[RFC PATCH 3/3] dm ima: add documentation target update event

[Thore Sommer <public@thson.de>]

The dm_target_update event can be triggered by targets to remeasure their
state to reflect that change also in IMA.

This is event is currently only supported by verity.

Signed-off-by: Thore Sommer <public@thson.de>
---
 .../admin-guide/device-mapper/dm-ima.rst      | 33 +++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/Documentation/admin-guide/device-mapper/dm-ima.rst b/Documentation/admin-guide/device-mapper/dm-ima.rst
index a4aa50a828e0..ac9418ea99d3 100644
--- a/Documentation/admin-guide/device-mapper/dm-ima.rst
+++ b/Documentation/admin-guide/device-mapper/dm-ima.rst
@@ -93,6 +93,7 @@ Following device state changes will trigger IMA measurements:
  #. Device remove
  #. Table clear
  #. Device rename
+ #. Target update
 
 1. Table load:
 ---------------
@@ -321,6 +322,38 @@ The IMA measurement log has the following format for 'dm_device_rename':
  new_name=linear\=2,new_uuid=1234-5678;
  current_device_capacity=1024;
 
+6. Target update:
+------------------
+When a target changes updates its table it can trigger an remeasurement of that table.
+
+This is currently only implemented for 'verity' targets to detect measure corruption occurrences.
+Note that the active table hash of the device does not get updated.
+
+The IMA measurement log has the following format for 'dm_target_update':
+
+::
+
+ EVENT_NAME := "dm_target_update"
+ EVENT_DATA := <dm_version_str> ";" <device_active_metadata> ";" <target_data_row> ";"
+
+ dm_version_str := As described in the 'Table load' section above.
+ device_active_metadata := Device metadata that reflects the currently loaded active table.
+                           The format is same as 'device_metadata' described in the 'Table load' section above.
+ target_data_row
+ E.g: if a verity device gets corrupted then IMA ASCII measurement log will have an entry with:
+ (converted from ASCII to text for readability)
+
+ 10 1cc9c660afb7fddd1b7167f0c4e997ebca8b1c09 ima-buf sha256:e991f7692724257701c8e652682bd3246837ed2d655407b9e9f5a5b469e6c75b
+ dm_target_update
+ dm_version=4.45.0;
+ name=test,uuid=CRYPT-VERITY-e0d2a85fd61e41238174adaa32d296fe-test,major=253,minor=0,minor_count=1,num_targets=1;
+ target_index=0,target_begin=0,target_len=8,target_name=verity,target_version=1.8.0,hash_failed=C,
+ verity_version=1,data_device_name=7:1,hash_device_name=7:0,verity_algorithm=sha256,
+ root_digest=8c2eff0b45fc9815b94350f7a913683ef34085c734229bcf1345c31b07ac61b8,
+ salt=63010b7c63e28e6929a2f020dc71c97a0660a9f377a83c674a62feb01c5ca6b3,
+ ignore_zero_blocks=n,check_at_most_once=n;
+
+
 Supported targets:
 ==================
 
-- 
2.34.1