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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 = "${INTEGRITY_BASE}/data/debug-keys"
IMA_EVM_KEY_DIR ?= "IMA_EVM_KEY_DIR_NOT_SET"
# Private key for IMA signing. The default is okay when
# using the example key directory.
IMA_EVM_PRIVKEY ?= "${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 ?= "${IMA_EVM_KEY_DIR}/x509_ima.der"
# Root CA to be compiled into the kernel, none by default.
# Must be the absolute path to a der-encoded x509 CA certificate
# with a .x509 suffix. See linux-%.bbappend for details.
#
# ima-local-ca.x509 is what ima-gen-local-ca.sh creates.
IMA_EVM_ROOT_CA ?= "${IMA_EVM_KEY_DIR}/ima-local-ca.pem"
# 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 ?= ""
# Avoid re-generating fstab when ima is enabled.
WIC_CREATE_EXTRA_ARGS:append = "${@bb.utils.contains('DISTRO_FEATURES', 'ima', ' --no-fstab-update', '', d)}"
# Add necessary tools (e.g., keyctl) to image
IMAGE_INSTALL:append = "${@bb.utils.contains('DISTRO_FEATURES', 'ima', ' ima-evm-utils', '', d)}"
ima_evm_sign_rootfs () {
cd ${IMAGE_ROOTFS}
# Beware that all operations below must also work when
# ima_evm_sign_rootfs was already called earlier for the same
# rootfs. That's because do_image might again run for various
# reasons (including a change of the signing keys) without also
# re-running do_rootfs.
# Fix /etc/fstab: it must include the "i_version" mount option for
# those file systems where writing files is allowed, otherwise
# these changes will not get detected at runtime.
#
# Note that "i_version" is documented in "man mount" only for ext4,
# whereas "iversion" is said to be filesystem-independent. In practice,
# there is only one MS_I_VERSION flag in the syscall and ext2/ext3/ext4
# all support it.
#
# coreutils translates "iversion" into MS_I_VERSION. busybox rejects
# "iversion" and only understands "i_version". systemd only understands
# "iversion". We pick "iversion" here for systemd, whereas rootflags
# for initramfs must use "i_version" for busybox.
#
# Deduplicates iversion in case that this gets called more than once.
if [ -f etc/fstab ]; then
perl -pi -e 's;(\S+)(\s+)(${@"|".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
# Detect 32bit target to pass --m32 to evmctl by looking at libc
tmp="$(file "${IMAGE_ROOTFS}/lib/libc.so.6" | grep -o 'ELF .*-bit')"
if [ "${tmp}" = "ELF 32-bit" ]; then
evmctl_param="--m32"
elif [ "${tmp}" = "ELF 64-bit" ]; then
evmctl_param=""
else
bberror "Unknown target architecture bitness: '${tmp}'" >&2
exit 1
fi
bbnote "IMA/EVM: Signing root filesystem at ${IMAGE_ROOTFS} with key ${IMA_EVM_PRIVKEY}"
evmctl sign --imasig ${evmctl_param} --portable -a sha256 --key ${IMA_EVM_PRIVKEY} -r "${IMAGE_ROOTFS}"
# check signing key and signature verification key
evmctl ima_verify ${evmctl_param} --key "${IMA_EVM_X509}" "${IMAGE_ROOTFS}/lib/libc.so.6" || exit 1
evmctl verify ${evmctl_param} --key "${IMA_EVM_X509}" "${IMAGE_ROOTFS}/lib/libc.so.6" || exit 1
# Optionally install custom policy for loading by systemd.
if [ "${IMA_EVM_POLICY}" ]; then
install -d ./${sysconfdir}/ima
rm -f ./${sysconfdir}/ima/ima-policy
install "${IMA_EVM_POLICY}" ./${sysconfdir}/ima/ima-policy
bbnote "IMA/EVM: Signing IMA policy with key ${IMA_EVM_PRIVKEY}"
evmctl sign --imasig ${evmctl_param} --portable -a sha256 --key "${IMA_EVM_PRIVKEY}" "${IMAGE_ROOTFS}/etc/ima/ima-policy"
fi
# Optionally write the file names and ima and evm signatures into files
if [ "${IMA_FILE_SIGNATURES_FILE}" ]; then
getfattr -R -m security.ima --e hex --dump ./ 2>/dev/null | \
sed -n -e 's|# file: |/|p' -e 's|security.ima=|ima:|p' | \
sed '$!N;s/\n/ /' > ./${IMA_FILE_SIGNATURES_FILE}
fi
if [ "${EVM_FILE_SIGNATURES_FILE}" ]; then
getfattr -R -m security.evm --e hex --dump ./ 2>/dev/null | \
sed -n -e 's|# file: |/|p' -e 's|security.evm=|evm:|p' | \
sed '$!N;s/\n/ /' > ./${EVM_FILE_SIGNATURES_FILE}
fi
}
# Signing must run as late as possible in the do_rootfs task.
# To guarantee that, we append it to IMAGE_PREPROCESS_COMMAND in
# RecipePreFinalise event handler, this ensures it's the last
# function in IMAGE_PREPROCESS_COMMAND.
python ima_evm_sign_handler () {
if not e.data or 'ima' not in e.data.getVar('DISTRO_FEATURES').split():
return
e.data.appendVar('IMAGE_PREPROCESS_COMMAND', ' ima_evm_sign_rootfs; ')
e.data.appendVar('IMAGE_INSTALL', ' ima-evm-keys')
e.data.appendVarFlag('do_rootfs', 'depends', ' ima-evm-utils-native:do_populate_sysroot')
}
addhandler ima_evm_sign_handler
ima_evm_sign_handler[eventmask] = "bb.event.RecipePreFinalise"
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