Gary Ching-Pang Lin of SuSE has submitted a proposal for Linux kernel and Shim to include a Security Version. In addition to below shim wiki page, there is active discussion on this on the Linux-EFI list.
When a vulnerability is found, every distro will release the patch as soon as possible and push it into the update channel. However, since the signature of the old kernel is still valid, the attacker may trick the user to boot the old and insecure kernel to exploit the system. For the system with UEFI Secure Boot, although the admin can add the hashes of the insecure kernels into MokX, it could be burdensome to do this in large scale. Besides, it’s almost impossible to obsolete the kernels before a certain version. Not to mention that the old kernel sometimes might be useful for debugging. To keep the system secure and also flexible, we propose “Security Version”. The basic concept of Security Version is to use a whitelist to record the “version” of the latest known secure linux kernel. If the “version” of the kernel is lower than that in the whitelist, then the kernel is considered as “not secure”. The “version” in the whitelist can only be incremented monotonically unless the user decides to lower it.[…]
PS: Hmm, Gmane’s linux-efi links aren’t working for me.