This is not an issue specific to Linux, Windows installations can be downgraded as well. As for the mechanism, UEFI devices, alongside key updates, also get revocation list updates.
Strangely I feel like I've never seen one of these. It would be needed after every major kernel / user land exploit. It would also need rollback protection on the motherboard itself so you couldn't just remove the updated keys / revocations.
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This is not an issue specific to Linux, Windows installations can be downgraded as well. As for the mechanism, UEFI devices, alongside key updates, also get revocation list updates.
Strangely I feel like I've never seen one of these. It would be needed after every major kernel / user land exploit. It would also need rollback protection on the motherboard itself so you couldn't just remove the updated keys / revocations.