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What: security/evm
Date: March 2011
Contact: Mimi Zohar <zohar@us.ibm.com>
Description:
EVM protects a file's security extended attributes(xattrs)
against integrity attacks. The initial method maintains an
HMAC-sha1 value across the extended attributes, storing the
value as the extended attribute 'security.evm'.
EVM depends on the Kernel Key Retention System to provide it
with a trusted/encrypted key for the HMAC-sha1 operation.
The key is loaded onto the root's keyring using keyctl. Until
EVM receives notification that the key has been successfully
loaded onto the keyring (echo 1 > <securityfs>/evm), EVM
can not create or validate the 'security.evm' xattr, but
returns INTEGRITY_UNKNOWN. Loading the key and signaling EVM
should be done as early as possible. Normally this is done
in the initramfs, which has already been measured as part
of the trusted boot. For more information on creating and
loading existing trusted/encrypted keys, refer to:
Documentation/security/keys/trusted-encrypted.rst. (A sample
dracut patch, which loads the trusted/encrypted key and enables
EVM, is available from http://linux-ima.sourceforge.net/#EVM.)
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