Re: [PATCH 2/3] dmaengine: idxd: Prevent use after free on completion memory

[Dave Jiang <dave.jiang@intel.com>]

On 12/2/2022 11:25 AM, Reinette Chatre wrote:
> On driver unload any pending descriptors are flushed at the
> time the interrupt is freed:
> idxd_dmaengine_drv_remove() ->
> 	drv_disable_wq() ->
> 		idxd_wq_free_irq() ->
> 			idxd_flush_pending_descs().
> 
> If there are any descriptors present that need to be flushed this
> flow triggers a "not present" page fault as below:
> 
>   BUG: unable to handle page fault for address: ff391c97c70c9040
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
> 
> The address that triggers the fault is the address of the
> descriptor that was freed moments earlier via:
> drv_disable_wq()->idxd_wq_free_resources()
> 
> Fix the use after free by freeing the descriptors after any possible
> usage. This is done after idxd_wq_reset() to ensure that the memory
> remains accessible during possible completion writes by the device.
> 
> Fixes: 63c14ae6c161 ("dmaengine: idxd: refactor wq driver enable/disable operations")
> Suggested-by: Dave Jiang <dave.jiang@intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>   drivers/dma/idxd/device.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
> index fcd03d29a941..b4d7bb923a40 100644
> --- a/drivers/dma/idxd/device.c
> +++ b/drivers/dma/idxd/device.c
> @@ -1408,11 +1408,11 @@ void drv_disable_wq(struct idxd_wq *wq)
>   		dev_warn(dev, "Clients has claim on wq %d: %d\n",
>   			 wq->id, idxd_wq_refcount(wq));
>   
> -	idxd_wq_free_resources(wq);
>   	idxd_wq_unmap_portal(wq);
>   	idxd_wq_drain(wq);
>   	idxd_wq_free_irq(wq);
>   	idxd_wq_reset(wq);
> +	idxd_wq_free_resources(wq);
>   	percpu_ref_exit(&wq->wq_active);
>   	wq->type = IDXD_WQT_NONE;
>   	wq->client_count = 0;