Re: [PATCH 4.19 72/98] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h

Thomas Gleixner
2019-08-28T10:47:38Z

Pavel,

On Wed, 28 Aug 2019, Pavel Machek wrote:
> On Tue 2019-08-27 15:30:30, Thomas Gleixner wrote:
> > There is no way to reinitialize RDRAND from the kernel otherwise we would
> > have exactly done that. If you know how to do that please tell.
>
> Would they? AMD is not exactly doing good job with communication

Yes they would. Stop making up weird conspiracy theories.

> here. If BIOS can do it, kernel can do it, too...

May I recommend to read up on SMM and BIOS being able to lock down access
to certain facilities?

> or do you have information saying otherwise?

Yes. It was clearly stated by Tom that it can only be done in the BIOS.

> > Also disabling it for every BIOS is the only way which can be done because
> > there is no way to know whether the BIOS is fixed or not at cold boot
> > time. And it has to be known there because applications cache the
>
> I'm pretty sure DMI-based whitelist would help here. It should be
> reasonably to fill it with the common machines at least.

Send patches to that effect.

> Plus, where is the CVE, and does AMD do anything to make BIOS vendors
> fix them?

May I redirect you to: https://www.amd.com/en/corporate/contact

Thanks,

tglx