linux-kernel - Re: [PATCH] KVM: X86: Raise #GP when clearing CR0

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Message-ID: <51bb6e75-4f0a-e544-d2e4-ff23c5aa2f49@redhat.com>
Date:   Thu, 9 Dec 2021 18:55:05 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] KVM: X86: Raise #GP when clearing CR0_PG in 64 bit mode

On 12/7/21 10:52, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@...ux.alibaba.com>
> 
> In the SDM:
> If the logical processor is in 64-bit mode or if CR4.PCIDE = 1, an
> attempt to clear CR0.PG causes a general-protection exception (#GP).
> Software should transition to compatibility mode and clear CR4.PCIDE
> before attempting to disable paging.
> 
> Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
> ---
>   arch/x86/kvm/x86.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 00f5b2b82909..78c40ac3b197 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -906,7 +906,8 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>   	    !load_pdptrs(vcpu, kvm_read_cr3(vcpu)))
>   		return 1;
>   
> -	if (!(cr0 & X86_CR0_PG) && kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE))
> +	if (!(cr0 & X86_CR0_PG) &&
> +	    (is_64_bit_mode(vcpu) || kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE)))
>   		return 1;
>   
>   	static_call(kvm_x86_set_cr0)(vcpu, cr0);
> 

Queued, thanks.

Paolo