[PATCH 2/8] drm/edid: Don't accept any old garbage as a display descriptor

[Alex Deucher]

On Fri, Jan 24, 2020 at 3:02 PM Ville Syrjala
<ville.syrjala at linux.intel.com> wrote:
>
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> Currently we assume any 18 byte descriptor to be a display descritor
> if only the tag byte matches the expected value. But for detailed
> timing descriptors that same byte is just the lower 8 bits of
> hblank, and as such can match any display descriptor tag. To
> properly validate that the 18 byte descriptor is in fact a
> display descriptor we must also examine bytes 0-2 (just byte 1
> should actually suffice but the spec does say that bytes 0 and
> 2 must also always be zero for display descriptors so we check
> those too).
>
> Unlike Allen's original proposed patch to just fix is_rb() we
> roll this out across the board to fix everything.
>
> Cc: Allen Chen <allen.chen at ite.com.tw>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Acked-by: Alex Deucher <alexander.deucher at amd.com>

> ---
>  drivers/gpu/drm/drm_edid.c | 65 ++++++++++++++++++++++++--------------
>  1 file changed, 41 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 1b6e544cf5c7..96ae1fde4ce2 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -2196,6 +2196,12 @@ struct drm_display_mode *drm_mode_find_dmt(struct drm_device *dev,
>  }
>  EXPORT_SYMBOL(drm_mode_find_dmt);
>
> +static bool is_display_descriptor(const u8 d[18], u8 tag)
> +{
> +       return d[0] == 0x00 && d[1] == 0x00 &&
> +               d[2] == 0x00 && d[3] == tag;
> +}
> +
>  typedef void detailed_cb(struct detailed_timing *timing, void *closure);
>
>  static void
> @@ -2257,9 +2263,12 @@ static void
>  is_rb(struct detailed_timing *t, void *data)
>  {
>         u8 *r = (u8 *)t;
> -       if (r[3] == EDID_DETAIL_MONITOR_RANGE)
> -               if (r[15] & 0x10)
> -                       *(bool *)data = true;
> +
> +       if (!is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE))
> +               return;
> +
> +       if (r[15] & 0x10)
> +               *(bool *)data = true;
>  }
>
>  /* EDID 1.4 defines this explicitly.  For EDID 1.3, we guess, badly. */
> @@ -2279,7 +2288,11 @@ static void
>  find_gtf2(struct detailed_timing *t, void *data)
>  {
>         u8 *r = (u8 *)t;
> -       if (r[3] == EDID_DETAIL_MONITOR_RANGE && r[10] == 0x02)
> +
> +       if (!is_display_descriptor(r, EDID_DETAIL_MONITOR_RANGE))
> +               return;
> +
> +       if (r[10] == 0x02)
>                 *(u8 **)data = r;
>  }
>
> @@ -2818,7 +2831,7 @@ do_inferred_modes(struct detailed_timing *timing, void *c)
>         struct detailed_non_pixel *data = &timing->data.other_data;
>         struct detailed_data_monitor_range *range = &data->data.range;
>
> -       if (data->type != EDID_DETAIL_MONITOR_RANGE)
> +       if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_MONITOR_RANGE))
>                 return;
>
>         closure->modes += drm_dmt_modes_for_range(closure->connector,
> @@ -2897,10 +2910,11 @@ static void
>  do_established_modes(struct detailed_timing *timing, void *c)
>  {
>         struct detailed_mode_closure *closure = c;
> -       struct detailed_non_pixel *data = &timing->data.other_data;
>
> -       if (data->type == EDID_DETAIL_EST_TIMINGS)
> -               closure->modes += drm_est3_modes(closure->connector, timing);
> +       if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_EST_TIMINGS))
> +               return;
> +
> +       closure->modes += drm_est3_modes(closure->connector, timing);
>  }
>
>  /**
> @@ -2949,19 +2963,19 @@ do_standard_modes(struct detailed_timing *timing, void *c)
>         struct detailed_non_pixel *data = &timing->data.other_data;
>         struct drm_connector *connector = closure->connector;
>         struct edid *edid = closure->edid;
> +       int i;
>
> -       if (data->type == EDID_DETAIL_STD_MODES) {
> -               int i;
> -               for (i = 0; i < 6; i++) {
> -                       struct std_timing *std;
> -                       struct drm_display_mode *newmode;
> +       if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_STD_MODES))
> +               return;
>
> -                       std = &data->data.timings[i];
> -                       newmode = drm_mode_std(connector, edid, std);
> -                       if (newmode) {
> -                               drm_mode_probed_add(connector, newmode);
> -                               closure->modes++;
> -                       }
> +       for (i = 0; i < 6; i++) {
> +               struct std_timing *std = &data->data.timings[i];
> +               struct drm_display_mode *newmode;
> +
> +               newmode = drm_mode_std(connector, edid, std);
> +               if (newmode) {
> +                       drm_mode_probed_add(connector, newmode);
> +                       closure->modes++;
>                 }
>         }
>  }
> @@ -3056,10 +3070,11 @@ static void
>  do_cvt_mode(struct detailed_timing *timing, void *c)
>  {
>         struct detailed_mode_closure *closure = c;
> -       struct detailed_non_pixel *data = &timing->data.other_data;
>
> -       if (data->type == EDID_DETAIL_CVT_3BYTE)
> -               closure->modes += drm_cvt_modes(closure->connector, timing);
> +       if (!is_display_descriptor((const u8 *)timing, EDID_DETAIL_CVT_3BYTE))
> +               return;
> +
> +       closure->modes += drm_cvt_modes(closure->connector, timing);
>  }
>
>  static int
> @@ -4285,8 +4300,10 @@ drm_parse_hdmi_vsdb_audio(struct drm_connector *connector, const u8 *db)
>  static void
>  monitor_name(struct detailed_timing *t, void *data)
>  {
> -       if (t->data.other_data.type == EDID_DETAIL_MONITOR_NAME)
> -               *(u8 **)data = t->data.other_data.data.str.str;
> +       if (!is_display_descriptor((const u8 *)t, EDID_DETAIL_MONITOR_NAME))
> +               return;
> +
> +       *(u8 **)data = t->data.other_data.data.str.str;
>  }
>
>  static int get_monitor_name(struct edid *edid, char name[13])
> --
> 2.24.1
>
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