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[GUIDE] Re-locking the bootloader on the OnePlus 8t with a self-signed build of LOS 18.1

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WhitbyGreg

Senior Member
Following the LineageOS signing build steps, these files are generated:
media.pk8, networkstack.pk8, platform.pk8, releasekey.x509.pem, shared.x509.pem, testkey.x509.pem, media.x509.pem , networkstack.x509.pem , platform.x509.pem , releasekey.pk8, shared.pk8, testkey.pk8

I'm sorry, for the last 2 days I'm spinning around myself to figure out how to complete your guide and get a successful build.

Could you please, if you do not mind, just tell me how to generate this releasekey.key plaintext private key for the release certificate?

Your help is highly appreciated, thank you
Try this command:

openssl pkcs8 -in releasekey.pk8 -inform DER -out releasekey.key -nocrypt
 

ahmed.elsersi

Senior Member
Oct 1, 2010
58
10
Now, I finished a successful user build of LineageOS with OEM re-lock support for OnePlus 7 Pro.

The only step i did not do, is patching the build/core/Makefile

Unfortunately, after the phone flashed, the re-lock did not work, which i do not understand why.

it worked when i used only this option ro.oem_unlock_supported=1


Thank You for your time and effort, i really appreciate it.
 
Last edited:

ahmed.elsersi

Senior Member
Oct 1, 2010
58
10
I followed every single step on this guide, and the build, signing, and generating OTA file are all successful.

avbtool through error:

b = 2L**32 # pylint: disable=long-suffix
^
SyntaxError: invalid syntax

So, i used your other post to extract the pubkey using the ruby script to flash the avb_custom_key.

I flashed my OnePlus 7 Pro successfully, and it's working fine, the bootloader is locked, and OEM disabled in developer menu.


Thank You for your guide and help.

have a blessed life.
 
Last edited:
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ahmed.elsersi

Senior Member
Oct 1, 2010
58
10
Hello,

Just to share with you.

I successfully built a LineageOS 4 MicroG with OEM unlock support, the build is user build.

I merged your guide with the needed steps from the build.sh script in the docker-lineage-cicd src/ directory.

Now, my OnePlus 7 Pro, has lineageos 4 microg installed with OEM unlock support in developer options menu, same as CalyxOS on Pixel phones. 😁

Thank You again, I really appreciate your shared information.🙏

Wish you a blessed life.
 
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WhitbyGreg

Senior Member
Will your custom avb key work after flashing official lineage os and gapps ?
No?

This guide is how to build your own custom/unofficial build of LineageOS and relock the bootloader. The avb key created during this process only works for builds signed by the same private key, so official builds would fail.

Likewise, you can't just "flash" gapps on top of your custom build, it has to be included in the build process so that the correct hash values are calculated for the system partition in vbmeta, otherwise the OS will fail to boot as it will think it is corrupted.
 

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  • 5
    What is this tutorial?
    This tutorial will:
    • Creating an unofficial build of LineageOS 18.1 suitable for using to re-lock the bootloader on a OnePlus 8t
    • Take you through the process of re-locking your bootloader after installing the above

    This tutorial will NOT:
    • Remove *all* warning messages during boot (the yellow "Custom OS" message will be present though the orange "Unlocked bootloader" message will not)
    • Allow you to use official builds of LineageOS 18.1 on your device with a re-locked bootloader (more details near the end of the tutorial)
    This tutorial will assume you are working on an Ubuntu 18.04 installation, if you are using Windows or another Linux distro, the commands may be different.

    Supported devices:
    The following devices have been tested and confirmed to work:
    • OnePlus 7 Pro (guacamole)
    • OnePlus 8t (kebab)
    • Pixel 4 (flame)
    Other OnePlus devices that support AVBv2 (OnePlus 6t and newer as well as most Pixel devices) and LineageOS 18.1 (see current support list over on the LineageOS download page) should work as well.

    For simplicities sake, all further references will only be to the 8t (kebab).

