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Subject: Re: [PATCH] KVM: x86: Inject #GP if guest attempts to toggle CR4.LA57
 in 64-bit mode
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Sebastien Boeuf <sebastien.boeuf@intel.com>
References: <20200703021714.5549-1-sean.j.christopherson@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <b5d05192-08ea-1915-03b2-e2c7b6337b74@redhat.com>
Date:   Fri, 3 Jul 2020 18:16:03 +0200
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On 03/07/20 04:17, Sean Christopherson wrote:
> Inject a #GP on MOV CR4 if CR4.LA57 is toggled in 64-bit mode, which is
> illegal per Intel's SDM:
> 
>   CR4.LA57
>     57-bit linear addresses (bit 12 of CR4) ... blah blah blah ...
>     This bit cannot be modified in IA-32e mode.
> 
> Note, the pseudocode for MOV CR doesn't call out the fault condition,
> which is likely why the check was missed during initial development.
> This is arguably an SDM bug and will hopefully be fixed in future
> release of the SDM.
> 
> Fixes: fd8cb433734ee ("KVM: MMU: Expose the LA57 feature to VM.")
> Cc: stable@vger.kernel.org
> Reported-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/x86.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 00c88c2f34e4..2bb48896dbdc 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -975,6 +975,8 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  	if (is_long_mode(vcpu)) {
>  		if (!(cr4 & X86_CR4_PAE))
>  			return 1;
> +		if ((cr4 ^ old_cr4) & X86_CR4_LA57)
> +			return 1;
>  	} else if (is_paging(vcpu) && (cr4 & X86_CR4_PAE)
>  		   && ((cr4 ^ old_cr4) & pdptr_bits)
>  		   && !load_pdptrs(vcpu, vcpu->arch.walk_mmu,
> 

Queued, thanks.

Paolo