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Diffstat (limited to 'Documentation/ABI/testing/evm')
| -rw-r--r-- | Documentation/ABI/testing/evm | 48 |
1 files changed, 34 insertions, 14 deletions
diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm index 8374d4557e5d..9578247e1792 100644 --- a/Documentation/ABI/testing/evm +++ b/Documentation/ABI/testing/evm @@ -7,17 +7,37 @@ Description: 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/keys-trusted-encrypted.txt. (A sample dracut - patch, which loads the trusted/encrypted key and enables - EVM, is available from http://linux-ima.sourceforge.net/#EVM.) + EVM supports two classes of security.evm. The first is + an HMAC-sha1 generated locally with a + trusted/encrypted key stored in the Kernel Key + Retention System. The second is a digital signature + generated either locally or remotely using an + asymmetric key. These keys are loaded onto root's + keyring using keyctl, and EVM is then enabled by + echoing a value to <securityfs>/evm: + + 1: enable HMAC validation and creation + 2: enable digital signature validation + 3: enable HMAC and digital signature validation and HMAC + creation + + Further writes will be blocked if HMAC support is enabled or + if bit 32 is set: + + echo 0x80000002 ><securityfs>/evm + + will enable digital signature validation and block + further writes to <securityfs>/evm. + + Until this is done, EVM can not create or validate the + 'security.evm' xattr, but returns INTEGRITY_UNKNOWN. + Loading keys 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. Both dracut + (via 97masterkey and 98integrity) and systemd (via + core/ima-setup) have support for loading keys at boot + time. |