    Pre-requisites:
    • a mid level knowledge of terminal commands and features
    • a supported phone
    • a PC with enough CPU/RAM to build LineageOS 18.1 (recommended 8 cores, 24g of RAM)
    • a working USB cable
    • fastboot/adb installed and functional
    • LineageOS 18.1 source code downloaded
    • at least one successful build of LineageOS
    • at least one successful signing of your build with your own keys

    Misc. notes:
    • the basics of building/signing of LineageOS is outside the scope of this tutorial, refer to the LineageOS Wiki for details on how to complete these tasks
    • you'll be modifying some code in LineageOS, so if you are not comfortable using basic editing utilities as well as patch, do not proceed any further
    • the path to your LineageOS source code is going to be assumed to be ~/android/lineageos, if it is somewhere else, substitute the correct path in the tutorial
    • the path to your private certificate files is going to be assumed to be ~/android-certs, if it is somewhere else, substitute the correct path in the tutorial


    *** WARNING ****
    This process may brick your device. Do not proceed unless you are comfortable taking this risk.


    *** WARNING ****
    This process will delete all data on your phone! Do not proceed unless you have backed up your data!


    *** WARNING ****
    Make sure you have read through this entire process at least once before attempting, if you are uncomfortable with any steps include in this guide, do not continue.



    And now on with the show!

    Step 1: Basic setup

    You need a few places to store things, so create some working directories:
    Code:
    mkdir ~/android/kebab
    mkdir ~/android/kebab/patches
    mkdir ~/android/kebab/pkmd
    You also need to add "~/android/lineageos/out/host/linux-x86/bin" to your shell's profile path. Make sure to close and restart your session afterwards otherwise the signing will fail later on with a "file not found" error message (this may no longer be required).

    Step 2: Update kebab's BoardConfig.mk

    You will need to add a few parameters to the end of ~/android/lineageos/device/oneplus/kebab/BoardConfig.mk, they are:

    Code:
    BOARD_AVB_ALGORITHM := SHA256_RSA2048
    BOARD_AVB_KEY_PATH := /home/<userid>/.android-certs/releasekey.key
    Note you cannot use "~" in the path names above to signify your home directory, so give the full absolute path to make sure the files are found.

    Step 3: Update sm8250-common's BoardConfigCommon.mk

    LineageOS by default disables Android Verified Boot's partition verification, but you can enable it now as all the required parts will be in place.

    To enable partition verification do the following:

    Code:
    cd ~/android/lineageos/device/oneplus/sm8250-common
    sed -i 's/^BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flags 2/#BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --flags 2/' BoardConfigCommon.mk
    sed -i 's/^BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --set_hashtree_disabled_flag/#BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS += --set_hashtree_disabled_flag/' BoardConfigCommon.mk
    sed -i 's/^BOARD_AVB_VBMETA_SYSTEM_KEY_PATH := external\/avb\/test\/data\/testkey_rsa2048.pem/BOARD_AVB_KEY_PATH := \/home\/<userid>\/.android-certs\/releasekey.key/' BoardConfigCommon.mk

    Don't forget to replace your <userid> in the third sed command above with your current logged in user id.

    Step 4: Patch the AOSP and Device Makefile

    You also need to patch the Makefile included with AOSP as it will otherwise fail during the build.

    The required patch can be found here:

    Download it and store in ~/android/kebab/patches.

    Now apply it with the following command:

    Code:
    cd ~/android/lineageos/build/core
    patch Makefile ~/android/kebab/patches/core-Makefile-fix-18.1.patch

    If you would like to know more about this patch, see the additional info at the bottom of this post.

    There is also a small addition to the device's common.mk required to enable the OEM unlock option in developers options, do this via the following commands:

    Code:
    cd ~/android/lineageos/device/oneplus/sm8250-common
    sed -i 's/^# OMX/# OEM Unlock reporting\nPRODUCT_DEFAULT_PROPERTY_OVERRIDES += \\\n    ro.oem_unlock_supported=1\n\n# OMX/' common.mk

    Step 5: Build LineageOS

    You are now ready to build:

    Code:
    cd ~/android/lineageos
    breakfast kebab
    source build/envsetup.sh
    croot
    mka target-files-package otatools

    Step 6: Sign the APKs

    You are now ready to sign the apks with sign_target_files_apks:

    Code:
    ./build/tools/releasetools/sign_target_files_apks -o -d ~/.android-certs $OUT/obj/PACKAGING/target_files_intermediates/*-target_files-*.zip signed-target_files.zip

    Step 7: Build the OTA

    Now it is time to complete the OTA package:

    Code:
    ./build/tools/releasetools/ota_from_target_files -k ~/.android-certs/releasekey --block signed-target_files.zip lineage-18.1-[date]-UNOFFICIAL-kebab-signed.zip

    Note, replace [date] with today's date in YYYYMMDD format.

