Quantifiable Run-Time Kernel Attack Surface Reduction

The sheer size of commodity operating system kernels makes them a prime target for local attackers aiming to escalate privileges. At the same time, as much as 90% of kernel functions are not required for processing system calls originating from a typical network daemon. This results in an unnecessarily high exposure. In this paper, we introduce kRazor, an approach to reduce the kernel’s attack surface by limiting the amount of kernel code accessible to an application. KRAZOR first traces individual kernel functions used by an application. KRAZOR can then detect and prevent uses of unnecessary kernel functions by a process. This step is implemented as a kernel module that instruments select kernel functions. A heuristic on the kernel function selection allows KRAZOR to have negligible performance overhead. We evaluate results under real-world workloads for four typical server applications. Results show that the performance overhead and false positives remain low, while the attack surface reduction can be as high as 80%.