[Hook] 免root，自己进程内，startActivity hook的几种姿势

首先关于startActivity 我们平时会经常使用到在activity内直接startActivity(intent)
其实这里还有一种start方式我们可能没怎么用过 getApplicationContext.startActivity(intent) 通过这种方式可以开启其它程序中的activity

代理
在说Hook之前先说下代理包括静态代理和动态代理如果不熟悉的可以看下

http://www.jianshu.com/p/8507b4364f11

反射
其次就是java反射方面的知识
如何通过变量获取实例对象再进行替换

Hook:我们把修改参数，替换返回值，称之为Hook
Hook点：静态变量和单利；即就是不容易发生改变的对象，容易定位普通的对象容易发生改变所以我们可以根据这个原则去hook

1. 首先我们分析下我们平时直接使用的startActivity()方法

源码

@Override

    public void startActivity(Intent intent) {

        this.startActivity(intent, null);

    }

@Override

    public void startActivity(Intent intent, @Nullable Bundle options) {

        if (options != null) {

            startActivityForResult(intent, -1, options);

        } else {

            // Note we want to go through this call for compatibility with

            // applications that may have overridden the method.

            startActivityForResult(intent, -1);

        }

    }

@Override

    public void startActivityForResult(

            String who, Intent intent, int requestCode, @Nullable Bundle options) {

        Uri referrer = onProvideReferrer();

        if (referrer != null) {

            intent.putExtra(Intent.EXTRA_REFERRER, referrer);

        }

        Instrumentation.ActivityResult ar =

            mInstrumentation.execStartActivity(

                this, mMainThread.getApplicationThread(), mToken, who,

                intent, requestCode, options);

        if (ar != null) {

            mMainThread.sendActivityResult(

                mToken, who, requestCode,

                ar.getResultCode(), ar.getResultData());

        }

        cancelInputsAndStartExitTransition(options);

    }

最终调用了startActivityForResult()方法在方法内调用了mInstrumentation变量的execStartActivity()方法所以最终startActivity的是Instrumentation类的execStartActivity()方法（nativie层面的）其实是通过远端的ActivityManagerService启动的是一个跨进程通信的过程

public ActivityResult execStartActivity(

            Context who, IBinder contextThread, IBinder token, Activity target,

            Intent intent, int requestCode, Bundle options) {

       ...

        try {

            intent.migrateExtraStreamToClipData();

            intent.prepareToLeaveProcess();

            int result = ActivityManagerNative.getDefault()

                .startActivity(whoThread, who.getBasePackageName(), intent,

                        intent.resolveTypeIfNeeded(who.getContentResolver()),

                        token, target != null ? target.mEmbeddedID : null,

                        requestCode, 0, null, options);

            checkStartActivityResult(result, intent);

        } catch (RemoteException e) {

            throw new RuntimeException("Failure from system", e);

        }

        return null;

    }

这里呢我们可以去hook掉activity类内变量 mInstrumentation 将它替换成我们自己的Instrumentation
通过手写静态代理类，替换掉原始的方法

public class EvilInstrumentation extends Instrumentation {

    private static final String TAG = "EvilInstrumentation";

    // ActivityThread中原始的对象, 保存起来

    Instrumentation mBase;

    public EvilInstrumentation(Instrumentation base) {

        mBase = base;

    }

    public ActivityResult execStartActivity(

            Context who, IBinder contextThread, IBinder token, Activity target,

            Intent intent, int requestCode, Bundle options) {

        // Hook之前, XXX到此一游!

        Log.e(TAG, "\n执行了startActivity, 参数如下: \n" + "who = [" + who + "], " +

                "\ncontextThread = [" + contextThread + "], \ntoken = [" + token + "], " +

                "\ntarget = [" + target + "], \nintent = [" + intent +

                "], \nrequestCode = [" + requestCode + "], \noptions = [" + options + "]");

        Uri uri = Uri.parse("http://www.jianshu.com/u/3d228ed8d54d");

        Intent intent1 = new Intent(Intent.ACTION_VIEW,uri);

        // 开始调用原始的方法, 调不调用随你,但是不调用的话, 所有的startActivity都失效了.

