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

[Doug Anderson]

Hi,

On Mon, Jun 12, 2023 at 3:40 PM Dmitry Baryshkov
<dmitry.baryshkov at linaro.org> wrote:
>
> On 13/06/2023 01:01, Bjorn Andersson wrote:
> > 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.
>
> I hoped that proper usage of of_dp_aux_populate_bus(), with the callback
> function being non-NULL would have solved at least this part. But it
> seems I'll never see this patch.

Agreed. This has been pending for > 1 year now with no significant
progress. Abhinav: Is there anything that can be done about this? Not
following up on agreed-to cleanups in a timely manner doesn't set a
good precedent. Next time the Qualcomm display wants to land something
and promises to land a followup people will be less likely to believe
them...


> > 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 at quicinc.com>
>
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>

Reviewed-by: Douglas Anderson <dianders at chromium.org>