Re: [PATCH] dma-mapping: benchmark: check the validity of dma mask bits

[Robin Murphy <robin.murphy@arm.com>]

On 2020-12-12 10:18, Barry Song wrote:
> While dma_mask_bits is larger than 64, the bahvaiour is undefined. On the
> other hand, dma_mask_bits which is smaller than 20 (1MB) makes no sense
> in real hardware.
> 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> ---
>   kernel/dma/map_benchmark.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c
> index b1496e744c68..19f661692073 100644
> --- a/kernel/dma/map_benchmark.c
> +++ b/kernel/dma/map_benchmark.c
> @@ -214,6 +214,12 @@ static long map_benchmark_ioctl(struct file *file, unsigned int cmd,
>   			return -EINVAL;
>   		}
>   
> +		if (map->bparam.dma_bits < 20 ||

FWIW I don't think we need to bother with a lower limit here - it's 
unsigned, and a pointlessly small value will fail gracefully when we 
come to actually set the mask anyway. We only need to protect kernel 
code from going wrong, not userspace from being stupid to its own detriment.

Robin.

> +		    map->bparam.dma_bits > 64) {
> +			pr_err("invalid dma_bits\n");
> +			return -EINVAL;
> +		}
> +
>   		if (map->bparam.node != NUMA_NO_NODE &&
>   		    !node_possible(map->bparam.node)) {
>   			pr_err("invalid numa node\n");
> 
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