Previously if no symmetric key was configured for EVM, then the
initialization process was aborted. It can be a valid use case, however,
to only use EVM digital signatures. In this case only X.509 certificates
need to be loaded.
With this change EVM initialization will continue if any of the
symmetric or X.509 keys could be loaded.
This implements logic analogous to the one already implemented in
ima-keys-load.sh, only for the .evm/_evm keyrings.
If the kernel was built with CONFIG_IMA_TRUSTED_KEYRING then the kernel
initially creates and configures .ima and .evm keyrings. These keyrings
only accept x509 certificates that have been signed by a local CA which
belongs to the kernel builtin trusted keyring.
Thus if such a keyring is already present then additional evm keys
should be loaded into them. If this is not the case then the _evm
keyring needs to be created in userspace and keys will be loaded into
it instead.
Before this change dracut always created the _evm keyring and loaded
keys into it without considering an existing .evm keyring. In case of
CONFIG_IMA_TRUSTED_KEYRING being enabled, the _evm keyring will not be
used by the kernel, however, and EVM digital signatures will not work as
expected.
This module initializes the EVM software and permits to load a custom IMA
policy.
Signed-off-by: Roberto Sassu <roberto.sassu@polito.it>
Acked-by: Gianluca Ramunno <ramunno@polito.it>
Sullivan (CTR), Austin