Re: [PATCH] x86/cpuid: Fix up "virtual" IBRS/IBPB/STIBP feature bits on Intel

[Arjan van de Ven <arjan@linux.intel.com>]

On 1/30/2018 5:11 AM, Borislav Petkov wrote:
> On Tue, Jan 30, 2018 at 01:57:21PM +0100, Thomas Gleixner wrote:
>> So much for the theory. That's not going to work. If the boot cpu has the
>> feature then the alternatives will have been applied. So even if the flag
>> mismatch can be observed when a secondary CPU comes up the outcome will be
>> access to a non existing MSR and #GP.
> 
> Yes, with mismatched microcode we're f*cked.

I think in the super early days of SMP there was an occasional broken BIOS.
(and when Linux then did the ucode update it was sane again)

Not since a long time though (I think the various certification suites check for it now)

> 
> So my question is: is there such microcode out there or is this
> something theoretical which we want to address?

at this point it's insane theoretical; no OS can actually cope with this, so
if you're an OEM selling this, your customer can run zero OSes ;-)


> 
> (.. and adressing this will be ugly, no matter what.)
> 
> And if I were able to wish, I'd like to blacklist that microcode in
> dracut so that it doesn't come anywhere near my system.

I'm not sure what you'd want dracut to do... panic() the system
on such a bios?