additional compiler hardening flags

[Darren Tucker]

On Fri, Dec 20, 2013 at 11:01:12AM -0800, Iain Morgan wrote:
> I don't recall seeing these improvements to the build system being
> committed. Is there any chance of adding them for the next release, or
> is it too late in the development cycle?

Sorry, this was on my list to get back to and I didn't.

Here's the current diff.  Given that there's an off switch I think I
should just commit it.  Damien?


Index: aclocal.m4
===================================================================
RCS file: /home/dtucker/openssh/cvs/openssh/aclocal.m4,v
retrieving revision 1.9
diff -u -p -r1.9 aclocal.m4
--- aclocal.m4	2 Jun 2013 21:31:27 -0000	1.9
+++ aclocal.m4	30 Jul 2013 01:34:12 -0000
@@ -10,7 +10,7 @@ dnl 'check_flag'.
 AC_DEFUN([OSSH_CHECK_CFLAG_COMPILE], [{
 	AC_MSG_CHECKING([if $CC supports $1])
 	saved_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $1"
+	CFLAGS="$CFLAGS $WERROR $1"
 	_define_flag="$2"
 	test "x$_define_flag" = "x" && _define_flag="$1"
 	AC_COMPILE_IFELSE([AC_LANG_SOURCE([[int main(void) { return 0; }]])],
@@ -28,6 +28,23 @@ fi],
 	)
 }])
 
+dnl OSSH_CHECK_CFLAG_LINK(check_flag[, define_flag])
+dnl Check that $LD accepts a flag 'check_flag'. If it is supported append
+dnl 'define_flag' to $LDFLAGS. If 'define_flag' is not specified, then append
+dnl 'check_flag'.
+AC_DEFUN([OSSH_CHECK_LDFLAG_LINK], [{
+	AC_MSG_CHECKING([if $LD supports $1])
+	saved_LDFLAGS="$LDFLAGS"
+	LDFLAGS="$LDFLAGS $WERROR $1"
+	_define_flag="$2"
+	test "x$_define_flag" = "x" && _define_flag="$1"
+	AC_LINK_IFELSE([AC_LANG_SOURCE([[int main(void) { return 0; }]])],
+		[ AC_MSG_RESULT([yes])
+		  LDFLAGS="$saved_LDFLAGS $_define_flag"],
+		[ AC_MSG_RESULT([no])
+		  LDFLAGS="$saved_LDFLAGS" ]
+	)
+}])
 
 dnl OSSH_CHECK_HEADER_FOR_FIELD(field, header, symbol)
 dnl Does AC_EGREP_HEADER on 'header' for the string 'field'
Index: configure.ac
===================================================================
RCS file: /home/dtucker/openssh/cvs/openssh/configure.ac,v
retrieving revision 1.547
diff -u -p -r1.547 configure.ac
--- configure.ac	19 Dec 2013 00:00:12 -0000	1.547
+++ configure.ac	16 Jan 2014 21:40:45 -0000
@@ -121,18 +121,35 @@ AC_CHECK_DECL([PR_SET_NO_NEW_PRIVS], [ha
 	#include <linux/prctl.h>
 ])
 use_stack_protector=1
+use_toolchain_hardening=1
 AC_ARG_WITH([stackprotect],
     [  --without-stackprotect  Don't use compiler's stack protection], [
     if test "x$withval" = "xno"; then
 	use_stack_protector=0
     fi ])
+AC_ARG_WITH([hardening],
+    [  --without-hardening     Don't use toolchain hardening flags], [
+    if test "x$withval" = "xno"; then
+	use_stack_protector=0
+	use_toolchain_hardening=0
+    fi ])
 
+# We use -Werror for the tests only so that we catch warnings like "this is
+# on by default" for things like -fPIE.
+AC_MSG_CHECKING([if $CC supports -Werror])
+saved_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -Werror"
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[int main(void) { return 0; }]])],
+	[ AC_MSG_RESULT([yes])
+	  WERROR="-Werror"],
+	[ AC_MSG_RESULT([no])
+	  WERROR="" ]
+)
+CFLAGS="$saved_CFLAGS"
 
 if test "$GCC" = "yes" || test "$GCC" = "egcs"; then
-	OSSH_CHECK_CFLAG_COMPILE([-Qunused-arguments -Werror],
-	    [-Qunused-arguments])
-	OSSH_CHECK_CFLAG_COMPILE([-Wunknown-warning-option -Werror],
-	    [-Wno-unknown-warning-option])
+	OSSH_CHECK_CFLAG_COMPILE([-Qunused-arguments])
+	OSSH_CHECK_CFLAG_COMPILE([-Wunknown-warning-option])
 	OSSH_CHECK_CFLAG_COMPILE([-Wall])
 	OSSH_CHECK_CFLAG_COMPILE([-Wpointer-arith])
 	OSSH_CHECK_CFLAG_COMPILE([-Wuninitialized])
@@ -143,6 +160,14 @@ if test "$GCC" = "yes" || test "$GCC" = 
 	OSSH_CHECK_CFLAG_COMPILE([-Wunused-result], [-Wno-unused-result])
 	OSSH_CHECK_CFLAG_COMPILE([-fno-strict-aliasing])
 	OSSH_CHECK_CFLAG_COMPILE([-D_FORTIFY_SOURCE=2])
+    if test "x$use_toolchain_hardening" = "x1"; then
+	OSSH_CHECK_CFLAG_COMPILE([-ftrapv])
+	OSSH_CHECK_CFLAG_COMPILE([-fPIE])
+	OSSH_CHECK_LDFLAG_LINK([-pie])
+	OSSH_CHECK_LDFLAG_LINK([-Wl,-z,relro])
+	OSSH_CHECK_LDFLAG_LINK([-Wl,-z,now])
+	OSSH_CHECK_LDFLAG_LINK([-Wl,-z,noexecstack])
+    fi
 	AC_MSG_CHECKING([gcc version])
 	GCC_VER=`$CC -v 2>&1 | $AWK '/gcc version /{print $3}'`
 	case $GCC_VER in

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.