[v3,4/5] vfio-ccw: Don't call cp_free if we are processing a channel program
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Message ID 62e87bf67b38dc8d5760586e7c96d400db854ebe.1562854091.git.alifm@linux.ibm.com
State New
Headers show
Series
  • Some vfio-ccw fixes
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Commit Message

Farhan Ali July 11, 2019, 2:28 p.m. UTC
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(-)

Comments

Eric Farman July 12, 2019, 1:19 p.m. UTC | #1
On 7/11/19 10:28 AM, Farhan Ali 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.>
> 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>

I think this seems like a reasonable fix.

Reviewed-by: Eric Farman <farman@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);
>

Patch
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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);