linux-kernel - Re: [PATCH 1/2] VMware detection support for x86 and x86-64

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Date:	Wed, 24 Sep 2008 21:54:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	akataria@...are.com
CC:	Alok kataria <alokkataria1@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Yan Li <elliot.li.tech@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joerg.roedel@....com" <joerg.roedel@....com>,
	"rjmaomao@...il.com" <rjmaomao@...il.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Hecht <dhecht@...are.com>, Zach Amsden <zach@...are.com>
Subject: Re: [PATCH 1/2] VMware detection support for x86 and x86-64

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

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