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

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Message-ID: <20200203121620.9002-1-benjamin.gaignard@st.com>
Date:   Mon, 3 Feb 2020 13:16:20 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...com>
To:     <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>,
        Benjamin Gaignard <benjamin.gaignard@...com>,
        <lyude@...hat.com>, <jani.nikula@...ux.intel.com>
Subject: [PATCH] drm/dp_mst: Check crc4 value while building sideband message

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;
-- 
2.15.0