    Step 8: Create pkmd.bin for your phone

    Before you can lock your phone, you have to tell it what your public key is so it knows it can trust your build.

    To do this you need to create a pkmd.bin file:

    Code:
    ~/android/lineageos/external/avb/avbtool extract_public_key --key ~/.android-certs/releasekey.key --output ~/android/kebab/pkmd/pkmd.bin

    Step 9: Flashing your LineageOS build

    It's time to flash your build to your phone. The following steps assume you have already unlocked your phone and have flashed an official version of LineageOS to it. You don't need to have flashed LineageOS yet, you could use TWRP through "fastboot boot" if you prefer. Or, if you want to use the recovery that was just created, it is located in ~/android/lineageos/out/target/product/kebab and is called recovery.img.

    • Reboot your phone in to recovery mode
    • In LineageOS Recovery return to the main menu and select "Apply update"
    • From your PC, run:
    Code:
    adb sideload ~/android/lineageos/lineage-18.1-[date]-UNOFFICIAL-kebab-signed.zip

    When the sideload is complete, reboot in to LineageOS. Make sure everything looks good with your build.

    You may also need to format your data partition at this time depending on what you had installed on your phone previously.

    Step 10: Flashing your signing key

    Now it's time to add your signing key to the Android Verified Boot process. To do so, do the following:

    • Reboot your phone in to fastboot mode
    • From your PC, run:
    Code:
    fastboot flash avb_custom_key ~/android/kebab/pkmd/pkmd.bin
    fastboot reboot bootloader
    fastboot oem lock
    • On your phone, confirm you want to re-lock and it will reboot

    Your phone will then factory reset and then reboot in to LineageOS.

    Which of course means you have to go through the first time setup wizard, so do so now.

    Step 11: Disable OEM unlock

    Congratulations! Your boot loader is now locked, but you can still unlock it again using fastboot, so it's time to disable that as well.

    • Unlock you phone and go to Settings->About phone
    • Scroll to the bottom and find "Build number"
    • Tap on it you enable the developer options
    • Go to Settings->System->Advanced->Developer options
    • Disable the "OEM unlocking" slider
    • Reboot

    Step 12: Profit!


    Other things

    • The above will build a standard USERDEBUG version of LineageOS, however this will still allow LineageOS Recovery to sideload non-signed files as well as give you root shell access through ADB. Step 3/4 above protects your system/vendor/boot/dtbo/etc. partitions, but none of the others. Likewise USERDEBUG builds will allow for rolling back to a previous builds/versions of LineageOS. To increase security and disallow both of these scenarios you may want to build a USER version of LineageOS to install. However this brings in other issues, such as flashing newer firmware from OnePlus so make sure you understand the implications of both choices. For more details on build types, see https://source.android.com/setup/develop/new-device#build-variants.
    • In the above example the releasekey from your LineageOS install has been used to sign AVB, but AVB supports other key strengths up to SHA512_RSA8192. You could create a key just for signing AVB that used different options than the default keys generated to sign LineageOS.
    • If you want to remove you signing key from your phone, you can do it by running "fastboot erase avb_custom_key".
    • The changes you made to the AOSP Makefile may conflict with future updates that you pull from LineageOS through repo sync, if you have to reset the file to get repo sync to complete successfully, you'll have to reapply the changes afterwards.

    So why can't I do this with official LineageOS builds?

    NEW: You can! See this thread for more details.

    For Android Verified Boot (AVB) to work, it must have the hash values for each of the system/vendor/boot/dtbo/etc. partitions stored in vbmeta. Official LineageOS builds for kebab do include the vendor.img in them along with everything else that is needed, however that is not true for all phones.

