一种基于硬件辅助虚拟化的软件行为分析器的设计与实现

基于虚拟化技术的软件行为分析是近年来出现的分析软件的方法。文本提出一种基于硬件辅助虚拟化技术的软件行为分析器——HVA。HVA是一个利用了安全虚拟机(SVM)、二级页表(NPT)和虚拟机自省等多种虚拟化技术完成的、专门针对软件行为分析的微型VMM。结果表明,HVA在软件行为分析方面表现良好。     

基于硬件虚拟化的虚拟机进程代码分页式度量方法

云环境下恶意软件可利用多种手段篡改虚拟机（VM）中关键业务代码,威胁其运行的稳定性。传统的基于主机的度量系统易被绕过或攻击而失效,针对在虚拟机监视器（VMM）层难以获取虚拟机中运行进程完整代码段并对其进行完整性验证的问题,提出基于硬件虚拟化的虚拟机进程代码分页式度量方法。该方法以基于内核的虚拟机（KVM）作为虚拟机监视器,在VMM层捕获虚拟机进程的系统调用作为度量流程的触发点,基于相对地址偏移解决了不同版本虚拟机之间的语义差异,实现了分页式度量方法在VMM层透明地验证虚拟机中运行进程代码段的完整性。实现的原型系统——虚拟机分页式度量系统（VMPMS）能有效度量虚拟机中进程,性能损耗在可接受范围内。     

基于可信轻量虚拟机监控器的安全架构*

虚拟化技术越来越多地被用于增强商用操作系统的安全性。现有的解决方案通常将虚拟机管理软件（VMM）作为可信集,利用其作为底层架构的优势来为上层软件提供安全功能。这些方案都是基于通用虚拟机管理软件,因而存在以下问题：a）虚拟化性能上开销大;b）作为可信集相对比较庞大;c）不能提供有效的信任链证明自身可信性。针对上述问题,提出以轻量虚拟机监控器作为可信集的安全架构——Cherub架构,Cherub利用主流处理器的安全扩展指令和硬件辅助虚拟化技术在运行的操作系统中插入轻量级的虚拟机监控器,并利用该虚拟机监控器作为可信集用于实现多种安全目标。实验结果证明了该架构的有效性,并具有代码量小、动态可加载和虚拟化开销小等优点。     

基于VMM的操作系统隐藏对象关联检测技术

恶意软件通过隐藏自身行为来逃避安全监控程序的检测.当前的安全监控程序通常位于操作系统内部,难以有效检测恶意软件,特别是内核级恶意软件的隐藏行为.针对现有方法中存在的不足,提出了基于虚拟机监控器(virtual machine monitor,简称VMM)的操作系统隐藏对象关联检测方法,并设计和实现了相应的检测系统vDetector.采用隐式和显式相结合的方式建立操作系统对象的多个视图,通过对比多视图间的差异性来识别隐藏对象,支持对进程、文件及网络连接这3种隐藏对象的检测,并基于操作系统语义建立隐藏对象间的关联关系以识别完整攻击路径.在KVM虚拟化平台上实现了vDetector的系统原型,并通过实验评测vDetector的有效性和性能.结果表明,vDetector能够有效检测出客户操作系统(guest OS)中的隐藏对象,且性能开销在合理范围内.     

基于硬件虚拟化的安全高效内核监控模型

传统的基于虚拟化内核监控模型存在两个方面的不足:(1) 虚拟机监控器(virtual machine monitor,简称VMM)过于复杂,且存在大量攻击面(attack surface),容易受到攻击;(2) VMM执行过多虚拟化功能,产生严重的性能损耗.为此,提出了一种基于硬件虚拟化的安全、高效的内核监控模型HyperNE.HyperNE舍弃VMM中与隔离保护无关的虚拟化功能,允许被监控系统直接执行特权操作,而无需与VMM交互;同时,HyperNE利用硬件虚拟化中的新机制,在保证安全监控软件与被监控系统隔离的前提下,两者之间的控制流切换也无需VMM干预.这样,HyperNE一方面消除了VMM的攻击面,有效地削减了监控模型TCB(trusted computing base);另一方面也避免了虚拟化开销,显著提高了系统运行效率和监控性能.     

