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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
Answering myself: No. System avb flags create a chain system signing so that system could be updated independently, but with a key that is known to vbmeta partition. So, if user modifyes system, that prlbably would not work. I am looking for a way to let users flash Gapps without trigerring rejection.
Short answer: no

Longer answer: kinda... but it would break the security model and make relocking the bootloader pointless.

Basically, yes you might be able to create an empty vbmeta and relock the bootloader, but then any changes to any of the partitions would be valid. So if malware exploited a hole that allowed it to write to system (or vendor or any other partition), any changes would be kept through a reboot or even a system reset.

As for adding GAPPS "afterwards", you could then create your own build of GAPPS and sign it with the same key as you signed your build and allow users to flash it as part of install. Or simply create two separate distros of your ROM, one without GAPPS and one with, as you can certainly build GAPPS into a build.
 

optimumpro

Senior Member
Jan 18, 2013
6,789
14,306
Short answer: no

Longer answer: kinda... but it would break the security model and make relocking the bootloader pointless.

Basically, yes you might be able to create an empty vbmeta and relock the bootloader, but then any changes to any of the partitions would be valid. So if malware exploited a hole that allowed it to write to system (or vendor or any other partition), any changes would be kept through a reboot or even a system reset.

As for adding GAPPS "afterwards", you could then create your own build of GAPPS and sign it with the same key as you signed your build and allow users to flash it as part of install. Or simply create two separate distros of your ROM, one without GAPPS and one with, as you can certainly build GAPPS into a build.
Well. You can't bundle Gapps into the build - licensing issue. Second, have you tried to modify System partition and boot? Guess what, I did, and it booted. Turns out chaining is the way to be able to modify partitions independently without touching vbmeta. Here is what Google says about it:

"Note that the hash-tree descriptors for system.img, system_ext.img and product.img will be included only in vbmeta_system.img, but not vbmeta.img. With the above setup, partitions system.img, system_ext.img, product.img and vbmeta_system.img can be updated independently - but as a group - of the rest of the partitions, or as part of the traditional updates that update all the partitions."

So, when you create a chain, it turns out that the chained partitions are wide open (of course subject to root and sepolicy rights).
 
Last edited:

optimumpro

Senior Member
Jan 18, 2013
6,789
14,306
Well. You can't bundle Gapps into the build - licensing issue. Second, have you tried to modify System partition and boot? Guess what, I did, and it booted. Turns out chaining is the way to be able to modify partitions independently without touching vbmeta. Here is what Google says about it:


"Note that the hash-tree descriptors for system.img, system_ext.img and product.img will be included only in vbmeta_system.img, but not vbmeta.img. With the above setup, partitions system.img, system_ext.img, product.img and vbmeta_system.img can be updated independently - but as a group - of the rest of the partitions, or as part of the traditional updates that update all the partitions."

So, when you create a chain, it turns out that the chained partitions are wide open (of course subject to root and sepolicy).
Actually, removal of 'BOARD_AVB_VBMETA_SYSTEM' flags broke the build. And it makes sense. System partition gets modified constantly by system processes and apps, so it would be impossible to keep it unchanged. You tick toggles, make adjustments, and all those things modify system... .
 

WhitbyGreg

Senior Member
Well. You can't bundle Gapps into the build - licensing issue.
Technically even just downloading GAPPS and installing it seperatly is an licensing issue.. so 🤷
Second, have you tried to modify System partition and boot? Guess what, I did, and it booted.
I have, and it did boot but it rolled back the changes (as it should).

Turns out chaining is the way to be able to modify partitions independently without touching vbmeta. Here is what Google says about it:

"Note that the hash-tree descriptors for system.img, system_ext.img and product.img will be included only in vbmeta_system.img, but not vbmeta.img. With the above setup, partitions system.img, system_ext.img, product.img and vbmeta_system.img can be updated independently - but as a group - of the rest of the partitions, or as part of the traditional updates that update all the partitions."

