[libvirt] [PATCH dbus 4/5] Enable full RELRO mode

[Daniel P. Berrange]

By passing the flags -z relro -z now to the linker, we can force
it to resolve all library symbols at startup, instead of on-demand.
This allows it to then make the global offset table (GOT) read-only,
which makes some security attacks harder.

Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
---
 configure.ac            |  1 +
 m4/virt-linker-relro.m4 | 35 +++++++++++++++++++++++++++++++++++
 src/Makefile.am         |  4 +++-
 3 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 m4/virt-linker-relro.m4

diff --git a/configure.ac b/configure.ac
index 4c96fbe..b9ccf93 100644
--- a/configure.ac
+++ b/configure.ac
@@ -37,6 +37,7 @@ PKG_CHECK_MODULES(LIBVIRT, libvirt >= $LIBVIRT_REQUIRED)
 PKG_CHECK_MODULES(SYSTEMD, libsystemd >= $SYSTEMD_REQUIRED)
 
 LIBVIRT_COMPILE_WARNINGS
+LIBVIRT_LINKER_RELRO
 
 AC_ARG_WITH(dbus-services,
 		  [AC_HELP_STRING([--with-dbus-services=<dir>],
diff --git a/m4/virt-linker-relro.m4 b/m4/virt-linker-relro.m4
new file mode 100644
index 0000000..7669b23
--- /dev/null
+++ b/m4/virt-linker-relro.m4
@@ -0,0 +1,35 @@
+dnl
+dnl Check for -z now and -z relro linker flags
+dnl
+dnl Copyright (C) 2013 Red Hat, Inc.
+dnl
+dnl This library is free software; you can redistribute it and/or
+dnl modify it under the terms of the GNU Lesser General Public
+dnl License as published by the Free Software Foundation; either
+dnl version 2.1 of the License, or (at your option) any later version.
+dnl
+dnl This library is distributed in the hope that it will be useful,
+dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
+dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+dnl Lesser General Public License for more details.
+dnl
+dnl You should have received a copy of the GNU Lesser General Public
+dnl License along with this library.  If not, see
+dnl <http://www.gnu.org/licenses/>.
+dnl
+
+AC_DEFUN([LIBVIRT_LINKER_RELRO],[
+    AC_MSG_CHECKING([for how to force completely read-only GOT table])
+
+    RELRO_LDFLAGS=
+    ld_help=`ld --help 2>&1`
+    case $ld_help in
+        *"-z relro"*) RELRO_LDFLAGS="-Wl,-z -Wl,relro" ;;
+    esac
+    case $ld_help in
+        *"-z now"*) RELRO_LDFLAGS="$RELRO_LDFLAGS -Wl,-z -Wl,now" ;;
+    esac
+    AC_SUBST([RELRO_LDFLAGS])
+
+    AC_MSG_RESULT([$RELRO_LDFLAGS])
+])
diff --git a/src/Makefile.am b/src/Makefile.am
index 17b4fe1..8dd8ecd 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -24,7 +24,9 @@ libvirt_dbus_CFLAGS = \
 
 libvirt_dbus_LDFLAGS = \
 	$(SYSTEMD_LDFLAGS) \
-	$(LIBVIRT_LDFLAGS)
+	$(LIBVIRT_LDFLAGS) \
+	$(RELRO_LDFLAGS) \
+	$(NULL)
 
 libvirt_dbus_LDADD = \
 	$(SYSTEMD_LIBS) \
-- 
2.13.6