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Bugtraq archives for 4th quarter (Oct-Dec) 1997: Re: Intel Pentium Bug

Re: Intel Pentium Bug

Ian McWilliam (I.McWilliamST.NEPEAN.UWS.EDU.AU)
Sat, 8 Nov 1997 23:13:59 +1100 

On Fri, 7 Nov 1997, Aleph One wrote:

> On Sat, 8 Nov 1997, Daniele Orlandi wrote:
>
> > If the CPU microcode is really updateable, it's realistic to think that:
> >
> > 1- Upload requires to be done only when running in ring-0, just like all the
> >    other protected instructions. No user program will be able to use this
> >    feature.
>
> As you (and Eric) point out this is correct. But at the time we where
> thinking Windows 95 viruses so running in ring-0 is not an issue. Of
> curse under Unix you should have to subvert the root account and from
> there install something like a loadable module (similarly under NT).
> But it happens all to often.

>From my info on the pentium cpu's, mainly  the P6, the upgradable
microcode is a "segment of bios code provided by INTEL to fix processor
bugs. Each different processor has different microcode and it is
intergrated into the bios INT15 function call."

There is publically available a utility (I have a copy of micode.exe) to
check the microcode in the bios and update it as needed.

I think that the function of upgrading the microcode is mainly intended
for BIOS manufacturers.

At worse the BIOS of the motherboard not the cpu is likely to be the
target, but with the advent of flash BIOS updates that can be done from
DOS with out setting jumpers on the motherboard aka aopen AP5T ver 3.X,
this should scare you more than replacing the microcode.




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Ian McWilliam
Technical Officer
Department of Computing.
Faculty of Science & Technology.
University of Western Sydney, Nepean.

Phone: (047) 360757     Fax: (047) 360 770

Mailto:i.mcwilliamst.nepean.uws.edu.au
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