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References: <20221102154712.540548-1-nathan@kernel.org>
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From:   Chun-Kuang Hu <chunkuang.hu@kernel.org>
Date:   Mon, 14 Nov 2022 08:02:54 +0800
Message-ID: <CAAOTY_9nH8tW6yP=3giQmSKQjnQ+pmaGRQ0N3_ODFg1uS-rvCA@mail.gmail.com>
Subject: Re: [PATCH] drm/mediatek: Fix return type of mtk_hdmi_bridge_mode_valid()
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        dri-devel@lists.freedesktop.org,
        linux-mediatek@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, Kees Cook <keescook@chromium.org>,
        Sami Tolvanen <samitolvanen@google.com>, llvm@lists.linux.dev,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev
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 Hi, Nathan:

Nathan Chancellor <nathan@kernel.org> =E6=96=BC 2022=E5=B9=B411=E6=9C=882=
=E6=97=A5 =E9=80=B1=E4=B8=89 =E6=99=9A=E4=B8=8A11:47=E5=AF=AB=E9=81=93=EF=
=BC=9A
>
> With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),
> indirect call targets are validated against the expected function
> pointer prototype to make sure the call target is valid to help mitigate
> ROP attacks. If they are not identical, there is a failure at run time,
> which manifests as either a kernel panic or thread getting killed. A
> proposed warning in clang aims to catch these at compile time, which
> reveals:
>
>   drivers/gpu/drm/mediatek/mtk_hdmi.c:1407:16: error: incompatible functi=
on pointer types initializing 'enum drm_mode_status (*)(struct drm_bridge *=
, const struct drm_display_info *, const struct drm_display_mode *)' with a=
n expression of type 'int (struct drm_bridge *, const struct drm_display_in=
fo *, const struct drm_display_mode *)' [-Werror,-Wincompatible-function-po=
inter-types-strict]
>           .mode_valid =3D mtk_hdmi_bridge_mode_valid,
>                         ^~~~~~~~~~~~~~~~~~~~~~~~~~
>   1 error generated.
>
> ->mode_valid() in 'struct drm_bridge_funcs' expects a return type of
> 'enum drm_mode_status', not 'int'. Adjust the return type of
> mtk_hdmi_bridge_mode_valid() to match the prototype's to resolve the
> warning and CFI failure.

Applied to mediatek-drm-next [1], thanks.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/chunkuang.hu/linux.git/=
log/?h=3Dmediatek-drm-next

Chun-Kuang.

>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Reported-by: Sami Tolvanen <samitolvanen@google.com>
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  drivers/gpu/drm/mediatek/mtk_hdmi.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_hdmi.c b/drivers/gpu/drm/mediat=
ek/mtk_hdmi.c
> index 4c80b6896dc3..6e8f99554f54 100644
> --- a/drivers/gpu/drm/mediatek/mtk_hdmi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_hdmi.c
> @@ -1202,9 +1202,10 @@ static enum drm_connector_status mtk_hdmi_detect(s=
truct mtk_hdmi *hdmi)
>         return mtk_hdmi_update_plugged_status(hdmi);
>  }
>
> -static int mtk_hdmi_bridge_mode_valid(struct drm_bridge *bridge,
> -                                     const struct drm_display_info *info=
,
> -                                     const struct drm_display_mode *mode=
)
> +static enum drm_mode_status
> +mtk_hdmi_bridge_mode_valid(struct drm_bridge *bridge,
> +                          const struct drm_display_info *info,
> +                          const struct drm_display_mode *mode)
>  {
>         struct mtk_hdmi *hdmi =3D hdmi_ctx_from_bridge(bridge);
>         struct drm_bridge *next_bridge;
>
> base-commit: 9abf2313adc1ca1b6180c508c25f22f9395cc780
> --
> 2.38.1
>