From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Dmitry Muhomor <muhomor.dmitry@gmail.com>
Date: Thu, 30 Mar 2023 17:42:56 +0300
Subject: [PATCH] exec spawning: support runtime resource overlays

---
 core/java/android/app/IActivityManager.aidl   |  2 ++
 .../android/content/res/AssetManager.java     | 33 +++++++++++++++++--
 .../com/android/internal/os/ExecInit.java     |  4 +++
 .../server/am/ActivityManagerService.java     |  6 ++++
 4 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/core/java/android/app/IActivityManager.aidl b/core/java/android/app/IActivityManager.aidl
index 8367441b1b95..e582ea40ccf5 100644
--- a/core/java/android/app/IActivityManager.aidl
+++ b/core/java/android/app/IActivityManager.aidl
@@ -760,4 +760,6 @@ interface IActivityManager {
      * </p>
      */
     int getBackgroundRestrictionExemptionReason(int uid);
+
+    String[] getSystemIdmapPaths();
 }
diff --git a/core/java/android/content/res/AssetManager.java b/core/java/android/content/res/AssetManager.java
index 4d9c3258f659..2e0ba40c6552 100644
--- a/core/java/android/content/res/AssetManager.java
+++ b/core/java/android/content/res/AssetManager.java
@@ -24,6 +24,7 @@ import android.annotation.Nullable;
 import android.annotation.StringRes;
 import android.annotation.StyleRes;
 import android.annotation.TestApi;
+import android.app.ActivityManager;
 import android.compat.annotation.UnsupportedAppUsage;
 import android.content.pm.ActivityInfo;
 import android.content.res.Configuration.NativeConfig;
@@ -38,6 +39,7 @@ import android.util.TypedValue;
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.content.om.OverlayConfig;
+import com.android.internal.os.ExecInit;
 
 import java.io.FileDescriptor;
 import java.io.FileNotFoundException;
@@ -233,6 +235,9 @@ public final class AssetManager implements AutoCloseable {
         }
     }
 
+    /** @hide */
+    public static volatile String[] systemIdmapPaths_;
+
     /**
      * This must be called from Zygote so that system assets are shared by all applications.
      * @hide
@@ -249,8 +254,32 @@ public final class AssetManager implements AutoCloseable {
             final ArrayList<ApkAssets> apkAssets = new ArrayList<>();
             apkAssets.add(ApkAssets.loadFromPath(frameworkPath, ApkAssets.PROPERTY_SYSTEM));
 
-            final String[] systemIdmapPaths =
-                    OverlayConfig.getZygoteInstance().createImmutableFrameworkIdmapsInZygote();
+            // createImmutableFrameworkIdmapsInZygote() should be called only in zygote, it fails
+            // in regular processes and is unnecessary there.
+            // When it's called in zygote, overlay state is cached in /data/resource-cache/*@idmap
+            // files. These files are readable by regular app processes.
+            //
+            // When exec-based spawning in used, in-memory cache of assets is lost, and the spawned
+            // process is unable to recreate it, since it's not allowed to create idmaps.
+            //
+            // As a workaround, ask the ActivityManager to return paths of cached idmaps and use
+            // them directly. ActivityManager runs in system_server, which always uses zygote-based
+            // spawning.
+
+            String[] systemIdmapPaths;
+            if (ExecInit.isExecSpawned) {
+                try {
+                    systemIdmapPaths = ActivityManager.getService().getSystemIdmapPaths();
+                    Objects.requireNonNull(systemIdmapPaths);
+                } catch (Throwable t) {
+                    Log.e(TAG, "unable to retrieve systemIdmapPaths", t);
+                    systemIdmapPaths = new String[0];
+                }
+            } else {
+                systemIdmapPaths = OverlayConfig.getZygoteInstance().createImmutableFrameworkIdmapsInZygote();
+                systemIdmapPaths_ = systemIdmapPaths;
+            }
+
             for (String idmapPath : systemIdmapPaths) {
                 apkAssets.add(ApkAssets.loadOverlayFromPath(idmapPath, ApkAssets.PROPERTY_SYSTEM));
             }
diff --git a/core/java/com/android/internal/os/ExecInit.java b/core/java/com/android/internal/os/ExecInit.java
index 749c67abf389..39f08b6a0f15 100644
--- a/core/java/com/android/internal/os/ExecInit.java
+++ b/core/java/com/android/internal/os/ExecInit.java
@@ -84,6 +84,8 @@ public class ExecInit {
         }
     }
 
+    public static boolean isExecSpawned;
+
     /**
      * The main function called when an application is started with exec-based spawning.
      *
@@ -99,6 +101,8 @@ public class ExecInit {
             Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from exec");
         }
 
+        isExecSpawned = true;
+
         // Check whether the first argument is a "-cp" in argv, and assume the next argument is the
         // classpath. If found, create a PathClassLoader and use it for applicationInit.
         ClassLoader classLoader = null;
diff --git a/services/core/java/com/android/server/am/ActivityManagerService.java b/services/core/java/com/android/server/am/ActivityManagerService.java
index 62b5df33df15..58f379421c3e 100644
--- a/services/core/java/com/android/server/am/ActivityManagerService.java
+++ b/services/core/java/com/android/server/am/ActivityManagerService.java
@@ -18626,4 +18626,10 @@ public class ActivityManagerService extends IActivityManager.Stub
             Trace.traceBegin(traceTag, methodName + subInfo);
         }
     }
+
+    @Override
+    public String[] getSystemIdmapPaths() {
+        // see comment in AssetManager#createSystemAssetsInZygoteLocked()
+        return android.content.res.AssetManager.systemIdmapPaths_;
+    }
 }