Linux Security Summit Europe 2024

Restricting system calls can significantly reduce the attack surface. However, solutions like seccomp can be bypassed(CVE-2009-0835, CVE-2019-2054, CVE-2023-2431, etc.). If unused syscalls can be eliminated at config level and compile time, the attack surface can be fundamentally controlled.
However, the widespread presence of .pushsection in kernel code prevents linker to perform code garbage collection. The associated KEEP() directive also causes ownership reversal issues, resulting in related sections that should be removed to remain, leaving more unused code for potential exploitation by hackers.
By systematically reworking the .pushsection directive, we propose dead syscalls elimination. After specifying the syscalls that need to be retained, it can remove other syscalls' code without affecting the normal operation of the kernel. Attackers cannot exploit something that does not exist. This not only reduces the kernel size and eliminates the overhead of seccomp but also completely eradicates the possibility of exploitation.
Besides, the approach of eliminating the KEEP() directive can be generalized, further reducing the kernel's dead code and decreasing the attack surface.