Re: A quote from Crypto-Gram

From: Tim Smith (reply_in_group_at_mouse-potato.com)
Date: 08/19/04 

Date: Thu, 19 Aug 2004 17:22:53 GMT

On 2004-08-19, David Eather <eather@tpg.com.au> wrote:
>> How about a backdoor that lets an application read/write any memory
>> location? Or that lets it access any I/O port?
>
> It *can't* be done. It seems that the role and scope of microcode is The
> most you could do is write a malicious instruction. For example one

Yeah, like a malicious instruction that allows peeking at arbitrary physical
memory without any access checks, or a malicious instruction that switches
from user mode to kernel mode.

...
> Even so, having succeeded in creating such an instruction you can't
> deliver your "payload" - as no main boards provide the necessary hardware
> support to update the CPU microcode.

Pentium Pro, PII, PIII, P4, Celeron, Xeon, etc., all provide the necessary
support for updating microcode. Same for modern AMD processors. No main
board support is needed. 

-- 
--Tim Smith
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