基于系统虚拟化的安全技术研究

为提高操作系统和应用程序的安全性,研究了系统虚拟化的相关技术,讨论典型的基于系统虚拟化技术的安全技术应用和系统.根据研究目标的软件层次,分别从应用程序安全、操作系统安全和虚拟机监控器自身安全性三方面,对当前的研究现状和未来的发展趋势进行了分析和归纳.设计一种基于系统虚拟化技术实现对恶意软件透明安全的动态调试分析方案,通过在Intel-VT平台上实现系统原型,验证了该方法的可行性和有效性.     

基于VMM的Windows文件系统监控

文件系统监控是文件保护的基础。针对现有文件系统监控容易被恶意软件破坏的问题,提出一种基于VMM的Windows文件系统监控方法。该方法利用硬件虚拟化技术,通过监控系统调用监控文件系统操作,且监控手段对客户系统透明,保证实施的监控安全可信。最后设计并实现了相应的原型系统,同时对原型系统的监控效果和时间开销进行测试。实验结果表明,原型系统能够监控常见的Windows文件系统操作,并且时间开销在可接受的范围内。     

一种Xen细粒度强制访问控制框架的设计与实现

利用强制访问控制技术可实现虚拟机间安全的隔离与共享,但现有强制访问控制技术无法对虚拟机内部资源进行有效的保护。在深入分析Xen虚拟化技术和强制访问控制技术的基础上,针对Xen Security Module(XSM)/Flask架构,提出虚拟化强制访问控制VMAC(Virtual Mandatory Access Control)框架,提供了Virtual Machine(VM)和Virtual Machine Monitor(VMM)两级安全策略的集中管理和操作,实现了Xen的细粒度强制访问控制。     

基于VMM层系统调用分析的软件完整性验证

在虚拟化云计算平台中,如何保证其上运行软件的可信性是云平台广泛应用的关键.完整性测量与验证技术是保证软件系统可信性的一种主要方法.然而,现有的软件完整性验证系统大多需要修改操作系统内核,很难为大规模虚拟机环境中的众多异构系统提供一致解决方案,且无法抵御内核级恶意攻击.针对当前方法在兼容性、安全性以及可管理性上存在的问题,设计并实现了一种在VMM层基于系统调用分析技术来验证软件完整性的方法VMGuard.它通过截获客户操作系统中的系统调用来识别软件加载,并基于系统调用关联性分析和虚拟机文件系统元数据重构技术来验证客户操作系统中软件的完整性.在Qemu和KVM两种主流虚拟化平台上实现了VMGuard,并通过实验评测VMGuard的有效性和性能.实验结果表明,VMGuard能够有效验证客户操作系统中软件的完整性,且性能开销在10%以内.     

一种基于VMM的内核级Rootkit检测技术

针对云平台中的虚拟机内核级Rootkit破坏租户虚拟机完整性的问题,文章提出一种基于VMM(虚拟机监视器,Virtual Machine Monitor)的内核级Rootkit检测技术。该技术以在关键路径设置陷入点的方式构建TML(True Module List),得到虚拟机中真实的内核模块视图,在VMM层利用自下而上的调用方式获取虚拟机用户态视图,并在VMM层获取重构的虚拟机内核态视图,通过交叉对比这三个视图检测隐藏在虚拟机中的Rootkit。最后,利用该技术在KVM(基于内核的虚拟机,Kernel-based Virtual Machine)中实现了原型系统,实验结果表明系统能迅速准确地检测出虚拟机中的Rootkit,并依据TML报告内核级Rootkit的详细信息,系统的综合性能损耗在可接受范围内。     

Design and verification of a lightweight reliable virtual machine monitor for a many-core architecture

Virtual machine monitors (VMMs) play a central role in cloud computing. Their reliability and availability are critical for cloud computing. Virtualization and device emulation make the VMM code base large and the interface between OS and VMM complex. This results in a code base that is very hard to verify the security of the VMM. For example, a misuse of a VMM hyper-call by a malicious guest OS can corrupt the whole VMM. The complexity of the VMM also makes it hard to formally verify the correctness of the system’s behavior. In this paper a new VMM, operating system virtualization (OSV), is proposed. The multiprocessor boot interface and memory configuration interface are virtualized in OSV at boot time in the Linux kernel. After booting, only inter-processor interrupt operations are intercepted by OSV, which makes the interface between OSV and OS simple. The interface is verified using formal model checking, which ensures a malicious OS cannot attack OSV through the interface. Currently, OSV is implemented based on the AMD Opteron multi-core server architecture. Evaluation results show that Linux running on OSV has a similar performance to native Linux. OSV has a performance improvement of 4%–13% over Xen.     

