diff --git a/core/java/android/os/Binder.java b/core/java/android/os/Binder.java
index 9c4a36f..2fa75f1 100644
--- a/core/java/android/os/Binder.java
+++ b/core/java/android/os/Binder.java
@@ -913,6 +913,18 @@
         resultReceiver.send(0, null);
     }
 
+    /** @hide */
+    @Override
+    public final native @Nullable IBinder getExtension();
+
+    /**
+     * Set the binder extension.
+     * This should be called immediately when the object is created.
+     *
+     * @hide
+     */
+    public final native void setExtension(@Nullable IBinder extension);
+
     /**
      * Default implementation rewinds the parcels and calls onTransact.  On
      * the remote side, transact calls into the binder to do the IPC.
diff --git a/core/java/android/os/BinderProxy.java b/core/java/android/os/BinderProxy.java
index c35b05f..a26bd39 100644
--- a/core/java/android/os/BinderProxy.java
+++ b/core/java/android/os/BinderProxy.java
@@ -454,6 +454,10 @@
         return null;
     }
 
+    /** @hide */
+    @Override
+    public native @Nullable IBinder getExtension() throws RemoteException;
+
     /**
      * Perform a binder transaction on a proxy.
      *
diff --git a/core/java/android/os/IBinder.java b/core/java/android/os/IBinder.java
index d9ed327..c43644d 100644
--- a/core/java/android/os/IBinder.java
+++ b/core/java/android/os/IBinder.java
@@ -244,6 +244,18 @@
             @NonNull ResultReceiver resultReceiver) throws RemoteException;
 
     /**
+     * Get the binder extension of this binder interface.
+     * This allows one to customize an interface without having to modify the original interface.
+     *
+     * @return null if don't have binder extension
+     * @throws RemoteException
+     * @hide
+     */
+    public default @Nullable IBinder getExtension() throws RemoteException {
+        throw new IllegalStateException("Method is not implemented");
+    }
+
+    /**
      * Perform a generic operation with the object.
      * 
      * @param code The action to perform.  This should
diff --git a/core/jni/android_util_Binder.cpp b/core/jni/android_util_Binder.cpp
index a236f31..079c265 100644
--- a/core/jni/android_util_Binder.cpp
+++ b/core/jni/android_util_Binder.cpp
@@ -463,6 +463,9 @@
             if (mVintf) {
                 ::android::internal::Stability::markVintf(b.get());
             }
+            if (mExtension != nullptr) {
+                b.get()->setExtension(mExtension);
+            }
             mBinder = b;
             ALOGV("Creating JavaBinder %p (refs %p) for Object %p, weakCount=%" PRId32 "\n",
                  b.get(), b->getWeakRefs(), obj, b->getWeakRefs()->getWeakCount());
@@ -481,6 +484,24 @@
         mVintf = true;
     }
 
+    sp<IBinder> getExtension() {
+        AutoMutex _l(mLock);
+        sp<JavaBBinder> b = mBinder.promote();
+        if (b != nullptr) {
+            return b.get()->getExtension();
+        }
+        return mExtension;
+    }
+
+    void setExtension(const sp<IBinder>& extension) {
+        AutoMutex _l(mLock);
+        mExtension = extension;
+        sp<JavaBBinder> b = mBinder.promote();
+        if (b != nullptr) {
+            b.get()->setExtension(mExtension);
+        }
+    }
+
 private:
     Mutex           mLock;
     wp<JavaBBinder> mBinder;
@@ -489,6 +510,8 @@
     // is too much binder state here, we can think about making JavaBBinder an
     // sp here (avoid recreating it)
     bool            mVintf = false;
+
+    sp<IBinder>     mExtension;
 };
 
 // ----------------------------------------------------------------------------
@@ -1033,6 +1056,17 @@
     return javaObjectForIBinder(env, service);
 }
 
+static jobject android_os_Binder_getExtension(JNIEnv* env, jobject obj) {
+    JavaBBinderHolder* jbh = (JavaBBinderHolder*) env->GetLongField(obj, gBinderOffsets.mObject);
+    return javaObjectForIBinder(env, jbh->getExtension());
+}
+
+static void android_os_Binder_setExtension(JNIEnv* env, jobject obj, jobject extensionObject) {
+    JavaBBinderHolder* jbh = (JavaBBinderHolder*) env->GetLongField(obj, gBinderOffsets.mObject);
+    sp<IBinder> extension = ibinderForJavaObject(env, extensionObject);
+    jbh->setExtension(extension);
+}
+
 // ----------------------------------------------------------------------------
 
 static const JNINativeMethod gBinderMethods[] = {
@@ -1062,7 +1096,9 @@
     { "getNativeBBinderHolder", "()J", (void*)android_os_Binder_getNativeBBinderHolder },
     { "getNativeFinalizer", "()J", (void*)android_os_Binder_getNativeFinalizer },
     { "blockUntilThreadAvailable", "()V", (void*)android_os_Binder_blockUntilThreadAvailable },
-    { "waitForService", "(Ljava/lang/String;)Landroid/os/IBinder;", (void*)android_os_Binder_waitForService }
+    { "waitForService", "(Ljava/lang/String;)Landroid/os/IBinder;", (void*)android_os_Binder_waitForService },
+    { "getExtension", "()Landroid/os/IBinder;", (void*)android_os_Binder_getExtension },
+    { "setExtension", "(Landroid/os/IBinder;)V", (void*)android_os_Binder_setExtension },
 };
 
 const char* const kBinderPathName = "android/os/Binder";
@@ -1502,6 +1538,21 @@
     return (jlong) BinderProxy_destroy;
 }
 
