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...on stock operating systems, including buffer overrun protection (e.g., [5, 18]), system call interposition (e.g., [11, 12, 16, 27, 32]), isolation techniques (e.g., [13, 17]), virtual machines (e.g., =-=[14, 33, 35]-=-), and recovering from compromises (e.g., [7]). Flume uses some of these techniques for its implementation (e.g., LSMs [36] and systrace [27]), but Flume is more closely related to mandatory access co...

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...d capabilities with authority checks [4], interposition [15], or even labels [16]. Mandatory access control can also be achieved with unmodified traditional operating systems through virtual machines =-=[11, 17]-=-. For example, the NetTop project [42] uses VMware for multi-level security. Virtual machines have two principal limitations, however: performance [19, 46] and coarse granularity. One of the goals of ...

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...llysuccessful virtualized cloud. In this paper, we propose an alternative approach that protects leased virtual machines in a multitenant cloud. Our approach uses the concept of nested virtualization =-=[23, 13]-=- and introduces a tiny security monitor called CloudVisor underneath a mostly unmodified commodity VMM. Unlike previous approaches that incorporate nested virtualization functionality into a commodity...

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...lable. We address each of the following areas: CPU (e.g., instruction-set) virtualization, memory (MMU) virtualization, and I/O virtualization. x86 virtualization follows the “trap and emulate” model =-=[21,22,36]-=-. Since every trap by a guest hypervisor or operating system results in a trap to the lowest (most privileged) hypervisor, our approach for CPU virtualization works by having the lowest hypervisor ins...

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...entially a useful step towards improving the reliability of legacy kernels. PARAVIRTUAL MACHINES A second approach has its roots in the concept of a virtual machine, which goes back to the late 1960s =-=[3]-=-. In short, this idea is to run a special control program, called a virtual machine monitor, on the bare hardware instead of an operating system, Its job is to create multiple instances of the true ma...

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...sly, and taking a very careful approach to design and implementation, with extensive micro-optimisation of algorithms and data structures [39]. While Mach and its contemporaries exhibited IPC costs that were 1–2 orders of magnitude above the architectural limit, his L4 kernel came within tens of percent of that limit, outperforming Mach by more than an order of magnitude. Unfortunately, the Mach experience had already given microkernels a very bad image, and Liedtke’s results were largely ignored. The academic community by and large lost all interest in microkernels. Instead, virtual machines [20] are experiencing a renaissance [1], driven by a need to provide stronger resource isolation between subsystems than what is offered by mainstream operating systems, and the desire to run multiple operating systems on the same hardware platform. Virtual machines have a lot in common with microkernel, in the sense that both are (potentially) small kernels with very limited functionality. In fact, microkernels have long been used as virtual-machine monitors [21,24]. Interestingly, most hypervisors seem much larger (in terms of code size) than L4. 2.4 Microkernels in the embedded-systems domain D...

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...he proposed architecture for proactive recovery. Section 5 evaluates our prototype, and Section 6 concludes. 2 Related Work Virtualization is an old technology that was introduced by IBM in the 1960s =-=[15]-=-. Systems such as Xen [3] and VMware [23] made this technology popular on standard PC hardware. Virtualization enables the execution of multiple operating system instances simultaneously in isolated e...