linux-kernel - RE: [RFC] Randomness on confidential computing platforms

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Date: Mon, 29 Jan 2024 07:15:05 +0000
From: "Reshetova, Elena" <elena.reshetova@...el.com>
To: Nikolay Borisov <nik.borisov@...e.com>,
	Daniel P. Berrangé <berrange@...hat.com>
CC: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Thomas Gleixner
	<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
	<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin"
	<hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>, Theodore Ts'o
	<tytso@....edu>, "Jason A. Donenfeld" <Jason@...c4.com>, "Kuppuswamy
 Sathyanarayanan" <sathyanarayanan.kuppuswamy@...ux.intel.com>, "Nakajima,
 Jun" <jun.nakajima@...el.com>, Tom Lendacky <thomas.lendacky@....com>,
	"Kalra, Ashish" <ashish.kalra@....com>, Sean Christopherson
	<seanjc@...gle.com>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [RFC] Randomness on confidential computing platforms


> On 26.01.24 г. 17:57 ч., Daniel P. Berrangé wrote:
> > If the CPU performance counters could report RDRAND exhaustion directly,
> > then the host admin could trust that information and monitor it, but the
> > host shouldn't rely on the (hostile) guest software to tell it about
> 
> I guess it really depends on the POV - from the POV of an encrypted
> guest the VMM is hostile so we ideally don't like to divulge more
> information than is absolutely necessary.
> 
> OTOH, from the POV of the VMM we could say that the guest could be
> running anything and so a facility like that could cause some confusion
> on the VMM site.
> 
> I think it would be very hard to reconcile the 2 views.

I agree that both views need to be taken into account, and in the confidential
computing threat model nobody has removed the possibility that a CoCo guest
can be malicious. So any action VMM is about to take has to be considered
carefully. We were not prescribing any action here, just asking if VMM would
want to have such a control/option. But since Sean clearly doesn’t find this
approach viable, we will drop the VMM-based option. 

Best Regards,
Elena.