Messages in this thread | | | Date | Mon, 8 Jan 2018 07:53:05 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v6 01/10] x86/retpoline: Add initial retpoline support |
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On Mon, Jan 08, 2018 at 02:46:32PM +0100, Thomas Gleixner wrote: > On Mon, 8 Jan 2018, Josh Poimboeuf wrote: > > 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. > > It still allows to get the ASM part covered. If that's worth it I can't tell.
If there's a makefile error above, then CONFIG_RETPOLINE would already imply compiler support, so the ASM code with the new '%V' option could just do 'ifdef CONFIG_RETPOLINE'.
-- Josh
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