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Date: Wed, 24 Sep 2008 21:54:28 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: akataria@vmware.com
CC: Alok kataria <alokkataria1@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       Yan Li <elliot.li.tech@gmail.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "joerg.roedel@amd.com" <joerg.roedel@amd.com>,
       "rjmaomao@gmail.com" <rjmaomao@gmail.com>,
       Yinghai Lu <yhlu.kernel@gmail.com>,
       Thomas Gleixner <tglx@linutronix.de>, Daniel Hecht <dhecht@vmware.com>,
       Zach Amsden <zach@vmware.com>
Subject: Re: [PATCH 1/2] VMware detection support for x86 and x86-64
References: <20080221115452.GB13948@elte.hu>	 <20080907234510.GA24133@yantp.cn.ibm.com>	 <20080908140423.GG11993@elte.hu>	 <35f686220809241928k3669e30bi8a98b440443c4bff@mail.gmail.com>	 <48DB15DB.8040501@zytor.com> <1222317978.23524.117.camel@alok-dev1>
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Alok Kataria wrote:
> On Wed, 2008-09-24 at 21:38 -0700, H. Peter Anvin wrote:
>> Alok kataria wrote:
>>> Even if there is anything on that port on native hardware it would
>>> work perfectly well and is _safe_.
>>> First let me post the code to access this backdoor port (the way it
>>> should really be done )
>>>
>>> So whenever we query port  0x5658 , with the GETVERSION command (which
>>> is the first thing we do with this port), we expect that  eax !=
>>> 0xFFFFFFFF   and ebx has a  VMWARE specific MAGIC value.  Please note
>>> that ebx has been initialized to zero in the code above.
>>>
>> You have no idea what you just did to a real piece of hardware.
> Why ? what do you mean ? 
> ebx is a local variable in the code above that i posted. 
> Only when on hypervisor will we write the magic value over there.
> How can this affect native hardware, i fail to understand. 
> Please explain.
> 

You accessed a bloody I/O port!

If you think it's harmless because it was an IN, you're sorely mistaken.

	-hpa