In the Linux kernel, the following vulnerability has been resolved:
drm/sti: Fix return type of sti_{dvo,hda,hdmi}_connector_mode_valid()
With clangs 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/sti/sti_hda.c:637:16: 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 = sti_hda_connector_mode_valid, ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/gpu/drm/sti/sti_dvo.c:376:16: 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 = sti_dvo_connector_mode_valid, ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ drivers/gpu/drm/sti/sti_hdmi.c:1035:16: 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 = sti_hdmi_connector_mode_valid, ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
->mode_valid() in struct drm_connector_helper_funcs expects a return type of enum drm_mode_status, not int. Adjust the return type of sti_{dvo,hda,hdmi}_connector_mode_valid() to match the prototypes to resolve the warning and CFI failure.