linux-kernel - Re: [PATCH v2 5/5] KVM: s390: vsie: Do the CRYCB validation first

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Message-Id: <01047750-cdc6-b462-1e4f-c79c1036ab94@linux.ibm.com>
Date:   Thu, 23 Aug 2018 09:17:38 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, cohuck@...hat.com,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        frankja@...ux.ibm.com, akrowiak@...ux.ibm.com,
        borntraeger@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH v2 5/5] KVM: s390: vsie: Do the CRYCB validation first

On 22/08/2018 19:15, David Hildenbrand wrote:
> On 22.08.2018 18:51, Pierre Morel wrote:
>> When entering the SIE the CRYCB validation better
>> be done independently of the instruction's
>> availability.
>>
>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>> ---
>>   arch/s390/kvm/vsie.c | 11 ++++++-----
>>   1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
>> index 7ee4329..fca25aa 100644
>> --- a/arch/s390/kvm/vsie.c
>> +++ b/arch/s390/kvm/vsie.c
>> @@ -164,17 +164,18 @@ static int shadow_crycb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>>   	/* format-1 is supported with message-security-assist extension 3 */
>>   	if (!test_kvm_facility(vcpu->kvm, 76))
>>   		return 0;
>> -	/* we may only allow it if enabled for guest 2 */
>> -	ecb3_flags = scb_o->ecb3 & vcpu->arch.sie_block->ecb3 &
>> -		     (ECB3_AES | ECB3_DEA);
>> -	if (!ecb3_flags)
>> -		return 0;
>>   
>>   	if ((crycb_addr & PAGE_MASK) != ((crycb_addr + 128) & PAGE_MASK))
>>   		return set_validity_icpt(scb_s, 0x003CU);
>>   	if (!crycb_addr)
>>   		return set_validity_icpt(scb_s, 0x0039U);
>>   
>> +	/* we may only allow it if enabled for guest 2 */
>> +	ecb3_flags = scb_o->ecb3 & vcpu->arch.sie_block->ecb3 &
>> +		     (ECB3_AES | ECB3_DEA);
>> +	if (!ecb3_flags)
>> +		return 0;
>> +
>>   	/* copy only the wrapping keys */
>>   	if (read_guest_real(vcpu, crycb_addr + 72,
>>   			    vsie_page->crycb.dea_wrapping_key_mask, 56))
>>
> 
> That makes sense, especially if ECB3_AES is used but effectively turned
> off by us.
> 
> What is the expected behavior if ECB3_AES | ECB3_DEA are not set by g2
> for g3?
> 

The use of functions PCKMO-Encrypt-DEA/AES induce a specification error.

However other MSA3 function will continue to be usable.

Regards,
Pierre

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany