linux-kernel - Re: [PATCH v2 1/4] x86: KVM: SVM: always update the x2avic msr interception

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Date:   Thu, 28 Sep 2023 17:24:18 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, iommu@...ts.linux.dev,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        x86@...nel.org,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Robin Murphy <robin.murphy@....com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/4] x86: KVM: SVM: always update the x2avic msr interception

On Thu, Sep 28, 2023, Maxim Levitsky wrote:
> The following problem exists since x2avic was enabled in the KVM:
> 
> svm_set_x2apic_msr_interception is called to enable the interception of

Nit, svm_set_x2apic_msr_interception().

Definitely not worth another version though.

> the x2apic msrs.
> 
> In particular it is called at the moment the guest resets its apic.
> 
> Assuming that the guest's apic was in x2apic mode, the reset will bring
> it back to the xapic mode.
> 
> The svm_set_x2apic_msr_interception however has an erroneous check for
> '!apic_x2apic_mode()' which prevents it from doing anything in this case.
> 
> As a result of this, all x2apic msrs are left unintercepted, and that
> exposes the bare metal x2apic (if enabled) to the guest.
> Oops.
> 
> Remove the erroneous '!apic_x2apic_mode()' check to fix that.
> 
> This fixes CVE-2023-5090
> 
> Fixes: 4d1d7942e36a ("KVM: SVM: Introduce logic to (de)activate x2AVIC mode")
> Cc: stable@...r.kernel.org
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>