linux-kernel - Re: [PATCH 0/1] expand_downwards: don't require the gap if !vm

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Message-ID: <20170630132439.GL22917@dhcp22.suse.cz>
Date:   Fri, 30 Jun 2017 15:24:39 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Oleg Nesterov <oleg@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Larry Woodman <lwoodman@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/1] expand_downwards: don't require the gap if !vm_prev

On Wed 28-06-17 16:26:33, Linus Torvalds wrote:
[...]
> In fact, I'd even be quite open to adding a kernel warning about badly
> behaved binaries that grow their stack by a big amount in one go. Not
> only is it bad taste (and we really should encourage compilers to do
> probing every page when growing the stack), but it migth be a sign of
> an attempted attack.

FWIW our gcc guys shown an interest in having something to tell the
kernel how much the stack can grow at once. They want it for testing of
the new stack probing alloca implementation. I have something
preliminary with /proc/<pid>/stack_expand_limit for the internal testing
purpose but maybe there will be more interest for this. I didn't plan to
post it public because it basically duplicates the stack_gap but it is
also true that it can help some applications which won't use the proposed
__save_alloca (or whatever it will be) without increasing stack_gap too
much.

What do you think?
-- 
Michal Hocko
SUSE Labs