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From: Paul Mackerras <paulus@samba.org>
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Date: Thu, 3 Jan 2002 14:12:19 +1100 (EST)
To: Joe Buck <jbuck@synopsys.COM>
Cc: dewar@gnat.com, velco@fadata.bg, gcc@gcc.gnu.org,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.linuxppc.org,
        trini@kernel.crashing.org
Subject: Re: [PATCH] C undefined behavior fix
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Joe Buck writes:

> There is already such a project under development: see
> 
> http://gcc.gnu.org/projects/bp/main.html
> 
> This is a modification to gcc that implements pointers as triples.
> While there is a performance penalty for doing this, it can completely
> eliminate the problem of exploitable buffer overflows.  However, programs
> that violate the rules of ISO C by generating out-of-range pointers will
> fail.

What will it do if I cast a pointer to unsigned long?  Or if I cast an
unsigned long to a pointer?  The kernel does both of these things, and
in a lot of places.

Part of my beef with what gcc-3 is doing is that I take a pointer,
cast it to unsigned long, do something to it, cast it back to a
pointer, and gcc _still_ thinks it's knows what I am doing.  It
doesn't.

Paul.
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