configure: build position independent executables on x86-Linux hosts

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 <avi@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

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