        // 由于这个方法是隐藏的,因此需要使用反射调用;首先找到这个方法

        try {

            //这里通过反射找到原始Instrumentation类的execStartActivity方法

            Method execStartActivity = Instrumentation.class.getDeclaredMethod(

                    "execStartActivity",

                    Context.class, IBinder.class, IBinder.class, Activity.class,

                    Intent.class, int.class, Bundle.class);

            execStartActivity.setAccessible(true);

            //执行原始Instrumentation的execStartActivity方法 再次之前 you can do whatever you want ...

            return (ActivityResult) execStartActivity.invoke(mBase, who,

                    contextThread, token, target, intent1, requestCode, options);

        } catch (Exception e) {

            // 某该死的rom修改了  需要手动适配

            throw new RuntimeException("do not support!!! pls adapt it");

        }

    }

}

在这里我们可以拿到Intent 当然你可以将这个intent对象进行替换跳转到另一个界面（whatever you want）

有了代理对象下面使用反射直接进行替换

public static void replaceInstrumentation(Activity activity){

            Class<?> k = Activity.class;

        try {

            //通过Activity.class 拿到 mInstrumentation字段

            Field field = k.getDeclaredField("mInstrumentation");

            field.setAccessible(true);

            //根据activity内mInstrumentation字段 获取Instrumentation对象

            Instrumentation instrumentation = (Instrumentation)field.get(activity);

            //创建代理对象

            Instrumentation instrumentationProxy = new EvilInstrumentation(instrumentation);

            //进行替换

            field.set(activity,instrumentationProxy);

        } catch (IllegalAccessException e){

            e.printStackTrace();

        }catch (NoSuchFieldException e){

            e.printStackTrace();

        }

    }

有注释不用过多解释了

@Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        HookActivityHelper.replaceInstrumentation(this);

       Button tv = new Button(this);

        tv.setText("测试界面");

        setContentView(tv);

        tv.setOnClickListener(new View.OnClickListener() {

            @Override

            public void onClick(View v) {

                Intent intent = new Intent(Intent.ACTION_VIEW);

                intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);

                intent.setData(Uri.parse("http://www.baidu.com"));

                startActivity(intent);

            }

        });

    }

测试当我们点击button后跳转到了自己的简书主页而不是百度同时看到log

image.png

可见我们确实hook成功了

2.下面使用 getApplicationContext().startActivity(intent)这种方式开启另一个activity

Context开启activity 实质为 ContextImpl(Context的实现类)去真正开启的

final ActivityThread mMainThread;

 @Override

    public void startActivity(Intent intent, Bundle options) {

        warnIfCallingFromSystemProcess();

        if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {

            throw new AndroidRuntimeException(

                    "Calling startActivity() from outside of an Activity "

                    + " context requires the FLAG_ACTIVITY_NEW_TASK flag."

                    + " Is this really what you want?");

        }

        mMainThread.getInstrumentation().execStartActivity(

                getOuterContext(), mMainThread.getApplicationThread(), null,

                (Activity) null, intent, -1, options);

    }

可以看到是调用了ActivityThread类的getInstrumentation()方法返回mInstrumentation变量后再调用execStartActivity()方法

Instrumentation mInstrumentation;

public Instrumentation getInstrumentation()

    {

        return mInstrumentation;

    }

整个流程 almost like this

未命名文件.png

所以现在变成了我们需要替换ActivityThread类（不是主线程类 final类只不过运行在主线程而已）中的mInstrumentation，首先我们需要拿到ActivityThread对象吧刚好在ActivityThread类中有个静态方法currentActivityThread可以帮助我们拿到这个对象类

private static ActivityThread sCurrentActivityThread;

public static ActivityThread currentActivityThread() {

        return sCurrentActivityThread;

    }

so 我们的反射代码如下

      // 先获取到当前的ActivityThread对象

        Class<?> activityThreadClass = Class.forName("android.app.ActivityThread");

        Method currentActivityThreadMethod =

        activityThreadClass.getDeclaredMethod("currentActivityThread");

        currentActivityThreadMethod.setAccessible(true);

        //currentActivityThread是一个static函数所以可以直接invoke，不需要带实例参数

        Object currentActivityThread = currentActivityThreadMethod.invoke(null);

拿到ActivityThread对象之后后面的就和第一种方法一样了将ActivityThread类中的mInstrumentaion换为EvilInstrumentation

其实比较这两种方法的区别：

Activity的startActivity 是替换 Activity类内部的mInstrumentation
Context的startActivity 是替换 ActivityThread类内部的mInstrumentation

