[PATCH 6.1.y] drm/msm/dp: Drop aux devices together with DP controller

[PATCH 6.1.y] drm/msm/dp: Drop aux devices together with DP controller

[Artem Dinaburg]

From: Bjorn Andersson <quic_bjorande@quicinc.com>

[ Upstream commit a7bfb2ad2184a1fba78be35209b6019aa8cc8d4d ]

Using devres to depopulate the aux bus made sure that upon a probe
deferral the EDP panel device would be destroyed and recreated upon next
attempt.

But the struct device which the devres is tied to is the DPUs
(drm_dev->dev), which may be happen after the DP controller is torn
down.

Indications of this can be seen in the commonly seen EDID-hexdump full
of zeros in the log, or the occasional/rare KASAN fault where the
panel's attempt to read the EDID information causes a use after free on
DP resources.

It's tempting to move the devres to the DP controller's struct device,
but the resources used by the device(s) on the aux bus are explicitly
torn down in the error path. The KASAN-reported use-after-free also
remains, as the DP aux "module" explicitly frees its devres-allocated
memory in this code path.

As such, explicitly depopulate the aux bus in the error path, and in the
component unbind path, to avoid these issues.

Fixes: 2b57f726611e ("drm/msm/dp: fix aux-bus EP lifetime")
Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/542163/
Link: https://lore.kernel.org/r/20230612220106.1884039-1-quic_bjorande@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

[ Backport to 6.1.y: the source change is unchanged; refresh context
  around the older DP bridge layout. ]
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
Hi Greg, Sasha, and MSM DRM maintainers,

I am continuing backporting CVEs still missing from 6.1.y.
This fix is inherited by v6.6 and every later mainline release, but 6.1.y
still has the affected code. The target-specific adjustment is described
in the bracketed note above.

Could you please queue it for 6.1.y?

Thanks,
Artem Dinaburg

CVE: CVE-2023-53851

Build: This patch was included in an x86_64 allmodconfig and
CONFIG_WERROR=y build.
It produced vmlinux and modules with no new warnings or errors.

AI assistance: An LLM helped find, adapt, and validate this
backport; I reviewed the patch and test output.

 drivers/gpu/drm/msm/dp/dp_display.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index 5beb727f8437f9..ddd0279bc8963a 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -322,6 +322,8 @@ static void dp_display_unbind(struct device *dev, struct device *master,
 
 	kthread_stop(dp->ev_tsk);
 
+	of_dp_aux_depopulate_bus(dp->aux);
+
 	dp_power_client_deinit(dp->power);
 	dp_unregister_audio_driver(dev, dp->audio);
 	dp_aux_unregister(dp->aux);
@@ -1535,11 +1537,6 @@ void msm_dp_debugfs_init(struct msm_dp *dp_display, struct drm_minor *minor)
 	}
 }
 
-static void of_dp_aux_depopulate_bus_void(void *data)
-{
-	of_dp_aux_depopulate_bus(data);
-}
-
 static int dp_display_get_next_bridge(struct msm_dp *dp)
 {
 	int rc;
@@ -1568,12 +1565,6 @@ static int dp_display_get_next_bridge(struct msm_dp *dp)
 		of_node_put(aux_bus);
 		if (rc)
 			goto error;
-
-		rc = devm_add_action_or_reset(dp->drm_dev->dev,
-						of_dp_aux_depopulate_bus_void,
-						dp_priv->aux);
-		if (rc)
-			goto error;
 	} else if (dp->is_edp) {
 		DRM_ERROR("eDP aux_bus not found\n");
 		return -ENODEV;
@@ -1597,6 +1588,7 @@ static int dp_display_get_next_bridge(struct msm_dp *dp)
 
 error:
 	if (dp->is_edp) {
+		of_dp_aux_depopulate_bus(dp_priv->aux);
 		disable_irq(dp_priv->irq);
 		dp_display_host_phy_exit(dp_priv);
 		dp_display_host_deinit(dp_priv);
-- 
2.39.5