Re: [PATCH v2 1/4] venus: hfi: add checks to perform sanity on queue pointers

[Bryan O'Donoghue <bryan.odonoghue@linaro.org>]

On 10/08/2023 03:25, Vikash Garodia wrote:
> Read and write pointers are used to track the packet index in the memory
> shared between video driver and firmware. There is a possibility of OOB
> access if the read or write pointer goes beyond the queue memory size.
> Add checks for the read and write pointer to avoid OOB access.
> 
> Cc: stable@vger.kernel.org
> Fixes: d96d3f30c0f2 ("[media] media: venus: hfi: add Venus HFI files")
> Signed-off-by: Vikash Garodia <quic_vgarodia@quicinc.com>
> ---
>   drivers/media/platform/qcom/venus/hfi_venus.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/media/platform/qcom/venus/hfi_venus.c b/drivers/media/platform/qcom/venus/hfi_venus.c
> index f0b4638..4ddabb1 100644
> --- a/drivers/media/platform/qcom/venus/hfi_venus.c
> +++ b/drivers/media/platform/qcom/venus/hfi_venus.c
> @@ -206,6 +206,11 @@ static int venus_write_queue(struct venus_hfi_device *hdev,
>   
>   	new_wr_idx = wr_idx + dwords;
>   	wr_ptr = (u32 *)(queue->qmem.kva + (wr_idx << 2));
> +
> +	if (wr_ptr < (u32 *)queue->qmem.kva ||
> +	    wr_ptr > (u32 *)(queue->qmem.kva + queue->qmem.size - sizeof(*wr_ptr)))
> +		return -EINVAL;
> +
>   	if (new_wr_idx < qsize) {
>   		memcpy(wr_ptr, packet, dwords << 2);
>   	} else {
> @@ -273,6 +278,11 @@ static int venus_read_queue(struct venus_hfi_device *hdev,
>   	}
>   
>   	rd_ptr = (u32 *)(queue->qmem.kva + (rd_idx << 2));
> +
> +	if (rd_ptr < (u32 *)queue->qmem.kva ||
> +	    rd_ptr > (u32 *)(queue->qmem.kva + queue->qmem.size - sizeof(*rd_ptr)))
> +		return -EINVAL;
> +
>   	dwords = *rd_ptr >> 2;
>   	if (!dwords)
>   		return -EINVAL;

What is the bit-shifting for ?