Genuine lab experiences for students in resource constrained environments: The RealLab with integrated intelligent assessment.

Laboratory activities are indispensable for developing engineering skills. Computer Aided Learning (CAL) tools can be used to enhance laboratory learning in various ways, the latest approach being the virtual laboratory technique that emulates traditional laboratory processes. This new approach makes it possible to give students complete and genuine laboratory experiences in situations constrained by limited resources in the provision of laboratory facilities and infrastructure and/or where there is need for laboratory education, for large classes, with only one laboratory stand. This may especially be the case in countries in transition. Most existing virtual laboratories are not available for purchase. Where they are, they may not be cost friendly for resource constrained environments. Also, most do not integrate any form of assessment structure. In this paper, we present a very cost friendly virtual laboratory solution for genuine laboratory experiences in resource constrained environments, with integrated intelligent assessment

Open Source Software Evolution and Its Dynamics

This thesis undertakes an empirical study of software evolution by analyzing open source software (OSS) systems. The main purpose is to aid in understanding OSS evolution. The work centers on collecting large quantities of structural data cost-effectively and analyzing such data to understand software evolution dynamics (the mechanisms and causes of change or growth). We propose a multipurpose systematic approach to extracting program facts (e. g. , function calls). This approach is supported by a suite of C and C++ program extractors, which cover different steps in the program build process and handle both source and binary code. We present several heuristics to link facts extracted from individual files into a combined system model of reasonable accuracy. We extract historical sequences of system models to aid software evolution analysis. We propose that software evolution can be viewed as Punctuated Equilibrium (i. e. , long periods of small changes interrupted occasionally by large avalanche changes). We develop two approaches to study such dynamical behavior. One approach uses the evolution spectrograph to visualize file level changes to the implemented system structure. The other approach relies on automated software clustering techniques to recover system design changes. We discuss lessons learned from using these approaches. We present a new perspective on software evolution dynamics. From this perspective, an evolving software system responds to external events (e. g. , new functional requirements) according to Self-Organized Criticality (SOC). The SOC dynamics is characterized by the following: (1) the probability distribution of change sizes is a power law; and (2) the time series of change exhibits long range correlations with power law behavior. We present empirical evidence that SOC occurs in open source software systems

