linux-kernel - Re: [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be disabled in the guest

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Date:   Tue, 4 May 2021 21:26:53 -0700
From:   Reiji Watanabe <reijiw@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be
 disabled in the guest

On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Intercept RDTSCP to inject #UD if RDTSC is disabled in the guest.
>
> Note, SVM does not support intercepting RDPID.  Unlike VMX's
> ENABLE_RDTSCP control, RDTSCP interception does not apply to RDPID.  This
> is a benign virtualization hole as the host kernel (incorrectly) sets
> MSR_TSC_AUX if RDTSCP is supported, and KVM loads the guest's MSR_TSC_AUX
> into hardware if RDTSCP is supported in the host, i.e. KVM will not leak
> the host's MSR_TSC_AUX to the guest.
>
> But, when the kernel bug is fixed, KVM will start leaking the host's
> MSR_TSC_AUX if RDPID is supported in hardware, but RDTSCP isn't available
> for whatever reason.  This leak will be remedied in a future commit.
>
> Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Reiji Watanabe <reijiw@...gle.com>