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

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Date:   Fri, 1 Feb 2019 14:37:30 +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 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.

Thanks,
Pierre

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