메모리 보호를 위한 보안 정책을 시행하기 위한 코드 변환 기술

학위논문(박사)--서울대학교 대학원 :공과대학 전기·컴퓨터공학부,2020. 2. 백윤흥.Computer memory is a critical component in computer systems that needs to be protected to ensure the security of computer systems. It contains security sensitive data that should not be disclosed to adversaries. Also, it contains the important data for operating the system that should not be manipulated by the attackers. Thus, many security solutions focus on protecting memory so that sensitive data cannot be leaked out of the computer system or on preventing illegal access to computer data. In this thesis, I will present various code transformation techniques for enforcing security policies for memory protection. First, I will present a code transformation technique to track implicit data flows so that security sensitive data cannot leak through implicit data flow channels (i.e., conditional branches). Then I will present a compiler technique to instrument C/C++ program to mitigate use-after-free errors, which is a type of vulnerability that allow illegal access to stale memory location. Finally, I will present a code transformation technique for low-end embedded devices to enable execute-only memory, which is a strong security policy to protect secrets and harden the computing device against code reuse attacks.컴퓨터 메모리는 컴퓨터 시스템의 보안을 위해 보호되어야 하는 중요한 컴포넌트이다. 컴퓨터 메모리는 보안상 중요한 데이터를 담고 있을 뿐만 아니라, 시스템의 올바른 동작을 위해 공격자에 의해 조작되어서는 안되는 중요한 데이터 값들을 저장한다. 따라서 많은 보안 솔루션은 메모리를 보호하여 컴퓨터 시스템에서 중요한 데이터가 유출되거나 컴퓨터 데이터에 대한 불법적인 접근을 방지하는 데 중점을 둔다. 본 논문에서는 메모리 보호를 위한 보안 정책을 시행하기 위한 다양한 코드 변환 기술을 제시한다. 먼저, 프로그램에서 분기문을 통해 보안에 민감한 데이터가 유출되지 않도록 암시적 데이터 흐름을 추적하는 코드 변환 기술을 제시한다. 그 다음으로 C / C ++ 프로그램을 변환하여 use-after-free 오류를 완화하는 컴파일러 기술을 제시한다. 마지막으로, 중요 데이터를 보호하고 코드 재사용 공격으로부터 디바이스를 강화할 수 있는 강력한 보안 정책인 실행 전용 메모리(execute-only memory)를 저사양 임베디드 디바이스에 구현하기 위한 코드 변환 기술을 제시한다.1 Introduction 1 2 Background 4 3 A Hardware-based Technique for Efficient Implicit Information Flow Tracking 8 3.1 Introduction 8 3.2 Related Work 10 3.3 Our Approach for Implicit Flow Tracking 12 3.3.1 Implicit Flow Tracking Scheme with Program Counter Tag 12 3.3.2 tP C Management Technique 15 3.3.3 Compensation for the Untaken Path 20 3.4 Architecture Design of IFTU 22 3.4.1 Overall System 22 3.4.2 Tag Computing Core 24 3.5 Performance and Area Analysis 26 3.6 Security Analysis 28 3.7 Summary 30 4 CRCount: Pointer Invalidation with Reference Counting to Mitigate Useafter-free in Legacy C/C++ 31 4.1 Introduction 31 4.2 Related Work 36 4.3 Threat Model 40 4.4 Implicit Pointer Invalidation 40 4.4.1 Invalidation with Reference Counting 40 4.4.2 Reference Counting in C/C++ 42 4.5 Design 44 4.5.1 Overview 45 4.5.2 Pointer Footprinting 46 4.5.3 Delayed Object Free 50 4.6 Implementation 53 4.7 Evaluation 56 4.7.1 Statistics 56 4.7.2 Performance Overhead 58 4.7.3 Memory Overhead 62 4.8 Security Analysis 67 4.8.1 Attack Prevention 68 4.8.2 Security considerations 69 4.9 Limitations 69 4.10 Summary 71 5 uXOM: Efficient eXecute-Only Memory on ARM Cortex-M 73 5.1 Introduction 73 5.2 Background 78 5.2.1 ARMv7-M Address Map and the Private Peripheral Bus (PPB) 78 5.2.2 Memory Protection Unit (MPU) 79 5.2.3 Unprivileged Loads/Stores 80 5.2.4 Exception Entry and Return 80 5.3 Threat Model and Assumptions 81 5.4 Approach and Challenges 82 5.5 uXOM 85 5.5.1 Basic Design 85 5.5.2 Solving the Challenges 89 5.5.3 Optimizations 98 5.5.4 Security Analysis 99 5.6 Evaluation 100 5.6.1 Runtime Overhead 103 5.6.2 Code Size Overhead 106 5.6.3 Energy Overhead 107 5.6.4 Security and Usability 107 5.6.5 Use Cases 108 5.7 Discussion 110 5.8 Related Work 111 5.9 Summary 113 6 Conclusion and Future Work 114 6.1 Future Work 115 Abstract (In Korean) 132 Acknowlegement 133Docto

Program analysis of temporal memory mismanagement

In the use of C/C++ programs, the performance benefits obtained from flexible low-level memory access and management sacrifice language-level support for memory safety and garbage collection. Memory-related programming mistakes are introduced as a result, rendering C/C++ programs prone to memory errors. A common category of programming mistakes is defined by the misplacement of deallocation operations, also known as temporal memory mismanagement, which can generate two types of bugs: (1) use-after-free (UAF) bugs and (2) memory leaks. The former are severe security vulnerabilities that expose programs to both data and control-flow exploits, while the latter are critical performance bugs that compromise software availability and reliability. In the case of UAF bugs, existing solutions that almost exclusively rely on dynamic analysis suffer from limitations, including low code coverage, binary incompatibility, and high overheads. In the case of memory leaks, detection techniques are abundant; however, fixing techniques have been poorly investigated. In this thesis, we present three novel program analysis frameworks to address temporal memory mismanagement in C/C++. First, we introduce Tac, the first static UAF detection framework to combine typestate analysis with machine learning. Tac identifies representative features to train a Support Vector Machine to classify likely true/false UAF candidates, thereby providing guidance for typestate analysis used to locate bugs with precision. We then present CRed, a pointer analysis-based framework for UAF detection with a novel context-reduction technique and a new demand-driven path-sensitive pointer analysis to boost scalability and precision. A major advantage of CRed is its ability to substantially and soundly reduce search space without losing bug-finding ability. This is achieved by utilizing must-not-alias information to truncate unnecessary segments of calling contexts. Finally, we propose AutoFix, an automated memory leak fixing framework based on value-flow analysis and static instrumentation that can fix all leaks reported by any front-end detector with negligible overheads safely and with precision. AutoFix tolerates false leaks with a shadow memory data structure carefully designed to keep track of the allocation and deallocation of potentially leaked memory objects. The contribution of this thesis is threefold. First, we advance existing state-of-the-art solutions to detecting memory leaks by proposing a series of novel program analysis techniques to address temporal memory mismanagement. Second, corresponding prototype tools are fully implemented in the LLVM compiler framework. Third, an extensive evaluation of open-source C/C++ benchmarks is conducted to validate the effectiveness of the proposed techniques