linux-kernel - Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED

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Message-ID: <1515604047.22302.218.camel@infradead.org>
Date:   Wed, 10 Jan 2018 17:07:27 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Liran Alon <liran.alon@...cle.com>
Cc:     jmattson@...gle.com, konrad.wilk@...cle.com, x86@...nel.org,
        nadav.amit@...il.com, bp@...en8.de, arjan@...ux.intel.com,
        aliguori@...zon.com, thomas.lendacky@....com, rkrcmar@...hat.com,
        pbonzini@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and
 MSR_IA32_PRED_CMD down to the guest

On Wed, 2018-01-10 at 08:51 -0800, Liran Alon wrote:
> 
> Hmm... This is exactly how Google Project-Zero PoC leaks kvm-
> intel.ko, kvm.ko & vmlinux...
> See section "Locating the host kernel" here:
> https://googleprojectzero.blogspot.co.il/2018/01/reading-privileged-m
> emory-with-side.html
> 
> This was an important primitive in order for them to actually launch
> the attack of reading host's memory pages. As they needed the
> hypervisor addresses such that they will be able to later poison the
> BTB/BHB to gadgets residing in known host addresses.

Ah, joy. I'm not sure that leak is being plugged. Even setting IBRS=1
when entering the guest isn't guaranteed to plug it, as it's only
defined to prevent predictions from affecting a *more* privileged
prediction mode than they were 'learned' in.

Maybe IBPB would suffice? I'm not sure.
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