14 DAY TRIAL // Typically, CPU manufacturers tend to provide some pretty serious security features for their CPUs, so that the specifics of their internal architecture will remain a secret, but it would seem that AMD might have overlooked a few security details in some of their CPUs, since a hacker has just posted a rather lengthy proof of concept regarding a super-secret, password-protected debug mode found in some of the company's CPUs.
So, as Xbit Labs reports, the respective security researcher, who goes by the name of Czerno, discovered that certain AMD processors (Athlon XP and up) pack a special debugging mechanism that practically allows anyone who breaks it to view exactly how AMD's chips work and perhaps even reverse engineer them.
In fact, it would seem that the firmware-based debugging features can actually be used in order to seriously expand an AMD CPU's performance over standard, architecturally defined capabilities of x86.
Discovering this debug mode was no easy task, since the researcher had to check out the undocumented machine specific registers (MSRs), where certain hints regarding its existence were to be found.
According to Czerno, there are at least four new machine specific registers (MSR) that are involved in the expanded debug facilities, all of which are password-protected against access.
The read/write access (RDMSR/WRMSR) to the registers is granted only if EDI holds the correct password value, viz. EDI=9C5A203A, because, otherwise, a GPF exception occurs.
There's no info on what the original purpose of these registers is, but it might have something to do with the CPU's self-testing routines, or the implementation of code during development.
Of course, this opens up a whole world of possibilities for intrepid hardware-oriented security researchers, and we're pretty sure that, once the cat has been released from the proverbial bag, many extraordinary things will follow.
As for the nature of those things...well, guess that only time will tell.