Re: [RFC v2 4/5] vfio-ccw: Don't call cp_free if we are processing a channel program

[Farhan Ali <alifm@linux.ibm.com>]

On 07/09/2019 06:16 AM, Cornelia Huck wrote:
> On Mon,  8 Jul 2019 16:10:37 -0400
> Farhan Ali <alifm@linux.ibm.com> wrote:
> 
>> There is a small window where it's possible that we could be working
>> on an interrupt (queued in the workqueue) and setting up a channel
>> program (i.e allocating memory, pinning pages, translating address).
>> This can lead to allocating and freeing the channel program at the
>> same time and can cause memory corruption.
>>
>> Let's not call cp_free if we are currently processing a channel program.
>> The only way we know for sure that we don't have a thread setting
>> up a channel program is when the state is set to VFIO_CCW_STATE_CP_PENDING.
> 
> Can we pinpoint a commit that introduced this bug, or has it been there
> since the beginning?
> 

I think the problem was always there.

>>
>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>> ---
>>   drivers/s390/cio/vfio_ccw_drv.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
>> index 4e3a903..0357165 100644
>> --- a/drivers/s390/cio/vfio_ccw_drv.c
>> +++ b/drivers/s390/cio/vfio_ccw_drv.c
>> @@ -92,7 +92,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
>>   		     (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT));
>>   	if (scsw_is_solicited(&irb->scsw)) {
>>   		cp_update_scsw(&private->cp, &irb->scsw);
>> -		if (is_final)
>> +		if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING)
>>   			cp_free(&private->cp);
>>   	}
>>   	mutex_lock(&private->io_mutex);
> 
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> 
> 
Thanks for reviewing.

Thanks
Farhan