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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 14 Jul 2020 11:49:20 -0700
Message-ID: <CAHk-=wgRS_WpRdC9nyXzVZ7aWNQt0HKMbyFjhrgrNo49AFNWzg@mail.gmail.com>
Subject: Re: WARNING: at mm/mremap.c:211 move_page_tables in i386
To:     Joel Fernandes <joel@joelfernandes.org>
Cc:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        linux- stable <stable@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>, Michal Hocko <mhocko@kernel.org>,
        lkft-triage@lists.linaro.org, Chris Down <chris@chrisdown.name>,
        Michel Lespinasse <walken@google.com>,
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        Jerome Glisse <jglisse@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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On Tue, Jul 14, 2020 at 11:12 AM Joel Fernandes <joel@joelfernandes.org> wrote:
>
> I think you misunderstood me. I was not advocating breaking the stack
> movement code or breaking stack randomization, I was going to try to
> see if I could keep that working while not having to do an overlapping
> move.

I'm not really seeing how you'd do that with a big stack that gets
close to the stack ulimit.

Except by avoiding randomization.

But the existing randomization may be so bad that it doesn't much
matter. And I do think we limit the execve stack to a reasonably small
fraction of the whole ulimit. So worth exploring, I guess.

The current code with "align_stack" doing randomization could also do
with a lot of clarifications. The code is odd.

            Linus