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# No default! Either this or IMA_EVM_PRIVKEY/IMA_EVM_X509 have to be
# set explicitly in a local.conf before activating ima-evm-rootfs.
# To use the insecure (because public) example keys, use
# IMA_EVM_KEY_DIR = "${IMA_EVM_BASE}/data/debug-keys"
IMA_EVM_KEY_DIR ?= "IMA_EVM_KEY_DIR_NOT_SET"
# Private key for IMA signing. The default is okay when
# using the example key directory.
IMA_EVM_PRIVKEY ?= "${IMA_EVM_KEY_DIR}/privkey_ima.pem"
# Public part of certificates (used for both IMA and EVM).
# The default is okay when using the example key directory.
IMA_EVM_X509 ?= "${IMA_EVM_KEY_DIR}/x509_ima.der"
# Root CA to be compiled into the kernel, none by default.
# Must be the absolute path to a der-encoded x509 CA certificate
# with a .x509 suffix. See linux-%.bbappend for details.
#
# ima-local-ca.x509 is what ima-gen-local-ca.sh creates.
IMA_EVM_ROOT_CA ?= ""
# Sign all regular files by default.
IMA_EVM_ROOTFS_SIGNED ?= ". -type f"
# Hash nothing by default.
IMA_EVM_ROOTFS_HASHED ?= ". -depth 0 -false"
# Mount these file systems (identified via their mount point) with
# the iversion flags (needed by IMA when allowing writing).
IMA_EVM_ROOTFS_IVERSION ?= ""
ima_evm_sign_rootfs () {
cd ${IMAGE_ROOTFS}
# Beware that all operations below must also work when
# ima_evm_sign_rootfs was already called earlier for the same
# rootfs. That's because do_image might again run for various
# reasons (including a change of the signing keys) without also
# re-running do_rootfs.
# Copy file(s) which must be on the device. Note that
# evmctl uses x509_evm.der also for "ima_verify", which is probably
# a bug (should default to x509_ima.der). Does not matter for us
# because we use the same key for both.
install -d ./${sysconfdir}/keys
rm -f ./${sysconfdir}/keys/x509_evm.der
install "${IMA_EVM_X509}" ./${sysconfdir}/keys/x509_evm.der
ln -sf x509_evm.der ./${sysconfdir}/keys/x509_ima.der
# Fix /etc/fstab: it must include the "i_version" mount option for
# those file systems where writing files is allowed, otherwise
# these changes will not get detected at runtime.
#
# Note that "i_version" is documented in "man mount" only for ext4,
# whereas "iversion" is said to be filesystem-independent. In practice,
# there is only one MS_I_VERSION flag in the syscall and ext2/ext3/ext4
# all support it.
#
# coreutils translates "iversion" into MS_I_VERSION. busybox rejects
# "iversion" and only understands "i_version". systemd only understands
# "iversion". We pick "iversion" here for systemd, whereas rootflags
# for initramfs must use "i_version" for busybox.
#
# Deduplicates iversion in case that this gets called more than once.
if [ -f etc/fstab ]; then
perl -pi -e 's;(\S+)(\s+)(${@"|".join((d.getVar("IMA_EVM_ROOTFS_IVERSION", True) or "no-such-mount-point").split())})(\s+)(\S+)(\s+)(\S+);\1\2\3\4\5\6\7,iversion;; s/(,iversion)+/,iversion/;' etc/fstab
fi
# Sign file with private IMA key. EVM not supported at the moment.
bbnote "IMA/EVM: signing files 'find ${IMA_EVM_ROOTFS_SIGNED}' with private key '${IMA_EVM_PRIVKEY}'"
find ${IMA_EVM_ROOTFS_SIGNED} | xargs -d "\n" --no-run-if-empty --verbose evmctl ima_sign --key ${IMA_EVM_PRIVKEY}
bbnote "IMA/EVM: hashing files 'find ${IMA_EVM_ROOTFS_HASHED}'"
find ${IMA_EVM_ROOTFS_HASHED} | xargs -d "\n" --no-run-if-empty --verbose evmctl ima_hash
# Optionally install custom policy for loading by systemd.
if [ "${IMA_EVM_POLICY_SYSTEMD}" ]; then
install -d ./${sysconfdir}/ima
rm -f ./${sysconfdir}/ima/ima-policy
install "${IMA_EVM_POLICY_SYSTEMD}" ./${sysconfdir}/ima/ima-policy
fi
}
# Signing must run as late as possible in the do_rootfs task.
# IMAGE_PREPROCESS_COMMAND runs after ROOTFS_POSTPROCESS_COMMAND, so
# append (not prepend!) to IMAGE_PREPROCESS_COMMAND, and do it with
# _append instead of += because _append gets evaluated later. In
# particular, we must run after prelink_image in
# IMAGE_PREPROCESS_COMMAND, because prelinking changes executables.
IMAGE_PREPROCESS_COMMAND_append = " ima_evm_sign_rootfs ; "
# evmctl must have been installed first.
do_rootfs[depends] += "ima-evm-utils-native:do_populate_sysroot"
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