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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id 85-20020a621658000000b005609d3d3008sm9054723pfw.171.2022.11.02.12.22.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Nov 2022 12:22:11 -0700 (PDT) Date: Wed, 2 Nov 2022 12:22:11 -0700 From: Kees Cook To: Nathan Chancellor Cc: Chun-Kuang Hu , Philipp Zabel , dri-devel@lists.freedesktop.org, linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Nick Desaulniers , Tom Rix , Sami Tolvanen , llvm@lists.linux.dev, linux-kernel@vger.kernel.org, patches@lists.linux.dev Subject: Re: [PATCH] drm/mediatek: Fix return type of mtk_hdmi_bridge_mode_valid() Message-ID: <202211021222.1E8A8BCB43@keescook> References: <20221102154712.540548-1-nathan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221102154712.540548-1-nathan@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221102_122214_372352_8EC19CEB X-CRM114-Status: GOOD ( 14.03 ) X-BeenThere: linux-mediatek@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-mediatek" Errors-To: linux-mediatek-bounces+linux-mediatek=archiver.kernel.org@lists.infradead.org On Wed, Nov 02, 2022 at 08:47:12AM -0700, Nathan Chancellor wrote: > 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 > Signed-off-by: Nathan Chancellor Reviewed-by: Kees Cook -- Kees Cook