linux-kernel - Re: [PATCH] paravirt.h

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Date:	Tue, 22 Aug 2006 07:59:55 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@....de>,
	Andrew Morton <akpm@...l.org>,
	virtualization <virtualization@...ts.osdl.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH] paravirt.h

Alan Cox wrote:
> It would be nice not to export it at all or to protect it, paravirt_ops
> is a rootkit authors dream ticket. I'm opposed to paravirt_ops until it
> is properly protected, its an unpleasantly large security target if not.
>   

Do you have an example of an attack which would become significantly 
easier with pv_ops in use?  I agree it might make a juicy target, but 
surely it is just a matter of degree given that any attacker who can get 
to pv_ops can do pretty much anything else.

> It would be a lot safer if we could have the struct paravirt_ops in
> protected read-only const memory space, set it up in the core kernel
> early on in boot when we play "guess todays hypervisor" and then make
> sure it stays in read only (even to kernel) space.
>   

Yes, I'd thought about doing something like that, but as Arjan pointed 
out, nothing is actually read-only in the kernel when using a 2M 
mapping.  It's also ameliorated by the fact that some of the entrypoints 
are never used at runtime, because the code has been patched inline (but 
I don't think it would ever be desirable to patch every entrypoint, 
since some are just not worth the effort, complexity or obfuscation 
which result from patching).

    J
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