Re: [PATCH] [RFC] Introduce mmap randomization

[Jason Cooper]

Hi William,

On Tue, Jul 26, 2016 at 08:13:23PM +0000, Roberts, William C wrote:
> > > From: Jason Cooper [mailto:jason@xxxxxxxxxxxxxx]
> > > On Tue, Jul 26, 2016 at 11:22:26AM -0700, william.c.roberts@xxxxxxxxx wrote:
> > > > 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.

> > 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?

thx,

Jason.