[PATCH 2/6] kernel-build.eclass: option to use different key for measured boot

The algorithms supported by the UEFI/shim for Secure Boot verification
are not necessary the same as those supported by the systems TPM.
For this reason users might want to use two separate sets of keys.
This is added here as an option using the established naming scheme
for the user variables. We also add a switch that allows the user to
select which PCR banks to use. If unset, we return to the default
behaviour of using all PCR banks, which may cause issues on systems
with TPMs that do not support all those banks.

Closes: https://bugs.gentoo.org/973344
Signed-off-by: Nowa Ammerlaan <[email protected]>
---
 eclass/kernel-build.eclass | 97 +++++++++++++++++++++++++++++---------
 1 file changed, 76 insertions(+), 21 deletions(-)

diff --git a/eclass/kernel-build.eclass b/eclass/kernel-build.eclass
index 10f86423bb1b..0b8603e5f31a 100644
--- a/eclass/kernel-build.eclass
+++ b/eclass/kernel-build.eclass
@@ -65,6 +65,37 @@ fi
 IUSE="+strip modules-sign"
 REQUIRED_USE="secureboot? ( modules-sign )"
 
+# @ECLASS_VARIABLE: MEASUREDBOOT_SIGN_CERT
+# @USER_VARIABLE
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Used with USE=generic-uki.  May be set to the path of the public key
+# certificate in PEM format to use for signing PCR policies. Useful
+# for automatically unlocking encrypted disks with a TPM.
+# If unspecified defaults to the value of SECUREBOOT_SIGN_CERT.
+: "${MEASUREDBOOT_SIGN_CERT:=${SECUREBOOT_SIGN_CERT}}"
+
+# @ECLASS_VARIABLE: MEASUREDBOOT_SIGN_HASH
+# @USER_VARIABLE
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Used with USE=generic-uki.  Can be set to a comma or space-separated
+# list specifying which PCR banks to perform measurements for. If
+# unset all PCR banks are used which will fail if not supported by the
+# system.
+#
+# Valid values: sha512,sha384,sha256,sha1
+
+# @ECLASS_VARIABLE: MEASUREDBOOT_SIGN_KEY
+# @USER_VARIABLE
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Used with USE=generic-uki.  May be set to the path of the private
+# key in PEM format to use for signing PCR policies. Useful for
+# automatically unlocking encrypted disks with a TPM.
+# If unspecified defaults to the value of SECUREBOOT_SIGN_KEY.
+: "${MEASUREDBOOT_SIGN_KEY:=${SECUREBOOT_SIGN_KEY}}"
+
 # @ECLASS_VARIABLE: MODULES_SIGN_HASH
 # @USER_VARIABLE
 # @DEFAULT_UNSET
@@ -162,6 +193,30 @@ kernel-build_pkg_setup() {
 				fi
 			fi
 		fi
+
+		if [[ ${KERNEL_IUSE_GENERIC_UKI} ]] && use generic-uki; then
+			if [[ -n ${MEASUREDBOOT_SIGN_KEY} ]]; then
+				if [[ -z ${MEASUREDBOOT_SIGN_CERT} ]]; then
+					ewarn "A MEASUREDBOOT_SIGN_KEY was specified but no MEASUREDBOOT_SIGN_CERT"
+					ewarn "was set. Assuming the certificate is in the same file as the key."
+					export MEASUREDBOOT_SIGN_CERT=${MEASUREDBOOT_SIGN_KEY}
+				fi
+
+				# Sanity check: fail early if key/cert in DER format or does not exist
+				local openssl_args=(
+					-inform PEM -in "${MEASUREDBOOT_SIGN_CERT}"
+					-noout -nocert
+				)
+				if [[ ${MEASUREDBOOT_SIGN_KEY} == pkcs11:* ]]; then
+					openssl_args+=( -engine pkcs11 -keyform ENGINE -key "${MEASUREDBOOT_SIGN_KEY}" )
+				else
+					openssl_args+=( -keyform PEM -key "${MEASUREDBOOT_SIGN_KEY}" )
+				fi
+
+				openssl x509 "${openssl_args[@]}" ||
+					die "Measured Boot signing certificate or key not found or not PEM format."
+			fi
+		fi
 	fi
 }
 
@@ -625,37 +680,37 @@ kernel-build_src_install() {
 			done
 
 			if use secureboot; then
+				if [[ ${SECUREBOOT_SIGN_KEY} == pkcs11:* ]]; then
+					ukify_args+=(
+						--signing-engine="pkcs11"
+					)
+				fi
+				ukify_args+=(
+					--secureboot-private-key="${SECUREBOOT_SIGN_KEY}"
+					--secureboot-certificate="${SECUREBOOT_SIGN_CERT}"
+				)
+			fi
+			if [[ -n ${MEASUREDBOOT_SIGN_KEY} ]]; then
 				# The PCR public key option should contain *only* the
 				# public key, not the full certificate containing the
 				# public key. Bug #960276
 				openssl x509 \
-					-in "${SECUREBOOT_SIGN_CERT}" -inform PEM \
+					-in "${MEASUREDBOOT_SIGN_CERT}" -inform PEM \
 					-noout -pubkey > "${T}/pcrpkey.pem" ||
 						die "Failed to extract public key"
 				ukify_args+=(
-					--secureboot-private-key="${SECUREBOOT_SIGN_KEY}"
-					--secureboot-certificate="${SECUREBOOT_SIGN_CERT}"
-					--pcrpkey="${T}/pcrpkey.pem"
 					--measure
+					--pcrpkey="${T}/pcrpkey.pem"
+					--pcr-private-key="${MEASUREDBOOT_SIGN_KEY}"
+					--pcr-public-key="${T}/pcrpkey.pem"
+					--phases="enter-initrd"
+					--pcr-private-key="${MEASUREDBOOT_SIGN_KEY}"
+					--pcr-public-key="${T}/pcrpkey.pem"
+					--phases="enter-initrd:leave-initrd enter-initrd:leave-initrd:sysinit enter-initrd:leave-initrd:sysinit:ready"
 				)
-				if [[ ${SECUREBOOT_SIGN_KEY} == pkcs11:* ]]; then
-					ukify_args+=(
-						--signing-engine="pkcs11"
-						--pcr-private-key="${SECUREBOOT_SIGN_KEY}"
-						--pcr-public-key="${T}/pcrpkey.pem"
-						--phases="enter-initrd"
-						--pcr-private-key="${SECUREBOOT_SIGN_KEY}"
-						--pcr-public-key="${T}/pcrpkey.pem"
-						--phases="enter-initrd:leave-initrd enter-initrd:leave-initrd:sysinit enter-initrd:leave-initrd:sysinit:ready"
-					)
-				else
+				if [[ -n ${MEASUREDBOOT_SIGN_HASH} ]]; then
 					ukify_args+=(
-						--pcr-private-key="${SECUREBOOT_SIGN_KEY}"
-						--pcr-public-key="${T}/pcrpkey.pem"
-						--phases="enter-initrd"
-						--pcr-private-key="${SECUREBOOT_SIGN_KEY}"
-						--pcr-public-key="${T}/pcrpkey.pem"
-						--phases="enter-initrd:leave-initrd enter-initrd:leave-initrd:sysinit enter-initrd:leave-initrd:sysinit:ready"
+						--pcr-banks="${MEASUREDBOOT_SIGN_HASH}"
 					)
 				fi
 			fi
-- 
2.54.0