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

Cornelia Huck
2019-07-09T10:16:18Z

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?

>
> 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>