linux-kernel - Re: [PATCH v1 1/4] KVM: MMU: check guest CR3 reserved bits based on its physical address width.

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Date:   Mon, 14 Aug 2017 09:36:59 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rkrcmar@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        xiaoguangrong@...cent.com, joro@...tes.org
Subject: Re: [PATCH v1 1/4] KVM: MMU: check guest CR3 reserved bits based on
 its physical address width.

On 12/08/2017 15:35, Yu Zhang wrote:
> +			ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL, NULL);
> +			maxphyaddr = eax * 0xff;

This is "&", not "*".  You can also use rsvd_bits here.

> +			rsvd = (~((1UL << maxphyaddr) - 1)) &
> +				~CR3_PCID_INVD;
> +		}
>  
>  		if (new_val & rsvd)
>  			return emulate_gp(ctxt, 0);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e40a779..d9100c4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -813,10 +813,10 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
>  		return 0;
>  	}
>  
> -	if (is_long_mode(vcpu)) {
> -		if (cr3 & CR3_L_MODE_RESERVED_BITS)
> -			return 1;
> -	} else if (is_pae(vcpu) && is_paging(vcpu) &&
> +	if (is_long_mode(vcpu) &&
> +	    (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 63)))
> +		return 1;

62 is a little better, since 63 is the PCID invalidate bit.

Paolo

> +	else if (is_pae(vcpu) && is_paging(vcpu) &&
>  		   !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3))
>  		return 1;
>