Messages in this thread | | | Date | Tue, 16 Aug 2022 16:51:49 +0000 | From | Ashok Raj <> | Subject | Re: [PATCH] x86/microcode/AMD: Attempt applying on every logical thread |
| |
On Tue, Aug 16, 2022 at 02:41:39PM +0200, Borislav Petkov wrote: > On Tue, Aug 16, 2022 at 09:00:14AM +0000, Ashok Raj wrote: > > A re-application means, you want to apply even if the cpu_rev <= patch.rev > > Yes.
I see, so we probably shouldn't remove the rev check completely but just permit to reload if the rev is equal?
> > > if cpu_rev is > patch_rev, clearly its ahead?. say BIOS has a newer > > version than in the initrd image, do we want to replace the BIOS > > version since we do no revid checks here. > > Can you even downgrade the microcode through the MSR?
I'm not sure what is true for AMD.
For Intel's there is a Security Version Number in the signed encrypted part of the microcode. As long as the new image has SVN >= what the CPU's SVN is you can update the microcode.
So if a rev2 is loaded, and rev1 is the new MCU, and rev2 and rev1 have the same SVN, you can go down rev from rev2->rev1 where rev2 > rev1.
Microcode enforcement for rollback protection has been the SVN. Version number is a SW feel good thing to identifying which image you are running, not intended for preventing rollback or any security enforcement.
Cheers, Ashok
| |