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List:       openbsd-tech
Subject:    Re: New to OpenBSD, noticed something "odd"
From:       alanschu <alanschu () gmail ! com>
Date:       2008-01-31 2:44:29
Message-ID: 15197081.post () talk ! nabble ! com
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Gregg Reynolds-4 wrote:
> 
> On 1/30/08, alanschu <alanschu@gmail.com> wrote:
> > Hi everyone,
> > 
> > I was going over the memory pages allocated to a program I was using, and
> > noticed that in OpenBSD, the mapping had alternating pages of read only
> > and
> > read-writeable memory chunks.  It doesn't do this in linux however.
> > 
> > Why would it do this?
> 
> http://www.openbsd.org/papers/
> 
> Start with "Exploit Mitigation Techniques".
> 
> -g
> 
> 
> 

Thanks Greg, I'll take a look at that.  It looks similar to some
investigating I did with Google that had me find guard pages, but from what
I could tell, the information I found on guard pages was that it would
typically fire a SIGSEGV while reading the memory as well, not just writing
it.  So I wasn't too convinced that the read-only blocks were in fact guard
pages in the sense that I had read up about on the internet, because these
were still readable.  The place where I was stuck thinking about was around
the idea of why even make those blocks in between readable?  Wouldn't it be
just as effective, and maybe even more secure (or less wasteful) to not even
allow that process access to that particular block of memory?  (stuff I'll
look into that presentation list about...thanks again Greg).


To make reference to Bob, I am a student at his University (though not in
his section, we have the same assignment as his section though), and I was
looking for some alternative thoughts as to why.  (While I don't have Bob's
class specifically, I have heard about his involvement with OpenBSD, and am
not too surprised that he eventually chimed in :P)

Cheers.
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