Make getCallingUidOrThrow() not throw in clearCallingIdentity() blocks

The new method hasExplicitIdentity will track whether the caller is
within a Binder.clearCallingIdentity/restoreCallingIdentity block based
on packing this state information into the token returned by clearCallingIdentity.

Bug: b/252975769
Test: android.os.cts.BinderTest
Change-Id: I162db933f9e52cd6f9f46796bda11ad6216d3d66

core/java/android/os/Binder.java

@@ -327,17 +327,29 @@ public class Binder implements IBinder {
     @CriticalNative
     public static final native boolean isDirectlyHandlingTransaction();
 
+    /**
+    * Returns {@code true} if the current thread has had its identity
+    * set explicitly via {@link #clearCallingIdentity()}
+    *
+    * @hide
+    */
+    @CriticalNative
+    private static native boolean hasExplicitIdentity();
+
     /**
      * Return the Linux UID assigned to the process that sent the transaction
      * currently being processed.
      *
      * @throws IllegalStateException if the current thread is not currently
-     * executing an incoming transaction.
+     * executing an incoming transaction and the calling identity has not been
+     * explicitly set with {@link #clearCallingIdentity()}
      */
     public static final int getCallingUidOrThrow() {
-        if (!isDirectlyHandlingTransaction()) {
+        if (!isDirectlyHandlingTransaction() && !hasExplicitIdentity()) {
             throw new IllegalStateException(
-                  "Thread is not in a binder transcation");
+                  "Thread is not in a binder transaction, "
+                  + "and the calling identity has not been "
+                  + "explicitly set with clearCallingIdentity");
         }
         return getCallingUid();
     }

core/jni/android_util_Binder.cpp

@@ -983,6 +983,10 @@ static void android_os_Binder_restoreCallingIdentity(jlong token)
     IPCThreadState::self()->restoreCallingIdentity(token);
 }
 
+static jboolean android_os_Binder_hasExplicitIdentity() {
+    return IPCThreadState::self()->hasExplicitIdentity();
+}
+
 static void android_os_Binder_setThreadStrictModePolicy(jint policyMask)
 {
     IPCThreadState::self()->setStrictModePolicy(policyMask);
@@ -1079,6 +1083,8 @@ static const JNINativeMethod gBinderMethods[] = {
     // @CriticalNative
     { "restoreCallingIdentity", "(J)V", (void*)android_os_Binder_restoreCallingIdentity },
     // @CriticalNative
+    { "hasExplicitIdentity", "()Z", (void*)android_os_Binder_hasExplicitIdentity },
+    // @CriticalNative
     { "setThreadStrictModePolicy", "(I)V", (void*)android_os_Binder_setThreadStrictModePolicy },
     // @CriticalNative
     { "getThreadStrictModePolicy", "()I", (void*)android_os_Binder_getThreadStrictModePolicy },

core/tests/coretests/src/android/os/BinderTest.java

@@ -20,6 +20,8 @@ import androidx.test.filters.SmallTest;
 
 import junit.framework.TestCase;
 
+import static org.testng.Assert.assertThrows;
+
 public class BinderTest extends TestCase {
     private static final int UID = 100;
 
@@ -45,12 +47,8 @@ public class BinderTest extends TestCase {
     }
 
     @SmallTest
-    public void testGetCallingUidOrThrow() throws Exception {
-        try {
-            Binder.getCallingUidOrThrow();
-            throw new AssertionError("IllegalStateException expected");
-        } catch (IllegalStateException expected) {
-        }
+    public void testGetCallingUidOrThrow_throws() throws Exception {
+        assertThrows(IllegalStateException.class, () -> Binder.getCallingUidOrThrow());
     }
 
     @SmallTest