diff options
| -rw-r--r-- | Documentation/ABI/testing/evm | 26 | ||||
| -rw-r--r-- | security/integrity/evm/evm_secfs.c | 8 |
2 files changed, 28 insertions, 6 deletions
diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm index 3c477ba48a31..2243b72e4110 100644 --- a/Documentation/ABI/testing/evm +++ b/Documentation/ABI/testing/evm @@ -49,8 +49,30 @@ Description: modification of EVM-protected metadata and disable all further modification of policy - Note that once a key has been loaded, it will no longer be - possible to enable metadata modification. + Echoing a value is additive, the new value is added to the + existing initialization flags. + + For example, after:: + + echo 2 ><securityfs>/evm + + another echo can be performed:: + + echo 1 ><securityfs>/evm + + and the resulting value will be 3. + + Note that once an HMAC key has been loaded, it will no longer + be possible to enable metadata modification. Signaling that an + HMAC key has been loaded will clear the corresponding flag. + For example, if the current value is 6 (2 and 4 set):: + + echo 1 ><securityfs>/evm + + will set the new value to 3 (4 cleared). + + Loading an HMAC key is the only way to disable metadata + modification. Until key loading has been signaled EVM can not create or validate the 'security.evm' xattr, but returns diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c index 0007d3362754..5f0da41bccd0 100644 --- a/security/integrity/evm/evm_secfs.c +++ b/security/integrity/evm/evm_secfs.c @@ -81,12 +81,12 @@ static ssize_t evm_write_key(struct file *file, const char __user *buf, if (!i || (i & ~EVM_INIT_MASK) != 0) return -EINVAL; - /* Don't allow a request to freshly enable metadata writes if - * keys are loaded. + /* + * Don't allow a request to enable metadata writes if + * an HMAC key is loaded. */ if ((i & EVM_ALLOW_METADATA_WRITES) && - ((evm_initialized & EVM_KEY_MASK) != 0) && - !(evm_initialized & EVM_ALLOW_METADATA_WRITES)) + (evm_initialized & EVM_INIT_HMAC) != 0) return -EPERM; if (i & EVM_INIT_HMAC) { |