linux-kernel - Re: [PATCH] arm64: increase stack size for KASAN

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Date:   Tue, 11 Dec 2018 22:43:26 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     cai@....pw
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: increase stack size for KASAN_EXTRA

On Tue, Dec 11, 2018 at 6:18 PM Qian Cai <cai@....pw> wrote:
>
> On Tue, 2018-12-11 at 13:42 +0100, Arnd Bergmann wrote:
> > On Fri, Dec 7, 2018 at 11:35 PM Qian Cai <cai@....pw> wrote:
> > >
> > > If the kernel is configured with KASAN_EXTRA, the stack size is
> > > increasted significantly due to enable this option will set
> > > -fstack-reuse to "none" in GCC [1]. As the results, it could trigger
> > > stack overrun quite often with 32k stack size compiled using GCC 8. For
> > > example, this reproducer
> > >
> > > size
> > > 7536 shrink_inactive_list
> > > 7440 shrink_page_list
> > > 6560 fscache_stats_show
> > > 3920 jbd2_journal_commit_transaction
> > > 3216 try_to_unmap_one
> > > 3072 migrate_page_move_mapping
> > > 3584 migrate_misplaced_transhuge_page
> > > 3920 ip_vs_lblcr_schedule
> > > 4304 lpfc_nvme_info_show
> > > 3888 lpfc_debugfs_nvmestat_data.constprop
> > >
> > > There are other 49 functions are over 2k in size while compiling kernel
> > > with "-Wframe-larger-than=" on this machine. Hence, it is too much work
> > > to change Makefiles for each object to compile without
> > > -fsanitize-address-use-after-scope individually.
> > >
> > > [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715#c23
> >
> > Could you clarify: are the numbers you see with or without the bugfix
> > from that bugzilla?
> >
>
> The numbers were from GCC8 which does NOT contain this patch [1].
>
> GCC9 is awesome which reduced the numbers in half even for KASAN_EXTRA. Only
> thing is that GCC9 has not been officially released yet, so it is a bit
> inconvenient for users need to compile the compiler by themselves first.
>
> I am fine either way to drop this patch or keep it until GCC9 is GA.
>
> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715#c35

Maybe we can make the constant depend on the compiler version?
It may also be possible to reduce the KASAN_THREAD_SHIFT
constant for the normal case with gcc-9 and go back to the
default frame size then.

       Arnd