From 34945b1fd2d8f9201c7db1b7ff915eaea78d33ac Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Sat, 23 Jul 2022 00:28:01 +0000
Subject: [PATCH] AndroidKeyStore: support platform use of rollback-resistant
 keys

The keystore2 binder API supports rollback resistance when KeyMint
supports it, but until now this wasn't exposed to Java code that uses
AndroidKeyStore.  Add support for rollback-resistant keys to
KeyProtection and AndroidKeyStoreSpi.setSecretKeyEntry() so that
LockSettingsService can request it for SP protector keys.

This CL does *not* do any of the following:

- Add any non-hidden APIs.  KeyMint implementations only support a
  limited number of rollback-resistant keys; currently the available
  space is reserved for platform use only.  Note that other examples of
  "hidden", platform-only key properties are
  isCriticalToDeviceEncryption() and getBoundToSpecificSecureUserId().

- Support rollback resistance with keys directly generated by Keystore.
  This isn't currently needed.  Note that this would require changes
  KeyGenParameterSpec and AndroidKeyStoreKeyGeneratorSpi.

- Allow querying the rollback resistance property of keys.  This isn't
  currently needed.  Note that this would require changes to KeyInfo and
  AndroidKeyStoreSecretKeyFactorySpi.

Bug: 239632930
Test: see I05f3b7e5c139471febe5c266a39e3dc3bca4831f
Change-Id: Ifcfd0b8f1bf440ef1ac80a9ac2b0e9c7f62106dd
---
 .../security/keystore/KeyProtection.java      | 35 +++++++++++++++++--
 .../keystore2/AndroidKeyStoreSpi.java         |  6 ++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/keystore/java/android/security/keystore/KeyProtection.java b/keystore/java/android/security/keystore/KeyProtection.java
index c14c3c534cf42..5ab21bc5f4897 100644
--- a/keystore/java/android/security/keystore/KeyProtection.java
+++ b/keystore/java/android/security/keystore/KeyProtection.java
@@ -237,6 +237,7 @@ public final class KeyProtection implements ProtectionParameter, UserAuthArgs {
     private final boolean mUnlockedDeviceRequired;
     private final boolean mIsStrongBoxBacked;
     private final int mMaxUsageCount;
+    private final boolean mRollbackResistant;
 
     private KeyProtection(
             Date keyValidityStart,
@@ -259,7 +260,8 @@ public final class KeyProtection implements ProtectionParameter, UserAuthArgs {
             boolean userConfirmationRequired,
             boolean unlockedDeviceRequired,
             boolean isStrongBoxBacked,
-            int maxUsageCount) {
+            int maxUsageCount,
+            boolean rollbackResistant) {
         mKeyValidityStart = Utils.cloneIfNotNull(keyValidityStart);
         mKeyValidityForOriginationEnd = Utils.cloneIfNotNull(keyValidityForOriginationEnd);
         mKeyValidityForConsumptionEnd = Utils.cloneIfNotNull(keyValidityForConsumptionEnd);
@@ -283,6 +285,7 @@ public final class KeyProtection implements ProtectionParameter, UserAuthArgs {
         mUnlockedDeviceRequired = unlockedDeviceRequired;
         mIsStrongBoxBacked = isStrongBoxBacked;
         mMaxUsageCount = maxUsageCount;
+        mRollbackResistant = rollbackResistant;
     }
 
     /**
@@ -562,6 +565,17 @@ public final class KeyProtection implements ProtectionParameter, UserAuthArgs {
         return mMaxUsageCount;
     }
 
+    /**
+     * Returns {@code true} if the key is rollback-resistant, meaning that when deleted it is
+     * guaranteed to be permanently deleted and unusable.
+     *
+     * @see Builder#setRollbackResistant(boolean)
+     * @hide
+     */
+    public boolean isRollbackResistant() {
+        return mRollbackResistant;
+    }
+
     /**
      * Builder of {@link KeyProtection} instances.
      */
@@ -591,6 +605,7 @@ public final class KeyProtection implements ProtectionParameter, UserAuthArgs {
         private boolean mIsStrongBoxBacked = false;
         private int mMaxUsageCount = KeyProperties.UNRESTRICTED_USAGE_COUNT;
         private String mAttestKeyAlias = null;
+        private boolean mRollbackResistant = false;
 
         /**
          * Creates a new instance of the {@code Builder}.
@@ -1096,6 +1111,21 @@ public final class KeyProtection implements ProtectionParameter, UserAuthArgs {
             throw new IllegalArgumentException("maxUsageCount is not valid");
         }
 
+        /**
+         * Sets whether the key should be rollback-resistant, meaning that when deleted it is
+         * guaranteed to be permanently deleted and unusable.  Not all implementations support
+         * rollback-resistant keys.  This method is hidden because implementations only support a
+         * limited number of rollback-resistant keys; currently the available space is reserved for
+         * critical system keys.
+         *
+         * @hide
+         */
+        @NonNull
+        public Builder setRollbackResistant(boolean rollbackResistant) {
+            mRollbackResistant = rollbackResistant;
+            return this;
+        }
+
         /**
          * Builds an instance of {@link KeyProtection}.
          *
@@ -1124,7 +1154,8 @@ public final class KeyProtection implements ProtectionParameter, UserAuthArgs {
                     mUserConfirmationRequired,
                     mUnlockedDeviceRequired,
                     mIsStrongBoxBacked,
-                    mMaxUsageCount);
+                    mMaxUsageCount,
+                    mRollbackResistant);
         }
     }
 }
diff --git a/keystore/java/android/security/keystore2/AndroidKeyStoreSpi.java b/keystore/java/android/security/keystore2/AndroidKeyStoreSpi.java
index 33411e1ec5b97..dfda356ec35bc 100644
--- a/keystore/java/android/security/keystore2/AndroidKeyStoreSpi.java
+++ b/keystore/java/android/security/keystore2/AndroidKeyStoreSpi.java
@@ -783,6 +783,12 @@ public class AndroidKeyStoreSpi extends KeyStoreSpi {
                         params.getMaxUsageCount()
                 ));
             }
+
+            if (params.isRollbackResistant()) {
+                importArgs.add(KeyStore2ParameterUtils.makeBool(
+                        KeymasterDefs.KM_TAG_ROLLBACK_RESISTANT
+                ));
+            }
         } catch (IllegalArgumentException | IllegalStateException e) {
             throw new KeyStoreException(e);
         }