elf/dl-sym-post.h

   1 /* Post-processing of a symbol produced by dlsym, dlvsym.
   2    Copyright (C) 1999-2021 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    <https://www.gnu.org/licenses/>.  */
  18
  19
  20 /* Return the link map containing the caller address.  */
  21 static struct link_map *
  22 _dl_sym_find_caller_link_map (ElfW(Addr) caller)
  23 {
  24   struct link_map *l = _dl_find_dso_for_object (caller);
  25   if (l != NULL)
  26     return l;
  27   else
  28     /* If the address is not recognized the call comes from the main
  29        program (we hope).  */
  30     return GL(dl_ns)[LM_ID_BASE]._ns_loaded;
  31 }
  32
  33 /* Translates RESULT, *REF, VALUE into a symbol address from the point
  34    of view of MATCH.  Performs IFUNC resolution and auditing if
  35    necessary.  If MATCH is NULL, CALLER is used to determine it.  */
  36 static void *
  37 _dl_sym_post (lookup_t result, const ElfW(Sym) *ref, void *value,
  38               ElfW(Addr) caller, struct link_map *match)
  39 {
  40   /* Resolve indirect function address.  */
  41   if (__glibc_unlikely (ELFW(ST_TYPE) (ref->st_info) == STT_GNU_IFUNC))
  42     {
  43       DL_FIXUP_VALUE_TYPE fixup
  44         = DL_FIXUP_MAKE_VALUE (result, (ElfW(Addr)) value);
  45       fixup = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (fixup));
  46       value = (void *) DL_FIXUP_VALUE_CODE_ADDR (fixup);
  47     }
  48
  49 #ifdef SHARED
  50   /* Auditing checkpoint: we have a new binding.  Provide the
  51      auditing libraries the possibility to change the value and
  52      tell us whether further auditing is wanted.  */
  53   if (__glibc_unlikely (GLRO(dl_naudit) > 0))
  54     {
  55       const char *strtab = (const char *) D_PTR (result,
  56                                                  l_info[DT_STRTAB]);
  57       /* Compute index of the symbol entry in the symbol table of
  58          the DSO with the definition.  */
  59       unsigned int ndx = (ref - (ElfW(Sym) *) D_PTR (result,
  60                                                      l_info[DT_SYMTAB]));
  61
  62       if (match == NULL)
  63         match = _dl_sym_find_caller_link_map (caller);
  64
  65       if ((match->l_audit_any_plt | result->l_audit_any_plt) != 0)
  66         {
  67           unsigned int altvalue = 0;
  68           struct audit_ifaces *afct = GLRO(dl_audit);
  69           /* Synthesize a symbol record where the st_value field is
  70              the result.  */
  71           ElfW(Sym) sym = *ref;
  72           sym.st_value = (ElfW(Addr)) value;
  73
  74           for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
  75             {
  76               struct auditstate *match_audit
  77                 = link_map_audit_state (match, cnt);
  78               struct auditstate *result_audit
  79                 = link_map_audit_state (result, cnt);
  80               if (afct->symbind != NULL
  81                   && ((match_audit->bindflags & LA_FLG_BINDFROM) != 0
  82                       || ((result_audit->bindflags & LA_FLG_BINDTO)
  83                           != 0)))
  84                 {
  85                   unsigned int flags = altvalue | LA_SYMB_DLSYM;
  86                   uintptr_t new_value
  87                     = afct->symbind (&sym, ndx,
  88                                      &match_audit->cookie,
  89                                      &result_audit->cookie,
  90                                      &flags, strtab + ref->st_name);
  91                   if (new_value != (uintptr_t) sym.st_value)
  92                     {
  93                       altvalue = LA_SYMB_ALTVALUE;
  94                       sym.st_value = new_value;
  95                     }
  96                 }
  97
  98               afct = afct->next;
  99             }
 100
 101           value = (void *) sym.st_value;
 102         }
 103     }
 104 #endif
 105   return value;
 106 }