还有一点就是拦截的时机
第一种方式在Activity的onCreate()方法内部拦截即可而第二种方式需要在onCreate()方法之前attachBaseContext()方法中进行拦截
这里就牵扯到一些应用启动后的生命周期：当启动应用时，会孵化一个新进程，启动应用的启动入口为ActivityThread.main()，后面会新建一个ContextImpl实例给application,在后续的启动中，会进行activity的创建，其中ActivityThread会调用performLaunchActivity,先通过createBaseContextForActivity创建Context,然后再activity.attach()

在attach()方法中

final void attach(Context context, ActivityThread aThread,

            Instrumentation instr, IBinder token, int ident,

            Application application, Intent intent, ActivityInfo info,

            CharSequence title, Activity parent, String id,

            NonConfigurationInstances lastNonConfigurationInstances,

            Configuration config, String referrer, IVoiceInteractor voiceInteractor) {

        attachBaseContext(context);

        mInstrumentation = instr;

}

我们看到首先调用了attachBaseContext(context)这个方法
然后给成员mInstrumentation赋值
so 如果我们在onCreate()方法中去做hook是hook不到的时机已晚

@Override

    protected void attachBaseContext(Context newBase) {

        super.attachBaseContext(newBase);

        try {

            Log.e("activity","attachBaseContext");

            // 在这里进行Hook

            HookHelper.attachContext();

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

测试同样ok

3.前两种方法都是替换Instrumentation 这种方法我们看看在Instrumentation类中的execStartActivity()方法

 int result = ActivityManagerNative.getDefault()

                .startActivity(whoThread, who.getBasePackageName(), intent,

                        intent.resolveTypeIfNeeded(who.getContentResolver()),

                        token, target != null ? target.mEmbeddedID : null,

                        requestCode, 0, null, options);

真正开启的是这句 ActivityManagerNative.getDefault().startActivity()
首先ActivityManagerNative是个什么鬼点开后发现

ublic abstract class ActivityManagerNative extends Binder implements IActivityManager

继承了Binder 实现了 IActivityManager 而且是个抽象类类图如下

image.png

这张图得看半天
继续往下走

static public IActivityManager getDefault() {

      return gDefault.get();

  }

private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {

        protected IActivityManager create() {

            IBinder b = ServiceManager.getService("activity");

            if (false) {

                Log.v("ActivityManager", "default service binder = " + b);

            }

            IActivityManager am = asInterface(b);

            if (false) {

                Log.v("ActivityManager", "default service = " + am);

            }

            return am;

        }

getDefault返回的是一个IActivityManager对象
这里gDefault借助Singleton类实现单利模式 gDefault为static final 形式根据我们的hook原则这是一个比较好hook的点

代码如下：

public class HookUtil {

    private static final String TAG = "HookUtil";

    public void hookIActivityManager() {

        try {

            Class<?> c = Class.forName("android.app.ActivityManagerNative");

            Field field = c.getDeclaredField("gDefault");

            field.setAccessible(true);

            //返回ActivityManagerNative对象

            Object amn = field.get(null);

            Class<?> k = Class.forName("android.util.Singleton");

            Field field1 = k.getDeclaredField("mInstance");

            field1.setAccessible(true);

            //拿到ActivityManagerProxy对象 代理ActivityManagerNative对象的子类ActivityManagerService

            //为什么不是IActivityManager对象

            //因为在gDefault对象的 实现方法 onCreate()方法中 asInterface(b)返回的是  return new ActivityManagerProxy(obj) 具体可以看源码

            Object iActivityManager = field1.get(amn);

            IamInvocationHandler iamInvocationHandler = new IamInvocationHandler(iActivityManager);

            Object object = Proxy.newProxyInstance(iamInvocationHandler.getClass().getClassLoader(),iActivityManager.getClass().getInterfaces(),iamInvocationHandler);

            field1.set(amn,object);

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    class IamInvocationHandler implements InvocationHandler {

        Object iamObject;

        public IamInvocationHandler(Object iamObject) {

            this.iamObject = iamObject;

        }

        @Override

        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

//            Log.e(TAG, method.getName());

            if ("startActivity".equals(method.getName())) {

                Log.e(TAG, "要开始启动了 啦啦啦啦啦啦  ");

            }

            return method.invoke(iamObject, args);

        }

    }

}

image.png

测试也没问题

so that's all thanks for your time

参考文章：
Weishu's Notes
thanks weishu在某乎上答疑

作者：Allen_tong
链接：https://www.jianshu.com/p/5c6ff86331c8
來源：简书
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。