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

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Message-ID: <23912b0c-832a-fb68-adb9-f82779659d22@amd.com>
Date:   Tue, 3 Oct 2023 10:17:53 +0700
From:   "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        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, 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

Maxim,

Thanks for finding and fixing this.

On 9/29/2023 7:24 AM, Sean Christopherson wrote:
> 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>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>