Intel virtualization technology

A virtualized system includes a new layer of software, the virtual machine monitor. The VMM's principal role is to arbitrate accesses to the underlying physical host platform's resources so that multiple operating systems (which are guests of the VMM) can share them. The VMM presents to each guest OS a set of virtual platform interfaces that constitute a virtual machine (VM). Once confined to specialized, proprietary, high-end server and mainframe systems, virtualization is now becoming more broadly available and is supported in off-the-shelf systems based on Intel architecture (IA) hardware. This development is due in part to the steady performance improvements of IA-based systems, which mitigates traditional virtualization performance overheads. Intel virtualization technology provides hardware support for processor virtualization, enabling simplifications of virtual machine monitor software. Resulting VMMs can support a wider range of legacy and future operating systems while maintaining high performance.     

基于Xen的I／O准虚拟化驱动研究

针对全虚拟化下客户端虚拟机无法“感知”虚拟机监视器的问题,对基于Xen的I／O准虚拟化驱动进行研究,通过实验可知,准虚拟化驱动能够消除全虚拟化方式下虚拟机监视器“黑箱”特性的限制,可以实现和虚拟机监视器的密切配合,从而提高I／O性能。在虚拟机Xen的全虚拟化环境中加入准虚拟化驱动,采用对比测试方法验证了该驱动能大幅提升网络性能。     

基于硬件队列扩展的网卡虚拟化方案

多核架构的虚拟平台对偏重于I/O访问的应用普遍存在虚拟化性能开销大的问题。为此,提出一种基于驱动域的网卡虚拟化方案。通过具有独立中断的硬件队列对网卡进行硬件扩展,减少网卡I/O访问中虚拟机监控器的参与,提高访问效率。测试结果表明,在消息长度达到1 024 Byte时,使用虚拟接口的时延仅比非虚拟化环境高10%。     

On covert channels between virtual machines

Virtualization technology has become very popular because of better hardware utilization and easy maintenance. However, there are chances for information leakage and possibilities of several covert channels for information flow between the virtual machines. Our work focuses on the experimental study of security threats in virtualization, especially due to covert channels and other forms of information leakage. The existence of data leakage during migration shutdown and destruction of virtual machines, is tested on different hypervisors. For empirically showing the possibility of covert channels between virtual machines, three new network based covert channels are hypothesized and demonstrated through implementation, on different hypervisors. One of the covert channels hypothesized is a TCP/IP steganography based covert channel. Other covert channels are a timing covert channel and a new network covert channel having two pairs of socket programs. We propose a VMM (Virtual Machine Monitor) based network covert channel avoidance mechanism, tackling detection resistant covert channel problems. We also address issue of reducing the possibilities of network based covert channels using VMM-level firewalls. In order to emphasize the importance of addressing the issue of information leakage through virtual machines, we illustrate the simplicity of launching network covert channel based attacks, by demonstrating an attack on a virtual machine using covert channels through implementation.     

A disk bandwidth allocation mechanism with priority

Virtualization is a popular technology. Services and applications running on each virtual machine have to compete with each other for limited physical computer or network resources. Each virtual machine has different I/O requirement and special priority. Without proper scheduling resource management, a load surge in a virtual machine may inevitably degrade other’s performance. In addition, each virtual machine may run different kinds of application, which have different disk bandwidth demands and service priorities. When assigning I/O resources, we should deal with each case on demand. In this paper, we propose a dynamic virtual machine disk bandwidth control mechanism in virtualization environment. A Disk Credit Algorithm is introduced to support a fine-gained disk bandwidth allocation mechanism among virtual machines. We can assign disk bandwidth according to each virtual machine’s service priority/weight and its requirement. Related experiments show that the mechanism can improve the VMs’ isolation and guarantee the performance of the specific virtual machine well.     

Trochilidae:面向众核平台的高性能轻量级虚拟机监控器

虚拟化技术在云计算中广泛应用。传统虚拟化技术对操作系统的一些操作都进行了捕捉与封装,使其越来越复杂,同时也影响了操作系统的性能。针对众核平台的发展趋势和特点,面向众核平台设计并实现了一个轻量级的高性能虚拟机监控器——蜂鸟(Trochilidae)。多操作系统可以同时运行在此虚拟机监控器之上,同时对操作系统性能无损失。在提供传统虚拟机监控器功能的基础上,蜂鸟的代码量仅4000行左右(包括汇编与C代码),降低了系统的复杂度,便于系统的维护与调试。