[Qemu-devel] [PATCH v6 1.0] configure: build position independent executables on x86 hosts

[Avi Kivity <avi@redhat.com>]

Change the default on x86 hosts 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.

Non-x86 are not changed, as they require TCG changes.

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

v6: fix subject line. sigh.

v5: fix typos; only default enable for x86; mutually exclusive with -static

v4: say it's v4 and for 1.0

v3: detect toolchain support for PIE at configure time

v2: improve description to include relro

 configure |   55 +++++++++++++++++++++++++++++++++++++------------------
 1 files changed, 37 insertions(+), 18 deletions(-)

diff --git a/configure b/configure
index 6c77fbb..024e603 100755
--- a/configure
+++ b/configure
@@ -172,7 +172,7 @@ aix="no"
 blobs="yes"
 pkgversion=""
 check_utests=""
-user_pie="no"
+pie=""
 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 +1099,37 @@ for flag in $gcc_flags; do
     fi
 done
 
+if test "$pie" = "yes" -a "$static" = "yes" ; then
+  echo "static and pie are mutually incompatible"
+  exit 1
+fi
+
+if test "$pie" != "no" -a "$static" != "yes" ; then
+  case "$cpu" in
+    i386|x86_64)
+      pie="yes"
+      ;;
+    *)
+      ;;
+  esac
+fi
+
+if test "$pie" = "yes" ; then
+  cat > $TMPC << EOF
+int main(void) { return 0; }
+EOF
+  if compile_prog "-fPIE -DPIE" "-Wl,-pie"; then
+    QEMU_CFLAGS="-fPIE -DPIE $QEMU_CFLAGS"
+    LDFLAGS="-Wl,-pie $LDFLAGS"
+    if compile_prog "-fPIE -DPIE" "-Wl,-pie -Wl,-z,relro -Wl,-z,now"; then
+      LDFLAGS="-Wl,-z,relro -Wl,-z,now $LDFLAGS"
+    fi
+  else
+    echo "Disabling PIE due to missing toolchain support"
+    pie="no"
+  fi
+fi
+
 #
 # Solaris specific configure tool chain decisions
 #
@@ -2765,7 +2796,7 @@ 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 +3256,6 @@ 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 +3674,6 @@ 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 +3797,6 @@ 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