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

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Date:   Tue, 19 Feb 2019 17:17:44 -0500
From:   Qian Cai <cai@....pw>
To:     Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        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>,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        kasan-dev@...glegroups.com
Subject: Re: [PATCH] kasan: turn off asan-stack for clang-8 and earlier

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.
> 
> In the meantime, the best idea I have is to turn off asan-stack for clang-8
> and earlier, so we can produce a kernel that is safe to run.
> 
> I have posted three patches that address the frame overflow warnings that are
> not addressed by turning off asan-stack, so in combination with this change,
> we get much closer to a clean allmodconfig build, which in turn is necessary
> to do meaningful build regression testing.

Well, I am using clang 8.0 on arm64 and running the kernel just fine for a few
weeks now and never trigger a single stack overflow (THREAD_SHIFT = 15) because
I never use any of those drivers you mentioned above. I don't think it is a good
idea to blankly remove the testing coverage here and affect people don't use all
those offensive functions at all.