add signing.bbclass as infrastructure for build artifact signing

This adds common infrastructure to access and used asymmetric keys to
sign build artifacts. The approach and implementation was presented at
the recent OpenEmbedded Workshop:
https://pretalx.com/openembedded-workshop-2023/talk/3C8MFF/

A working demo setup for verified boot based on qemu is available at
https://github.com/jluebbe/meta-code-signing.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

1 files changed, 316 insertions, 0 deletions

diff --git a/meta-oe/classes/signing.bbclass b/meta-oe/classes/signing.bbclass
new file mode 100644
index 0000000000..5c74a319e4
--- /dev/null
+++ b/meta-oe/classes/signing.bbclass
@@ -0,0 +1,316 @@
+#
+# Copyright Jan Luebbe <jlu@pengutronix.de>
+#
+# SPDX-License-Identifier: MIT
+#
+
+# This class provides a common workflow to use asymmetric (i.e. RSA) keys to
+# sign artifacts. Usually, the keys are either stored as simple files in the
+# file system or on a HSM (Hardware Security Module). While files are easy to
+# use, it's hard to verify that no copies of the private have been made and
+# only authorized persons are able to use the key. Use of an HSM addresses
+# these risks by only allowing use of the key via an API (often PKCS #11). The
+# standard way of referring to a specific key in an HSM are PKCS #11 URIs (RFC
+# 7512).
+#
+# Many software projects support signing using PKCS #11 keys, but configuring
+# this is very project specific. Furthermore, as physical HSMs are not very
+# widespread, testing code signing in CI is not simple. To solve this at the
+# build system level, this class takes the approach of always using PKCS #11 at
+# the recipe level. For cases where the keys are available as files (i.e. test
+# keys in CI), they are imported into SoftHSM (a HSM emulation library).
+# 
+# Recipes access the available keys via a specific role. So, depending on
+# whether we're building during development or for release, a given role can
+# refer to different keys.
+# Each key recipe PROVIDES a virtual package corresponding to the role, allowing
+# the user to select one of multiple keys for a role when needed.
+#
+# For use with a real HSM, a PKCS #11 URI can be set (i.e. in local.conf) to
+# override the SoftHSM key with the real one:
+#
+#   SIGNING_PKCS11_URI[fit] = "pkcs11:serial=DENK0200554;object=ptx-dev-rauc&pin-value=123456"
+#   SIGNING_PKCS11_MODULE[fit] = "/usr/lib/x86_64-linux-gnu/opensc-pkcs11.so"
+#
+# Examples for defining roles and importing keys:
+# 
+#   meta-code-signing/recipes-security/signing-keys/dummy-rsa-key-native.bb
+#   meta-code-signing-demo/recipes-security/ptx-dev-keys/ptx-dev-keys-native_git.bb
+#
+# Examples for using keys for signing:
+#
+#   meta-code-signing-demo/recipes-security/fit-image/linux-fit-image.bb
+#   meta-code-signing-demo/recipes-core/bundles/update-bundle.bb
+#
+# Examples for using keys for authentication:
+#
+#   meta-code-signing-demo/recipes-security/fit-image/barebox_%.bbappend
+#   meta-code-signing-demo/recipes-core/rauc/rauc_%.bbappend
+#
+# Examples for using keys for both signing and authentication:
+#
+#   meta-code-signing-demo/recipes-kernel/linux/linux-yocto_6.1.bbappend
+
+SIGNING_PKCS11_URI ?= ""
+SIGNING_PKCS11_MODULE ?= ""
+
+DEPENDS += "softhsm-native libp11-native opensc-native openssl-native"
+
+def signing_class_prepare(d):
+    import os.path
+
+    def export(role, k, v):
+        k = k % (role, )
+        d.setVar(k, v)
+        d.setVarFlag(k, "export", "1")
+
+    roles = set()
+    roles |= (d.getVarFlags("SIGNING_PKCS11_URI") or {}).keys()
+    roles |= (d.getVarFlags("SIGNING_PKCS11_MODULE") or {}).keys()
+    for role in roles:
+        if not set(role).issubset("abcdefghijklmnopqrstuvwxyz0123456789_"):
+            bb.fatal("key role name '%s' must consist of only [a-z0-9_]" % (role,))
+
+        pkcs11_uri = d.getVarFlag("SIGNING_PKCS11_URI", role) or d.getVar("SIGNING_PKCS11_URI")
+        if not pkcs11_uri.startswith("pkcs11:"):
+            bb.fatal("URI for key role '%s' must start with 'pkcs11:'" % (role,))
+
+        pkcs11_module = d.getVarFlag("SIGNING_PKCS11_MODULE", role) or d.getVar("SIGNING_PKCS11_MODULE")
+        if not os.path.isfile(pkcs11_module):
