linux-kernel - Re: [PATCH v1] KVM: s390: vsie: fix Do the CRYCB validation first

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Message-Id: <206f8cb5-2be8-9c54-eafb-1a050e71aebc@linux.ibm.com>
Date:   Mon, 4 Feb 2019 17:17:30 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>, borntraeger@...ibm.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, pasic@...ux.ibm.com,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>
Subject: Re: [PATCH v1] KVM: s390: vsie: fix Do the CRYCB validation first

On 04/02/2019 16:15, David Hildenbrand wrote:
> On 01.02.19 14:37, Pierre Morel wrote:
>> On 01/02/2019 11:56, David Hildenbrand wrote:
>>> On 01.02.19 10:52, Pierre Morel wrote:
>>>> The case when the SIE for guest3 is not setup for using
>>>> encryption keys nor Adjunct processor but the guest2
>>>> does use these features was not properly handled.
>>>>
>>>> This leads SIE entry for guest3 to crash with validity intercept
>>>> because the guest2, not having the use of encryption keys nor
>>>> Adjunct Processor did not initialize the CRYCB designation.
>>>>
>>>> In the case where none of ECA_APIE, ECB3_AES or ECB3_DEA
>>>> are set in guest3 a format 0 CRYCB is allowed for guest3
>>>> and the CRYCB designation in the SIE for guest3 is not checked
>>>> on SIE entry.
>>>>
>>>> Let's allow the CRYCD designation to be ignored when the
>>>> SIE for guest3 is not initialized for encryption key usage
>>>> nor AP.
>>>>
>>>> Fixup: d6f6959 (KVM: s390: vsie: Do the CRYCB validation first)
>>>>
>>>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>>>> Reported-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
>>>> ---
>>>>    arch/s390/kvm/vsie.c | 3 +++
>>>>    1 file changed, 3 insertions(+)
>>>>
>>>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
>>>> index a153257..a748f76 100644
>>>> --- a/arch/s390/kvm/vsie.c
>>>> +++ b/arch/s390/kvm/vsie.c
>>>> @@ -300,6 +300,9 @@ static int shadow_crycb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>>>>    	if (!apie_h && !key_msk)
>>>>    		return 0;
>>>>    
>>>> +	if (!(scb_o->eca & ECA_APIE) && !(scb_o->ecb3 & (ECB3_AES | ECB3_DEA)))
>>>> +		return 0;
>>>> +
>>>>    	if (!crycb_addr)
>>>>    		return set_validity_icpt(scb_s, 0x0039U);
>>>>    
>>>>
>>>
>>> The original patch said
>>>
>>> "We need to handle the validity checks for the crycb, no matter what the
>>>    settings for the keywrappings are. So lets move the keywrapping checks
>>>    after we have done the validy checks."
>>>
>>> Can you explain why keywrapping now is important? These patches seem to
>>> contradict.
>>>
>>
>> No it does not, having the flags set or not is part of the validity check.
>> but, I acted too fast.
>>
>> The problem seems to be even clearer:
>> key_msk is defined as
>>      int key_msk = test_kvm_facility(vcpu->kvm, 76);
>>
>> If it is defined, as it should for a mask, as
>> 	(scb_o->ecb3 & (ECB3_AES | ECB3_DEA))
>>
>> all is clear..., key_msk is not use but for this test, so I do not
>> understand why it is set as facility 76.
>>
>> so I think I better do:
>>
>>
>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
>> index a153257..30843a8 100644
>> --- a/arch/s390/kvm/vsie.c
>> +++ b/arch/s390/kvm/vsie.c
>> @@ -289,7 +289,7 @@ static int shadow_crycb(struct kvm_vcpu *vcpu,
>> struct vsie_page *vsie_page)
>>           unsigned long *b1, *b2;
>>           u8 ecb3_flags;
>>           int apie_h;
>> -       int key_msk = test_kvm_facility(vcpu->kvm, 76);
>> +       int key_msk = scb_o->ecb3 & (ECB3_AES | ECB3_DEA);
>>           int fmt_o = crycbd_o & CRYCB_FORMAT_MASK;
>>           int fmt_h = vcpu->arch.sie_block->crycbd & CRYCB_FORMAT_MASK;
>>           int ret = 0;
>>
>>
>> So just define a mask a mask.
>> I verify the functionality and test on Monday  and if in between it
>> seems better to you so too I post the patch.
> 
> Without documentation at hand I cannot really judge what is the right
> approach. You have to read the architecture description very carefully
> and thimk about the different scenarios. I cannot help here.
> 
> test_kvm_facility(vcpu->kvm, 76) means "hardware knows key wrapping exists"
> 
> scb_o->ecb3 & (ECB3_AES | ECB3_DEA) means "key wrapping was actually
> enabled for AES or DEA"


Right.
We also must take care of the format.
So not sure my propositions are right.
And helas I have the documentation :)
So ... I have to read it again again.


Regards,
Pierre

> 
>>
>> Thanks,
>> Pierre
>>
> 
> 


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