elf: Extract _dl_sym_post, _dl_sym_find_caller_map from elf/dl-sym.c

The definitions are moved into a new file, elf/dl-sym-post.h, so that
this code can be used by the dynamic loader as well.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 106 insertions, 0 deletions

diff --git a/elf/dl-sym-post.h b/elf/dl-sym-post.h
new file mode 100644
index 0000000..4c4f574
--- /dev/null
+++ b/elf/dl-sym-post.h
@@ -0,0 +1,106 @@
+/* Post-processing of a symbol produced by dlsym, dlvsym.
+   Copyright (C) 1999-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+
+/* Return the link map containing the caller address.  */
+static struct link_map *
+_dl_sym_find_caller_link_map (ElfW(Addr) caller)
+{
+  struct link_map *l = _dl_find_dso_for_object (caller);
+  if (l != NULL)
+    return l;
+  else
+    /* If the address is not recognized the call comes from the main
+       program (we hope).  */
+    return GL(dl_ns)[LM_ID_BASE]._ns_loaded;
+}
+
+/* Translates RESULT, *REF, VALUE into a symbol address from the point
+   of view of MATCH.  Performs IFUNC resolution and auditing if
+   necessary.  If MATCH is NULL, CALLER is used to determine it.  */
+static void *
+_dl_sym_post (lookup_t result, const ElfW(Sym) *ref, void *value,
+              ElfW(Addr) caller, struct link_map *match)
+{
+  /* Resolve indirect function address.  */
+  if (__glibc_unlikely (ELFW(ST_TYPE) (ref->st_info) == STT_GNU_IFUNC))
+    {
+      DL_FIXUP_VALUE_TYPE fixup
+        = DL_FIXUP_MAKE_VALUE (result, (ElfW(Addr)) value);
+      fixup = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (fixup));
+      value = (void *) DL_FIXUP_VALUE_CODE_ADDR (fixup);
+    }
+
+#ifdef SHARED
+  /* Auditing checkpoint: we have a new binding.  Provide the
+     auditing libraries the possibility to change the value and
+     tell us whether further auditing is wanted.  */
+  if (__glibc_unlikely (GLRO(dl_naudit) > 0))
+    {
+      const char *strtab = (const char *) D_PTR (result,
+                                                 l_info[DT_STRTAB]);
+      /* Compute index of the symbol entry in the symbol table of
+         the DSO with the definition.  */
+      unsigned int ndx = (ref - (ElfW(Sym) *) D_PTR (result,
+                                                     l_info[DT_SYMTAB]));
+
+      if (match == NULL)
+        match = _dl_sym_find_caller_link_map (caller);
+
+      if ((match->l_audit_any_plt | result->l_audit_any_plt) != 0)
+        {
+          unsigned int altvalue = 0;
+          struct audit_ifaces *afct = GLRO(dl_audit);
+          /* Synthesize a symbol record where the st_value field is
+             the result.  */
+          ElfW(Sym) sym = *ref;
+          sym.st_value = (ElfW(Addr)) value;
+
+          for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
+            {
+              struct auditstate *match_audit
+                = link_map_audit_state (match, cnt);
+              struct auditstate *result_audit
+                = link_map_audit_state (result, cnt);
+              if (afct->symbind != NULL
+                  && ((match_audit->bindflags & LA_FLG_BINDFROM) != 0
+                      || ((result_audit->bindflags & LA_FLG_BINDTO)
+                          != 0)))
+                {
+                  unsigned int flags = altvalue | LA_SYMB_DLSYM;
+                  uintptr_t new_value
+                    = afct->symbind (&sym, ndx,
+                                     &match_audit->cookie,
+                                     &result_audit->cookie,
+                                     &flags, strtab + ref->st_name);
+                  if (new_value != (uintptr_t) sym.st_value)
+                    {
+                      altvalue = LA_SYMB_ALTVALUE;
+                      sym.st_value = new_value;
+                    }
+                }
+
+              afct = afct->next;
+            }
+
+          value = (void *) sym.st_value;
+        }
+    }
+#endif
+  return value;
+}