+static jobject android_os_BinderProxy_getExtension(JNIEnv* env, jobject obj) {
+    IBinder* binder = getBPNativeData(env, obj)->mObject.get();
+    if (binder == nullptr) {
+        jniThrowException(env, "java/lang/IllegalStateException", "Native IBinder is null");
+        return nullptr;
+    }
+    sp<IBinder> extension;
+    status_t err = binder->getExtension(&extension);
+    if (err != OK) {
+        signalExceptionForError(env, obj, err, true /* canThrowRemoteException */);
+        return nullptr;
+    }
+    return javaObjectForIBinder(env, extension);
+}
+
 // ----------------------------------------------------------------------------
 
 static const JNINativeMethod gBinderProxyMethods[] = {
@@ -1513,6 +1564,7 @@
     {"linkToDeath",         "(Landroid/os/IBinder$DeathRecipient;I)V", (void*)android_os_BinderProxy_linkToDeath},
     {"unlinkToDeath",       "(Landroid/os/IBinder$DeathRecipient;I)Z", (void*)android_os_BinderProxy_unlinkToDeath},
     {"getNativeFinalizer",  "()J", (void*)android_os_BinderProxy_getNativeFinalizer},
+    {"getExtension",        "()Landroid/os/IBinder;", (void*)android_os_BinderProxy_getExtension},
 };
 
 const char* const kBinderProxyPathName = "android/os/BinderProxy";
diff --git a/core/tests/coretests/AndroidManifest.xml b/core/tests/coretests/AndroidManifest.xml
index 9955c51..a9e0a77 100644
--- a/core/tests/coretests/AndroidManifest.xml
+++ b/core/tests/coretests/AndroidManifest.xml
@@ -1340,6 +1340,10 @@
         <service android:name="android.os.BinderWorkSourceNestedService"
                 android:process=":BinderWorkSourceNestedService" />
 
+        <!-- Used by BinderProxyTest -->
+        <service android:name="android.os.BinderProxyService"
+                android:process=":BinderProxyService" />
+
         <!-- Application components used for search manager tests -->
 
         <activity android:name="android.app.activity.SearchableActivity"
diff --git a/core/tests/coretests/src/android/os/BinderProxyService.java b/core/tests/coretests/src/android/os/BinderProxyService.java
new file mode 100644
index 0000000..bf1fbc5
--- /dev/null
+++ b/core/tests/coretests/src/android/os/BinderProxyService.java
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.os;
+
+import android.app.Service;
+import android.content.Intent;
+
+public class BinderProxyService extends Service {
+    private final Binder mBinder = new Binder();
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+        mBinder.setExtension(new Binder());
+    }
+
+    @Override
+    public IBinder onBind(Intent intent) {
+        return mBinder;
+    }
+}
diff --git a/core/tests/coretests/src/android/os/BinderProxyTest.java b/core/tests/coretests/src/android/os/BinderProxyTest.java
index aceda2d..3567d17 100644
--- a/core/tests/coretests/src/android/os/BinderProxyTest.java
+++ b/core/tests/coretests/src/android/os/BinderProxyTest.java
@@ -17,11 +17,17 @@
 package android.os;
 
 import android.annotation.Nullable;
+import android.content.ComponentName;
 import android.content.Context;
+import android.content.Intent;
+import android.content.ServiceConnection;
 import android.test.AndroidTestCase;
 
 import androidx.test.filters.MediumTest;
 
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
 public class BinderProxyTest extends AndroidTestCase {
     private static class CountingListener implements Binder.ProxyTransactListener {
         int mStartedCount;
@@ -86,4 +92,41 @@
         // Check it does not throw..
         mPowerManager.isInteractive();
     }
+
+    private IBinder mRemoteBinder = null;
+
+    @MediumTest
+    public void testGetExtension() throws Exception {
+        final CountDownLatch bindLatch = new CountDownLatch(1);
+        ServiceConnection connection =
+                new ServiceConnection() {
+                    @Override
+                    public void onServiceConnected(ComponentName name, IBinder service) {
+                        mRemoteBinder = service;
+                        bindLatch.countDown();
+                    }
+
+                    @Override
+                    public void onServiceDisconnected(ComponentName name) {}
+                };
+        try {
+            mContext.bindService(
+                    new Intent(mContext, BinderProxyService.class),
+                    connection,
+                    Context.BIND_AUTO_CREATE);
+            if (!bindLatch.await(500, TimeUnit.MILLISECONDS)) {
+                fail(
+                        "Timed out while binding service: "
+                                + BinderProxyService.class.getSimpleName());
+            }
+            assertTrue(mRemoteBinder instanceof BinderProxy);
+            assertNotNull(mRemoteBinder);
+
+            IBinder extension = mRemoteBinder.getExtension();
+            assertNotNull(extension);
+            assertTrue(extension.pingBinder());
+        } finally {
+            mContext.unbindService(connection);
+        }
+    }
 }
diff --git a/core/tests/coretests/src/android/os/BinderTest.java b/core/tests/coretests/src/android/os/BinderTest.java
index a354195..99dbe64 100644
--- a/core/tests/coretests/src/android/os/BinderTest.java
+++ b/core/tests/coretests/src/android/os/BinderTest.java
@@ -52,4 +52,18 @@
         } catch (IllegalStateException expected) {
         }
     }
+
+    @SmallTest
+    public void testGetExtension() throws Exception {
+        Binder binder = new Binder();
+        assertNull(binder.getExtension());
+
+        IBinder extension = new Binder();
+        binder.setExtension(extension);
+        assertNotNull(binder.getExtension());
+        assertSame(binder.getExtension(), extension);
+
+        binder.setExtension(null);
+        assertNull(binder.getExtension());
+    }
 }