vfio: ccw: only free cp on final interrupt

commit 50b7f1b7236bab08ebbbecf90521e84b068d7a17 upstream.

When we get an interrupt for a channel program, it is not
necessarily the final interrupt; for example, the issuing
guest may request an intermediate interrupt by specifying
the program-controlled-interrupt flag on a ccw.

We must not switch the state to idle if the interrupt is not
yet final; even more importantly, we must not free the translated
channel program if the interrupt is not yet final, or the host
can crash during cp rewind.

Fixes: e5f84dbaea59 ("vfio: ccw: return I/O results asynchronously")
Cc: stable@vger.kernel.org # v4.12+
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
index f47d16b..fabd979 100644 (file)
--- a/drivers/s390/cio/vfio_ccw_drv.c
+++ b/drivers/s390/cio/vfio_ccw_drv.c
@@ -72,20 +72,24 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
 {
        struct vfio_ccw_private *private;
        struct irb *irb;
+       bool is_final;
 
        private = container_of(work, struct vfio_ccw_private, io_work);
        irb = &private->irb;
 
+       is_final = !(scsw_actl(&irb->scsw) &
+                    (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT));
        if (scsw_is_solicited(&irb->scsw)) {
                cp_update_scsw(&private->cp, &irb->scsw);
-               cp_free(&private->cp);
+               if (is_final)
+                       cp_free(&private->cp);
        }
        memcpy(private->io_region->irb_area, irb, sizeof(*irb));
 
        if (private->io_trigger)
                eventfd_signal(private->io_trigger, 1);
 
-       if (private->mdev)
+       if (private->mdev && is_final)
                private->state = VFIO_CCW_STATE_IDLE;
 }