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

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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@xxxxxxxxxx
>     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@xxxxxxxxxx>
> 
>>
>> Cc: stable@xxxxxxxxxx
>> 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@xxxxxxxxxx>
>> ---
>>  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@xxxxxxxxxx>

-- 
Thanks,

David / dhildenb




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