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Message-ID: <20180302204808.GA671@bombadil.infradead.org>
Date: Fri, 2 Mar 2018 12:48:08 -0800
From: Matthew Wilcox <willy@...radead.org>
To: Ilya Smith <blackzert@...il.com>
Cc: Kees Cook <keescook@...omium.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Michal Hocko <mhocko@...e.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Jan Kara <jack@...e.cz>, Jerome Glisse <jglisse@...hat.com>,
Hugh Dickins <hughd@...gle.com>, Helge Deller <deller@....de>,
Andrea Arcangeli <aarcange@...hat.com>,
Oleg Nesterov <oleg@...hat.com>, Linux-MM <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC PATCH] Randomization of address chosen by mmap.
On Fri, Mar 02, 2018 at 11:30:28PM +0300, Ilya Smith wrote:
> This is a really good question. Lets think we choose address with random-length
> guard hole. This length is limited by some configuration as you described. For
> instance let it be 1MB. Now according to current implementation, we still may
> fill this gap with small allocations with size less than 1MB. Attacker will
> going to build attack base on this predictable behaviour - he jus need to spray
> with 1 MB chunks (or less, with some expectation). This attack harder but not
> impossible.
Ah, I didn't mean that. I was thinking that we can change the
implementation to reserve 1-N pages after the end of the mapping.
So you can't map anything else in there, and any load/store into that
region will segfault.
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