Merge remote-tracking branch 'fscl/5.4-2.3.x-imx' into toradex_5.4-2.3.x-imx

1 files changed, 24 insertions, 2 deletions

diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm
index 201d10319fa1..1df1177df68a 100644
--- a/Documentation/ABI/testing/evm
+++ b/Documentation/ABI/testing/evm
@@ -42,8 +42,30 @@ 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