现代处理器的优化技术，包括乱序执行和推测机制等，对性能至关重要.以Meltdown和Spectre为代表的侧信道攻击表明：由于异常延迟处理和推测错误而执行的指令结果虽然在架构级别上未显示，但仍可能在处理器微架构状态中留下痕迹.通过隐蔽信道可将微架构状态的变化传输到架构层，进而恢复出秘密数据，这种攻击方式称为瞬态执行攻击.该攻击有别于传统的缓存侧信道攻击，影响面更广，缓解难度更大.深入分析了瞬态执行攻击的机理和实现方式，对目前的研究现状与防御方法进行了总结.首先，介绍了处理器微架构采用的优化技术，并分析了其导致瞬态执行攻击的功能特征；然后，基于触发瞬态执行的原语对瞬态执行攻击进行系统化分析，揭示攻击面上的明显差异；最后，有侧重点地针对攻击模型中的关键步骤和关键组件总结了已有的防御方法，并展望了未来的研究方向.

Modern processor optimizations including out-of-order execution and speculative mechanism are critical for performance. Recent research such as Meltdown and Spectre exploit delayed exception handling and misprediction events to trigger transient execution, and leak otherwise inaccessible information via the CPU's microarchitectural state from instructions which are never committed. This type of attacks is called transient execution attack, which is different from the traditional cache side channel attack. It is more difficult to mitigate. This work deeply studied the mechanism and implementation of transient execution attacks, and summarized its research status and defenses. First, the optimizations adopted by the processor are introduced, and the essential causes of the transient execution attack are analyzed. Then, the transient execution attacks are generalized systematically based on the primitives that trigger the transient execution, in order to reveal the attack surface. Finally, the defenses are summarized in the view of the key steps and components in the attack model, and the future research directions of this field are presented.

核高基国家科技重大专项（2014ZX01029101-002）；中国科学院战略性先导科技专项（XDA-Y01-01）