An intrepid hacker has managed to uncover a hidden secret in AMD CPUs by unlocking a debug mode present in almost every one of the company's processors released in the past decade.
According to the discoverer, who goes by the name Czernobyl, all AMD chips starting with the Athlon XP have a firmware-based developer mode built in. This is meant to be used by the company's engineers during the development process to ensure that everything is working properly, and is apparently a fairly common feature on chips from any manufacturer.
However, AMD's has managed to be kept a secret until now because the mode - which is disabled by default - can only be accessed by entering the correct values into the processor's registers. Understandably, these values are highly guarded secrets known to only a limited number of people.
Using a brute-force approach, Czernobyl has now managed to discover what these keys are, granting access to the debugging features for anyone to enjoy. In theory, this will open up a whole new set of tools and possibilities for hacking, debugging and reverse engineering.
This particular hack is still very early in development though, and comes with the very clear warning that "the item is WORK IN PROGRESS, but USABLE hence released AS IS". Unfortunately, this makes the chance of inputting an incorrect key value all the more likely - a mistake that will instantly crash the entire system.
For anyone who wants to know more, Czernobyl has posted all of his findings so far to the RCE Knowledge Library.
UPDATE: AMD wanted to update on what impact this might all have. The short version is that there are no security concerns associated with the dubug mode and it won't allow any sort of hacking of reverse engineering of the processors themselves. So basically, there's nothing to worry about, in case you were concerned.
