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

David Hildenbrand
2019-02-04T15:15:42Z

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@linux.ibm.com>
>>> Reported-by: Claudio Imbrenda <imbrenda@linux.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"

>
> Thanks,
> Pierre
>

--

Thanks,

David / dhildenb