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Date:      Mon, 26 Aug 1996 02:08:34 -0400 (EDT)
From:      Gene Stark <gene@starkhome.cs.sunysb.edu>
To:        imp@village.org
Cc:        security@freebsd.org
Subject:   Re: Vulnerability in the Xt library (fwd) 
Message-ID:  <199608260608.CAA13408@starkhome.cs.sunysb.edu>
In-Reply-To: <199608260605.AAA07212@rover.village.org> (message from Warner Losh on Mon, 26 Aug 1996 00:05:52 -0600)

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>: However, this new system call could test to make sure that it is
>: being executed from the text segment, which is read-only, and refuse
>: to perform if not.
>
>Well, couldn't the code that was inserted onto the stack copy itself
>somewhere handy, make that a read only text segment, and make these
>calls?

The text segment is set up by the kernel when the process starts.
I don't think there are any system calls that allow it to be extended.

>Why is the stack segment executable in the first place?  Or does Intel
>require this?

I could be wrong, but I think there is no way to execute-protect pages on
the Intel architecture.  Just read and write.

							- Gene



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