From: Sean Christopherson <seanjc@google.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Pu Wen <puwen@hygon.cn>, Joerg Roedel <jroedel@suse.de>,
x86@kernel.org, joro@8bytes.org, thomas.lendacky@amd.com,
dave.hansen@linux.intel.com, peterz@infradead.org,
tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com,
sashal@kernel.org, gregkh@linuxfoundation.org,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] x86/sev: Check whether SEV or SME is supported first
Date: Tue, 1 Jun 2021 16:14:22 +0000 [thread overview]
Message-ID: <YLZc3sFKSjpd2yPS@google.com> (raw)
In-Reply-To: <YLZGuTYXDin2K9wx@zn.tnic>
On Tue, Jun 01, 2021, Borislav Petkov wrote:
> On Mon, May 31, 2021 at 10:56:50PM +0800, Pu Wen wrote:
> > Thanks for your suggestion, I'll try to set up early #GP handler to fix
> > the problem.
>
> Why? AFAICT, you only need to return early in sme_enable() if CPUID is
> not "AuthenticAMD". Just do that please.
I don't think that would suffice, presumably MSR_AMD64_SEV doesn't exist on older
AMD CPUs either. E.g. there's no mention of MSR 0xC001_0131 in the dev's guide
from 2015[*].
I also don't see the point in checking the vendor string. A malicious hypervisor
can lie about CPUID.0x0 just as easily as it can lie about CPUID.0x8000001f, so
for SEV the options are to either trust the hypervisor or eat #GPs on RDMSR for
non-SEV CPUs. If we go with "trust the hypervisor", then the original patch of
hoisting the CPUID.0x8000001f check up is simpler than checking the vendor string.
[*] https://www.amd.com/system/files/TechDocs/48751_16h_bkdg.pdf
next prev parent reply other threads:[~2021-06-01 16:14 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-26 7:24 [PATCH] x86/sev: Check whether SEV or SME is supported first Pu Wen
2021-05-26 17:27 ` Sean Christopherson
2021-05-27 15:08 ` Pu Wen
2021-05-31 9:37 ` Joerg Roedel
2021-05-31 14:56 ` Pu Wen
2021-06-01 14:39 ` Borislav Petkov
2021-06-01 16:14 ` Sean Christopherson [this message]
2021-06-01 16:36 ` Tom Lendacky
2021-06-01 16:59 ` Borislav Petkov
2021-06-01 17:16 ` Sean Christopherson
2021-06-01 17:48 ` Borislav Petkov
2021-06-01 18:08 ` Sean Christopherson
2021-06-01 18:24 ` Borislav Petkov
2021-06-01 17:09 ` Sean Christopherson
2021-06-01 18:30 ` Tom Lendacky
2021-06-02 6:55 ` Wen Pu
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