Android_boot_image_editor

This tool focuses on editing Android boot.img(also recovery.img, recovery-two-step.img and vbmeta.img).

Prerequisite

Host OS requirement:

Linux or Mac. Also need python 2.x(required by avbtool) and java 8.

Target Android requirement:

(1) Target boot.img(or recovery.img / recovery-two-step.img) MUST follows AOSP verified boot flow, either Boot image signature in VBoot 1.0 or AVB HASH footer in VBoot 2.0.

(2) These utilities are known to work for Nexus/Pixel boot.img(or recovery.img/recovery-two-step.img/vbmeta.img) for the following Android releases:

• AOSP master
• Lollipop (5.0) - Pi (9)

You can get a full Android version list here.

Usage

Get tools via git:

git clone https://github.com/cfig/Android_boot_image_editor.git
cd Android_boot_image_editor

Then put your boot.img at $(CURDIR)/boot.img, then start gradle 'unpack' task:

cp <original_boot_image> boot.img
./gradlew unpack

Your get the flattened kernel and /root filesystem under $(CURDIR)/build/unzip_boot:

build/unzip_boot/
├── boot.img.avb.json (AVB only)
├── bootimg.json (boot image info)
├── kernel
├── second (2nd bootloader, if exists)
└── root

Then you can edit the actual file contents, like rootfs or kernel. Now, pack the boot.img again

./gradlew pack

You get the repacked boot.img at $(CURDIR):

boot.img.signed

If you are working with recovery.img

If you are working with recovery.img, the steps are similar:

cp <original_recovery_image> recovery.img
./gradlew unpack
./gradlew pack

And you get recovery.img.signed

example & test

An example boot.img has been placed at src/test/resources/boot.img, which is extracted from Nexus 5x(code: bullhead) factory images from Google, you can take it as a quick start.

boot.img layout

Read layout of Android boot.img. We now support both VB 1.0 and AVB 2.0 layouts.

References

boot_signer https://android.googlesource.com/platform/system/extras

bouncycastle https://android.googlesource.com/platform/external/bouncycastle

cpio / fs_config https://android.googlesource.com/platform/system/core

AVB https://android.googlesource.com/platform/external/avb/