linux-kernel - Re: [PATCH] mm: larger stack guard gap, between vmas

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Date:   Mon, 3 Jul 2017 17:05:27 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Ben Hutchings <ben@...adent.org.uk>
Cc:     Michal Hocko <mhocko@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Willy Tarreau <w@....eu>, Oleg Nesterov <oleg@...hat.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Rik van Riel <riel@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Tony Luck <tony.luck@...el.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Diller <deller@....de>,
        James Hogan <james.hogan@...tec.com>,
        Laura Abbott <labbott@...hat.com>, Greg KH <greg@...ah.com>,
        "security@...nel.org" <security@...nel.org>,
        linux-distros@...openwall.org,
        Qualys Security Advisory <qsa@...lys.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: larger stack guard gap, between vmas

On Mon, Jul 3, 2017 at 4:55 PM, Ben Hutchings <ben@...adent.org.uk> wrote:
>
> Firstly, some Rust programs are crashing on ppc64el with 64 KiB pages.
> Apparently Rust maps its own guard page at the lower limit of the stack
> (determined using pthread_getattr_np() and pthread_attr_getstack()).  I
> don't think this ever actually worked for the main thread stack, but it
> now also blocks expansion as the default stack size of 8 MiB is smaller
> than the stack gap of 16 MiB.  Would it make sense to skip over
> PROT_NONE mappings when checking whether it's safe to expand?

Hmm. Maybe.

Also, the whole notion that the gap should be relative to the page
size never made sense to me. So I think we could/should just make the
default gap size be one megabyte, not that "256 pages" abortion.

> Secondly, LibreOffice is crashing on i386 when running components
> implemented in Java.  I don't have a diagnosis for this yet.

Ugh. Nobody seeing this inside SuSe/Red Hat? I don't think I've heard
about this..

                Linus