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-rw-r--r--Documentation/ABI/testing/evm26
-rw-r--r--security/integrity/evm/evm_secfs.c8
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 cfc3075769bb..a7042ae90b9e 100644
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c
@@ -80,12 +80,12 @@ 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) {