[reggen] Add SIDELOAD CM label

Signed-off-by: Michael Schaffner <msf@opentitan.org>
diff --git a/doc/rm/comportability_specification/index.md b/doc/rm/comportability_specification/index.md
index 1171fa9..73316c1 100644
--- a/doc/rm/comportability_specification/index.md
+++ b/doc/rm/comportability_specification/index.md
@@ -299,6 +299,7 @@
 | BKGN_CHK       | The asset is protected with a continuous background health check |
 | GLITCH_DETECT  | The asset is protected by an analog glitch detector | CTRL, FSM, CLK, RST
 | SW_UNREADABLE  | The asset is not accessible by software |
+| SIDELOAD       | The asset can be loaded without exposing it to software | KEY
 | SCA            | A countermeasure that provides side-channel attack resistance |
 | MASKING        | A more specific version of SCA where an asset is split into shares |
 | LOCAL_ESC      | A local escalation event is triggered when an attack is detected |
diff --git a/util/reggen/countermeasure.py b/util/reggen/countermeasure.py
index f59759d..9ba4f0d 100644
--- a/util/reggen/countermeasure.py
+++ b/util/reggen/countermeasure.py
@@ -49,6 +49,7 @@
     'BKGN_CHK',
     'GLITCH_DETECT',
     'SW_UNREADABLE',
+    'SIDELOAD',
     'SCA',
     'MASKING',
     'LOCAL_ESC',