tree 6bde9bdf4bacb4aedc78fbca49dad5dd0ed184e7
parent 8f849ff63bcbc77670da03cb8f2b78b06257f455
author Thomas Gleixner <tglx@linutronix.de> 1697577856 +0200
committer Borislav Petkov (AMD) <bp@alien8.de> 1698152755 +0200

x86/microcode: Prepare for minimal revision check

Applying microcode late can be fatal for the running kernel when the
update changes functionality which is in use already in a non-compatible
way, e.g. by removing a CPUID bit.

There is no way for admins which do not have access to the vendors deep
technical support to decide whether late loading of such a microcode is
safe or not.

Intel has added a new field to the microcode header which tells the
minimal microcode revision which is required to be active in the CPU in
order to be safe.

Provide infrastructure for handling this in the core code and a command
line switch which allows to enforce it.

If the update is considered safe the kernel is not tainted and the annoying
warning message not emitted. If it's enforced and the currently loaded
microcode revision is not safe for late loading then the load is aborted.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231017211724.079611170@linutronix.de