[Android Software/Hacking General [Developers Only]] Aqq123:
I haven't seen this shared anywhere but it's really quite straightforward if you know what you're doing. Maybe it helps someone to post it here. The next section is only for completeness, feel free to skip past it to get to the gist of it.

Background

Android by design depends for full functionality on Google services. These are normally provided by a proprietary application package com.google.android.gms. MicroG is an open-source replacement for Google services, allowing the user to take advantage of working notifications, location backends, installer, and other essential services, without compromising privacy and giving Google a backdoor to your device.

To operate properly, MicroG needs the ability to pretend it is the actual Google services application package, signed by Google. Hence the need for signature spoofing.

Official LineageOS builds do not include the ability to spoof signatures. Thus, using LineageOS with MicroG takes extra steps such as building patched LineageOS locally (a resource-consuming endeavor), or taking advantage of the LineageOS for MicroG builds helpfully provided in collaboration with the MicroG team (which however, due to resource constraints, are updated less often and lag behind the official builds).

A third solution is to patch an already-built system at installation time. This was initially implemented with Needle by souramoo, forked and improved upon as Tingle by @ale5000, which eventually inspired a wholly different approach with DexPatcher by @Lanchon, a tool allowing flexible patching of Dalvik executables, in particular services.jar, where signature spoofing is commonly implemented. Relevant patches for DexPatcher were authored by Lanchon himself up to Android 9. Later on, @oF2pks picked up the work to provide patches for Android 11.

Unfortunately, no such patch to be used with DexPatcher has existed from Android 12 onwards. One other option includes installing the FakeGApps Xposed module as forked and updated by whiz-inc. While it's great it exists, and the author's work should be appreciated, it's a complication and an unnecessary burden in many scenarios to depend on Xposed (and thus Magisk and LSPosed or the like) as a prerequisite for the patch to work. It's also worth it to be aware that the implementation makes it less secure than the traditional signature spoofing method.

The DexPatcher approach has several advantages. The patch can be more flexible and continues to apply as the underlying code changes. In comparison, the simple approach presented here is much more primitive and might require readjustment as new versions emerge over time. However it might still be good to know it works.

This way you can use the latest official LineageOS with MicroG, and update at will, as soon as new builds become available.

Patching

This is not a walkthrough, and I'm not going to explain everything step-by-step. Rather, the purpose is to give you the general idea what to do, which you can then adjust to your specific use case.

Obtain the file services.jar to patch. For example:

Pull it from your device: adb pull /system/framework/services.jar – or –

Extract it from a LineageOS image: payload-dumper-go -p system payload.bin and imgextractor system.img

Extract the file with APK Tool: apktool2 d -o services services.jar

Make the changes that allow signature spoofing. Either:

Apply the patch attached to this post: patch -i services.diff -p0 – or –

As of current LOS 19.1 builds (Nov 2022), you can just replace the single file: smali_classes2/com/android/server/pm/PackageManagerService$ComputerEngine.smali with the one attached to this post.

Note

: this might not always hold in the future. You might even need to apply the patch manually if the source changes too much. Either approach works for now.

Recompile the modified framework: apktool2 b -c -f -o services.jar services

Note

: This will overwrite the original services.jar. The -c flag to APK Tool is important as it keeps all the original META-INF inside it intact.

Copy services.jar over to the device: adb push services.jar /system/framework/ and you probably also have to adjust the permissions accordingly

This approach should work for any Android version in principle, although the exact patch might differ. However, since better options exist for Android 11 and below, you are probably interested in applying this to Android 12 or higher only.

One More Thing

For Android 12, an extra step is critical to ensure no bootloop on subsequent boot (2nd and then on), since oat_file_manager.cc now includes a check if OAT (.odex/.vdex) files are loaded from "trusted" locations only (effectively, the /system partition). You have to generate the optimization files and place them in the correct location, which is /system/framework/oat/arm64/:

dex2oat --dex-file=/system/framework/services.jar --instruction-set=arm64 --oat-file=/system/framework/oat/arm64/services.odex

The .vdex file will be created as well (these files already exist but should be overwritten, check the timestamps or you might want to delete them beforehand just to be sure). If you skip this step, the device will boot the 1st time but then the optimization files will be generated and saved in /data/dalvik-cache/. On any subsequent boot, an attempt to load these files from an "untrusted" location by the system will throw a fatal error and the Zygote process will die with the message: "Executing untrusted code from [...]". If you somehow find yourself in this predicament, delete the following files and reboot to temporarily make it work one more time:

/data/dalvik-cache/arm64/system@framework@services.jar@classes.dex

/data/dalvik-cache/arm64/system@framework@services.jar@classes.vdex

Further Steps

These are not all the required steps to install MicroG on an official LineageOS installation. You still want to, in particular:

Install at least the main MicroG app (GmsCore) and a dummy signature spoofing APK (also attached to this post) as priv-apps

Set up the priv-app permissions accordingly – otherwise you'll get a bootloop

Likely also install FakeStore, Aurora Store/F-Droid, and location backends of your choice, etc.

However: this is a simple solution to perhaps the most cumbersome aspect of signature spoofing. It's not necessary to resort to Xposed modules to get it working on Android 12, or to depend on a special build with the spoofing patched in at compilation time.

Credit

: The patch .smali code has been reverse-engineered from the spoofing patch for LineageOS for MicroG builds.