[Problem] How to get a modified BIOS accepted while Flashing it?

BIOS/UEFI Modding BIOS Modding Guides and Problems
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According to this post confidentiality - Do anti-cheat software actually "patch" the UEFI firmware on your motherboard? - Information Security Stack Exchange

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if updating the firmware it needs to be signed before it can be installed onto the motherboard. This can prevent even anti-cheats from writing into the firmware of the motherboard if I understand correctly?

So if this is the case then how do you guys end up modifying the bios firmware and install it into your motherboards if this check should prevent it?


Edit by Fernando: Thread title shortened and customized
(Original title: If mothernoard manufacturers require signed binary before it can overwrite to uefi how do you guys make custom uefi?)

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Nobody except the mainboard manufacturer is able to give a customized BIOS a valid signature.
Nevertheless it is possible to get a modified BIOS properly flashed.
>Here< is a Guide about how to circumvent the BIOS protection, which is done by nearly all mainboard manufacturers.

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I see mate. I am kinda worried that anti cheats can overwrite the uefi firmware on hte motherboard since it has complete access to the kernel.