Re: [PATCH] arm64: increase stack size for KASAN_EXTRA

Qian Cai
2018-12-11T17:18:33Z

On Tue, 2018-12-11 at 13:42 +0100, Arnd Bergmann wrote:
> On Fri, Dec 7, 2018 at 11:35 PM Qian Cai <cai@lca.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