In the Linux kernel, the following vulnerability has been resolved:
drm/sti: Fix return type of sti{dvo,hda,hdmi}connectormodevalid()
With clang's kernel control flow integrity (kCFI, CONFIGCFICLANG), 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/stihda.c:637:16: error: incompatible function pointer types initializing 'enum drmmodestatus (*)(struct drmconnector , 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 drmconnector *, struct drmdisplaymode *)' with an expression of type 'int (struct drmconnector , 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 drmconnector *, struct drmdisplaymode *)' with an expression of type 'int (struct drmconnector *, struct drmdisplaymode *)' [-Werror,-Wincompatible-function-pointer-types-strict] .modevalid = stihdmiconnectormode_valid, ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
->modevalid() in 'struct drmconnectorhelperfuncs' expects a return type of 'enum drmmodestatus', not 'int'. Adjust the return type of sti{dvo,hda,hdmi}connectormodevalid() to match the prototype's to resolve the warning and CFI failure.