From: Adrian Freihofer Date: Tue, 3 Jun 2025 08:23:17 +0000 (+0200) Subject: kernel-signing-keys-native: refactor key generation into a new recipe X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=88736bb53fd2f0ffa1d249fc1a37897d10c8be18;p=thirdparty%2Fopenembedded%2Fopenembedded-core-contrib.git kernel-signing-keys-native: refactor key generation into a new recipe The do_kernel_generate_rsa_keys function from kernel-fitimage.bbclass is moved to a new recipe, kernel-signing-keys-native.bb. This refactoring introduces no functional changes. Intention this change: - Remove the dependency of uboot-sign.bbclass on kernel-fitimage.bbclass. - Simplify the use of custom key generation implementations by isolating the functionality into a separate recipe. Known limitations of this (and also the previous) implementation: - When generating from an existing TMPDIR, the existing key is reused. However, when generating from an empty TMPDIR or an SDK using the sstate-cache, a new key is generated, which may lead to inconsistencies. - The use of random keys (via FIT_GENERATE_KEYS) is convenient for experiments but unsuitable for production environments requiring deterministic and secure key management. Future improvements to consider: - Ensure reproducibility, even when using the sstate-cache. However, simply storing the private key in a potentially shared sstate artifact may not always be ideal from a security perspective. - Support encrypted keys via `SRC_URI` for reliable key updates. - Enable signing with an HSM (Hardware Security Module) through mechanisms like PKCS#11 or post-processing scripts. Signed-off-by: Adrian Freihofer Signed-off-by: Richard Purdie --- diff --git a/meta/classes-recipe/kernel-fitimage.bbclass b/meta/classes-recipe/kernel-fitimage.bbclass index 07786647e19..f5f02f30f0a 100644 --- a/meta/classes-recipe/kernel-fitimage.bbclass +++ b/meta/classes-recipe/kernel-fitimage.bbclass @@ -27,7 +27,10 @@ def get_fit_replacement_type(d): return replacementtype KERNEL_IMAGETYPE_REPLACEMENT ?= "${@get_fit_replacement_type(d)}" -DEPENDS:append = " ${@'u-boot-tools-native dtc-native' if 'fitImage' in (d.getVar('KERNEL_IMAGETYPES') or '').split() else ''}" +DEPENDS:append = " \ + ${@'u-boot-tools-native dtc-native' if 'fitImage' in (d.getVar('KERNEL_IMAGETYPES') or '').split() else ''} \ + ${@'kernel-signing-keys-native' if d.getVar('FIT_GENERATE_KEYS') == '1' else ''} \ +" python __anonymous () { # Override KERNEL_IMAGETYPE_FOR_MAKE variable, which is internal @@ -754,53 +757,6 @@ do_assemble_fitimage_initramfs() { addtask assemble_fitimage_initramfs before do_deploy after do_bundle_initramfs -do_kernel_generate_rsa_keys() { - if [ "${UBOOT_SIGN_ENABLE}" = "0" ] && [ "${FIT_GENERATE_KEYS}" = "1" ]; then - bbwarn "FIT_GENERATE_KEYS is set to 1 even though UBOOT_SIGN_ENABLE is set to 0. The keys will not be generated as they won't be used." - fi - - if [ "${UBOOT_SIGN_ENABLE}" = "1" ] && [ "${FIT_GENERATE_KEYS}" = "1" ]; then - - # Generate keys to sign configuration nodes, only if they don't already exist - if [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".key ] || \ - [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".crt ]; then - - # make directory if it does not already exist - mkdir -p "${UBOOT_SIGN_KEYDIR}" - - bbnote "Generating RSA private key for signing fitImage" - openssl genrsa ${FIT_KEY_GENRSA_ARGS} -out \ - "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".key \ - "${FIT_SIGN_NUMBITS}" - - bbnote "Generating certificate for signing fitImage" - openssl req ${FIT_KEY_REQ_ARGS} "${FIT_KEY_SIGN_PKCS}" \ - -key "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".key \ - -out "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".crt - fi - - # Generate keys to sign image nodes, only if they don't already exist - if [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".key ] || \ - [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".crt ]; then - - # make directory if it does not already exist - mkdir -p "${UBOOT_SIGN_KEYDIR}" - - bbnote "Generating RSA private key for signing fitImage" - openssl genrsa ${FIT_KEY_GENRSA_ARGS} -out \ - "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".key \ - "${FIT_SIGN_NUMBITS}" - - bbnote "Generating certificate for signing fitImage" - openssl req ${FIT_KEY_REQ_ARGS} "${FIT_KEY_SIGN_PKCS}" \ - -key "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".key \ - -out "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".crt - fi - fi -} - -addtask kernel_generate_rsa_keys before do_assemble_fitimage after do_compile - kernel_do_deploy[vardepsexclude] = "DATETIME" kernel_do_deploy:append() { # Update deploy directory diff --git a/meta/classes-recipe/uboot-sign.bbclass b/meta/classes-recipe/uboot-sign.bbclass index 796c040e8b4..73e9ce3f11f 100644 --- a/meta/classes-recipe/uboot-sign.bbclass +++ b/meta/classes-recipe/uboot-sign.bbclass @@ -112,13 +112,14 @@ UBOOT_FIT_CONF_USER_LOADABLES ?