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integrity: Update the README for IMA support

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Update the README describing how IMA support can be used.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
This commit is contained in:
Stefan Berger
2023-04-28 08:23:14 -04:00
committed by Armin Kuster
parent 76f1f539a6
commit b9abf0e09b
1 changed files with 11 additions and 9 deletions
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meta-integrity/README.md
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@@ -76,7 +76,7 @@ other layers needed. e.g.:
It has some dependencies on a suitable BSP; in particular the kernel
must have a recent enough IMA/EVM subsystem. The layer was tested with
Linux 3.19 and uses some features (like loading X509 certificates
Linux 6.1 and uses some features (like loading X509 certificates
directly from the kernel) which were added in that release. Your
mileage may vary with older kernels.
@@ -89,10 +89,17 @@ Adding the layer only enables IMA (see below regarding EVM) during
compilation of the Linux kernel. To also activate it when building
the image, enable image signing in the local.conf like this:
DISTRO_FEATURES:append = " integrity ima"
IMAGE_CLASSES += "ima-evm-rootfs"
IMA_EVM_KEY_DIR = "${INTEGRITY_BASE}/data/debug-keys"
IMA_EVM_PRIVKEY = "${IMA_EVM_KEY_DIR}/privkey_ima.pem"
IMA_EVM_X509 = "${IMA_EVM_KEY_DIR}/x509_ima.der"
IMA_EVM_ROOT_CA = "${IMA_EVM_KEY_DIR}/ima-local-ca.pem"
# The following policy enforces IMA & EVM signatures
IMA_EVM_POLICY = "${INTEGRITY_BASE}/recipes-security/ima_policy_appraise_all/files/ima_policy_appraise_all"
This uses the default keys provided in the "data" directory of the layer.
Because everyone has access to these private keys, such an image
@@ -113,10 +120,7 @@ for that are included in the layer. This is also how the
cd $IMA_EVM_KEY_DIR
# In that shell, create the keys. Several options exist:
# 1. Self-signed keys.
$INTEGRITY_BASE/scripts/ima-gen-self-signed.sh
# 2. Keys signed by a new CA.
# 1. Keys signed by a new CA.
# When asked for a PEM passphrase, that will be for the root CA.
# Signing images then will not require entering that passphrase,
# only creating new certificates does. Most likely the default
@@ -125,13 +129,11 @@ for that are included in the layer. This is also how the
# $INTEGRITY_BASE/scripts/ima-gen-local-ca.sh
# $INTEGRITY_BASE/scripts/ima-gen-CA-signed.sh
# 3. Keys signed by an existing CA.
# 2. Keys signed by an existing CA.
# $INTEGRITY_BASE/scripts/ima-gen-CA-signed.sh <CA.pem> <CA.priv>
exit
When using ``ima-self-signed.sh`` as described above, self-signed keys
are created. Alternatively, one can also use keys signed by a CA. The
``ima-gen-local-ca.sh`` and ``ima-gen.sh`` scripts create a root CA
The ``ima-gen-local-ca.sh`` and ``ima-gen.sh`` scripts create a root CA
and sign the signing keys with it. The ``ima-evm-rootfs.bbclass`` then
supports adding tha CA's public key to the kernel's system keyring by
compiling it directly into the kernel. Because it is unknown whether