linux-kernel - Re: [Security] proactive defense: using read-only memory

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Date:	Sun, 2 Jan 2011 10:09:11 +0100
From:	Pavel Machek <pavel@....cz>
To:	Kees Cook <kees.cook@...onical.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [Security] proactive defense: using read-only memory

Hi!

> > > - Pointers to function table also need to be marked read-only after
> > >   they are set. An example of this is the security_ops table pointer. It
> > >   gets set once at boot, and never changes again. These need to be handled
> > >   so it isn't possible to just trivially reaim the entire security_ops
> > >   table lookup somewhere else.
> > 
> > But there are too many of those. You can't block them all...
> 
> Well, I don't think "too many" is a good reason. And I think it is possible
> to block them all if we're careful and diligent. Maybe I'm naive;
>   we'll see.

I believe "too many" is very good reason -- you do not want to uglify
the kernel too badly.

It is not like anything that makes attackers life harder is a good
thing... for example deleting all the comments would clearly make
attacking linux harder, but it is also clearly bad idea. 

> > > - Entry points to set_kernel_text_rw() and similar need to be blockable.
> > >   Having these symbols available make kernel memory modification trivial;
> > 
> > What prevents attacker to just inlining those functions in the
> > exploit?
> 
> The goal is to make it harder for an attacker to create, change, or hide
> kernel code in memory. If they're able to already execute arbitrary code,
> then yes, it's doesn't change anything. But the point is to make it harder
> to get to that point to start with.

So... what do you assume attacker _can_ do? What is it you are trying
to protect against?

									Pavel

-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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