On 08/21/2017 02:43 PM, David Hildenbrand wrote:
> On 21.08.2017 14:27, Christian Borntraeger wrote:
>> From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
>>
>> sthyi should only generate a specification exception if the function
>> code is zero and the response buffer is not on a 4k boundary.
>>
>> The current code would also test for unknown function codes if the
>> response buffer, that is currently only defined for function code 0,
>> is not on a 4k boundary and incorrectly inject a specification
>> exception instead of returning with condition code 3 and return code 4
>> (unsupported function code).
>>
>> Fix this by moving the boundary check.
>>
>> Fixes: 95ca2cb57985 ("KVM: s390: Add sthyi emulation")
>> Cc: <stable@xxxxxxxxxxxxxxx> # 4.8+
>> Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxxxxxxx>
>> Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
>> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
>> ---
>> arch/s390/kvm/sthyi.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/kvm/sthyi.c b/arch/s390/kvm/sthyi.c
>> index 2773a2f..a2e5c24 100644
>> --- a/arch/s390/kvm/sthyi.c
>> +++ b/arch/s390/kvm/sthyi.c
>> @@ -425,7 +425,7 @@ int handle_sthyi(struct kvm_vcpu *vcpu)
>> VCPU_EVENT(vcpu, 3, "STHYI: fc: %llu addr: 0x%016llx", code, addr);
>> trace_kvm_s390_handle_sthyi(vcpu, code, addr);
>>
>> - if (reg1 == reg2 || reg1 & 1 || reg2 & 1 || addr & ~PAGE_MASK)
>> + if (reg1 == reg2 || reg1 & 1 || reg2 & 1)
>> return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
>>
>> if (code & 0xffff) {
>> @@ -433,6 +433,9 @@ int handle_sthyi(struct kvm_vcpu *vcpu)
>> goto out;
>> }
>>
>> + if (addr & ~PAGE_MASK)
>> + return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
>> +
>> /*
>> * If the page has not yet been faulted in, we want to do that
>> * now and not after all the expensive calculations.
>>
>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
>
> Just wondering if this is really worth stable? (only function code 0 is
> defined, so this should not happen in sane environments. or is this used
> to test for support for new function codes (which would be strange but
> possible)?)
I think it is a safety net if we ever implement new function codes. So yes
we want software being able to test for the new codes without having to
handle a program check.
