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A number of existing compiler techniques hinge on the analysis of array accesses in a program. The most important task in array access analysis is to collect the information about array accesses of interest and summarize it in some standard form. Traditional forms used in array access analysis are sensitive to the complexity of array subscripts; that is, they are usually quite accurate and efficient for simple array subscripting expressions, but lose accuracy or require potentially expensive algorithms for complex subscripts. Our study has revealed that in many programs, particularly numerical applications, many access patterns are simple in nature even when the subscripting expressions are complex. Based on this analysis, we have developed a new, general array region representational form, called the linear memory access descriptor (LMAD). The key idea of the LMAD is to relate all memory accesses to the linear machine memory rather than to the shape of the logical data structures of a programming language. This form helps us expose the simplicity of the actual patterns of array accesses in memory, which may be hidden by complex array subscript expressions. Our recent experimental studies show that our new representation simplifies array access analysis and, thus, enables efficient and accurate compiler analysis.

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Pointer invalidation has been a popular approach adopted in many recent studies to mitigate use-after-free errors. The approach can be divided largely into two different schemes: explicit invalidation and implicit invalidation. The former aims to eradicate the root cause of use-after-free errors by explicitly invalidating every dangling pointer. In contrast, the latter aims to prevent dangling pointers by freeing an object only if there is no pointer referring to it. A downside of the explicit scheme is that it is expensive, as it demands high-cost algorithms or a large amount of space to maintain up-to-date lists of pointer locations linking to each object. Implicit invalidation is more efficient in that even without any explicit effort, it can eliminate dangling pointers by leaving objects undeleted until all the links between the objects and their referring pointers vanish by themselves during program execution. However, such an argument only holds if the scheme knows exactly when each link is created and deleted. Reference counting is a traditional method to determine the existence of reference links between objects and pointers. Unfortunately, impeccable reference counting for legacy C/C++ code is very difficult and expensive to achieve in practice, mainly because of the type unsafe operations in the code. In this paper, we present a solution, called CRCount, to the use-after-free problem in legacy C/C++. For effective and efficient problem solving, CRCount is armed with the pointer footprinting technique that enables us to compute, with high accuracy, the reference count of every object referred to by the pointers in the legacy code. Our experiments demonstrate that CRCount mitigates the useafter-free errors with a lower performance-wise and space-wise overhead than the existing pointer invalidation solutions.

Intel SGX is a security solution promising strong and practical security guarantees for trusted computing. However, recent reports demonstrated that such security guarantees of SGX are broken due to access pattern based side-channel attacks, including page fault, cache, branch prediction, and speculative execution. In order to stop these side-channel attackers, Oblivious RAM (ORAM) has gained strong attention from the security community as it provides cryptographically proven protection against access pattern based side-channels. While several proposed systems have successfully applied ORAM to thwart side-channels, those are severely limited in performance and its scalability due to notorious performance issues of ORAM. This paper presents TrustOre, addressing these issues that arise when using ORAM with Intel SGX. TrustOre leverages an external device, FPGA, to implement a trusted storage service within a completed isolated environment secure from side-channel attacks. TrustOre tackles several challenges in achieving such a goal: extending trust from SGX to FPGA without imposing architectural changes, providing a verifiably-secure connection between SGX applications and FPGA, and seamlessly supporting various access operations from SGX applications to FPGA. We implemented TrustOre on the commodity Intel Hybrid CPU-FPGA architecture. Then we evaluated with three state-of-the-art ORAM-based SGX applications, ZeroTrace, Obliviate, and Obfuscuro, as well as an endto-end key-value store application. According to our evaluation, TrustOre-based applications outperforms ORAM-based original applications ranging from 10× to 43×, while also showing far better scalability than ORAM-based ones. We emphasize that since TrustOre can be deployed as a simple plug-in to SGX machine's PCIe slot, it is readily used to thwart side-channel attacks in SGX, arguably one of the most cryptic and critical security holes today. CCS CONCEPTS • Security and privacy → Side-channel analysis and countermeasures; Security services; Security protocols.