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

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Date:   Tue, 4 Jul 2017 13:26:15 +0100
From:   John Haxby <john.haxby@...cle.com>
To:     Ben Hutchings <ben@...adent.org.uk>,
        Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>
Cc:     Willy Tarreau <w@....eu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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: [vs-plain] Re: [PATCH] mm: larger stack guard gap, between vmas

On 04/07/17 00:55, Ben Hutchings wrote:
> Unfortunately these regressions have not been completely fixed by
> switching to Hugh's fix.
> 
> 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?
> 
> Secondly, LibreOffice is crashing on i386 when running components
> implemented in Java.  I don't have a diagnosis for this yet.

We found that we needed f4cb767d76cf ("mm: fix new crash in
unmapped_area_topdown()")   Apologies if you've already covered that.

This may be needed in addition to the other patch you proposed.

jch