Hi Tomi,
On Fri, Nov 16, 2018 at 03:41:24PM +0200, Tomi Valkeinen wrote:
> On 16/11/18 01:06, Sebastian Reichel wrote:
> > The DSI encoder sets dssdev->ops->dsi.set_config, which is stored at the
> > same offset as dssdev->ops->hdmi.set_hdmi_mode. The code in omap_encoder
> > only checks if dssdev->ops->hdmi.set_hdmi_mode is NULL. Due to the way
> > union works, it won't be NULL if dsi.set_config is set. This means
> > dsi_set_config will be called with config=hdmi_mode=false=NULL parameter
> > resulting in a NULL dereference. Also the dereference happens while
> > console is locked, so kernel hangs without any debug output (can be
> > avoided by fbmem's lockless_register_fb=1 parameter).
> >
> > This fixes the issue by exiting early if the output type definitely
> > has no hdmi_set operations.
> >
> > Fixes: 83910ad3f51fb ("drm/omap: Move most omap_dss_driver operations to omap_dss_device_ops")
> > Signed-off-by: Sebastian Reichel <sebastian.reichel@xxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/omapdrm/omap_encoder.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/omapdrm/omap_encoder.c b/drivers/gpu/drm/omapdrm/omap_encoder.c
> > index 32bbe3a80e7d..ba0099f0644c 100644
> > --- a/drivers/gpu/drm/omapdrm/omap_encoder.c
> > +++ b/drivers/gpu/drm/omapdrm/omap_encoder.c
> > @@ -122,6 +122,14 @@ static void omap_encoder_mode_set(struct drm_encoder *encoder,
> >
> > dssdev = omap_encoder->output;
> >
> > + /* The following operations access dssdev->ops->hdmi, which is a union
> > + * also used by DSI. This ensures, that the field does not have data
> > + * for DSI (or any other future output type).
> > + */
> > + if (dssdev->output_type != OMAP_DISPLAY_TYPE_HDMI &&
> > + dssdev->output_type != OMAP_DISPLAY_TYPE_DVI)
>
> Good catch.
>
> Why DVI?
>
> I think the whole code block starting from
>
> /* Set the HDMI mode and HDMI infoframe if applicable. */
>
> to the end of the function should be inside
>
> if (dssdev->output_type == OMAP_DISPLAY_TYPE_HDMI)
When I identified the issue I whitelisted DVI, since I wasn't sure
if it also has the HDMI functionality. I planned to check the code
later and then forgot about it. You are right, this should only
check for HDMI.
-- Sebastian
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