[PATCH 3/4] Add run-time chesk for single global definition

[H.J. Lu]

When performing symbol lookup for references in an object without single
global definition:

1. Disallow copy relocations against protected data symbols in an object
with single global definition.
2. Disallow non-zero symbol values of undefined function symbols, which
are used as the function pointer, against protected function symbols in
an object with single global definition.
---
 elf/dl-lookup.c                |  5 ++++
 sysdeps/generic/dl-protected.h | 51 ++++++++++++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 sysdeps/generic/dl-protected.h

diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
index eea217eb28..430359af39 100644
--- a/elf/dl-lookup.c
+++ b/elf/dl-lookup.c
@@ -24,6 +24,7 @@
 #include <ldsodefs.h>
 #include <dl-hash.h>
 #include <dl-machine.h>
+#include <dl-protected.h>
 #include <sysdep-cancel.h>
 #include <libc-lock.h>
 #include <tls.h>
@@ -527,6 +528,10 @@ do_lookup_x (const char *undef_name, uint_fast32_t new_hash,
 	  if (__glibc_unlikely (dl_symbol_visibility_binds_local_p (sym)))
 	    goto skip;
 
+	  if (ELFW(ST_VISIBILITY) (sym->st_other) == STV_PROTECTED)
+	    _dl_check_protected_symbol (undef_name, undef_map, ref, map,
+					type_class);
+
 	  switch (ELFW(ST_BIND) (sym->st_info))
 	    {
 	    case STB_WEAK:
diff --git a/sysdeps/generic/dl-protected.h b/sysdeps/generic/dl-protected.h
new file mode 100644
index 0000000000..a530eb3e51
--- /dev/null
+++ b/sysdeps/generic/dl-protected.h
@@ -0,0 +1,51 @@
+/* Support for STV_PROTECTED visibility.  Generic version.
+   Copyright (C) 2021 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/>.  */
+
+#ifndef _DL_PROTECTED_H
+#define _DL_PROTECTED_H
+
+static inline void __attribute__ ((always_inline))
+_dl_check_protected_symbol (const char *undef_name,
+			    const struct link_map *undef_map,
+			    const ElfW(Sym) *ref,
+			    const struct link_map *map,
+			    int type_class)
+{
+  if (undef_map != NULL
+      && !(undef_map->l_1_needed
+	   & GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION)
+      && (map->l_1_needed
+	  & GNU_PROPERTY_1_NEEDED_SINGLE_GLOBAL_DEFINITION))
+    {
+      if ((type_class & ELF_RTYPE_CLASS_COPY))
+	/* Disallow copy relocations against protected data symbols in
+	   an object with single global definition.  */
+	_dl_fatal_printf ("copy relocation against non-copyable protected symbol=%s in file=%s\n",
+			  undef_name, DSO_FILENAME (map->l_name));
+      else if (ref->st_value != 0
+	       && ref->st_shndx == SHN_UNDEF
+	       && (type_class & ELF_RTYPE_CLASS_PLT))
+	/* Disallow non-zero symbol values of undefined symbols, which
+	   are used as the function pointer, against protected function
+	   symbols in an object with single global definition.  */
+	_dl_fatal_printf ("non-canonical reference to canonical protected function symbol=%s in file=%s\n",
+			  undef_name, DSO_FILENAME (map->l_name));
+    }
+}
+
+#endif /* _DL_PROTECTED_H */
-- 
2.31.1