Revert^2 "Zygote: Load system server code early"

This reverts commit 6be3b0e117.

Bug: 180949581
Test: atest odsign_e2e_tests
Change-Id: I7a7dd5b475af4502dc9671d2dce02ee3673ddf81

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

@@ -127,6 +127,12 @@ public class ZygoteInit {
 
     private static boolean sPreloadComplete;
 
+    /**
+     * Cached classloader to use for the system server. Will only be populated in the system
+     * server process.
+     */
+    private static ClassLoader sCachedSystemServerClassLoader = null;
+
     static void preload(TimingsTraceLog bootTimingsTraceLog) {
         Log.d(TAG, "begin preload");
         bootTimingsTraceLog.traceBegin("BeginPreload");
@@ -543,10 +549,8 @@ public class ZygoteInit {
 
             throw new IllegalStateException("Unexpected return from WrapperInit.execApplication");
         } else {
-            ClassLoader cl = null;
-            if (systemServerClasspath != null) {
-                cl = createPathClassLoader(systemServerClasspath, parsedArgs.mTargetSdkVersion);
-
+            ClassLoader cl = getOrCreateSystemServerClassLoader();
+            if (cl != null) {
                 Thread.currentThread().setContextClassLoader(cl);
             }
 
@@ -561,6 +565,23 @@ public class ZygoteInit {
         /* should never reach here */
     }
 
+    /**
+     * Create the classloader for the system server and store it in
+     * {@link sCachedSystemServerClassLoader}. This function may be called through JNI in
+     * system server startup, when the runtime is in a critically low state. Do not do
+     * extended computation etc here.
+     */
+    private static ClassLoader getOrCreateSystemServerClassLoader() {
+        if (sCachedSystemServerClassLoader == null) {
+            final String systemServerClasspath = Os.getenv("SYSTEMSERVERCLASSPATH");
+            if (systemServerClasspath != null) {
+                sCachedSystemServerClassLoader = createPathClassLoader(systemServerClasspath,
+                        VMRuntime.SDK_VERSION_CUR_DEVELOPMENT);
+            }
+        }
+        return sCachedSystemServerClassLoader;
+    }
+
     /**
      * Note that preparing the profiles for system server does not require special selinux
      * permissions. From the installer perspective the system server is a regular package which can

core/jni/com_android_internal_os_Zygote.cpp

@@ -122,6 +122,10 @@ static jclass gZygoteClass;
 static jmethodID gCallPostForkSystemServerHooks;
 static jmethodID gCallPostForkChildHooks;
 
+static constexpr const char* kZygoteInitClassName = "com/android/internal/os/ZygoteInit";
+static jclass gZygoteInitClass;
+static jmethodID gGetOrCreateSystemServerClassLoader;
+
 static bool gIsSecurityEnforced = true;
 
 /**
@@ -1572,6 +1576,17 @@ static void SpecializeCommon(JNIEnv* env, uid_t uid, gid_t gid, jintArray gids,
                                            instruction_set.value().c_str());
     }
 
+    if (is_system_server) {
+        // Prefetch the classloader for the system server. This is done early to
+        // allow a tie-down of the proper system server selinux domain.
+        env->CallStaticVoidMethod(gZygoteInitClass, gGetOrCreateSystemServerClassLoader);
+        if (env->ExceptionCheck()) {
+            // Be robust here. The Java code will attempt to create the classloader
+            // at a later point (but may not have rights to use AoT artifacts).
+            env->ExceptionClear();
+        }
+    }
+
     if (setresgid(gid, gid, gid) == -1) {
         fail_fn(CREATE_ERROR("setresgid(%d) failed: %s", gid, strerror(errno)));
     }
@@ -2635,6 +2650,13 @@ int register_com_android_internal_os_Zygote(JNIEnv* env) {
   gCallPostForkChildHooks = GetStaticMethodIDOrDie(env, gZygoteClass, "callPostForkChildHooks",
                                                    "(IZZLjava/lang/String;)V");
 
-  return RegisterMethodsOrDie(env, "com/android/internal/os/Zygote", gMethods, NELEM(gMethods));
+  gZygoteInitClass = MakeGlobalRefOrDie(env, FindClassOrDie(env, kZygoteInitClassName));
+  gGetOrCreateSystemServerClassLoader =
+          GetStaticMethodIDOrDie(env, gZygoteInitClass, "getOrCreateSystemServerClassLoader",
+                                 "()Ljava/lang/ClassLoader;");
+
+  RegisterMethodsOrDie(env, "com/android/internal/os/Zygote", gMethods, NELEM(gMethods));
+
+  return JNI_OK;
 }
 }  // namespace android