Re: [PATCH v2 1/2] KVM: s390: Disallow invalid bits in kvm_valid_regs and kvm_dirty_regs

Christian Borntraeger
2019-09-04T09:11:32Z

On 04.09.19 11:05, David Hildenbrand wrote:
> On 04.09.19 10:51, Thomas Huth wrote:
>> If unknown bits are set in kvm_valid_regs or kvm_dirty_regs, this
>> clearly indicates that something went wrong in the KVM userspace
>> application. The x86 variant of KVM already contains a check for
>> bad bits, so let's do the same on s390x now, too.
>>
>> Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>> arch/s390/include/uapi/asm/kvm.h | 6 ++++++
>> arch/s390/kvm/kvm-s390.c | 4 ++++
>> 2 files changed, 10 insertions(+)
>>
>> diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
>> index 47104e5b47fd..436ec7636927 100644
>> --- a/arch/s390/include/uapi/asm/kvm.h
>> +++ b/arch/s390/include/uapi/asm/kvm.h
>> @@ -231,6 +231,12 @@ struct kvm_guest_debug_arch {
>> #define KVM_SYNC_GSCB (1UL << 9)
>> #define KVM_SYNC_BPBC (1UL << 10)
>> #define KVM_SYNC_ETOKEN (1UL << 11)
>> +
>> +#define KVM_SYNC_S390_VALID_FIELDS \
>> + (KVM_SYNC_PREFIX | KVM_SYNC_GPRS | KVM_SYNC_ACRS | KVM_SYNC_CRS | \
>> + KVM_SYNC_ARCH0 | KVM_SYNC_PFAULT | KVM_SYNC_VRS | KVM_SYNC_RICCB | \
>> + KVM_SYNC_FPRS | KVM_SYNC_GSCB | KVM_SYNC_BPBC | KVM_SYNC_ETOKEN)
>> +
>
> We didn't care about the S390 for the actual flags, why care now?

I think it makes sense to have the interface as defined as possible. If for some
reason userspace sets a wrong bit this would be undetected. If we at a later point
in time use that bit this would resultin strange problems.
>
>
>> /* length and alignment of the sdnx as a power of two */
>> #define SDNXC 8
>> #define SDNXL (1UL << SDNXC)
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index 49d7722229ae..a7d7dedfe527 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -3998,6 +3998,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
>> if (kvm_run->immediate_exit)
>> return -EINTR;
>>
>> + if (kvm_run->kvm_valid_regs & ~KVM_SYNC_S390_VALID_FIELDS ||
>> + kvm_run->kvm_dirty_regs & ~KVM_SYNC_S390_VALID_FIELDS)
>> + return -EINVAL;
>> +
>> vcpu_load(vcpu);
>>
>> if (guestdbg_exit_pending(vcpu)) {
>>
>
> Reviewed-by: David Hildenbrand <david@redhat.com>
>