added uuid support for EVM

Latest version of EVM uses file system UUID as part of an HMAC
calculation to prevent pasting of inode metadata from other file
systems. This patch adds support for adding file system UUID
to HMAC calculation. It is necessary to specify '-u -' or '--uuid -'
on evmctl command line.

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>

README

@@ -3,10 +3,20 @@ ima-evm-utils - IMA/EVM signing utility
 
 Contents:
 
-   1. Key generation
-   2. Initialization
-   3. Signing
 
+   1. Key and signature formats
+   2. Key generation
+   3. Initialization
+   4. Signing
+
+
+Key and signature formats
+-------------------------
+
+EVM support (v2) in latest version of the kernel adds the file system UUID to
+the HMAC calculation. It is controlled by the CONFIG_EVM_HMAC_VERSION and
+version 2 is enabled by default. To include the UUID to the signature calculation,
+it is necessary to provide '--uuid -' or '-u -' parameter to the 'sign' command.
 
 Key generation
 --------------
@@ -61,17 +71,19 @@ Here is an example script /etc/initramfs-tools/scripts/local-top/ima.sh
 Signing
 -------
 
+Signing for using new the EVM HMAC format is done using '-u -' or '--uuid -' parameter.
+
 Sign file with EVM signature and use hash value for IMA - common case
 
-    $ evmctl sign --imahash test.txt
+    $ evmctl sign [-u -] --imahash test.txt
 
 Sign file with both IMA and EVM signatures - for immutable files
 
-    $ evmctl sign --imasig test.txt
+    $ evmctl sign [-u -] --imasig test.txt
 
 Label whole filesystem with EVM signatures
 
-    $ find / \( -fstype rootfs -o -fstype ext4 \) -exec evmctl sign --imahash '{}' \;
+    $ find / \( -fstype rootfs -o -fstype ext4 \) -exec evmctl sign [-u -] --imahash '{}' \;
 
 Label filesystem in fix mode - kernel sets correct values to IMA and EVM xattrs