GuaNary: Efficient Buffer Overflow Detection In Virtualized Clouds Using Intel EPT-based Sub-Page Write Protection Support

Abstract

Buffer overflow is a widespread memory safety violation in C/C++, reported as the top vulnerability in 2022. Secure memory allocators are generally used to protect systems against attacks that may exploit buffer overflows. Existing allocators mainly rely on two types of countermeasures to prevent or detect overflows: canaries and guard pages, each with pros and cons in terms of detection latency and memory footprint. This paper follows the Out of Hypervisor (OoH) trend for virtualized cloud applications. It introduces GuaNary, a novel safety guard against overflows allowing synchronous detection at a low memory footprint cost. OoH is a new virtualization research axis introduced in 2022 advocating the exposure of hardware features for virtualization to the guest OS so that its processes can take advantage of them. Based on the OoH principle, GuaNary leverages Intel Sub-Page write Permission (SPP), a recent hardware virtualization feature that allows to write-protect guest memory at the granularity of 128B (namely, sub-page) instead of 4KB. We implement a software stack, LeanGuard, which promotes the utilization of SPP from inside virtual machines by new secure allocators that use GuaNary. Our evaluation shows that for the same number of protected buffers, LeanGuard consumes 8.3x less memory than SlimGuard, a state-of-the-art secure allocator. Furthermore, for the same memory consumption, LeanGuard protecting 25x more buffers than SlimGuard.