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Date:      Wed, 4 Apr 2012 15:05:29 +0000 (UTC)
From:      jb <jb.1234abcd@gmail.com>
To:        freebsd-stable@freebsd.org
Subject:   Re:  Text relocations in kernel modules
Message-ID:  <loom.20120404T165909-66@post.gmane.org>
References:  <CAGE5yCpuvsVrc-%2BDTVas-W4fjuP2s%2B6PQONMOTyEbGnj2CY3ig@mail.gmail.com> <4F766F29.2030803@cs.stonybrook.edu> <CAFHbX1KiZx68MP4bCAvPc0Zui3fA4O35_z3kP781zoJqLYp7Bw@mail.gmail.com> <4F79D88B.3040102@cs.stonybrook.edu> <CAFHbX1KE15G9gx7Duw2R8zC5jL1jiEir0yMB0-s5%2B4xx517WtQ@mail.gmail.com> <4F79E27E.3000509@cs.stonybrook.edu> <CAGE5yCrwLosuTT2yq0DEx%2Bz8ztKpkrB=tORmURcuh_SCz=L7qg@mail.gmail.com> <4F79FCB8.1090003@cs.stonybrook.edu> <CAGE5yCrz45AWeJGv=2UWRq7xpXZVtvsx%2B5O6cvaE6ZzoFrz5mA@mail.gmail.com> <4F7A05C4.9070808@cs.stonybrook.edu> <20120403170259.GA94837@neutralgood.org> <loom.20120404T103230-175@post.gmane.org> <1333550029.1090.67.camel@revolution.hippie.lan>

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Ian Lepore <freebsd <at> damnhippie.dyndns.org> writes:

> ...
> > But of interest to me is this:
> > "...
> > Text relocations are a way in which references in the executable code to
> > addresses not known at link time are solved. Basically they just write
> > the appropriate address at runtime marking the code segment writable in
> > order to change the address then unmarking it. This can be a problem as
> > an attacker could try to exploit a bug when the text relocation happens
> > in order to be able to write arbitrary code in the text segment which
> > would be executed.
> > ..."
> ... 
> A kernel module is loaded and linked
> ONCE, at load time, into the kernel's address space.
> ...

>From the point of view of an attacker it does not matter whether kernel module
is loaded and linked once only. That's enough to create a window of opportunity
for interfering with relocation process and modifying text (code).

jb





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