qemu_template.sh: Add support for attaching a software TPM

For testing TPM2-backed rootfs encryption it is handy to have a software
TPM option for the qemu script.
Add a flag for a software TPM with swtpm like kola also does. The user
has to specify a folder for the secret state and this won't be removed
because the same store should be able to be passed when booting the VM
again after shutdown.

build_library/qemu_template.sh

@@ -17,6 +17,7 @@ SSH_KEYS=""
 CLOUD_CONFIG_FILE=""
 IGNITION_CONFIG_FILE=""
 CONFIG_IMAGE=""
+SWTPM_DIR=
 SAFE_ARGS=0
 USAGE="Usage: $0 [-a authorized_keys] [--] [qemu options...]
 Options:
@@ -28,6 +29,8 @@ Options:
     -p PORT     The port on localhost to map to the VM's sshd. [2222]
     -I FILE     Set a custom image file.
     -M MB       Set VM memory in MBs.
+    -T DIR      Add a software TPM2 device through swtpm which stores secrets
+                and the control socket to the given directory.
     -s          Safe settings: single simple cpu and no KVM.
     -h          this ;-)
 
@@ -84,6 +87,9 @@ while [ $# -ge 1 ]; do
         -M|-memory)
             VM_MEMORY="$2"
             shift 2 ;;
+        -T|-tpm)
+            SWTPM_DIR="$2"
+            shift 2 ;;
         -v|-verbose)
             set -x
             shift ;;
@@ -117,6 +123,29 @@ write_ssh_keys() {
     sed -e 's/^/ - /'
 }
 
+if [ -n "${SWTPM_DIR}" ]; then
+    mkdir -p "${SWTPM_DIR}"
+    if ! command -v swtpm >/dev/null; then
+        echo "$0: swtpm command not found!" >&2
+        exit 1
+    fi
+    case "${VM_BOARD}" in
+        amd64-usr)
+            TPM_DEV=tpm-tis ;;
+        arm64-usr)
+            TPM_DEV=tpm-tis-device ;;
+        *) die "Unsupported arch" ;;
+    esac
+    SWTPM_SOCK="${SWTPM_DIR}/socket"
+    swtpm socket --tpmstate "dir=${SWTPM_DIR}" --ctrl "type=unixio,path=${SWTPM_SOCK},terminate" --tpm2 &
+    SWTPM_PROC=$!
+    PARENT=$$
+    # The swtpm process exits if qemu disconnects but if we never started qemu because
+    # this script fails or qemu failed to start, we need to kill the process.
+    # The EXIT trap is already in use by the config drive cleanup and anyway doesn't work with kill -9.
+    (while [ -e "/proc/${PARENT}" ]; do sleep 1; done; kill "${SWTPM_PROC}" 2>/dev/null; exit 0) &
+    set -- -chardev "socket,id=chrtpm,path=${SWTPM_SOCK}" -tpmdev emulator,id=tpm0,chardev=chrtpm -device "${TPM_DEV}",tpmdev=tpm0 "$@"
+fi
 
 if [ -z "${CONFIG_IMAGE}" ]; then
     CONFIG_DRIVE=$(mktemp -d)