Use-before-Initialization (UBI) bugs in the Linux kernel have serious security impacts, such as information leakage and privilege escalation. Developers are adopting forced initialization to cope with UBI bugs, but this approach can still lead to undefined behaviors (e.g., NULL pointer dereference). As it is hard to infer correct initialization values, we believe that the best way to mitigate UBI bugs is detection and manual patching. Precise detection of UBI bugs requires path-sensitive analysis. The detector needs to track an associated variable’s initialization status along all the possible program execution paths to its uses. However, such exhaustive analysis prevents the detection from scaling to the whole Linux kernel. This paper presents UBITect, a UBI bug finding tool which combines flow-sensitive type qualifier analysis and symbolic execution to perform precise and scalable UBI bug detection. The scalable qualifier analysis guides symbolic execution to analyze variables that are likely to cause UBI bugs. UBITect also does not require manual effort for annotations and hence, it can be directly applied to the kernel without any source code or intermediate representation (IR) change. On the Linux kernel version 4.14, UBITect reported 190 bugs, among which 78 bugs were deemed by us as true positives and 52 were confirmed by Linux maintainers.

CPU memory prefetchers can substantially interfere with prime and probe cache side-channel attacks, especially on in-order CPUs which use aggressive prefetching. This interference is not accounted for in previous attacks. In this paper, we propose PAPP, a Prefetcher-Aware Prime Probe attack that can operate even in the presence of aggressive prefetchers. Specifically, we reverse engineer the prefetcher and replacement policy on several CPUs and use these insights to design a prime and probe attack that minimizes the impact of the prefetcher. We evaluate PAPP using Cache Side-channel Vulnerability (CSV) metric and demonstrate the substantial improvements in the quality of the channel under different conditions.