[PATCH v3 4/5] vfio-ccw: Don't call cp_free if we are processing a channel program

From: Farhan Ali <alifm@linux.ibm.com>
To: cohuck@redhat.com, farman@linux.ibm.com, pasic@linux.ibm.com
Cc: linux-s390@vger.kernel.org, kvm@vger.kernel.org, alifm@linux.ibm.com
Subject: [PATCH v3 4/5] vfio-ccw: Don't call cp_free if we are processing a channel program
Date: Thu, 11 Jul 2019 10:28:54 -0400	[thread overview]
Message-ID: <62e87bf67b38dc8d5760586e7c96d400db854ebe.1562854091.git.alifm@linux.ibm.com> (raw)
In-Reply-To: <cover.1562854091.git.alifm@linux.ibm.com>
In-Reply-To: <cover.1562854091.git.alifm@linux.ibm.com>

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.

Fixes: d5afd5d135c8 ("vfio-ccw: add handling for async channel instructions")
Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.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);
-- 
2.7.4
