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Date:   Wed, 9 Nov 2022 11:07:12 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Hyun Kwon <hyun.kwon@xilinx.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>,
        Sami Tolvanen <samitolvanen@google.com>, llvm@lists.linux.dev,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev,
        Nathan Huckleberry <nhuck@google.com>,
        Dan Carpenter <error27@gmail.com>
Subject: Re: [PATCH v2] drm: xlnx: Fix return type of
 zynqmp_dp_bridge_mode_valid
Message-ID: <202211091107.718BF1BE89@keescook>
References: <20221109001424.1422495-1-nathan@kernel.org>
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On Tue, Nov 08, 2022 at 05:14:25PM -0700, Nathan Chancellor wrote:
> From: Nathan Huckleberry <nhuck@google.com>
> 
> The mode_valid field in drm_bridge_helper_funcs is expected to be of
> type
> enum drm_mode_status (* mode_valid) (struct drm_bridge *bridge,
>                                      struct drm_display_mode *mode);
> 
> The mismatched return type breaks forward edge kCFI since the underlying
> function definition does not match the function hook definition. A new
> warning in clang will catch this at compile time:
> 
>   drivers/gpu/drm/xlnx/zynqmp_dp.c:1573:16: 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 = zynqmp_dp_bridge_mode_valid,
>                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>   1 error generated.
> 
> The return type of zynqmp_dp_bridge_mode_valid should be changed from
> int to enum drm_mode_status.
> 
> Reported-by: Dan Carpenter <error27@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1703
> Link: https://github.com/ClangBuiltLinux/linux/issues/1750
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook