linux-kernel - Re: [PATCH] drm/dp_mst: Check crc4 value while building sideband message

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Date:   Tue, 04 Feb 2020 14:00:09 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     Benjamin Gaignard <benjamin.gaignard@...com>,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        airlied@...ux.ie, daniel@...ll.ch
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        jani.nikula@...ux.intel.com
Subject: Re: [PATCH] drm/dp_mst: Check crc4 value while building sideband
 message

Reviewed-by: Lyude Paul <lyude@...hat.com>

On Mon, 2020-02-03 at 13:16 +0100, Benjamin Gaignard wrote:
> Check that computed crc value is matching the one encoded in the message.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...com>
> ---
> CC: lyude@...hat.com
> CC: airlied@...ux.ie
> CC: jani.nikula@...ux.intel.com
>  drivers/gpu/drm/drm_dp_mst_topology.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 822d2f177f90..eee899d6742b 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -736,6 +736,10 @@ static bool drm_dp_sideband_msg_build(struct
> drm_dp_sideband_msg_rx *msg,
>  	if (msg->curchunk_idx >= msg->curchunk_len) {
>  		/* do CRC */
>  		crc4 = drm_dp_msg_data_crc4(msg->chunk, msg->curchunk_len -
> 1);
> +		if (crc4 != msg->chunk[msg->curchunk_len - 1])
> +			print_hex_dump(KERN_DEBUG, "wrong crc",
> +				       DUMP_PREFIX_NONE, 16, 1,
> +				       msg->chunk,  msg->curchunk_len, false);
>  		/* copy chunk into bigger msg */
>  		memcpy(&msg->msg[msg->curlen], msg->chunk, msg->curchunk_len -
> 1);
>  		msg->curlen += msg->curchunk_len - 1;
-- 
Cheers,
	Lyude Paul