[Qemu-devel] [PATCH v2 1.0] configure: build position independent executables across the board, by default

[Avi Kivity <avi@redhat.com>]

Change the default to building PIE (position independent executables); instead
of restricting the option to user-only targets, apply it to all targets.

In addition, set the relocation sections to read-only (relro) when available;
this reduces the attack surface by disallowing changes to relocation tables
at runtime.

While PIE reduces performance and relro increases load time, it greatly
improves security, with the potential to reduce a code execution vulnerability
to a self denial of service.

Signed-off-by: Avi Kivity <avi@redhat.com>
---

v2: improves description to include relro

While we are past the feature freeze, I feel this deserves an exception.  I'd
much rather see "CVE-2012-wxyz QEMU Self denial of service" than
"CVE-2012-wxyz QEMU code execution".  The fact that the option is available
for user targets implies that it is compatible with TCG, and some light testing
agrees.

 configure |   35 +++++++++++++++++------------------
 1 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/configure b/configure
index 6c77fbb..7436361 100755
--- a/configure
+++ b/configure
@@ -172,7 +172,7 @@ aix="no"
 blobs="yes"
 pkgversion=""
 check_utests=""
-user_pie="no"
+pie="yes"
 zero_malloc=""
 trace_backend="nop"
 trace_file="trace"
@@ -701,9 +701,9 @@ for opt do
   ;;
   --disable-guest-base) guest_base="no"
   ;;
-  --enable-user-pie) user_pie="yes"
+  --enable-pie) pie="yes"
   ;;
-  --disable-user-pie) user_pie="no"
+  --disable-pie) pie="no"
   ;;
   --enable-uname-release=*) uname_release="$optarg"
   ;;
@@ -1031,8 +1031,8 @@ echo "  --disable-bsd-user       disable all BSD usermode emulation targets"
 echo "  --enable-guest-base      enable GUEST_BASE support for usermode"
 echo "                           emulation targets"
 echo "  --disable-guest-base     disable GUEST_BASE support"
-echo "  --enable-user-pie        build usermode emulation targets as PIE"
-echo "  --disable-user-pie       do not build usermode emulation targets as PIE"
+echo "  --enable-pie             build Position Independent Executables"
+echo "  --disable-pie            do not build Position Independent Executables"
 echo "  --fmod-lib               path to FMOD library"
 echo "  --fmod-inc               path to FMOD includes"
 echo "  --oss-lib                path to OSS library"
@@ -1099,6 +1099,17 @@ for flag in $gcc_flags; do
     fi
 done
 
+if test "$pie" = "yes" ; then
+  QEMU_CFLAGS="-fPIE -DPIE $QEMU_CFLAGS"
+  LDFLAGS="-Wl,-pie $LDFLAGS"
+  cat > $TMPC << EOF
+int main(void) { return 0; }
+EOF
+  if compile_prog "-fPIE -DPIE" "-Wl,-pie -Wl,-z,relro -Wl,-z,now"; then
+    LDFLAGS="-Wl,-z,relro -Wl,-z,now $LDFLAGS"
+  fi
+fi
+
 #
 # Solaris specific configure tool chain decisions
 #
@@ -2765,7 +2776,7 @@ echo "Documentation     $docs"
 echo "uname -r          $uname_release"
 echo "NPTL support      $nptl"
 echo "GUEST_BASE        $guest_base"
-echo "PIE user targets  $user_pie"
+echo "PIE               $pie"
 echo "vde support       $vde"
 echo "Linux AIO support $linux_aio"
 echo "ATTR/XATTR support $attr"
@@ -3225,9 +3236,6 @@ for d in libdis libdis-user; do
     symlink $source_path/Makefile.dis $d/Makefile
     echo > $d/config.mak
 done
-if test "$static" = "no" -a "$user_pie" = "yes" ; then
-  echo "QEMU_CFLAGS+=-fpie" > libdis-user/config.mak
-fi
 
 for target in $target_list; do
 target_dir="$target"
@@ -3646,12 +3654,6 @@ if test "$target_softmmu" = "yes" ; then
   esac
 fi
 
-if test "$target_user_only" = "yes" -a "$static" = "no" -a \
-	"$user_pie" = "yes" ; then
-  cflags="-fpie $cflags"
-  ldflags="-pie $ldflags"
-fi
-
 if test "$target_softmmu" = "yes" -a \( \
         "$TARGET_ARCH" = "microblaze" -o \
         "$TARGET_ARCH" = "cris" \) ; then
@@ -3775,9 +3777,6 @@ d=libuser
 mkdir -p $d
 mkdir -p $d/trace
 symlink $source_path/Makefile.user $d/Makefile
-if test "$static" = "no" -a "$user_pie" = "yes" ; then
-  echo "QEMU_CFLAGS+=-fpie" > $d/config.mak
-fi
 
 if test "$docs" = "yes" ; then
   mkdir -p QMP
-- 
1.7.7.1