Technology

That’s true today, but there’s no guarantee it will be true in the future.

It's in the specification.

The platform key establishes a trust relationship between the platform owner and the platform firmware. The platform owner enrolls the public half of the key (PKpub) into the platform firmware. The platform owner can later use the private half of the key (PKpriv) to change platform ownership or to enroll a Key Exchange Key. See “Enrolling The Platform Key” and “Clearing The Platform Key” for more information.

The platform owner clears the public half of the Platform Key (PKpub) by deleting the Platform Key variable using UEFI Runtime Service SetVariable(). The data buffer submitted to the SetVariable() must be signed with the current PKpriv - see Variable Services for details. The name and GUID of the Platform Key variable are specified in Globally Defined Variables. The platform key may also be cleared using a secure platform-specific method. When the platform key is cleared, the global variable SetupMode must also be updated to 1.

It's a matter of clearing the platform key & enrolling your own platform key. I've done this before.

Typically, computers with Secure Boot let us clear the platform key from the boot menu. (You can choose to purchase only those that do.) Some computer vendors ship Secure Boot in setup mode or let the customer provide public keys to ship preloaded.

Secure Boot has always been for enabling the owner to enforce integrity of the boot process through cryptographic signatures. Linus Torvalds thought the feature makes sense.

Linus: I actually think secure boot makes a lot of sense. I think we should sign our modules. I think we should use the technology to do cryptographic signatures to add security; and at the same time inside the open source community this is so unpopular that people haven’t really worked on it.

It’s true that secure boot can be used for horribly, horribly bad things but using that as an argument against its existence at all is I think a bit naive and not necessarily right. Because if you do things right then it’s a really good thing. I would like my own machine to have the option to not boot any kernel, or boot loader, that is not signed by this signature.

I have seen some platforms locked to Microsoft first party keys only. They boiled the frog by starting with it being optional, able to enroll your own keys, and Microsoft signing third party bootloaders, but now there exists a Microsoft-only certificate regime that at least some vendors have selected, or at least made a selectable option. The pitch being that Windows shops that don't trust their users can be assured they aren't deviating from the blessed windows os their IT trusts.