Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
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Date: Wed, 20 Sep 2017 19:04:10 -0600
From: Tycho Andersen <tycho@...ker.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel-hardening@...ts.openwall.com,
	Marco Benatto <marco.antonio.780@...il.com>,
	Juerg Haefliger <juerg.haefliger@...onical.com>, x86@...nel.org
Subject: Re: [PATCH v6 03/11] mm, x86: Add support for eXclusive Page Frame
 Ownership (XPFO)

On Wed, Sep 20, 2017 at 05:28:11PM -0700, Dave Hansen wrote:
> At a high level, does this approach keep an attacker from being able to
> determine the address of data in the linear map, or does it keep them
> from being able to *exploit* it?

It keeps them from exploiting it, by faulting when a physmap alias is
used.

> Can you have a ret2dir attack if the attacker doesn't know the
> address, for instance?

Yes, through a technique similar to heap spraying. The original paper
has a study of this, section 5.2 outlines the attack and 7.2 describes
their success rate:

http://www.cs.columbia.edu/~vpk/papers/ret2dir.sec14.pdf

Tycho

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