Re: [PATCH v2] KVM: s390: do not clobber user space registers during guest reset/store status

David Hildenbrand
2020-01-30T12:39:02Z

On 30.01.20 13:01, Christian Borntraeger wrote:
>
>
> On 30.01.20 12:42, Christian Borntraeger wrote:
>> The two ioctls for initial CPU reset and store status currently clobber
>> the userspace fpc and potentially access registers. This was an
>> oversight during a fixup for the lazy fpu reloading rework. The reset
>> calls are only done from userspace ioctls. No CPU context is loaded, so
>> we can (and must) act directly on the sync regs, not on the thread
>> context. Otherwise the fpu restore call will restore the zeroes fpc to
>> userspace.
>
> New patch description:
>
> KVM: s390: do not clobber registers during guest reset/store status
>
> The initial CPU reset clobbers the userspace fpc and the store status
> ioctl clobbers the guest acrs + fpr. As these calls are only done via
> ioctl (and not via vcpu_run), no CPU context is loaded, so we can (and
> must) act directly on the sync regs, not on the thread context.
>
> Cc: stable@kernel.org
> Fixes: e1788bb995be ("KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load")
> Fixes: 31d8b8d41a7e ("KVM: s390: handle access registers in the run ioctl not in vcpu_put/load")
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>
>>
>> Cc: stable@kernel.org
>> Fixes: e1788bb995be ("KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load")
>> Fixes: 31d8b8d41a7e ("KVM: s390: handle access registers in the run ioctl not in vcpu_put/load")
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> ---
>> arch/s390/kvm/kvm-s390.c | 5 ++---
>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index c059b86..936415b 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -2824,8 +2824,7 @@ static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
>> vcpu->arch.sie_block->gcr[14] = CR14_UNUSED_32 |
>> CR14_UNUSED_33 |
>> CR14_EXTERNAL_DAMAGE_SUBMASK;
>> - /* make sure the new fpc will be lazily loaded */
>> - save_fpu_regs();
>> + vcpu->run->s.regs.fpc = 0;
>> current->thread.fpu.fpc = 0;
>> vcpu->arch.sie_block->gbea = 1;
>> vcpu->arch.sie_block->pp = 0;
>> @@ -4343,7 +4342,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>> switch (ioctl) {
>> case KVM_S390_STORE_STATUS:
>> idx = srcu_read_lock(&vcpu->kvm->srcu);
>> - r = kvm_s390_vcpu_store_status(vcpu, arg);
>> + r = kvm_s390_vcpu_store_status_unloaded(vcpu, arg);
>> srcu_read_unlock(&vcpu->kvm->srcu, idx);
>> break;
>> case KVM_S390_SET_INITIAL_PSW: {
>>
>

With new description + fixed up call

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb