'Super-secret' Password-protected Debugger Discovered in AMD Processors

A hardware hacker has discovered a secret debugging feature hidden in all AMD chips made in the past decade. "The password-protected debugger came as a shock to reverse-engineers who've hungered for an on-chip mechanism for performing conditional and direct-hardware breakpoint operations. Although AMD has built the firmware-controlled feature into all chips since the Athlon XP, […]

A hardware hacker has discovered a secret debugging feature hidden in all AMD chips made in the past decade. "The password-protected debugger came as a shock to reverse-engineers who've hungered for an on-chip mechanism for performing conditional and direct-hardware breakpoint operations. Although AMD has built the firmware-controlled feature into all chips since the Athlon XP, the company kept it a closely guarded secret that was only disclosed by a hacker who goes by the name Czernobyl."

"AMD processors (Athlon XP and better) have included firmware-based debugging features that expand greatly over standard, architecturally defined capabilities of x86," the hacker wrote. "For some reason, though, AMD has been tightly secretive about these features; hint of their existence was gained by glancing at CBID's page."

To put a chip into developer mode, a user must first enter what amounts to a password -- 9C5A203A -- into the CPU's EDI register. Czernobyl was able to deduce the secret setting by brute forcing the key.

[Source]