linux-hardening - Re: [PATCH v1 6/6] bitfield: build kunit tests without structleak plugin

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Date:   Wed, 29 Sep 2021 14:04:30 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Shuah Khan <shuah@...nel.org>, David Gow <davidgow@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Rafael Wysocki <rafael@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Ulf Hansson <ulf.hansson@...aro.org>, andreas.noever@...il.com,
        michael.jamet@...el.com,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        yehezkelshb@...il.com, Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        gregkh <gregkh@...uxfoundation.org>, linux-iio@...r.kernel.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v1 6/6] bitfield: build kunit tests without structleak plugin

On Fri, Sep 17, 2021 at 12:22 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Fri, Sep 17, 2021 at 8:11 AM Brendan Higgins
> <brendanhiggins@...gle.com> wrote:
> >
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > The structleak plugin causes the stack frame size to grow immensely:
> >
> > lib/bitfield_kunit.c: In function 'test_bitfields_constants':
> > lib/bitfield_kunit.c:93:1: error: the frame size of 7440 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> >
> > Turn it off in this file.
> >
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Brendan Higgins <brendanhiggins@...gle.com>
> > ---
> >  lib/Makefile | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/Makefile b/lib/Makefile
> > index 5efd1b435a37c..c93c4b59af969 100644
> > --- a/lib/Makefile
> > +++ b/lib/Makefile
> > @@ -351,7 +351,7 @@ obj-$(CONFIG_OBJAGG) += objagg.o
> >  obj-$(CONFIG_PLDMFW) += pldmfw/
> >
> >  # KUnit tests
> > -CFLAGS_bitfield_kunit.o := $(call cc-option,-Wframe-larger-than=10240)
> > +CFLAGS_bitfield_kunit.o := $(call cc-option,-Wframe-larger-than=10240) $(DISABLE_STRUCTLEAK_PLUGIN)
>
> I think the  $(call cc-option,-Wframe-larger-than=10240) needs to be dropped
> here. This was not in my original patch and it is definitely broken on

Ah, someone else put that there, so I just left it, but I can drop it.

> all architectures
> with 8KB stack size or less if the function needs that much. What is the amount
> of actual stack usage you observe without this?

Well STRUCTLEAK claims 7440 bytes, but I don't entirely believe that.
Regardless, it is definitely less than 8KB.

> If we still get a warning, then
> I think this needs to be fixed in the code.
>
>        Arnd

Cheers