Developing system apps without AOSP

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Developing system apps without AOSP Erik Helman

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Custom Android Devices

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Android Developer Boards

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System Apps vs Regular Apps • Hidden & System APIs • Signature & Permissions • Pre-installed

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Why? • No AOSP modiﬁcations • Developer Tooling • macOS and Windows

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Using an emulator

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Using an emulator

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Using an emulator

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Using a physical device (Pixel) $ adb shell getprop ro.treble.enabled true

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Download a Generic System Image

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Prepare the GSI $ unzip aosp_arm64-img-10018685.zip $ simg2img system.img system_raw.img $ gzip -c system_raw.img > system_raw.gz $ adb push system_raw.gz /storage/emulated/0/Download/

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Flash a GSI using DSU $ adb shell am start-activity \ -n com.android.dynsystem/com.android.dynsystem.VerificationActivity \ -a android.os.image.action.START_INSTALL \ -d file:///storage/emulated/0/Download/system_raw.gz \ --el KEY_SYSTEM_SIZE $(du -b system_raw.img|cut -f1) \ --el KEY_USERDATA_SIZE

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Generic System Images documentation developer.android.com/topic/generic-system-image

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Permission protectionLevel

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Converting AOSP test certiﬁcates to Android keystore $ openssl pkcs8 -inform DER -nocrypt -in platform.pk8 -out platform-signing.key $ openssl pkcs12 -export -in platform.x509.pem -inkey platform.key \ -name platform -out platform-signing.pem -password pass:password $ openssl pkcs12 -export -in platform.x509.pem -inkey platform-signing.key \ -name platform -out platform-signing.pem -password pass:password $ keytool -importkeystore -destkeystore platform-signing.keystore \ -deststorepass password -srckeystore platform.pem -srcstoretype PKCS12 -srcstorepass password

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Using the platform key for signing signingConfigs { debug { keyAlias 'platform' keyPassword 'password' storeFile rootProject.file('platform-signing.keystore') storePassword 'password' } }

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Installing from Android Studio

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Installing on the /system/app or / system/priv-app partition $ adb root $ adb disable-verity $ adb reboot # Wait for device to reboot... $ adb root $ adb remount $ adb shell mkdir /system/app/YourSystemApp $ adb push YourSystemApp.apk /system/app/YourSystemApp $ adb reboot # Not usually needed Remember to bump versionCode!

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Calling System APIs

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Permissions frameworks/base/core/res/AndroidManifest.xml

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Inject input events (InputManager.java)

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Calling hidden APIs Refelctions (Slow!) private val injectMethod: Method = InputEvent::class.java .getMethod("injectInputEvent", InputEvent::class.java, Int::class.java) fun InputManager.injectEvent(inputEvent: InputEvent) { injectMethod.invoke(this, inputEvent, 0) }

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Calling hidden APIs Add an interface

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Calling hidden APIs Add an interface package android.hardware.input; import android.view.InputEvent; public interface InputManager { public boolean injectInputEvent(InputEvent event, int mode); }

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Calling hidden APIs Extract framework.jar & android.jar 1. Copy ﬁles from device or emulator 2. Convert from DEX to Java classes (DexTools) 3. Package into a new android.jar ﬁle 4. Replace android.jar in your SDK

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Calling hidden APIs Build a custom SDK $ mkdir ~/my-android-git $ cd ~/my-android-git $ repo init -u https://android.googlesource.com/platform/manifest \ -b master -g all,-notdefault,tools $ repo sync -j8 # Edit AOSP! $ . build/envsetup.sh $ lunch sdk-eng $ m

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Android Code Search cs.android.com

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Interesting @SystemAPI permissions

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Interesting @SystemAPI permissions

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Interesting @SystemAPI permissions

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Summary • How much System APIs do you need to use? • Reﬂection? • Custom interface • Custom Engineering SDK • Bookmark system AndroidManifest.xml • Navigating cs.andorid.com