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

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Date: Tue, 14 May 2024 09:31:47 +0200
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: Kees Cook <keescook@...omium.org>, Masahiro Yamada <masahiroy@...nel.org>
Cc: 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>, Marco Elver <elver@...gle.com>, Josh
 Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Peter Oberparleiter <oberpar@...ux.ibm.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 Mon, 2024-05-13 at 11:48 -0700, Kees Cook 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.
> 
> 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/

Yes, this patch set fixes the issue too.

Tested-by: Roberto Sassu <roberto.sassu@...wei.com>

Now UBSAN complains about misaligned address, such as:

[    0.150000][    T1] UBSAN: misaligned-access in kernel/workqueue.c:5514:3
[    0.150000][    T1] member access within misaligned address 0000000064c36f78 for type 'struct pool_workqueue'
[    0.150000][    T1] which requires 512 byte alignment
[    0.150000][    T1] CPU: 0 PID: 1 Comm: swapper Not tainted 6.9.0-dont-use-00003-g3b621c71dc5e #2244

But I guess this is for a separate thread.

Thanks

Roberto

> > 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?
> 
> -Kees
>