Re: [PATCH v2 1/2] mm/page_reporting: use system_freezable_wq to fix UAF during suspend

[David Hildenbrand (Arm)]

On 7/17/26 02:22, Link Lin wrote:
> During PM freeze (e.g. S3 suspend or S4 hibernation), device drivers like
> virtio_balloon reset their underlying virtio devices and delete their
> virtqueues via vdev->config->del_vqs().
> 
> However, page reporting work (page_reporting_process) was scheduled on
> the global system_wq. Because system_wq lacks the WQ_FREEZABLE flag, the
> PM freezer skips it, leaving page_reporting_process active during
> suspend. If pages are freed into the buddy allocator while suspending,
> page reporting invokes virtballoon_free_page_report() on deleted
> virtqueues:
> 
>     [  196.795226] general protection fault, probably for non-canonical address 0xaa1436fe70dae6df: 0000 [#1] SMP NOPTI
>     [  196.825967] Workqueue: events page_reporting_process
>     [  196.831038] RIP: 0010:virtqueue_add_split+0x233/0x4c0 [virtio_ring]
>     [  196.927073] virtballoon_free_page_report+0x3a/0xe0 [virtio_balloon]
>     [  196.946943] page_reporting_process+0x370/0x4f0
> 
> Fix this by switching page reporting work to system_freezable_wq. This
> ensures that the PM freezer pauses page_reporting_process before device
> drivers destroy their reporting virtqueues.
> 
> This aligns with the driver's existing design. The comment in
> virtballoon_freeze() states:
>     /*
>      * The workqueue is already frozen by the PM core before this
>      * function is called.
>      */
> 
> Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
> Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
> Fixes: 924a663f75e2 ("virtio-balloon: Reporting free page reservations")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Link Lin <linkl@xxxxxxxxxx>

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David