Re: [PATCH] KVM: emulator: Only allow VMCALL/VMMCALL trapped by #UD

[Dor Laor <dor.laor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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Dong, Eddie wrote:
> Anthony Liguori wrote:
>   
>> Yang, Sheng wrote:
>>     
>>> From 9743b5299bae1779c2b893cbeb86122bcccb9b2d Mon Sep 17 00:00:00
>>> 2001 
>>> From: Sheng Yang <sheng.yang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>>> Date: Wed, 2 Jan 2008 14:49:22 +0800
>>> Subject: [PATCH] KVM: emulator: Only allow VMCALL/VMMCALL trapped by
>>> #UD 
>>>
>>> When executing a test program called "crashme", we found the KVM
>>> guest 
>>> cannot survived more than ten seconds, then encounterd kernel panic.
>>> The basic concept of "crashme" is graduating random assembly code and
>>> trying to execute them in a fork process.
>>>
>>> After some fix on emulator valid judgment, we found it's hard to get
>>> the current emulator handle the invalid instructions correctly, for
>>> the #UD trap for hypercall patching caused troubles. The problem is,
>>> if the opcode itself was OK, but combination of opcode and modrm_reg
>>> was invalid, and one operand of the opcode was memory(SrcMem or
>>> DstMem), emulator would fetched the memory operand first rather than
>>> judged the validity, and may encounter error there. 
>>>
>>>       
>> Nice catch!
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>     
> Anthony:
> 	Actually I am wondering if the binary used for VMMCALL could be
> assumed will never be used by Intel processor or vice versa.  BTW, what
> is the nenefit to remove hypercall page, which provide more clean
> approach IMO?
> thx,eddie
>
>   
The benefit is that one can migrate a running guest from Intel to Amd 
and vise versa without
any effort  of the guest/host knowing that.
Can you offer other binary code for vmmcall that you're sure it won't be 
used in the future?
Regards,
Dor
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