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

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Message-ID: <93d301f3-7fdc-866c-a140-4afe0c0a8dab@linux.intel.com>
Date:   Mon, 14 Aug 2017 19:39:01 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.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 8/14/2017 3:36 PM, Paolo Bonzini wrote:
> 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.

Oops. Sorry for the typo. :-)

>> +			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.

Got it. Both kvm_set_cr3() and check_cr_write() should use 
rsvd_bits(maxphyaddr, 62) .

Thanks
Yu

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