linux-kernel - Re: [PATCH] drm/mediatek: Fix return type of mtk_hdmi_bridge_mode

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Date:   Thu, 3 Nov 2022 15:28:43 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH] drm/mediatek: Fix return type of
 mtk_hdmi_bridge_mode_valid()

Il 02/11/22 16:47, Nathan Chancellor ha scritto:
> 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 function pointer types initializing 'enum drm_mode_status (*)(struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' with an expression of type 'int (struct drm_bridge *, const struct drm_display_info *, const struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
>            .mode_valid = 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.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Reported-by: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> Reviewed-by: Kees Cook <keescook@...omium.org>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>