linux-hardening - Re: [PATCH 0/3] kbuild: remove many tool coverage variables

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Date: Tue, 14 May 2024 07:50:59 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Marco Elver <elver@...gle.com>
Cc: Kees Cook <keescook@...omium.org>, linux-kbuild@...r.kernel.org, 
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, 
	Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Peter Oberparleiter <oberpar@...ux.ibm.com>, 
	Roberto Sassu <roberto.sassu@...weicloud.com>, Johannes Berg <johannes@...solutions.net>, 
	kasan-dev@...glegroups.com, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 0/3] kbuild: remove many tool coverage variables

On Tue, May 14, 2024 at 4:55 AM Marco Elver <elver@...gle.com> wrote:
>
> On Mon, 13 May 2024 at 20:48, Kees Cook <keescook@...omium.org> wrote:
> >
> > In the future can you CC the various maintainers of the affected
> > tooling? :)
> >
> > On Mon, May 06, 2024 at 10:35:41PM +0900, Masahiro Yamada wrote:
> > >
> > > This patch set removes many instances of the following variables:
> > >
> > >   - OBJECT_FILES_NON_STANDARD
> > >   - KASAN_SANITIZE
> > >   - UBSAN_SANITIZE
> > >   - KCSAN_SANITIZE
> > >   - KMSAN_SANITIZE
> > >   - GCOV_PROFILE
> > >   - KCOV_INSTRUMENT
> > >
> > > Such tools are intended only for kernel space objects, most of which
> > > are listed in obj-y, lib-y, or obj-m.
>
> I welcome the simplification, but see below.
>
> > This is a reasonable assertion, and the changes really simplify things
> > now and into the future. Thanks for finding such a clean solution! I
> > note that it also immediately fixes the issue noticed and fixed here:
> > https://lore.kernel.org/all/20240513122754.1282833-1-roberto.sassu@huaweicloud.com/
> >
> > > The best guess is, objects in $(obj-y), $(lib-y), $(obj-m) can opt in
> > > such tools. Otherwise, not.
> > >
> > > This works in most places.
> >
> > I am worried about the use of "guess" and "most", though. :) Before, we
> > had some clear opt-out situations, and now it's more of a side-effect. I
> > think this is okay, but I'd really like to know more about your testing.
> >
> > It seems like you did build testing comparing build flags, since you
> > call out some of the explicit changes in patch 2, quoting:
> >
> > >  - include arch/mips/vdso/vdso-image.o into UBSAN, GCOV, KCOV
> > >  - include arch/sparc/vdso/vdso-image-*.o into UBSAN
> > >  - include arch/sparc/vdso/vma.o into UBSAN
> > >  - include arch/x86/entry/vdso/extable.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
> > >  - include arch/x86/entry/vdso/vdso-image-*.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
> > >  - include arch/x86/entry/vdso/vdso32-setup.o into KASAN, KCSAN, UBSAN, GCOV, KCOV
> > >  - include arch/x86/entry/vdso/vma.o into GCOV, KCOV
> > >  - include arch/x86/um/vdso/vma.o into KASAN, GCOV, KCOV
> >
> > I would agree that these cases are all likely desirable.
> >
> > Did you find any cases where you found that instrumentation was _removed_
> > where not expected?
>
> In addition, did you boot test these kernels?


No. I didn't.




> While I currently don't
> recall if the vdso code caused us problems (besides the linking
> problem for non-kernel objects), anything that is opted out from
> instrumentation in arch/ code needs to be carefully tested if it
> should be opted back into instrumentation. We had many fun hours
> debugging boot hangs or other recursion issues due to instrumented
> arch code.


As I replied to Kees, I checked the diff of .*.cmd files.

I believe checking the compiler flags for every object
is comprehensive testing.

If the same set of compiler flags is passed,
the same build artifact is generated.



-- 
Best Regards
Masahiro Yamada