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

[H. Peter Anvin]

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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