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Re: Buffer overflow prevention
From: "Patrick Dolan" <dolan () cc admin unt edu>
Date: Wed, 13 Aug 2003 18:31:09 -0500

Yes, it should be in all distributions of GCC.  I use it on a Gentoo Linux
server of mine.  The version is 3.2.3, just FYI.

----- Original Message ----- 
From: "Lance James" <lance.james () bakbone com>
To: <dolan () cc admin unt edu>; "'Eygene A. Ryabinkin'"
<rea () rea mbslab kiae ru>
Cc: <bugtraq () securityfocus com>
Sent: Wednesday, August 13, 2003 6:21 PM
Subject: RE: Buffer overflow prevention


Is that in universal gcc, or OpenBSD only?

Lance James

-----Original Message-----
From: Patrick Dolan [mailto:dolan () cc admin unt edu]
Sent: Wednesday, August 13, 2003 10:20 AM
To: Eygene A. Ryabinkin
Subject: Re: Buffer overflow prevention

There is a flag for the Gnu C/C++ compilers, -fstack-protector, that will
implement ProPolice stack protection.  It should prevent stack smashing
techniques.


On Wednesday 13 August 2003 05:28 am, Eygene A. Ryabinkin wrote:
  Hi!
 I have an idea on buffer overflow prevention. I doubt that it's new,
but
I
haven't seen an implementation of it in any freely distributable Un*x
system. So, I hardly need your comments on it.

 Preliminary: I'm talking about Intel x86 architecture, but maybe it
will
be applicable to others as well.

 The idea itself: all (correct me if I'm wrong) buffer overflows are
based
on the fact that we're using the stack, referenced by SS:ESP pair, both
for
procedure return address and for local variables. It seems to me, that
would we have two stacks -- one for real stack and one for variables -- 
it
will solve a bunch of problems. So, my suggestion: let us organise two
segments: one for normal stack, growing downwards, referenced by SS:ESP
pair and the second one, for local variables, referenced by GS:EBP pair,
with either upwards or downwards growing. Now, if we use first segment
for
passing variables and procedure return addresses (normal stack usage),
and
second segment only for local procedure variables, we will have the
following advantages:
 1) Local variables and return address will be physically (by means of
CPU)
    divided and it will not be possible to touch the return address by
    overflowing local buffer.
 2) The procedure introduces only one extra register -- GS, since EBP is
very often used for the stack frame.
Of course, this two segments can be made non-executable, just in case.

 What we need to implement the idea: first, rewrite kernel to organise
two
segments for every process and to place proper values into the segment
registers upon the program startup. Second, rewrite the compiler to
support
the new scheme of local variables addresation. So, the changes are
minimal,
in some sence.

 As I said, I hardly need your criticism, suggestions, etc. of any type.
rea

-- 
Patrick Dolan
UNT Information Security

PGP ID: E5571154
Primary key fingerprint: 5681 25E4 6BE6 298E 9CF0  6F8D B13B 2456 E557
1154



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