MIT researchers build custom OS to study chip behavior
Original: To study how chips work, MIT researchers built their own operating system
Why This Matters
Enables deeper security research into processor vulnerabilities and speculative attacks, advancing understanding of modern chip architecture risks.
MIT researchers developed Fractal, a new operating system kernel designed to study processor behavior at a detailed level. The kernel has already discovered previously unknown vulnerabilities in Apple's M1 chip, including evidence of Phantom speculative attacks affecting Apple Silicon.
MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL) created Fractal, an operating system kernel built from the ground up to serve as a research tool for understanding modern processor behavior. The project was led by Joseph Ravichandran, an MIT PhD student in electrical engineering and computer science. Researchers traditionally study processor security and behavior by patching existing operating systems like macOS or Linux, an approach that is unstable, difficult to reproduce, and facing deprecation on Apple platforms. Fractal introduces a new construct called the outer kernel thread, which executes with kernel privileges while sitting inside a user process's memory, enabling detailed observation of hardware behavior. The kernel's first major application focused on analyzing branch predictors in Apple's M1 processor—the CPU component that predicts which code instructions will execute next before confirmation, reducing processing delays. This analysis uncovered previously unknown behavior, including the first evidence that Phantom, a class of speculative attack, can affect Apple Silicon. Ravichandran described the tool as an electron microscope for operating systems, providing researchers with far greater visibility into processor operations than conventional methods allow.