Linux Security Summit North America 2020

Like all C/C++ programs, the Linux Kernel regularly suffers from memory corruption flaws. A common way for attackers to gain execution control is to target function pointers that were saved to memory. Control Flow Integrity (CFI) seeks to sanity-check these pointers and eliminate a huge portion of attack surface. It's possible to do this today with the Linux kernel (or any program) with Clang/LLVM's CFI implementation.

This presentation will discuss how Android is using Clang's CFI in the Linux kernel for recent phones, how it is being upstreamed, and what you can do to use CFI yourself. We will explore what Clang actually inserts for code, data, and symbols to protect indirect calls, what needed fixing in the kernel to support it, and what's still missing. We'll wrap up with a short demo of CFI foiling a kernel attack.