On Fri, Feb 18, 2022 at 11:04 AM Ville Syrjala
<ville.syrjala@xxxxxxxxxxxxxxx> wrote:
>
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> struct drm_display_mode embeds a list head, so overwriting
> the full struct with another one will corrupt the list
> (if the destination mode is on a list). Use drm_mode_copy()
> instead which explicitly preserves the list head of
> the destination mode.
>
> Even if we know the destination mode is not on any list
> using drm_mode_copy() seems decent as it sets a good
> example. Bad examples of not using it might eventually
> get copied into code where preserving the list head
> actually matters.
>
> Obviously one case not covered here is when the mode
> itself is embedded in a larger structure and the whole
> structure is copied. But if we are careful when copying
> into modes embedded in structures I think we can be a
> little more reassured that bogus list heads haven't been
> propagated in.
>
> @is_mode_copy@
> @@
> drm_mode_copy(...)
> {
> ...
> }
>
> @depends on !is_mode_copy@
> struct drm_display_mode *mode;
> expression E, S;
> @@
> (
> - *mode = E
> + drm_mode_copy(mode, &E)
> |
> - memcpy(mode, E, S)
> + drm_mode_copy(mode, E)
> )
>
> @depends on !is_mode_copy@
> struct drm_display_mode mode;
> expression E;
> @@
> (
> - mode = E
> + drm_mode_copy(&mode, &E)
> |
> - memcpy(&mode, E, S)
> + drm_mode_copy(&mode, E)
> )
>
> @@
> struct drm_display_mode *mode;
> @@
> - &*mode
> + mode
>
> Cc: Patrik Jakobsson <patrik.r.jakobsson@xxxxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Looks good. Thanks!
Acked-by: Patrik Jakobsson <patrik.r.jakobsson@xxxxxxxxx>
> ---
> drivers/gpu/drm/gma500/oaktrail_crtc.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/gma500/oaktrail_crtc.c b/drivers/gpu/drm/gma500/oaktrail_crtc.c
> index 36c7c2686c90..79fc602b35bc 100644
> --- a/drivers/gpu/drm/gma500/oaktrail_crtc.c
> +++ b/drivers/gpu/drm/gma500/oaktrail_crtc.c
> @@ -385,12 +385,8 @@ static int oaktrail_crtc_mode_set(struct drm_crtc *crtc,
> if (!gma_power_begin(dev, true))
> return 0;
>
> - memcpy(&gma_crtc->saved_mode,
> - mode,
> - sizeof(struct drm_display_mode));
> - memcpy(&gma_crtc->saved_adjusted_mode,
> - adjusted_mode,
> - sizeof(struct drm_display_mode));
> + drm_mode_copy(&gma_crtc->saved_mode, mode);
> + drm_mode_copy(&gma_crtc->saved_adjusted_mode, adjusted_mode);
>
> list_for_each_entry(connector, &mode_config->connector_list, head) {
> if (!connector->encoder || connector->encoder->crtc != crtc)
> --
> 2.34.1
>
