linux-kernel - Re: System call interposition/unprotecting the table

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Date:	Tue, 14 Aug 2007 13:27:17 -0400
From:	Hajime Inoue <hinoue@...l.carleton.ca>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	linux-kernel@...r.kernel.org
Subject: Re: System call interposition/unprotecting the table

Thanks for your comments.

Alan Cox wrote:
 > This is to protect it from being changed by an attacker or someone trying
 > to do strange and bogus things to the kernel.
 >
 > What are you actually trying to achieve ?

I am trying to emulate an attacker.  I'm helping develop a system that
that detects stealthy malware.  To that end, we need to test the system in
an environment we completely understand.

Just protecting the table does not stop rootkits.  A highly referenced
phrack article explains how to bypass the table.  Enyelkm and mood-nt
are both compatible with a protected system call table (I tested them
against the latest Fedora stock kernel).  I'm trying to simulate a
rootkit less capable then those publicly available.

Why isn't the rest of the kernel code protected along with the table?
Your response leads to the inverse of my question.  How would I protect
the system call table (and other areas) in systems, without recompiling,
that do not protect them?

Finally, system call interposition is used in several interesting
systems, most notably, systrace.  It's unclear to me how one would
implement something like systrace without modifying the table or doing
other rootkit-like antics.

If anyone has problems explaining this publicly, please contact me
privately.  If anyone doubts my motivation, read my home page
(http://www.ccsl.carleton.ca/~hinoue/), or google my name.

-Hajime Inoue

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