linux-kernel - Re: [KVM PATCH v8 3/3] KVM: add iosignalfd support

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Message-ID: <4A3F84FD.3090700@gmail.com>
Date:	Mon, 22 Jun 2009 09:19:57 -0400
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, avi@...hat.com, mtosatti@...hat.com,
	paulmck@...ux.vnet.ibm.com, markmc@...hat.com
Subject: Re: [KVM PATCH v8 3/3] KVM: add iosignalfd support

Michael S. Tsirkin wrote:
> On Mon, Jun 22, 2009 at 09:04:48AM -0400, Gregory Haskins wrote:
>   
>> Sorry, Michael.  I missed that you had other comments after the
>> grammatical one.  Will answer inline
>>
>> Michael S. Tsirkin wrote:
>>     
>>> On Mon, Jun 22, 2009 at 08:13:48AM -0400, Gregory Haskins wrote:
>>>   
>>>       
>>>
>>>> If thats true, we are in trouble ;)
>>>>     
>>>>         
>>> I think it works at least on x86:
>>> http://en.wikipedia.org/wiki/Packed#x86_and_x86-64
>>>   
>>>       
>> Right, understood.  What I meant specifically is that if the (void*)val
>> pointer is allowed to be misaligned we are in trouble ;).  I haven't
>> studied the implementation in front of the MMIO callback recently, but I
>> generally doubt thats the case.  More than likely this is some buffer
>> that was kmalloced and that should already be aligned to the machine word.
>>
>> Kind Regards,
>> -Greg
>>
>>     
>
> Yes, from what I saw of the code I think it can be BUG_ON.
> Avi?
>
>   

The question to ask is whether a guest can influence that condition.  If
they can, its an attack vector to crash the host.  I suspect they can't,
however.  Therefore, your recommendation is perhaps a good approach so
this condition cannot ever go unnoticed.  Avi?

-Greg


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