From e8ae62c0ce95703849d1e465e091dea59e2ee93a Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Fri, 4 Aug 2023 18:38:49 +0000
Subject: [PATCH 1/2] LockSettingsService: remove TODO for
 getCredentialTypeInternal()

The TODO for getCredentialTypeInternal() was added by ag/9569544
("Introduce Lockscreen PIN credential as first-class citizen"), which
predated ag/16692269 ("Add a binder cache to
ILockSettings#getCredentialType").  As the latter change effectively
addressed the TODO, remove the TODO.

Test: N/A
Change-Id: Ia9a33053f9e0db030bfd4272c2c4318278f896a4
---
 .../com/android/server/locksettings/LockSettingsService.java     | 1 -
 1 file changed, 1 deletion(-)

diff --git a/services/core/java/com/android/server/locksettings/LockSettingsService.java b/services/core/java/com/android/server/locksettings/LockSettingsService.java
index 489044f9486a8..a4d08b06d6206 100644
--- a/services/core/java/com/android/server/locksettings/LockSettingsService.java
+++ b/services/core/java/com/android/server/locksettings/LockSettingsService.java
@@ -1317,7 +1317,6 @@ public class LockSettingsService extends ILockSettings.Stub {
         return getCredentialTypeInternal(userId);
     }
 
-    // TODO: this is a hot path, can we optimize it?
     /**
      * Returns the credential type of the user, can be one of {@link #CREDENTIAL_TYPE_NONE},
      * {@link #CREDENTIAL_TYPE_PATTERN}, {@link #CREDENTIAL_TYPE_PIN} and

From 0fb946acae29a027f048a3c15d71faec3243aaf4 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Fri, 4 Aug 2023 21:27:49 +0000
Subject: [PATCH 2/2] Improve the LockSettingsService class comment

Test: N/A
Change-Id: I20d209b634fa1a45008273b242f72efb7673e7a6
---
 .../locksettings/LockSettingsService.java     | 37 +++++++++++++++++--
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/services/core/java/com/android/server/locksettings/LockSettingsService.java b/services/core/java/com/android/server/locksettings/LockSettingsService.java
index a4d08b06d6206..af66bef7ae590 100644
--- a/services/core/java/com/android/server/locksettings/LockSettingsService.java
+++ b/services/core/java/com/android/server/locksettings/LockSettingsService.java
@@ -195,9 +195,40 @@ import javax.crypto.SecretKey;
 import javax.crypto.spec.GCMParameterSpec;
 
 /**
- * Keeps the lock pattern/password data and related settings for each user. Used by
- * LockPatternUtils. Needs to be a service because Settings app also needs to be able to save
- * lockscreen information for secondary users.
+ * LockSettingsService (LSS) mainly has the following responsibilities:
+ * <p>
+ * <ul>
+ *   <li>Provide APIs to verify and change the Lock Screen Knowledge Factor (LSKF) ("lockscreen
+ *   credential") of each user.  Unlock users when their correct LSKF is given.</li>
+ *
+ *   <li>Store other lockscreen related settings, such as some Keyguard (UI) settings.</li>
+ *
+ *   <li>Manage each user's synthetic password (SP), which is their main cryptographic secret.
+ *   See {@link SyntheticPasswordManager}.</li>
+ *
+ *   <li>Protect each user's SP using their LSKF.  Use the Gatekeeper or Weaver HAL to ensure that
+ *   guesses of the LSKF are ratelimited by the TEE or secure element.</li>
+ *
+ *   <li>Protect each user's data using their SP.  For example, use the SP to encrypt/decrypt the
+ *   user's credential-encrypted (CE) key for file-based encryption (FBE).</li>
+ *
+ *   <li>Generate, protect, and use profile passwords for managed profiles.</li>
+ *
+ *   <li>Support unlocking the SP by alternative means: resume-on-reboot (reboot escrow) for easier
+ *   OTA updates, and escrow tokens when set up by the Device Policy Controller (DPC).</li>
+ *
+ *   <li>Implement part of the Factory Reset Protection (FRP) and Repair Mode features by storing
+ *   the information needed to verify a user's LSKF on the persist or metadata partition.</li>
+ *
+ *   <li>Support insider attack resistance using the AuthSecret HAL.</li>
+ *
+ *   <li>Implement "recoverable keystore", a feature that enables end-to-end encrypted backups.
+ *   See {@link android.security.keystore.recovery.RecoveryController}.</li>
+ * </ul>
+ * <p>
+ * The main clients of LockSettingsService are Keyguard (i.e. the lockscreen UI, which is part of
+ * System UI), the Settings app (com.android.settings), and other parts of system_server.  Most
+ * methods are protected by ACCESS_KEYGUARD_SECURE_STORAGE which only system processes can have.
  *
  * @hide
  */