linux-kernel - Re: [PATCH 1/3] kbuild: provide reasonable defaults for tool coverage

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Date: Fri, 31 May 2024 19:16:30 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Arnd Bergmann <arnd@...db.de>
Cc: linux-kbuild@...r.kernel.org, Linux-Arch <linux-arch@...r.kernel.org>, 
	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 1/3] kbuild: provide reasonable defaults for tool coverage

On Fri, May 31, 2024 at 6:06 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Fri, May 31, 2024, at 10:52, Masahiro Yamada wrote:
> > On Tue, May 28, 2024 at 8:36 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> >> I don't understand the nature of this warning, but I see
> >> that your patch ended up dropping -fsanitize=kernel-address
> >> from the compiler flags because the lib/test_fortify/*.c files
> >> don't match the $(is-kernel-object) rule. Adding back
> >> -fsanitize=kernel-address shuts up these warnings.
> >
> >
> > In my understanding, fortify-string is independent of KASAN.
> >
> > I do not understand why -fsanitize=kernel-address matters.
>
> Right, this is something I've failed to understand as well
> so far.
>
> >> I've applied a local workaround in my randconfig tree
> >>
> >> diff --git a/lib/Makefile b/lib/Makefile
> >> index ddcb76b294b5..d7b8fab64068 100644
> >> --- a/lib/Makefile
> >> +++ b/lib/Makefile
> >> @@ -425,5 +425,7 @@ $(obj)/$(TEST_FORTIFY_LOG): $(addprefix $(obj)/, $(TEST_FORTIFY_LOGS)) FORCE
> >>
> >>  # Fake dependency to trigger the fortify tests.
> >>  ifeq ($(CONFIG_FORTIFY_SOURCE),y)
> >> +ifndef CONFIG_KASAN
> >>  $(obj)/string.o: $(obj)/$(TEST_FORTIFY_LOG)
> >> +endif
> >>  endif
> >>
> >>
> >> which I don't think we want upstream. Can you and Kees come
> >> up with a proper fix instead?
> >
> > I set CONFIG_FORTIFY_SOURCE=y and CONFIG_KASAN=y,
> > but I did not observe such warnings.
> > Is this arch or compiler-specific?
> >
> >
> > Could you provide me with the steps to reproduce it?
>
> This is a randconfig .config file that shows it, but
> I've seen it in a lot of others:
> https://pastebin.com/raw/ESVzUeth
>
> If this doesn't reproduce it for you, I can try to narrow
> it down further.
>
>      Arnd


Thanks, I was able to reproduce it.

The issue happens with CONFIG_KASAN_SW_TAGS.

I do not see the issue with CONFIG_KASAN_GENERIC.



-- 
Best Regards
Masahiro Yamada