linux-kernel - Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't used at runtime

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Message-ID: <CANpmjNPnP2_4oHSnhEO89ZhpqNfUg51XzL0awWVkYGNhxUayhw@mail.gmail.com>
Date:   Tue, 17 Oct 2023 17:26:36 +0200
From:   Marco Elver <elver@...gle.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        "Kaplan, David" <David.Kaplan@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't
 used at runtime

On Tue, 17 Oct 2023 at 17:24, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>
> + Marco, Dmitry
>
> On Mon, Oct 16, 2023 at 10:28 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> >
> > On Tue, Oct 17, 2023 at 04:31:09AM +0000, Kaplan, David wrote:
> > > Perhaps another option would be to not compile these two files with KCSAN, as they are already excluded from KASAN and GCOV it looks like.
> >
> > I think the latter would be the easy fix, does this make it go away?
>
> Yeah, usually when I see the other sanitizers being disabled on a per
> object basis, I think "where there's smoke, there's fire."
>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Closes: https://lore.kernel.org/lkml/20231016214810.GA3942238@dev-arch.thelio-3990X/

Acked-by: Marco Elver <elver@...gle.com>

Instrumenting these files really doesn't make sense. Thanks for
catching this and the fix!

> >
> > diff --git a/init/Makefile b/init/Makefile
> > index ec557ada3c12..cbac576c57d6 100644
> > --- a/init/Makefile
> > +++ b/init/Makefile
> > @@ -60,4 +60,5 @@ include/generated/utsversion.h: FORCE
> >  $(obj)/version-timestamp.o: include/generated/utsversion.h
> >  CFLAGS_version-timestamp.o := -include include/generated/utsversion.h
> >  KASAN_SANITIZE_version-timestamp.o := n
> > +KCSAN_SANITIZE_version-timestamp.o := n
> >  GCOV_PROFILE_version-timestamp.o := n
> > diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
> > index 3cd6ca15f390..c9f3e03124d7 100644
> > --- a/scripts/Makefile.vmlinux
> > +++ b/scripts/Makefile.vmlinux
> > @@ -19,6 +19,7 @@ quiet_cmd_cc_o_c = CC      $@
> >
> >  ifdef CONFIG_MODULES
> >  KASAN_SANITIZE_.vmlinux.export.o := n
> > +KCSAN_SANITIZE_.vmlinux.export.o := n
> >  GCOV_PROFILE_.vmlinux.export.o := n
> >  targets += .vmlinux.export.o
> >  vmlinux: .vmlinux.export.o
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers