diff --git a/keymaster/4.0/IKeymasterDevice.hal b/keymaster/4.0/IKeymasterDevice.hal
index 5dac929..aef81c7 100644
--- a/keymaster/4.0/IKeymasterDevice.hal
+++ b/keymaster/4.0/IKeymasterDevice.hal
@@ -374,10 +374,27 @@
     /**
      * Upgrades an old key blob.  Keys can become "old" in two ways: Keymaster can be upgraded to a
      * new version with an incompatible key blob format, or the system can be updated to invalidate
-     * the OS version and/or patch level.  In either case, attempts to use an old key blob with
-     * getKeyCharacteristics(), exportKey(), attestKey() or begin() must result in Keymaster
-     * returning ErrorCode::KEY_REQUIRES_UPGRADE.  The caller must use this method to upgrade the
-     * key blob.
+     * the OS version (OS_VERSION tag), system patch level (OS_PATCHLEVEL tag), vendor patch level
+     * (VENDOR_PATCH_LEVEL tag), boot patch level (BOOT_PATCH_LEVEL tag) or other,
+     * implementation-defined patch level (keymaster implementers are encouraged to extend this HAL
+     * with a minor version extension to define validatable patch levels for other images; tags
+     * must be defined in the implemeter's namespace, starting at 10000).  In either case,
+     * attempts to use an old key blob with getKeyCharacteristics(), exportKey(), attestKey() or
+     * begin() must result in Keymaster returning ErrorCode::KEY_REQUIRES_UPGRADE.  The caller must
+     * use this method to upgrade the key blob.
+     *
+     * If upgradeKey is asked to update a key with any version or patch level that is higher than
+     * the current system version or patch level, it must return ErrorCode::INVALID_ARGUMENT.  There
+     * is one exception: it is always permissible to "upgrade" from any OS_VERSION number to
+     * OS_VERSION 0.  For example, if the key has OS_VERSION 080001, it is permisible to upgrade the
+     * key if the current system version is 080100, because the new version is larger, or if the
+     * current system version is 0, because upgrades to 0 are always allowed.  If the system version
+     * were 080000, however, keymaster must return ErrorCode::INVALID_ARGUMENT because that value is
+     * smaller than 080001.
+     *
+     * Note that Keymaster versions 2 and 3 required that the system and boot images have the same
+     * patch level and OS version.  This requirement is relaxed for Keymaster 4, and the OS version
+     * in the boot image footer is no longer used.
      *
      * @param keyBlobToUpgrade The opaque descriptor returned by generateKey() or importKey();
      *
diff --git a/keymaster/4.0/support/include/keymasterV4_0/keymaster_tags.h b/keymaster/4.0/support/include/keymasterV4_0/keymaster_tags.h
index 73e03fb..0dfc735 100644
--- a/keymaster/4.0/support/include/keymasterV4_0/keymaster_tags.h
+++ b/keymaster/4.0/support/include/keymasterV4_0/keymaster_tags.h
@@ -356,6 +356,8 @@
         case Tag::OS_PATCHLEVEL:
         case Tag::MAC_LENGTH:
         case Tag::AUTH_TIMEOUT:
+        case Tag::VENDOR_PATCHLEVEL:
+        case Tag::BOOT_PATCHLEVEL:
             return a.f.integer == b.f.integer;
 
         /* Long integer tags */
diff --git a/keymaster/4.0/types.hal b/keymaster/4.0/types.hal
index e890c6d..5714c4d 100644
--- a/keymaster/4.0/types.hal
+++ b/keymaster/4.0/types.hal
@@ -219,6 +219,30 @@
     ATTESTATION_ID_MODEL = TagType:BYTES | 717, /* Used to provide the device's model name to be
                                                  * included in attestation */
 
+    /**
+     * Patch level of vendor image.  The value is an integer of the form YYYYMM, where YYYY is the
+     * four-digit year when the vendor image was released and MM is the two-digit month.  During
+     * each boot, the bootloader must provide the patch level of the vendor image to keymaser
+     * (mechanism is implemntation-defined).  When keymaster keys are created or updated, the
+     * VENDOR_PATCHLEVEL tag must be cryptographically bound to the keys, with the current value as
+     * provided by the bootloader.  When keys are used, keymaster must verify that the
+     * VENDOR_PATCHLEVEL bound to the key matches the current value.  If they do not match,
+     * keymaster must return ErrorCode::KEY_REQUIRES_UPGRADE.  The client must then call upgradeKey.
+     */
+    VENDOR_PATCHLEVEL = TagType:UINT | 718,
+
+    /**
+     * Patch level of boot image.  The value is an integer of the form YYYYMM, where YYYY is the
+     * four-digit year when the boot image was released and MM is the two-digit month.  During each
+     * boot, the bootloader must provide the patch level of the boot image to keymaser (mechanism is
+     * implemntation-defined).  When keymaster keys are created or updated, the BOOT_PATCHLEVEL tag
+     * must be cryptographically bound to the keys, with the current value as provided by the
+     * bootloader.  When keys are used, keymaster must verify that the BOOT_PATCHLEVEL bound to the
+     * key matches the current value.  If they do not match, keymaster must return
+     * ErrorCode::KEY_REQUIRES_UPGRADE.  The client must then call upgradeKey.
+     */
+    BOOT_PATCHLEVEL = TagType:UINT | 719,
+
     /* Tags used only to provide data to or receive data from operations */
     ASSOCIATED_DATA = TagType:BYTES | 1000, /* Used to provide associated data for AEAD modes. */
     NONCE = TagType:BYTES | 1001,           /* Nonce or Initialization Vector */