From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.skyhub.de (mail.skyhub.de [5.9.137.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D4AB12C81 for ; Thu, 21 Oct 2021 16:55:17 +0000 (UTC) Received: from zn.tnic (p200300ec2f1912009d2c3fdc96041a10.dip0.t-ipconnect.de [IPv6:2003:ec:2f19:1200:9d2c:3fdc:9604:1a10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id D38931EC01A2; Thu, 21 Oct 2021 18:55:15 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1634835316; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=NZC8US/Sv4tJlK40hZBif2dVgLRnPir3aaoTZ1GDAZU=; b=WHEsNVOkCfiljBtHQ+4j3sgg9oxZ3XZ72tD3ReWZxsnZaE/K+hn3pPlrNc4ezF6zzThzeP 8uO+2w9FCg5R7ThkyJVSmryvGtbiYy6FJ/oU2mo0Q79kmHu9yDrhX6FkfpM7SaeFV28BYj 780hS9v0CwyRqL9Zmq9JMbWXRvTUsWM= Date: Thu, 21 Oct 2021 18:55:14 +0200 From: Borislav Petkov To: "Dr. David Alan Gilbert" Cc: Michael Roth , Brijesh Singh , x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, Thomas Gleixner , Ingo Molnar , Joerg Roedel , Tom Lendacky , "H. Peter Anvin" , Ard Biesheuvel , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Jim Mattson , Andy Lutomirski , Dave Hansen , Sergio Lopez , Peter Gonda , Peter Zijlstra , Srinivas Pandruvada , David Rientjes , Dov Murik , Tobin Feldman-Fitzthum , Vlastimil Babka , "Kirill A . Shutemov" , Andi Kleen , tony.luck@intel.com, marcorr@google.com, sathyanarayanan.kuppuswamy@linux.intel.com Subject: Re: [PATCH v6 08/42] x86/sev-es: initialize sev_status/features within #VC handler Message-ID: References: <20211008180453.462291-1-brijesh.singh@amd.com> <20211008180453.462291-9-brijesh.singh@amd.com> <20211018184003.3ob2uxcpd2rpee3s@amd.com> <20211020161023.hzbj53ehmzjrt4xd@amd.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Thu, Oct 21, 2021 at 04:56:09PM +0100, Dr. David Alan Gilbert wrote: > I can imagine a malicious hypervisor trying to return different cpuid > answers to different threads or even the same thread at different times. Haha, I guess that will fail not because of SEV* but because of the kernel not really being able to handle heterogeneous CPUIDs. > Well, the spec (AMD 56860 SEV spec) says: > > 'If firmware encounters a CPUID function that is in the standard or extended ranges, then the > firmware performs a check to ensure that the provided output would not lead to an insecure guest > state' > > so I take that 'firmware' to be the PSP; that wording doesn't say that > it checks that the CPUID is identical, just that it 'would not lead to > an insecure guest' - so a hypervisor could hide any 'no longer affected > by' flag for all the CPUs in it's migration pool and the firmware > shouldn't complain; so it should be OK to pessimise. AFAIU this, I think this would depend on "[t]he policy used by the firmware to assess CPUID function output can be found in [PPR]." So if the HV sets the "no longer affected by" flag but the firmware deems this set flag as insecure, I'm assuming the firmare will clear it when it returns the CPUID leafs. I guess I need to go find that policy... -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette