core: Defy usage of NGA in Google Assistant

Next-Generation Assistant (NGA) is nice to have for Google Assistant,
but it requires proprietary code in SystemUI to work properly. However,
newer Pixel devices (Pixel 4 and 5 series) automatically use NGA with no
way to opt out, which breaks the assistant entirely on custom ROMs
without NGA support.

Report the device as a "Pixel 3 XL" to the Google Assistant app during
app process specialization to force the usage of the generic assistant
UI and mitigate the issue. This is far from ideal, but we just need to
make Google Assistant work for now.

Screen-off voice match is not broken with this change because the model
name still matches that of a valid device with the feature.

Signed-off-by: Danny Lin <[email protected]>
Change-Id: I282e7e88cfda50578f016b2ae0bad2e77e9a7238

Author: kdrag0n

core/java/com/android/internal/os/Zygote.java

@@ -25,6 +25,7 @@
 import android.net.LocalServerSocket;
 import android.net.LocalSocket;
 import android.net.NetworkUtils;
+import android.os.Build;
 import android.os.FactoryTest;
 import android.os.IVold;
 import android.os.Process;
@@ -46,6 +47,7 @@
 import java.io.FileDescriptor;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.lang.reflect.Field;
 
 /** @hide */
 public final class Zygote {
@@ -285,6 +287,9 @@ public final class Zygote {
      */
     public static final String USAP_POOL_SECONDARY_SOCKET_NAME = "usap_pool_secondary";
 
+    private static final boolean PRODUCT_NEEDS_MODEL_EDIT =
+            SystemProperties.getBoolean("ro.product.needs_model_edit", false);
+
     private Zygote() {}
 
     private static boolean containsInetGid(int[] gids) {
@@ -786,6 +791,34 @@ private static void boostUsapPriority() {
 
     private static native void nativeBoostUsapPriority();
 
+    private static void maybeSetGoogleModel(String packageName, String loggingTag) {
+        if (PRODUCT_NEEDS_MODEL_EDIT &&
+                packageName != null &&
+                packageName.startsWith("com.google.android.googlequicksearchbox")) {
+            /*
+             * This would be much prettier if we just removed "final" from the MODEL field in Build,
+             * but that requires changing the API.
+             *
+             * While this an awful hack, it's technically safe because the field was populated at
+             * runtime (in pre-fork Zygote) and it's not a primitive.
+             */
+            try {
+                // Unlock
+                Field field = Build.class.getDeclaredField("MODEL");
+                field.setAccessible(true);
+
+                // Edit
+                String newModel = "Pixel 3 XL";
+                field.set(null, newModel);
+
+                // Lock
+                field.setAccessible(false);
+            } catch (NoSuchFieldException | IllegalAccessException e) {
+                Log.w(loggingTag, "Failed to set fake model name for Google", e);
+            }
+        }
+    }
+
     static void setAppProcessName(ZygoteArguments args, String loggingTag) {
         if (args.mNiceName != null) {
             Process.setArgV0(args.mNiceName);
@@ -794,6 +827,9 @@ static void setAppProcessName(ZygoteArguments args, String loggingTag) {
         } else {
             Log.w(loggingTag, "Unable to set package name.");
         }
+
+        // Modify model to defy Next-Generation Assistant in the Google app
+        maybeSetGoogleModel(args.mPackageName, loggingTag);
     }
 
     private static final String USAP_ERROR_PREFIX = "Invalid command to USAP: ";