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AMD K8 microcode dissected
Posted by: Jim_ on: 07/23/2004 01:52 PM [ Print | 1 comment(s) ]
I noticed a link to this article by way of The Inquirer. Would you like to look deeply into the microcode of the K8?
This document details the procedure for performing microcode updates on the AMD K8 processors. It also gives background information on the K8 microcode design and provides information on altering the microcode and loading the altered update for those who are interested in microcode hacking. Surprisingly, the microcode itself is in no way encrypted as it is in Intel microcode updates; the raw data loaded into the microcode patch array is directly exposed. The repetitive structure of the data, bit patterns and fields characteristic of microcode indicate that apparently no encryption was performed.If you'd like to know more, read the entire article over at Real World Technologies.
#30805 Posted on: 07/27/2004 10:20 AM
Imagine the fiasco that would ensue if a system were compromised by altering the CPU itself. This would be the hardware equivalent of Ken Thompson's legendary self-replicating compiler (http://www.acm.org/classics/sep95). A few years ago, Intel had to answer to public scrutiny over the exploitability of their own microcode update feature; their solution was security through obscurity and layers of encryption and authentication (see http://www.eetimes.com/news/97/963news/hole.html). Evidently AMD was not as wise by assuming their microcode was uncrackable.
This could give rise to semi-permanent viruses that survive a OS reinstall and require a CPU microcode update to remove.
Actually, if the CPU micro-code loader itself could be modified, the viruses could be permanent.