Introduction: The New Frontier of Android Flashing

Since Android 10, the landscape of device partitioning has undergone a significant transformation with the introduction of Dynamic Partitions. This innovation, while streamlining OTA updates and enhancing system flexibility, simultaneously created new hurdles for enthusiasts and developers aiming to flash custom kernels or modify system images. Traditional methods of flashing individual partitions directly became problematic, primarily due to the integrated verification mechanisms like Android Verified Boot (AVB) 2.0 and dm-verity, which are now deeply intertwined with the dynamic partition structure. This expert-level guide will demystify dynamic partitions and provide a comprehensive methodology to bypass their verification, enabling the use of unsigned custom kernels on Android 10+ devices.

Understanding Dynamic Partitions and Their Impact

Dynamic Partitions consolidate multiple physical partitions (like system, vendor, product, odm) into a single logical partition called the super partition. These logical partitions are dynamically sized and managed by a Linux device-mapper layer. This design allows for more flexible allocation of space during OTA updates, enabling A/B seamless updates by resizing partitions as needed.

Why This Matters for Custom Kernels

Historically, flashing a custom kernel involved replacing the boot.img. However, with dynamic partitions, the kernel often resides within boot.img, but critical verification information, and sometimes the kernel itself for Generic Kernel Image (GKI) devices, is handled by vendor_boot.img. The bootloader, before handing control to the kernel, verifies the integrity of critical partitions using AVB. Any modification to a verified partition, especially vendor_boot or the logical partitions within super, without proper signing, will trigger a verification failure, preventing the device from booting.

The Verification Challenge: AVB 2.0 and dm-verity

Android Verified Boot (AVB) 2.0 ensures that all executed code comes from a trusted source. It cryptographically verifies each stage of the boot process, from the bootloader to the kernel and system partitions. dm-verity, a kernel feature, provides transparent integrity checking of block devices, preventing persistent rootkits and malware from modifying the system partition. When you flash an unsigned custom kernel or modify system components, these mechanisms actively prevent your device from booting.

To bypass this, we need to:

• Disable AVB checks at the vbmeta level.
• Modify the vendor_boot image’s ramdisk to instruct the kernel to ignore dm-verity and AVB checks for logical partitions.

Prerequisites for Bypassing Verification

Before proceeding, ensure you have the following:

• An Android device with an unlocked bootloader. This is non-negotiable, as you cannot flash custom images otherwise.
• ADB and Fastboot tools installed and configured on your computer. (Android SDK Platform Tools).
• Device-specific firmware images: Specifically, boot.img, vendor_boot.img, and vbmeta.img from your device’s stock firmware. These are crucial for patching.
• A custom kernel image (e.g., a modified boot.img or a new kernel binary to be placed in vendor_boot).
• Magisk (specifically the Magisk app) for patching the boot.img if needed for root access, or if your custom kernel is packaged as a standard boot.img.
• A boot image unpacking/repacking tool such as ai_boot_image_editor (available on GitHub) or a similar script.

Methodology: Patching vbmeta and vendor_boot

The core of this bypass involves two main steps: disabling global AVB verification via vbmeta and instructing the kernel to ignore dm-verity for logical partitions by modifying vendor_boot‘s ramdisk.

Step 1: Obtain Stock Firmware Images

Download the full stock firmware package for your specific device model. Extract boot.img, vendor_boot.img, and vbmeta.img. These are essential baselines for our modifications.

Step 2: Disable Android Verified Boot (AVB)

This step tells your bootloader to ignore signature verification for future flashes. You must flash a ‘disabled’ vbmeta image.

fastboot --disable-verity --disable-verification flash vbmeta vbmeta.img

This command flashes the stock vbmeta.img but crucially modifies its flags in the bootloader to disable AVB and dm-verity checks globally. If your device supports it, `fastboot flash vbmeta_a vbmeta.img` or `fastboot flash vbmeta_b vbmeta.img` might be necessary for A/B devices.

Step 3: Unpack and Modify vendor_boot.img

vendor_boot.img contains the vendor ramdisk, which houses critical device-specific initialization scripts, including the fstab file that dictates how partitions are mounted and verified. We need to modify this fstab.

1. Extract vendor_boot.img:

   Use a tool like ai_boot_image_editor or a manual process:

   python3 ai_boot_image_editor.py --unpack-vendor-boot vendor_boot.img --output_dir vendor_boot_unpacked

   This will extract the contents, including ramdisk-vendor.img, to the vendor_boot_unpacked directory.

