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

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Date: Fri, 31 May 2024 09:09:19 -0700
From: Kees Cook <kees@...nel.org>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>, linux-kbuild@...r.kernel.org,
	Linux-Arch <linux-arch@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] kbuild: provide reasonable defaults for tool coverage

On Fri, May 31, 2024 at 07:16:30PM +0900, Masahiro Yamada wrote:
> 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.

I'll try to figure this out. I suspect some kind of symbol name changes
are happening? The fortify tests expect to find specifically-named
symbols, so perhaps something is disrupting that?

-- 
Kees Cook