= '' UBOOT_FIT_UBOOT_LOADADDRESS ?= "${UBOOT_LOADADDRESS}" UBOOT_FIT_UBOOT_ENTRYPOINT ?= "${UBOOT_ENTRYPOINT}" + +DEPENDS:append = " ${@'kernel-signing-keys-native' if d.getVar('FIT_GENERATE_KEYS') == '1' else ''}" + python() { # We need u-boot-tools-native if we're creating a U-Boot fitImage sign = d.getVar('UBOOT_SIGN_ENABLE') == '1' if d.getVar('UBOOT_FITIMAGE_ENABLE') == '1' or sign: d.appendVar('DEPENDS', " u-boot-tools-native dtc-native") - if d.getVar('FIT_GENERATE_KEYS') == '1' and sign: - d.appendVarFlag('do_uboot_assemble_fitimage', 'depends', ' virtual/kernel:do_kernel_generate_rsa_keys') } concat_dtb() { diff --git a/meta/recipes-kernel/kernel-signing-keys/kernel-signing-keys-native.bb b/meta/recipes-kernel/kernel-signing-keys/kernel-signing-keys-native.bb new file mode 100644 index 00000000000..704973dffb7 --- /dev/null +++ b/meta/recipes-kernel/kernel-signing-keys/kernel-signing-keys-native.bb @@ -0,0 +1,75 @@ +# Automatically generate key pairs in UBOOT_SIGN_KEYDIR if they do not exist. +# The key pair is generated by the kernel-signing-keys-native recipe and is not +# stored in the sstate cache. This can be beneficial from a security standpoint, +# as it avoids unintentionally caching and distributing private keys. +# However, this behavior can lead to non-reproducible builds. For example, if +# the keys are deleted, they must be manually restored, or you must run: +# bitbake -c cleanall kernel-signing-keys-native +# before new key pairs are generated. +# +# However, this approach is only suitable for simple or local development use +# cases. For more advanced or production-grade scenarios, a more robust solution +# is usually required—such as external signing or re-signing using e.g a HSM. + + +SUMMARY = "Signing keys for the kernel FIT image" +LICENSE = "MIT" +LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420" + +require conf/image-fitimage.conf + +DEPENDS += "openssl-native" + +inherit native + +do_fetch[noexec] = "1" +do_unpack[noexec] = "1" +do_patch[noexec] = "1" +do_configure[noexec] = "1" +do_install[noexec] = "1" + + +do_compile() { + if [ "${UBOOT_SIGN_ENABLE}" = "0" ] && [ "${FIT_GENERATE_KEYS}" = "1" ]; then + bbwarn "FIT_GENERATE_KEYS is set to 1 even though UBOOT_SIGN_ENABLE is set to 0. The keys will not be generated as they won't be used." + fi + + if [ "${UBOOT_SIGN_ENABLE}" = "1" ] && [ "${FIT_GENERATE_KEYS}" = "1" ]; then + + # Generate keys to sign configuration nodes, only if they don't already exist + if [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".key ] || \ + [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".crt ]; then + + # make directory if it does not already exist + mkdir -p "${UBOOT_SIGN_KEYDIR}" + + bbnote "Generating RSA private key for signing fitImage" + openssl genrsa ${FIT_KEY_GENRSA_ARGS} -out \ + "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".key \ + "${FIT_SIGN_NUMBITS}" + + bbnote "Generating certificate for signing fitImage" + openssl req ${FIT_KEY_REQ_ARGS} "${FIT_KEY_SIGN_PKCS}" \ + -key "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".key \ + -out "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_KEYNAME}".crt + fi + + # Generate keys to sign image nodes, only if they don't already exist + if [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".key ] || \ + [ ! -f "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".crt ]; then + + # make directory if it does not already exist + mkdir -p "${UBOOT_SIGN_KEYDIR}" + + bbnote "Generating RSA private key for signing fitImage" + openssl genrsa ${FIT_KEY_GENRSA_ARGS} -out \ + "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".key \ + "${FIT_SIGN_NUMBITS}" + + bbnote "Generating certificate for signing fitImage" + openssl req ${FIT_KEY_REQ_ARGS} "${FIT_KEY_SIGN_PKCS}" \ + -key "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".key \ + -out "${UBOOT_SIGN_KEYDIR}/${UBOOT_SIGN_IMG_KEYNAME}".crt + fi + fi +}