2. Unpack ramdisk-vendor.img:

   The ramdisk-vendor.img is typically a CPIO archive. Create a directory and extract its contents:

   mkdir vendor_ramdisk_contentcd vendor_ramdisk_contentgzip -dc ../vendor_boot_unpacked/ramdisk-vendor.img | cpio -id

3. Modify the fstab file:

   Navigate to the extracted ramdisk content. Look for files named fstab. or similar (e.g., fstab.qcom, fstab.pixel) usually in the root or an /etc directory within the ramdisk. Open this file with a text editor.

   Identify lines corresponding to /system, /vendor, /product, etc., which are usually mounted from the super partition. These lines will often contain `avb` or `verify` flags. You need to change or remove these flags. Look for something like:

   /dev/block/by-name/system /system ext4 ro,barrier=1,wait,avb=vbmeta_system,verify=vbmeta_system wait/dev/block/by-name/vendor /vendor ext4 ro,barrier=1,wait,avb=vbmeta_vendor,verify=vbmeta_vendor wait

   Modify these lines to effectively disable verification. The common approach is to add forcefdeorfbe=1,disable-verity or replace `avb` and `verify` with `noavb`. A robust modification would look like this:

   /dev/block/by-name/system /system ext4 ro,barrier=1,wait,forcefdeorfbe=1,disable-verity,noavb wait/dev/block/by-name/vendor /vendor ext4 ro,barrier=1,wait,forcefdeorfbe=1,disable-verity,noavb wait

   Save the modified fstab. file.

4. Repack ramdisk-vendor.img:

   Go back to the vendor_ramdisk_content directory and repack it:

   find . | cpio -o -H newc | gzip > ../vendor_boot_unpacked/ramdisk-vendor_patched.img

5. Rebuild vendor_boot.img:

   Now use your boot image editor or mkbootimg to rebuild the vendor_boot.img with the patched ramdisk. If using ai_boot_image_editor, it might look like:

   python3 ai_boot_image_editor.py --repack-vendor-boot vendor_boot_unpacked --output vendor_boot_patched.img

   Make sure to specify the kernel and original headers correctly if using mkbootimg directly. The tool typically handles this for you.

Step 4: Flash the Patched vendor_boot.img

Now, flash your newly created vendor_boot_patched.img to your device:

fastboot flash vendor_boot vendor_boot_patched.img

Step 5: Prepare and Flash Your Custom Kernel

This step depends on how your custom kernel is packaged:

• If your custom kernel is a standalone boot.img: Patch this boot.img with Magisk. Copy the custom boot.img to your phone, install Magisk, then select “Install” -> “Select and Patch a File” and choose your custom boot.img. Magisk will output a magisk_patched_boot.img. Transfer this back to your PC and flash it:

fastboot flash boot magisk_patched_boot.img

• If your custom kernel modifies the kernel within vendor_boot: You would have replaced the kernel binary (e.g., Image or Image.gz-dtb) within the vendor_boot_unpacked directory *before* rebuilding vendor_boot_patched.img in Step 3. In this scenario, the `vendor_boot_patched.img` already contains your custom kernel.

Once all images are flashed, reboot your device:

fastboot reboot

Troubleshooting and Considerations

• Bootloop: If your device bootloops, ensure your fstab modifications are correct and you haven’t introduced syntax errors. Re-flash your stock boot.img and vendor_boot.img if necessary, then re-attempt the process carefully.
• Device Specifics: Partition names, fstab locations, and specific mkbootimg arguments can vary slightly between devices and Android versions. Always consult device-specific forums (e.g., XDA Developers) for nuances.
• Security Implications: Disabling AVB and dm-verity significantly reduces your device’s security posture. Only proceed if you understand and accept these risks. Your device will likely show a warning about unlocked bootloader and disabled verification on startup.
• OTA Updates: Modifying vendor_boot and disabling verification will break OTA updates. You’ll need to re-flash stock images and re-patch after every major update.

Conclusion

Bypassing dynamic partition verification on Android 10+ is a more intricate process than with older Android versions, but it’s entirely achievable with a clear understanding of AVB, dm-verity, and the dynamic partition structure. By carefully modifying the vbmeta and the vendor_boot ramdisk’s fstab, you can successfully enable unsigned custom kernels and reclaim full control over your device’s software. This detailed guide equips you with the knowledge and steps to navigate this advanced customization challenge.