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

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Date:	Tue, 22 Aug 2006 10:16:32 -0700
From:	Zachary Amsden <zach@...are.com>
To:	Andi Kleen <ak@....de>
Cc:	virtualization@...ts.osdl.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...l.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] paravirt.h

Andi Kleen wrote:
> I don't see why paravirt ops is that much more sensitive
> than most other kernel code. 
>
>   
>> 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.
>>     
>
> By default we don't make anything read only because that would
> mess up the 2MB kernel mapping.
>
> In general i don't think making select code in the kernel
> read only is a good idea, because as long as you don't
> protect everything including stacks etc. there will be always
> attack points where supposedly protected code relies 
> on unprotected state. If someone can write to kernel
> memory you already lost.
>
> And it adds TLB pressure.
>   

And it doesn't work for VMI or lhype, both of which might modify 
paravirt_ops way later in the boot process, when loaded as a module.  
Where did this conversation come from?  I don't see it on any list I'm 
subscribed to.

Zach
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