diff --git a/src/cmd-buildextend-metal b/src/cmd-buildextend-metal
index 3e5ad56d62..1bd1fdfd34 100755
--- a/src/cmd-buildextend-metal
+++ b/src/cmd-buildextend-metal
@@ -161,9 +161,6 @@ if [ "$arch" == "s390x" ]; then
 fi
 kargs="$kargs $tty ignition.platform.id=$image_type"
 
-ostree_remote="$(python3 -c 'import sys, yaml; print(yaml.safe_load(sys.stdin).get("ostree-remote", "NONE"))' < "$configdir/image.yaml")"
-save_var_subdirs="$(python3 -c 'import sys, yaml; print(yaml.safe_load(sys.stdin).get("save-var-subdirs-for-selabel-workaround", "NONE"))' < "$configdir/image.yaml")"
-
 if [ -z "${use_anaconda}" ]; then
     qemu-img create -f ${image_format} "${path}.tmp" "$size"
     # In the anaconda path, run_virtinstall dereferences in the ref_is_temp
@@ -173,8 +170,11 @@ if [ -z "${use_anaconda}" ]; then
         ref_arg=${commit}
     fi
 
-    runvm -drive "if=virtio,id=target,format=${image_format},file=${path}.tmp" -- /usr/lib/coreos-assembler/create_disk.sh /dev/vda "$ostree_repo" "${ref_arg}" "${ostree_remote}" /usr/lib/coreos-assembler/grub.cfg "$name" "${save_var_subdirs}" "\"$kargs\""
+    # Transcode to JSON so it's easier to parse from shell script
+    python3 -c 'import sys, yaml, json; json.dump(yaml.safe_load(sys.stdin), sys.stdout)' < "${configdir}/image.yaml" > tmp/image.json
+    runvm -drive "if=virtio,id=target,format=${image_format},file=${path}.tmp" -- /usr/lib/coreos-assembler/create_disk.sh "$ostree_repo" "${ref_arg}" "$name" "\"$kargs\""
     mv "${path}.tmp" "$path"
+    rm tmp/image.json
     echo "{}" > tmp/vm-iso-checksum.json
 else
     [ "${image_type}" == qemu ]
diff --git a/src/cmdlib.sh b/src/cmdlib.sh
index ce5302a6b5..244ab56daa 100755
--- a/src/cmdlib.sh
+++ b/src/cmdlib.sh
@@ -402,6 +402,7 @@ runvm() {
 set -xeuo pipefail
 export PATH=/usr/sbin:$PATH
 workdir=${workdir}
+builddir=$(pwd)
 
 # use the builder user's id, otherwise some operations like
 # chmod will set ownership to root, not builder
diff --git a/src/create_disk.sh b/src/create_disk.sh
index 9270bb50f4..fa7ac23a51 100755
--- a/src/create_disk.sh
+++ b/src/create_disk.sh
@@ -10,8 +10,8 @@
 # an issue and we can discuss configuration needs.
 set -euo pipefail
 
-if [ "$#" -ne 8 ]; then
-	echo 'create_disk <device> <ostree-repo> <ostree-ref> <ostree-remote> <grub-script> <os-name> <save-var-subdirs> <space separated kargs>'
+if [ "$#" -ne 4 ]; then
+	echo 'create_disk <ostree-repo> <ostree-ref> <os-name> <space separated kargs>'
 	exit 1
 fi
 
@@ -19,15 +19,16 @@ export PATH=$PATH:/sbin:/usr/sbin
 
 arch="$(uname -m)"
 
-disk="$1" && shift
+disk=/dev/vda
+
 ostree="$1" && shift
 ref="$1" && shift
-remote_name="$1" && shift
-grub_script="$1" && shift
 os_name="$1" && shift
-save_var_subdirs="$1" && shift
 extrakargs="$1" && shift
 
+remote_name=$(jq -r '.["ostree-remote"]' < tmp/image.json)
+save_var_subdirs=$(jq -r '.["save-var-subdirs"]' < tmp/image.json)
+
 set -x
 
 # Partition and create fs's. The 0...4...a...1 uuid is a sentinal used by coreos-gpt-setup
@@ -90,7 +91,7 @@ ostree admin deploy "${deploy_ref}" --sysroot rootfs --os "$os_name" $kargsargs
 # See the equivalent code in gf-anaconda-cleanup
 # /var hack: we'd like to remove all of /var, but SELinux issues prevent that.
 # see https://github.com/coreos/ignition-dracut/pull/79#issuecomment-488446949
-if [ "${save_var_subdirs}" != NONE ]; then
+if [ "${save_var_subdirs}" != "null" ]; then
 	vardir=rootfs/ostree/deploy/${os_name}/var
 	mkdir -p ${vardir}/{home,log/journal,lib/systemd}
 	# And /home is the only one that doesn't have a filename transition today
@@ -124,7 +125,7 @@ normal
 EOF
 
 	# copy the grub config and any other files we might need
-	cp $grub_script rootfs/boot/grub2/grub.cfg
+	cp /usr/lib/coreos-assembler/grub.cfg rootfs/boot/grub2/grub.cfg
 else
 	# current zipl expects 'title' to be first line, and no blank lines in BLS file
 	# see https://github.com/ibm-s390-tools/s390-tools/issues/64
diff --git a/src/supermin-init-prelude.sh b/src/supermin-init-prelude.sh
index e98b8dddab..17b8da5506 100644
--- a/src/supermin-init-prelude.sh
+++ b/src/supermin-init-prelude.sh
@@ -45,4 +45,4 @@ update-alternatives --install /etc/alternatives/iptables iptables /usr/sbin/ipta
 update-alternatives --install /etc/alternatives/ip6tables ip6tables /usr/sbin/ip6tables-legacy 1
 
 # https://github.com/koalaman/shellcheck/wiki/SC2164
-cd "${workdir}" || exit
+cd "${builddir}" || exit