linux-kernel - Re: [PATCH 0/7] KVM: x86: expose CVE-2017-5715 ("Spectre variant 2") mitigations to guest

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Date:   Tue, 9 Jan 2018 12:12:00 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        jmattson@...gle.com, aliguori@...zon.com, thomas.lendacky@....com,
        dwmw@...zon.co.uk, bp@...en8.de
Subject: Re: [PATCH 0/7] KVM: x86: expose CVE-2017-5715 ("Spectre variant 2")
 mitigations to guest

On 09/01/2018 11:15, Thomas Gleixner wrote:
> On Mon, 8 Jan 2018, Paolo Bonzini wrote:
> 
>> This series allows guests to use the MSR_IA32_SPEC_CTRL and
>> MSR_IA32_PRED_CMD model specific registers that were added as mitigations
>> for CVE-2017-5715.
>>
>> These are only the KVM specific parts of the fix.  It does *not* yet
>> include any protection for reading host memory from the guest, because
>> that would be done in the same way as the rest of Linux.  So there is no
>> IBRS *usage* here, no retpolines, no stuffing of the return stack buffer.
>> (KVM already includes a fix to clear all registers on vmexit, which is
>> enough to block Google Project Zero's PoC exploit).
>>
>> However, I am including the changes to use IBPB (indirect branch
>> predictor barrier) if available.  That occurs only when there is a VCPU
>> switch on a physical CPU, thus it has a small impact on performance.
>>
>> The patches are a bit hackish because the relevant cpufeatures have
>> not been included yet, and because I wanted to make the patches easier
>> to backport to distro kernels if desired, but I would still like to
>> have them in 4.16.
>>
>> Please review.
> 
> CC'ing x86@...nel.org on this would have been asked too much, right?

Sorry, my mistake.  I'll CC you on v2.

Paolo