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Re: Linux Distribution Recomendation
From: peter () devbox adamantix org (Peter Busser)
Date: Tue, 16 Mar 2004 15:27:20 +0100


The debian-devel discussion was mostly about Russel Coker and Ingo's claims
that his patch does everything that PaX does, without breaking compatibility.
That is simply not true. It provides less protection and even then still
breaks compatibility. You cannot download the XFree86 source code, recompile
it with ELFLoader module support and run it as is on his kernel patch. I
respect the fact that people make trade-offs, OpenBSD made similar trade-offs.
Basically they trade in a bit of security for a bit of compatibility. That is
ok, if compatibility is more important than security.

Are we talking about the same thread?
In this one Ingo explicitly states a few times PaX is more secure than exec-shield.

Yeah, it looks like that is one of those discussions. These discussions with
Red Hat employees normally have a few standard themes.

One important aspect is to assert that exec-shield is almost equal to PaX,
because the extra things that PaX does are not important (even though there is
no proof that this is indeed the case).

If people start quoting PaXtest output that proves the opposite, it is no
longer possible to repeat that assertion. So the second theme starts. That is,
to question my integrity and claim that PaXtest is rigged to show bad results
for exec-shield. But why is PaX able to stop these simulated attacks and why
is exec-shield not able to do that?

(FYI, I am not involved in PaX development in any way. I wrote PaXtest in my
free time and I develop Adamantix in my free time. And I have no commercial
interests to defend.)

When you start to talk about the differences in design between PaX and
exec-shield, and that exec-shield allows applications to do things that PaX
does not allow, then it is obvious that killing the messenger does not work
either. If you continue to use some more torturing, then they will finally
admit that yes, PaX is more powerful (note: admitting that it is more secure
requires even more torture).


With my admittingly limited knowledge of the subject I interpret this to be
something like the old standards compliant GCC issue where it broke apps, but
only cause those apps were relying on a broken implementation. He said X was
used properly on other archs but on i386 it did not. I guess cause read-only
memory can be executed people used it which sounds like a design flaw to me.

XFree86 is ugly.

I use fedora and have heard people mention breakage of wine with exec-shield
enabled but haven't looked into why so it obviously isn't 100%.

Of course it breaks. It is trying to do all kinds of nasty stuff in the process
memory. The vision of the PaX author is that introducing and executing new
executable code in process memory should be a privileged operation. It should
not be allowed to just anybody.

The problem with this whole thing is that it is damn convenient for programmers
to just mess around in the process memory and then execute that mess. But it
is damn convenient for attackers too.

This is the
'middle ground' stuff you were talking about, not as good as others, but better
than the default. Now I'm off to actually get informed on this whole subject =)

BTW, the PaX site contains good documentation about this subject. It describes
the design and the trade-offs being made. It is well worth a read. And on
www.adamantix.org, you can follow a link to a Linux Magazine article I wrote.
It is not a very technical article. It should provide a general overview of
what PaX does and why. (I would point to exec-shield or OpenBSD design
documents too, if there were any.)

Peter Busser

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