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

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Message-ID: <20170704144817.GT14722@dhcp22.suse.cz>
Date:   Tue, 4 Jul 2017 16:48:17 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Ximin Luo <infinity0@...ian.org>
Cc:     Ben Hutchings <ben@...adent.org.uk>, Willy Tarreau <w@....eu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        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 Tue 04-07-17 14:19:00, Ximin Luo wrote:
[...]
> I've written up an explanation of what happens in the Rust case here:
> 
> https://github.com/rust-lang/rust/issues/43052

The most important part is https://github.com/rust-lang/rust/blob/master/src/libstd/sys/unix/thread.rs#L248
        // Rellocate the last page of the stack.
        // This ensures SIGBUS will be raised on
        // stack overflow.
        let result = mmap(stackaddr, psize, PROT_NONE, MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);

so this is basically the same thing Java does. Except that Java doesn't
do that on main thread usually. Only some JNI runtimes do that.
pthread_attr_getstack() usage on the main thread sounds like a real bug
in rust to me.

Thanks for the writeup!
-- 
Michal Hocko
SUSE Labs