the bind flags say this auditor is not interested,
 333                        set the bits manually.  */
 334                     reloc_result->enterexit
 335                       |= ((LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT)
 336                           << ((cnt + 1) * 2));
 337
 338                   afct = afct->next;
 339                 }
 340
 341               reloc_result->flags = flags;
 342               value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 343             }
 344           else
 345             /* Set all bits since this symbol binding is not interesting.  */
 346             reloc_result->enterexit = (1u << DL_NNS) - 1;
 347         }
 348 #endif
 349
 350       /* Store the result for later runs.  */
 351       if (__glibc_likely (! GLRO(dl_bind_not)))
 352         *resultp = value;
 353     }
 354
 355   /* By default we do not call the pltexit function.  */
 356   long int framesize = -1;
 357
 358 #ifdef SHARED
 359   /* Auditing checkpoint: report the PLT entering and allow the
 360      auditors to change the value.  */
 361   if (DL_FIXUP_VALUE_CODE_ADDR (value) != 0 && GLRO(dl_naudit) > 0
 362       /* Don't do anything if no auditor wants to intercept this call.  */
 363       && (reloc_result->enterexit & LA_SYMB_NOPLTENTER) == 0)
 364     {
 365       ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 366                                                 l_info[DT_SYMTAB])
 367                            + reloc_result->boundndx);
 368
 369       /* Set up the sym parameter.  */
 370       ElfW(Sym) sym = *defsym;
 371       sym.st_value = DL_FIXUP_VALUE_ADDR (value);
 372
 373       /* Get the symbol name.  */
 374       const char *strtab = (const void *) D_PTR (reloc_result->bound,
 375                                                  l_info[DT_STRTAB]);
 376       const char *symname = strtab + sym.st_name;
 377
 378       /* Keep track of overwritten addresses.  */
 379       unsigned int flags = reloc_result->flags;
 380
 381       struct audit_ifaces *afct = GLRO(dl_audit);
 382       for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 383         {
 384           if (afct->ARCH_LA_PLTENTER != NULL
 385               && (reloc_result->enterexit
 386                   & (LA_SYMB_NOPLTENTER << (2 * (cnt + 1)))) == 0)
 387             {
 388               long int new_framesize = -1;
 389               uintptr_t new_value
 390                 = afct->ARCH_LA_PLTENTER (&sym, reloc_result->boundndx,
 391                                           &l->l_audit[cnt].cookie,
 392                                           &reloc_result->bound->l_audit[cnt].cookie,
 393                                           regs, &flags, symname,
 394                                           &new_framesize);
 395               if (new_value != (uintptr_t) sym.st_value)
 396                 {
 397                   flags |= LA_SYMB_ALTVALUE;
 398                   sym.st_value = new_value;
 399                 }
 400
 401               /* Remember the results for every audit library and
 402                  store a summary in the first two bits.  */
 403               reloc_result->enterexit
 404                 |= ((flags & (LA_SYMB_NOPLTENTER | LA_SYMB_NOPLTEXIT))
 405                     << (2 * (cnt + 1)));
 406
 407               if ((reloc_result->enterexit & (LA_SYMB_NOPLTEXIT
 408                                               << (2 * (cnt + 1))))
 409                   == 0 && new_framesize != -1 && framesize != -2)
 410                 {
 411                   /* If this is the first call providing information,
 412                      use it.  */
 413                   if (framesize == -1)
 414                     framesize = new_framesize;
 415                   /* If two pltenter calls provide conflicting information,
 416                      use the larger value.  */
 417                   else if (new_framesize != framesize)
 418                     framesize = MAX (new_framesize, framesize);
 419                 }
 420             }
 421
 422           afct = afct->next;
 423         }
 424
 425       value = DL_FIXUP_ADDR_VALUE (sym.st_value);
 426     }
 427 #endif
 428
 429   /* Store the frame size information.  */
 430   *framesizep = framesize;
 431
 432   (*mcount_fct) (retaddr, DL_FIXUP_VALUE_CODE_ADDR (value));
 433
 434   return value;
 435 }
 436
 437 #endif /* PROF */
 438
 439
 440 #include <stdio.h>
 441 void
 442 ARCH_FIXUP_ATTRIBUTE
 443 _dl_call_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
 444                   const void *inregs, void *outregs)
 445 {
 446 #ifdef SHARED
 447   /* This is the address in the array where we store the result of previous
 448      relocations.  */
 449   // XXX Maybe the bound information must be stored on the stack since
 450   // XXX with bind_not a new value could have been stored in the meantime.
 451   struct reloc_result *reloc_result = &l->l_reloc_result[reloc_index];
 452   ElfW(Sym) *defsym = ((ElfW(Sym) *) D_PTR (reloc_result->bound,
 453                                             l_info[DT_SYMTAB])
 454                        + reloc_result->boundndx);
 455
 456   /* Set up the sym parameter.  */
 457   ElfW(Sym) sym = *defsym;
 458   sym.st_value = DL_FIXUP_VALUE_ADDR (reloc_result->addr);
 459
 460   /* Get the symbol name.  */
 461   const char *strtab = (const void *) D_PTR (reloc_result->bound,
 462                                              l_info[DT_STRTAB]);
 463   const char *symname = strtab + sym.st_name;
 464
 465   struct audit_ifaces *afct = GLRO(dl_audit);
 466   for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 467     {
 468       if (afct->ARCH_LA_PLTEXIT != NULL
 469           && (reloc_result->enterexit
 470               & (LA_SYMB_NOPLTEXIT >> (2 * cnt))) == 0)
 471         {
 472           afct->ARCH_LA_PLTEXIT (&sym, reloc_result->boundndx,
 473                                  &l->l_audit[cnt].cookie,
 474                                  &reloc_result->bound->l_audit[cnt].cookie,
 475                                  inregs, outregs, symname);
 476         }
 477
 478       afct = afct->next;
 479     }
 480 #endif
 481 }