+            bb.fatal("module path for key role '%s' must be an existing file" % (role,))
+
+        if pkcs11_uri and not pkcs11_module:
+            bb.warn("SIGNING_PKCS11_URI[%s] is set without SIGNING_PKCS11_MODULE[%s]" % (role, role))
+        if pkcs11_module and not pkcs11_uri:
+            bb.warn("SIGNING_PKCS11_MODULE[%s] is set without SIGNING_PKCS11_URI[%s]" % (role, role))
+
+        export(role, "SIGNING_PKCS11_URI_%s_", pkcs11_uri)
+        export(role, "SIGNING_PKCS11_MODULE_%s_", pkcs11_module)
+
+signing_pkcs11_tool() {
+    pkcs11-tool --module "${STAGING_LIBDIR_NATIVE}/softhsm/libsofthsm2.so" --login --pin 1111 $*
+}
+
+signing_import_prepare() {
+    export _SIGNING_ENV_FILE_="${B}/meta-signing.env"
+    rm -f "$_SIGNING_ENV_FILE_"
+
+    export SOFTHSM2_CONF="${B}/softhsm2.conf"
+    export SOFTHSM2_DIR="${B}/softhsm2.tokens"
+    export SOFTHSM2_MOD="${STAGING_LIBDIR_NATIVE}/softhsm/libsofthsm2.so"
+
+    echo "directories.tokendir = $SOFTHSM2_DIR" > "$SOFTHSM2_CONF"
+    echo "objectstore.backend = db" >> "$SOFTHSM2_CONF"
+    rm -rf "$SOFTHSM2_DIR"
+    mkdir -p "$SOFTHSM2_DIR"
+
+    softhsm2-util --module $SOFTHSM2_MOD --init-token --free --label ${PN} --pin 1111 --so-pin 222222
+}
+
+signing_import_define_role() {
+    local role="${1}"
+    case "${1}" in
+        (*[!a-z0-9_]*) false;;
+        (*) true;;
+    esac || bbfatal "invalid role name '${1}', must consist of [a-z0-9_]"
+
+    echo "_SIGNING_PKCS11_URI_${role}_=\"pkcs11:token=${PN};object=$role;pin-value=1111\"" >> $_SIGNING_ENV_FILE_
+    echo "_SIGNING_PKCS11_MODULE_${role}_=\"softhsm\"" >> $_SIGNING_ENV_FILE_
+}
+
+# signing_import_cert_from_der <role> <der>
+#
+# Import a certificate from DER file to a role. To be used
+# with SoftHSM.
+signing_import_cert_from_der() {
+    local role="${1}"
+    local der="${2}"
+
+    signing_pkcs11_tool --type cert --write-object "${der}" --label "${role}"
+}
+
+# signing_import_cert_from_pem <role> <pem>
+#
+# Import a certificate from PEM file to a role. To be used
+# with SoftHSM.
+signing_import_cert_from_pem() {
+    local role="${1}"
+    local pem="${2}"
+
+    openssl x509 \
+        -in "${pem}" -inform pem -outform der |
+    signing_pkcs11_tool --type cert --write-object /proc/self/fd/0 --label "${role}"
+}
+
+# signing_import_pubkey_from_der <role> <pem>
+#
+# Import a public key from DER file to a role. To be used with SoftHSM.
+signing_import_pubkey_from_pem() {
+    local role="${1}"
+    local der="${2}"
+
+    signing_pkcs11_tool --type pubkey --write-object "${der}" --label "${role}"
+}
+
+# signing_import_pubkey_from_pem <role> <pem>
+#
+# Import a public key from PEM file to a role. To be used with SoftHSM.
+signing_import_pubkey_from_pem() {
+    local openssl_keyopt
+    local role="${1}"
+    local pem="${2}"
+
+    if [ -n "${IMPORT_PASS_FILE}" ]; then
+        openssl rsa \
+            -passin "file:${IMPORT_PASS_FILE}" \
+            -in "${pem}" -inform pem -pubout -outform der
+    else
+        openssl rsa \
+            -in "${pem}" -inform pem -pubout -outform der
+    fi |
+    signing_pkcs11_tool --type pubkey --write-object /proc/self/fd/0 --label "${role}"
+}
+
+# signing_import_privkey_from_der <role> <pem>
+#
+# Import a private key from DER file to a role. To be used with SoftHSM.
+signing_import_privkey_from_der() {
+    local role="${1}"
+    local der="${2}"
+    signing_pkcs11_tool --type privkey --write-object "${der}" --label "${role}"
+}
+
+# signing_import_privkey_from_pem <role> <pem>
+#
+# Import a private key from PEM file to a role. To be used with SoftHSM.
+signing_import_privkey_from_pem() {
+    local openssl_keyopt
+    local role="${1}"
+    local pem="${2}"
+
+    if [ -n "${IMPORT_PASS_FILE}" ]; then
+        openssl rsa \
+            -passin "file:${IMPORT_PASS_FILE}" \
+            -in "${pem}" -inform pem -outform der
+    else
+        openssl rsa \
+            -in "${pem}" -inform pem -outform der
+    fi |
+    signing_pkcs11_tool --type privkey --write-object /proc/self/fd/0 --label "${role}"
+}
+
+# signing_import_key_from_pem <role> <pem>
+#
+# Import a private and public key from PEM file to a role. To be used
+# with SoftHSM.