    There are two "issues" that stop someone from using the official kebab builds:
    • LineageOS does not provide a pkmd.bin file to flash to your phone to include the public key in your AVB process (NEW: this thread shows you how to extract the key).
    • AVB is enabled in the official LineageOS builds but does not validate the hash trees during boot which limits the protection offered.
    Ok, what messages do I see during the boot process then?

    During a boot you will of course see the standard OnePlus power up screen, followed by the yellow "custom os" message and then the standard LineageOS boot animation.

    For more details on AVB boot messages, see https://source.android.com/security/verifiedboot/boot-flow

    So what does that patch to the Makefile do?

    AOSP's default Makefile makes an assumption that when AVB is enabled, that all the img files will be available well before vbmeta.img is created. This is simply NOT true and AOSP seems to know this as well from the following comment in the Makefile:

    Code:
    # Not using INSTALLED_VBMETA_SYSTEMIMAGE_TARGET as it won't be set yet.
    ifdef BOARD_AVB_VBMETA_SYSTEM
    $(eval $(call check-and-set-avb-args,vbmeta_system))
    endif
    
    ifdef BOARD_AVB_VBMETA_VENDOR
    $(eval $(call check-and-set-avb-args,vbmeta_vendor))
    endif

    These two calls eventual evaluate to returning the path to the partitions based upon the INSTALLED_*IMAGE_TARGET variable, which isn't created until later in the build process.

    Because of this, the command to build vbmeta.img gets corrupted due to the missing make variable being empty and an invalid command line is passed to avbtool near the end of the build.

    The corruption happens due to the fact that the following line from the original Makefile:

    Code:
    --include_descriptors_from_image $(call images-for-partitions,$(1))))))

    Gets added to the avbtool call even if "$(call images-for-partitions,$(1))" turns out to be an empty string. Avbtool then throws an error message as it is expecting a parameter after the "--include_descriptors_from_image" flag that is added for the "empty" partition path.

    The fix is to call "$(call images-for-partitions,$(1))" earlier, set it to a variable and check to make sure it isn't an empty string before letting the "--include_descriptors_from_image" be added to the avbtool command line to be used later.

    This technically generates an incomplete vbmeta.img file during the build process, but since the signing process recreates it from scratch anyway; no harm, no foul.

    Thank You's
    1
    Hello,

    I did extract the proprietary blobs from payload-based.

    Do you mean I should compile LinageOS successfully first using:
    source build/envsetup.sh
    breakfast guacamole
    croot
    brunch guacamole

    before i follow the steps listed here in this guide??

    Thank You
    Check the extraction script for errors or switch to the muppets, sometimes the extraction script isn't up to date.

    In general, yes, make sure you have a version of LineageOS that compiles successfully, that way you know you have a valid base to start from.

    Pre-requisites:
    • at least one successful build of LineageOS
    • at least one successful signing of your build with your own keys
    1
    Thank You so much.

    One last question if i may, can these steps applied on LinageOS 4 MicroG using the automated build by their docker image docker-lineage-cicd ?

    Thank You
    You'd have to modify the docker image from my understanding as it includes all the source and tools required to do the build.
    1
    Hello,

    Kindly Please, Could you clarify what do you mean by ~/.android-certs/releasekey.key and ~/.android-certs/releasekey.key/ ??

    I created my own signing keys, and the output contains releasekey.pk8 and releasekey.x509.pem, that is why I'm confused.
    You might need to convert your pk8 in to plain text using openssl like so:

    openssl pkcs8 -in releasekey.pk8 -out releasekey.key
    1
    I followed every single step on this guide, and the build, signing, and generating OTA file are all successful.

    avbtool through error:

    b = 2L**32 # pylint: disable=long-suffix
    ^
    SyntaxError: invalid syntax

    So, i used your other post to extract the pubkey using the ruby script to flash the avb_custom_key.

    I flashed my OnePlus 7 Pro successfully, and it's working fine, the bootloader is locked, and OEM disabled in developer menu.


    Thank You for your guide and help.

    have a blessed life.