linux-kernel - Re: [PATCH 07/14] KVM: x86: SVM: add warning for CVE-2021-3656

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Date:   Tue, 12 Oct 2021 10:51:07 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>, kvm@...r.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>, Bandan Das <bsd@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        Wei Huang <wei.huang2@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH 07/14] KVM: x86: SVM: add warning for CVE-2021-3656

On Tue, 2021-10-12 at 01:30 +0800, Xiaoyao Li wrote:
> On 9/14/2021 11:48 PM, Maxim Levitsky wrote:
> > Just in case, add a warning ensuring that on guest entry,
> > either both VMLOAD and VMSAVE intercept is enabled or
> > vVMLOAD/VMSAVE is enabled.
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> > ---
> >   arch/x86/kvm/svm/svm.c | 6 ++++++
> >   1 file changed, 6 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index 861ac9f74331..deeebd05f682 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -3784,6 +3784,12 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
> >   
> >   	WARN_ON_ONCE(kvm_apicv_activated(vcpu->kvm) != kvm_vcpu_apicv_active(vcpu));
> >   
> > +	/* Check that CVE-2021-3656 can't happen again */
> > +	if (!svm_is_intercept(svm, INTERCEPT_VMSAVE) ||
> > +	    !svm_is_intercept(svm, INTERCEPT_VMSAVE))
> 
> either one needs to be INTERCEPT_VMLOAD, right?

Oops! Of course.

Best regards,
	Maxim Levitsky
> 
> > +		WARN_ON(!(svm->vmcb->control.virt_ext &
> > +			  VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK));
> > +
> >   	sync_lapic_to_cr8(vcpu);
> >   
> >   	if (unlikely(svm->asid != svm->vmcb->control.asid)) {
> >