On Sun, Jan 07, 2018 at 10:11:16PM +0000, David Woodhouse wrote: > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index a20eacd..918e550 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -235,6 +235,16 @@ KBUILD_CFLAGS += -Wno-sign-compare > # > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > > +# Avoid indirect branches in kernel to deal with Spectre > +ifdef CONFIG_RETPOLINE > + RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern > -mindirect-branch-register) > + ifneq ($(RETPOLINE_CFLAGS),) > + KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE > + else > + $(warning Retpoline not supported in compiler. System may be > insecure.) > + endif > +endif
I wonder if an error might be more appropriate than a warning. I learned from experience that a lot of people don't see these Makefile warnings, and this would be a dangerous one to miss. Also if this were an error, you could get rid of the RETPOLINE define, and that would be one less define cluttering up the already way-too-long GCC arg list. -- Josh
