linux-kernel - Re: [PATCH] kasan: turn off asan-stack for clang-8 and earlier

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Date:   Wed, 20 Feb 2019 10:19:33 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Kostya Serebryany <kcc@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Qian Cai <cai@....pw>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Brown <broonie@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Christoph Lameter <cl@...ux.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Evgenii Stepanov <eugenis@...gle.com>
Subject: Re: [PATCH] kasan: turn off asan-stack for clang-8 and earlier

On Wed, Feb 20, 2019 at 7:44 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Wed, Feb 20, 2019 at 1:34 AM Kostya Serebryany <kcc@...gle.com> wrote:
> >
> > On Tue, Feb 19, 2019 at 2:43 PM Nick Desaulniers
> > <ndesaulniers@...gle.com> wrote:
> > >
> > > + Evgenii, Kostya for KASAN
> > >
> > > On Tue, Feb 19, 2019 at 2:17 PM Qian Cai <cai@....pw> wrote:
> > > >
> > > > On Tue, 2019-02-19 at 22:49 +0100, Arnd Bergmann wrote:
> > > > > Building an arm64 allmodconfig kernel with clang results in over 140 warnings
> > > > > about overly large stack frames, the worst ones being:
> > > > >
> > > > > drivers/gpu/drm/panel/panel-sitronix-st7789v.c:196:12: error: stack frame size
> > > > > of 20224 bytes in function 'st7789v_prepare'
> > > > > drivers/video/fbdev/omap2/omapfb/displays/panel-tpo-td028ttec1.c:196:12:
> > > > > error: stack frame size of 13120 bytes in function 'td028ttec1_panel_enable'
> > > > > drivers/usb/host/max3421-hcd.c:1395:1: error: stack frame size of 10048 bytes
> > > > > in function 'max3421_spi_thread'
> > > > > drivers/net/wan/slic_ds26522.c:209:12: error: stack frame size of 9664 bytes
> > > > > in function 'slic_ds26522_probe'
> > > > > drivers/crypto/ccp/ccp-ops.c:2434:5: error: stack frame size of 8832 bytes in
> > > > > function 'ccp_run_cmd'
> > > > > drivers/media/dvb-frontends/stv0367.c:1005:12: error: stack frame size of 7840
> > > > > bytes in function 'stv0367ter_algo'
> > > > >
> > > > > None of these happen with gcc today, and almost all of these are the result
> > > > > of a single known bug in llvm.  Hopefully it will eventually get fixed with
> > > > > the
> > > > > clang-9 release.
> >
> > I am not confident we can fix this in clang.
> > The difference between gcc and clang, AFAICT, is not in the asan
> > instrumentation, but in inining.
> > Looking at the reproducer from https://bugs.llvm.org/show_bug.cgi?id=38809#c4,
> > if I change ltv350qv_write_reg to always inline, gcc also produces a
> > huge 10K stack frame,
> > and making it noinline fixes the stack frame for both gcc and clang.
>
> Does your gcc have fix for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715 ?
>
> For me gcc rejects to inline it:
>
> gcc version 7.3.0 (Debian 7.3.0-5)
>
> $ gcc /tmp/test.c -Wframe-larger-than=128 -c -fsanitize=kernel-address
> -O2 --param asan-stack=1
> /tmp/test.c:23:13: warning: always_inline function might not be
> inlinable [-Wattributes]

I don't see that warning here

>  static void ltv350qv_write_reg(void) {
>              ^~~~~~~~~~~~~~~~~~
> /tmp/test.c: In function ‘ltv350qv_power_on’:
> /tmp/test.c:57:1: warning: the frame size of 416 bytes is larger than
> 128 bytes [-Wframe-larger-than=]
>  }

but I also see the small stack size here: https://godbolt.org/z/Uz5Ruv

gcc definitely inlines the function here but only has one copy of
spi_message and spi_transfer on the stack, while clang inserts
a call to __asan_report_store8_noabort() and has one copy per
inlined call to ltv350qv_write_reg().

      Arnd