So, when you create a chain, it turns out that the chained partitions are wide open (of course subject to root and sepolicy rights).
Yes, but you have to update the vbmeta_system.img at the same time that has to be signed with the same key as vbmeta, so you can't just change those partitions willy nilly.
Actually, removal of 'BOARD_AVB_VBMETA_SYSTEM' flags broke the build. And it makes sense. System partition gets modified constantly by system processes and apps, so it would be impossible to keep it unchanged. You tick toggles, make adjustments, and all those things modify system... .
My build is working fine without the "BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS" flags, I've removed both "--set_hashtree_disabled_flag" and "--flags 2".
 

optimumpro

Senior Member
Jan 18, 2013
6,789
14,306
Technically even just downloading GAPPS and installing it seperatly is an licensing issue.. so 🤷

I have, and it did boot but it rolled back the changes (as it should).


Yes, but you have to update the vbmeta_system.img at the same time that has to be signed with the same key as vbmeta, so you can't just change those partitions willy nilly.

My build is working fine without the "BOARD_AVB_MAKE_VBMETA_IMAGE_ARGS" flags, I've removed both "--set_hashtree_disabled_flag" and "--flags 2".
I was talking about BOARD_AVB_VBMETA_SYSTEM, not VBMETA_IMAGE flags. When I removed the former, the build stopped and asked for VBMETA_SYSTEM.

And it's not clear to me, as users make plenty of prebuilt changes that modify system, and they don't get rolled back on reboot.

Any way, how would I sign let's say a GAPPS zip? I have never signed anything independently of the build. And which signature? BOAD_AVB? That's the one that goes into VBMETA. BOARD_AVB_VBMETA_SYSTEM? Probably the rom signing key, which is different? But wouldn't that zip have to modify VBMETA_SYSTEM? How? And what's the command to sign let's say GAPPS.zip?.
 

WhitbyGreg

Senior Member
I was talking about BOARD_AVB_VBMETA_SYSTEM, not VBMETA_IMAGE flags. When I removed the former, the build stopped and asked for VBMETA_SYSTEM.

And it's not clear to me, as users make plenty of prebuilt changes that modify system, and they don't get rolled back on reboot.
That's because standard builds of LineageOS have "--set_hashtree_disabled_flag", which basically turns off the hashtree, and "--flags 2" which tells the system not to rollback changes.
Any way, how would I sign let's say a GAPPS zip? I have never signed anything independently of the build. And which signature? BOAD_AVB? That's the one that goes into VBMETA. BOARD_AVB_VBMETA_SYSTEM? Probably the rom signing key, which is different? But wouldn't that zip have to modify VBMETA_SYSTEM? How? And what's the command to sign let's say GAPPS.zip?.
I wouldn't bother trying to independently sign a GAPPS package, instead going for the pre-built OS/GAPPS route which is relativly easy. However you should be able to sign GAPPS with signapk if you really wanted to try it. As for which key, it should be the releasekey.
 

optimumpro

Senior Member
Jan 18, 2013
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That's because standard builds of LineageOS have "--set_hashtree_disabled_flag", which basically turns off the hashtree, and "--flags 2" which tells the system not to rollback changes.

I wouldn't bother trying to independently sign a GAPPS package, instead going for the pre-built OS/GAPPS route which is relativly easy. However you should be able to sign GAPPS with signapk if you really wanted to try it. As for which key, it should be the releasekey.
When Cyanogen bundled Gapps, they got a cease and desist letter from Google. Also, even if I sign Gapps.zip with the release key, system would still be modified.

My rom doesn't have "--flags 2". Yet I still don't understand how it is possible that user changes to system (even when they change brightness or move volume panel or a hundred of other changes) don't get to roll back.
 

WhitbyGreg

Senior Member
When Cyanogen bundled Gapps, they got a cease and desist letter from Google. Also, even if I sign Gapps.zip with the release key, system would still be modified.
Yep, it's a risk, there are several custom ROM's that do ship GAPPS though. I completely understand (and agree with) why LineageOS doesn't ship GAPPS, both from a licensing perspective and a user choice perspective.

I still don't understand how it is possible that user changes to system (even when they change brightness or move volume panel or a hundred of other changes) don't get to roll back.
Because those aren't stored on the system partition, those are part of the user data or in memory. The system partition is not written to during day to day operations, and in fact on Android 11 is only mounted as read only.
 
