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

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Message-ID: <alpine.DEB.2.21.1908281231480.1869@nanos.tec.linutronix.de>
Date:   Wed, 28 Aug 2019 12:47:10 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Pavel Machek <pavel@...x.de>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>,
        Borislav Petkov <bp@...e.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chen Yu <yu.c.chen@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 4.19 72/98] x86/CPU/AMD: Clear RDRAND CPUID bit on AMD
 family 15h/16h

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