Commit a6fa67d2 authored by Imre Deak's avatar Imre Deak
Browse files

drm/dp_mst: Fix resetting msg rx state after topology removal 

If the MST topology is removed during the reception of an MST down reply
or MST up request sideband message, the
drm_dp_mst_topology_mgr::up_req_recv/down_rep_recv states could be reset
from one thread via drm_dp_mst_topology_mgr_set_mst(false), racing with
the reading/parsing of the message from another thread via
drm_dp_mst_handle_down_rep() or drm_dp_mst_handle_up_req(). The race is
possible since the reader/parser doesn't hold any lock while accessing
the reception state. This in turn can lead to a memory corruption in the
reader/parser as described by commit bd2fccac ("drm/dp_mst: Fix MST
sideband message body length check").

Fix the above by resetting the message reception state if needed before
reading/parsing a message. Another solution would be to hold the
drm_dp_mst_topology_mgr::lock for the whole duration of the message
reception/parsing in drm_dp_mst_handle_down_rep() and
drm_dp_mst_handle_up_req(), however this would require a bigger change.
Since the fix is also needed for stable, opting for the simpler solution
in this patch.

Cc: Lyude Paul <lyude@redhat.com>
Cc: <stable@vger.kernel.org>
Fixes: 1d082618 ("drm/display/dp_mst: Fix down/up message handling after sink disconnect")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13056


Reviewed-by: default avatarLyude Paul <lyude@redhat.com>
Signed-off-by: default avatarImre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241203160223.2926014-2-imre.deak@intel.com
parent 86e8f947

drivers/gpu/drm/display/drm_dp_mst_topology.c

+19 −2
Original line number Diff line number Diff line
@@ -3700,8 +3700,7 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms 
		ret = 0;

		mgr->payload_id_table_cleared = false;



		memset(&mgr->down_rep_recv, 0, sizeof(mgr->down_rep_recv));

		memset(&mgr->up_req_recv, 0, sizeof(mgr->up_req_recv));

		mgr->reset_rx_state = true;

	}



out_unlock:
@@ -3859,6 +3858,11 @@ int drm_dp_mst_topology_mgr_resume(struct drm_dp_mst_topology_mgr *mgr, 
}

EXPORT_SYMBOL(drm_dp_mst_topology_mgr_resume);



static void reset_msg_rx_state(struct drm_dp_sideband_msg_rx *msg)

{

	memset(msg, 0, sizeof(*msg));

}



static bool

drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up,

		      struct drm_dp_mst_branch **mstb)
@@ -4141,6 +4145,17 @@ static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr) 
	return 0;

}



static void update_msg_rx_state(struct drm_dp_mst_topology_mgr *mgr)

{

	mutex_lock(&mgr->lock);

	if (mgr->reset_rx_state) {

		mgr->reset_rx_state = false;

		reset_msg_rx_state(&mgr->down_rep_recv);

		reset_msg_rx_state(&mgr->up_req_recv);

	}

	mutex_unlock(&mgr->lock);

}



/**

 * drm_dp_mst_hpd_irq_handle_event() - MST hotplug IRQ handle MST event

 * @mgr: manager to notify irq for.
@@ -4175,6 +4190,8 @@ int drm_dp_mst_hpd_irq_handle_event(struct drm_dp_mst_topology_mgr *mgr, const u 
		*handled = true;

	}



	update_msg_rx_state(mgr);



	if (esi[1] & DP_DOWN_REP_MSG_RDY) {

		ret = drm_dp_mst_handle_down_rep(mgr);

		*handled = true;

include/drm/display/drm_dp_mst_helper.h

+7 −0
Original line number Diff line number Diff line
@@ -699,6 +699,13 @@ struct drm_dp_mst_topology_mgr { 
	 */

	bool payload_id_table_cleared : 1;



	/**

	 * @reset_rx_state: The down request's reply and up request message

	 * receiver state must be reset, after the topology manager got

	 * removed. Protected by @lock.

	 */

	bool reset_rx_state : 1;



	/**

	 * @payload_count: The number of currently active payloads in hardware. This value is only

	 * intended to be used internally by MST helpers for payload tracking, and is only safe to