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

[Sean Christopherson]

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@xxxxxxxxxxxxxxx
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> ---

Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>