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

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Message-ID: <76848d3f-3eda-f8cb-ab3c-366c302c757b@redhat.com>
Date:   Tue, 9 Jan 2018 15:06:14 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        jmattson@...gle.com, aliguori@...zon.com, thomas.lendacky@....com,
        dwmw@...zon.co.uk, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 0/7] KVM: x86: expose CVE-2017-5715 ("Spectre variant 2")
 mitigations to guest

On 09/01/2018 13:03, Thomas Gleixner wrote:
> On Tue, 9 Jan 2018, Paolo Bonzini wrote:
>> 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.
> 
> We really want to coordinate that proper with the ongoing integration of
> the IB** for bare metal.

Yes, this can get merged to master together with the bare-metal parts.
If, as I expect, the -rc rules will be be bent a bit for IB** (and
perhaps retpolines too) in 4.16, we have some time to sort it out.

Thanks,

Paolo

> And that stuff really does not need to be hackish at all. We've spent a lot
> of effort keeping all of it clean _AND_ available for 4.14 stable
> consumption. Everything before 4.9 is a big fricking and incompatible mess
> anyway.