+signing_import_key_from_pem() {
+    local role="${1}"
+    local pem="${2}"
+
+    signing_import_pubkey_from_pem "${role}" "${pem}"
+    signing_import_privkey_from_pem "${role}" "${pem}"
+}
+
+signing_import_finish() {
+    echo "loaded objects:"
+    signing_pkcs11_tool --list-objects
+}
+
+signing_import_install() {
+    install -d ${D}${localstatedir}/lib/softhsm/tokens/${PN}
+    install -m 600 -t ${D}${localstatedir}/lib/softhsm/tokens/${PN} ${B}/softhsm2.tokens/*/*
+    install -d ${D}${localstatedir}/lib/meta-signing.env.d
+    install -m 644 "${B}/meta-signing.env" ${D}${localstatedir}/lib/meta-signing.env.d/${PN}
+}
+
+signing_prepare() {
+    if [ -f ${OPENSSL_CONF} ]; then
+        echo "Using '${OPENSSL_CONF}' for OpenSSL configuration"
+    else
+        echo "Missing 'openssl.cnf' at '${STAGING_ETCDIR_NATIVE}/ssl'"
+        return 1
+    fi
+    if [ -d ${OPENSSL_MODULES} ]; then
+        echo "Using '${OPENSSL_MODULES}' for OpenSSL run-time modules"
+    else
+        echo "Missing OpenSSL module directory at '${OPENSSL_MODULES}'"
+        return 1
+    fi
+    if [ -d ${OPENSSL_ENGINES} ]; then
+        echo "Using '${OPENSSL_ENGINES}' for OpenSSL run-time PKCS#11 modules"
+    else
+        echo "Missing OpenSSL PKCS11 engine directory at '${OPENSSL_ENGINES}'"
+        return 1
+    fi
+
+    export SOFTHSM2_CONF="${WORKDIR}/softhsm2.conf"
+    export SOFTHSM2_DIR="${STAGING_DIR_NATIVE}/var/lib/softhsm/tokens"
+
+    echo "directories.tokendir = $SOFTHSM2_DIR" > "$SOFTHSM2_CONF"
+    echo "objectstore.backend = db" >> "$SOFTHSM2_CONF"
+
+    for env in $(ls "${STAGING_DIR_NATIVE}/var/lib/meta-signing.env.d"); do
+        . "${STAGING_DIR_NATIVE}/var/lib/meta-signing.env.d/$env"
+    done
+}
+# make sure these functions are exported
+signing_prepare[vardeps] += "signing_get_uri signing_get_module"
+
+signing_use_role() {
+    local role="${1}"
+
+    export PKCS11_MODULE_PATH="$(signing_get_module $role)"
+    export PKCS11_URI="$(signing_get_uri $role)"
+
+    if [ -z "$PKCS11_MODULE_PATH" ]; then
+        echo "No PKCS11_MODULE_PATH found for role '${role}'"
+        exit 1
+    fi
+    if [ -z "$PKCS11_URI" ]; then
+        echo "No PKCS11_URI found for role '${role}'"
+        exit 1
+    fi
+}
+
+signing_get_uri() {
+    local role="${1}"
+
+    # prefer local configuration
+    eval local uri="\$SIGNING_PKCS11_URI_${role}_"
+    if [ -n "$uri" ]; then
+        echo "$uri"
+        return
+    fi
+
+    # fall back to softhsm
+    eval echo "\$_SIGNING_PKCS11_URI_${role}_"
+}
+
+signing_get_module() {
+    local role="${1}"
+
+    # prefer local configuration
+    eval local module="\$SIGNING_PKCS11_MODULE_${role}_"
+    if [ -n "$module" ]; then
+        echo "$module"
+        return
+    fi
+
+    # fall back to softhsm
+    eval local module="\$_SIGNING_PKCS11_MODULE_${role}_"
+    if [ "$module" = "softhsm" ]; then
+        echo "${STAGING_LIBDIR_NATIVE}/softhsm/libsofthsm2.so"
+    else
+        echo "$module"
+    fi
+}
+
+python () {
+    signing_class_prepare(d)
+}
+
+export OPENSSL_MODULES="${STAGING_LIBDIR_NATIVE}/ossl-modules"
+export OPENSSL_ENGINES="${STAGING_LIBDIR_NATIVE}/engines-3"
+export OPENSSL_CONF="${STAGING_LIBDIR_NATIVE}/ssl-3/openssl.cnf"
+export SSL_CERT_DIR="${STAGING_LIBDIR_NATIVE}/ssl-3/certs"
+export SSL_CERT_FILE="${STAGING_LIBDIR_NATIVE}/ssl-3/cert.pem"