[Qemu-devel] [PATCH v8 1.0] configure: build position independent executables on x86-Linux hosts

[Avi Kivity]

Change the default on x86 Linux 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; neither are
non-Linux, due to lack of test coverage.

Signed-off-by: Avi Kivity <address@hidden>
---

v8: restrict further to Linux hosts
    use linker option '-pie' instead of '-Wl,-pie'; fixes link on x86_64

v7: avoid 'test -a'
    optimize relro/now linker flag test
    fail if toolchain doesn't support pie while the user explicitly asked for it

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 |   65 ++++++++++++++++++++++++++++++++++++++++++++----------------
 1 files changed, 47 insertions(+), 18 deletions(-)

diff --git a/configure b/configure
index 6c77fbb..75e1f10 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 +1099,47 @@ for flag in $gcc_flags; do
     fi
 done
 
+if test "$static" = "yes" ; then
+  if test "$pie" = "yes" ; then
+    echo "static and pie are mutually incompatible"
+    exit 1
+  else
+    pie="no"
+  fi
+fi
+
+if test "$pie" = ""; then
+  case "$cpu-$targetos" in
+    i386-Linux|x86_64-Linux)
+      ;;
+    *)
+      pie="no"
+      ;;
+  esac
+fi
+
+if test "$pie" != "no" ; then
+  cat > $TMPC << EOF
+int main(void) { return 0; }
+EOF
+  if compile_prog "-fPIE -DPIE" "-pie"; then
+    QEMU_CFLAGS="-fPIE -DPIE $QEMU_CFLAGS"
+    LDFLAGS="-pie $LDFLAGS"
+    pie="yes"
+    if compile_prog "" "-Wl,-z,relro -Wl,-z,now" ; then
+      LDFLAGS="-Wl,-z,relro -Wl,-z,now $LDFLAGS"
+    fi
+  else
+    if test "$pie" = "yes"; then
+      echo "PIE not available due to missing toolchain support"
+      exit 1
+    else
+      echo "Disabling PIE due to missing toolchain support"
+      pie="no"
+    fi
+  fi
+fi
+
 #
 # Solaris specific configure tool chain decisions
 #
@@ -2765,7 +2806,7 @@ 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 +3266,6 @@ 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 +3684,6 @@ 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 +3807,6 @@ 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