On Wed, Nov 02, 2022 at 08:42:15AM -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/fsl-dcu/fsl_dcu_drm_rgb.c:74:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_connector *, struct drm_display_mode *)' with an expression of type 'int (struct drm_connector *, struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict] > .mode_valid = fsl_dcu_drm_connector_mode_valid, > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > 1 error generated. > > ->mode_valid() in 'struct drm_connector_helper_funcs' expects a return > type of 'enum drm_mode_status', not 'int'. Adjust the return type of > fsl_dcu_drm_connector_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@xxxxxxxxxx> > Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
