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

H. Peter Anvin
2008-09-25T04:54:49Z

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