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Historically I've always unlocked the bootloader on my phones (and installed a close to AOSP ROM and made use of root access) - however - and I bristle at the thought - I am almost at the point where the cons of unlocking the bootloader may exceed the pros.

If I purchase a phone, use it with a locked bootloader, and the firmware then gets upgraded - is it possible for the upgrade to remove the ability to unlock the bootloader? (My thinking is probably not, and anyway I should be able to downgrade the firmware - however in a world of efuses and software patches to hardware defects I'm not sure).

(Its almost peripheral to my question, but I'm probably looking at a OnePlus 12 or Nothing Phone 2A phone)

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Yes this is not only possible but had already happened several times: Huawei and Asus and most likely many more. Regarding the Asus case, there was just recently something in the press because a dissatisfied user took Asus to court because of the removed bootloader unlock.

For Huawei, as far as I remember, several years ago there was an unlocking service provided by Huawei where you could retrieve an unlocking key that allowed for you to unlock the bootloader of your device. Some day Huawei shut down this service...

Also, downgrading will not help in such a case, as the ability to downgrade a bootloader (if it works at all) can also be removed at any time. I had such a case with a Pixel device where Google even noticed the user that by installing a certain bootloader version a downgrade of the bootloader would be impossible (and with it a downgrade of the Android version).

In conclusion, one can say that on a bootloader locked device you can only perform those operations the company who controls the software allows you to do (not considering vulnerabilities and exploits). In certain cases, this can even happen without any change to the device.

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  • Thank you! This is informative and fleshes out my understanding. I did not tick accept yet as most of the supporting links are around taking away tools required to unlock a bootloader (not an issue in the case of my phone candidates, and not actually related to flashing, and something I was aware of). The link about the Pixel was more interesting and much closer to ,y question - but did not mention locking the boot loader - only preventing OS downgrades - still - reasonable inferences can be made that it could be possible to prevent locking the bootloader based on the technologies used.
    – davidgo
    Commented Apr 15 at 21:04
  • @davidgo May be I picked the wrong article, but from what I remember the OS downgrade prevention is enforced by the bootloader, thus the OS downgrade prevention implies a bootloader downgrade prevention.
    – Robert
    Commented Apr 15 at 21:37
  • Agreed. My question (and based on your answer I think the answer may well be yes) is can changes to the bootloader prevent unlocking it. Ie is the bootloader lock part of the bootloader?
    – davidgo
    Commented Apr 15 at 23:23
  • @davidgo Google/Android does not define anything regarding the bootloader, so the botloader can be implemented just like manufacturer want's it to be. Therefore the bootloader lock part can be part of the bootloader and it can be outside, just as the manufacturer decides.
    – Robert
    Commented Apr 16 at 7:28

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