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

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Date:	Wed, 24 Sep 2008 22:02:08 -0700
From:	Alok Kataria <akataria@...are.com>
To:	"H. Peter Anvin" <hpa@...or.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

On Wed, 2008-09-24 at 21:54 -0700, H. Peter Anvin wrote:
> 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.

Hi Peter, 

It would be really helpful if you could explain me when can this go
wrong or what kinds of problems can this cause on native hardware.

Thanks,
Alok
> 
>         -hpa
> 

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