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optimumpro

Senior Member
Jan 18, 2013
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Yep, it's a risk, there are several custom ROM's that do ship GAPPS though. I completely understand (and agree with) why LineageOS doesn't ship GAPPS, both from a licensing perspective and a user choice perspective.


Because those aren't stored on the system partition, those are part of the user data or in memory. The system partition is not written to during day to day operations, and in fact on Android 11 is only mounted as read only.
I think in my case it is magisk that's doing it, as nothing gets rolled back on my phone. I guess for my users I can do --flag 2, so they can install Gapps themselves.

Gapps: I think there was a class action case years ago which resulted in a court approved settlement that allowed users to install Gapps, but no bundling with releases by developers.
 

optimumpro

Senior Member
Jan 18, 2013
6,789
14,306
Yep, it's a risk, there are several custom ROM's that do ship GAPPS though. I completely understand (and agree with) why LineageOS doesn't ship GAPPS, both from a licensing perspective and a user choice perspective.


Because those aren't stored on the system partition, those are part of the user data or in memory. The system partition is not written to during day to day operations, and in fact on Android 11 is only mounted as read only.
Here is what Magisk script does during the final stages of the build:
Code:
Remove pattern [,avb=vbmeta_system]
Remove pattern [,avb]
 

YulNicolai

Member
Feb 15, 2021
40
2
It applys the sed command to two of extracted libraries from the phone (or in the muppets if your using that). After makeing the change you can recompile LineageOS and update your phone with the new software and your finger print reader should work again.
Does this work with oxygenos? My fingerprint does not work on my oxygenos either. The problem is with persist.img.
 
It's not the hal. The blob 'libgf_g6_ud_hal.so' doesn't get built from source, where you can make modifications It's a proprietary vendor blob supplied by Oneplus. All we can do is try a similar blob from other devices or just remove it. By the way, Oneplus 9 vendor doesn't have this blob, so, it is possible that it's not needed at all.
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  • 10
    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
    2
    Also, if you disable OEM unlock, that's pretty secure, but if something goes wrong with your phone, i.e., you can't boot in recovery and system, the only way to restore the phone is flashing with MSM tool. I had it once on my Oneplus 5. I had a paranoid TWRP, with Cancel button removed. So, all of a sudden, TWRP refused to recognize my password. So, you can't press cancel to access system to do a factory reset. All right, I thought, I am just going to boot into system and enable OEM unlock. Well, no can do: the phone refused to boot into system and instead booted into TWRP with the password prompt. Bootloader locked, remote flashing is not allowed. The only option - MSM tool. I set up Windows on my virtual machine, but forget it, MSM tool can't connect to the phone no matter what I tried. So, I had to find on old laptop with Windows and then it worked... .
    Correct, once OEM unlocking is disabled, just like with OxygenOS, if something goes horribly wrong, you're using MSM to get back to stock and re-installing.

    I don't use TWRP, and build both LineageOS and Lineage Recovery in user mode. Building recvoery in user mode (and only with my certificates) also means you can't "rollback" to an older version of Lineage as it won't flash older zips.

    As I said in my reddit post, most people don't really want to do this. Too much risk, too little reward. But if you're wiling to take the risk, you do get as close to a "stock" security footprint as you can without using the OEM's OS.
    2
    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
    thanks for the guide. ps regarding the path requirements and the absolutely annoying signapk.jar issues when on the signing step, one can simple add a flag to the command like so
    Code:
    ./build/tools/releasetools/sign_target_files_apks -p out/host/linux-x86/ -o -d ~/.android-certs $OUT/obj/PACKAGING/target_files_intermediates/*-target_files-*.zip signed-target_files.zip
    the addition of -p out/host/linux-x86/ takes care of the pathing issues
    If anyone runs into the unicode encoding error with common.py, run repopick 305886
    which will cherry-pick https://review.lineageos.org/c/LineageOS/android_build/+/305886 and fix that error.

    Aside from those 2 things, (y) 🍻
    2
    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.
    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