OP-TEE Hello World Example Android port

This repository aims to describe the steps to build the Hello World TA example into an Android app.

Requirements

• Android Studio v.4.2.2
• Hikey960
• AOSP+OPTEE
• Android Debug Bridge v1.0+

Procedure

AOSP + OP-TEE Setup

Follow the OP-TEE official documentation at https://optee.readthedocs.io/en/latest/building/aosp/aosp.html

App Creation and Installation

App Creation

Start by creating a new project that follows the Native C++ template. After that, you must fill in with information regarding the project, and in the Minimum SDK field you must specify that you intend to use the API 28: Android 9.0 (Pie). Both steps are presented in the following figures

The project will be generated and you will have a simple app that prints a "Hello World" in the main screen.

Our objective is now to move the OP-TEE Hello World [1] main file located in the host directory to the cpp directory. Since the original file will have to suffer some changes in order to be used in our app, I recommend you to use the one located at app/app/src/main/cpp/hello_word.c. Next, in the app/app/src/main/cpp/CMakeLists.txt, you must replace your hello_world.c file with the pre-generated native-lib.cpp file, so that the project can use its functions. Additionally, you must call the function specified in the .c file, so that we can test if the app communicated with OP-TEE.

In the following step, you must create a directory named app/app/src/main/cpp/include and put inside the header files the hello_world.c needs. Your Project structure at the moment must resemble the next figure.

After synchronizing your project, you will notice that the tee_api.h functions are still invalid to use. This means you must include the library file that has the functions' implementation. So, we must create a new directory named app/app/src/main/cpp/libs and add the libteec.so file generated during the AOSP+OPTEE build process. The file can be found at out/target/product/hikey960/vendor/lib/libteec.so.

Our cpp directory structure should now look like the figure:

For the file to be recognized, you must add the libteec.so file as an external library to CMakeList.txt file. See app/app/src/main/cpp/CMakeList.txt for reference.

The process of building the app is almost done, but you must complete this last step. In the app/build.gradle file, you must specify the ndk abiFilters the android studio will use to build your application. Since the libteec.so for the hikey960 is from a 64-bit build, specify arm64-v8a for the ndk abiFilters inside the android field, as illustrated in the figure below.

With this, you can build your app and generate an apk. The next step should be its installation in the Android system.

Installation

To run the App in the AOSP + OP-TEE system successfully you need to install the app as a system app, otherwise the application will not be able to communicate with OP-TEE. To do this, you must type the following set of commands:

$ adb root
$ adb remount
$ adb push filename.apk  /system/app/
$ adb shell chmod 644 /system/app/filename.apk
$ adb reboot

Finally, you can disconnect the board from your computer and run the app. If everything was correctly done, you can see your new app in the Android menu like the following figure,

and running the app, it must output something similar to this in your display:

References

[1] https://github.com/linaro-swg/optee_examples/tree/master/hello_world