Riru

Riru only does one thing, inject into zygote in order to allow modules to run their codes in apps or the system server.

The name, Riru, comes from a character. (https://www.pixiv.net/member_illust.php?mode=medium&illust_id=74128856)

Requirements

Android 6.0+ devices rooted with Magisk

Guide

Install

From Magisk Manager
1. Search "Riru" in Magisk Manager
2. Install the module named "Riru"
The Magisk version requirement is enforced by Magisk Manager. You can check Magisk's module installer script.
Manually
1. Download the zip from the GitHub release
2. Install in Magisk Manager (Modules - Install from storage - Select downloaded zip)

Common problems

Third-party ROMs have incorrect SELinux rule

https://github.com/RikkaApps/Riru/wiki/Explanation-about-incorrect-SELinux-rules-from-third-party-ROMs-cause-Riru-not-working
Have low quality module that changes ro.dalvik.vm.native.bridge installed

If you are using other modules that change ro.dalvik.vm.native.bridge, Riru will not work. (Riru will automatically set it back)

A typical example is, some "optimize" modules change this property. Since changing this property is meaningless for "optimization", their quality is very questionable. In fact, changing properties for optimization is a joke.

How Riru works?

How to inject into the zygote process?

Before v22.0, we use the method of replacing a system library (libmemtrack) that will be loaded by zygote. However, it seems to cause some weird problems. Maybe because libmemtrack is used by something else.

Then we found a super easy way, the "native bridge" (ro.dalvik.vm.native.bridge). The specific "so" file will be automatically "dlopen-ed" and "dlclose-ed" by the system. This way is from here.
How to know if we are in an app process or a system server process?

Some JNI functions (com.android.internal.os.Zygote#nativeForkAndSpecialize & com.android.internal.os.Zygote#nativeForkSystemServer) is to fork the app process or the system server process. So we need to replace these functions with ours. This part is simple, hook jniRegisterNativeMethods since all Java native methods in libandroid_runtime.so is registered through this function. Then we can call the original jniRegisterNativeMethods again to replace them.

How does Hide works?

From v22.0, Riru provides a hidden mechanism (idea from Haruue Icymoon), make the memory of Riru and module to anonymous memory to hide from "/proc/maps string scanning".

Build

Gradle tasks:

:riru:assembleDebug/Release

Generate Magisk module zip to out.
:riru:pushDebug/Release

Push the zip with adb to /data/local/tmp.
:riru:flashDebug/Release

Flash the zip with adb shell su -c magisk --install-module.
:riru:flashAndRebootDebug/Release

Flash the zip and reboot the device.

Module template

https://github.com/RikkaApps/Riru-ModuleTemplate

Module API changes

https://github.com/RikkaApps/Riru-ModuleTemplate/blob/master/README.md#api-changes

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