The article investigates undocumented x86 opcodes, describing a depth‑first search that uses page‑faults to locate hidden instruction boundaries, and reports finding dozens of executable but undocumented instructions on Intel and AMD CPUs, highlighting potential security risks and the need for vigilant hardware analysis.
This article explores whether modern CPUs contain undocumented or hidden instructions, explains the challenges of searching the variable‑length x86 ISA, presents a depth‑first algorithm that skips irrelevant bytes, shows how to infer instruction length using page‑fault side‑effects, and reveals discovered hidden opcodes on Intel and AMD processors.
The article investigates whether modern x86 CPUs contain undocumented or hidden instructions, explains how to search the instruction space using a depth‑first algorithm that leverages page‑fault side‑effects to determine instruction length, and presents the results of uncovering such hidden opcodes on Intel and AMD processors, highlighting the potential security risks.
