-----Original Message-----
From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On
Behalf Of Jason Cooper
Sent: Tuesday, July 26, 2016 2:00 PM
To: Roberts, William C <redacted>
Cc: linux-mm@kvack.org; linux-kernel@vger.kernel.org; kernel-
hardening@lists.openwall.com; akpm@linux-foundation.org;
keescook@chromium.org; gregkh@linuxfoundation.org; nnk@google.com;
jeffv@google.com; salyzyn@android.com; dcashman@android.com
Subject: Re: [PATCH] [RFC] Introduce mmap randomization

Hi William,

On Tue, Jul 26, 2016 at 08:13:23PM +0000, Roberts, William C wrote:

quoted

quoted

quoted

From: Jason Cooper [mailto:jason@lakedaemon.net] On Tue, Jul 26,
2016 at 11:22:26AM -0700, william.c.roberts@intel.com wrote:

quoted

Performance Measurements:
Using strace with -T option and filtering for mmap on the
program ls shows a slowdown of approximate 3.7%

I think it would be helpful to show the effect on the resulting object code.

Do you mean the maps of the process? I have some captures for
whoopsie on my Ubuntu system I can share.

No, I mean changes to mm/mmap.o.

Sure I can post the objdump of that, do you just want a diff of old vs new?

quoted

quoted

One thing I didn't make clear in my commit message is why this is
good. Right now, if you know An address within in a process, you
know all offsets done with mmap(). For instance, an offset To libX
can yield libY by adding/subtracting an offset. This is meant to
make rops a bit harder, or In general any mapping offset mmore difficult to

find/guess.

Are you able to quantify how many bits of entropy you're imposing on the
attacker?  Is this a chair in the hallway or a significant increase in the chances of
crashing the program before finding the desired address?

I'd likely need to take a small sample of programs and examine them, especially considering
That as gaps are harder to find, it forces the randomization down and randomization can
Be directly altered with length on mmap(), versus randomize_addr() which didn't have this
restriction but OOM'd do to fragmented easier.

thx,

Jason.

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