Application security traditionally strongly relies upon security of the underlying operating system. However, operating systems often fall victim to software attacks, compromising security of applications as well. To overcome this dependency, Intel SGX allows to protect application code against a subverted or malicious OS by running it in a hardware-protected enclave. However, SGX lacks support for generic trusted I O paths to protect user input and output between enclaves and I O devices. This work presents SGXIO, a generic trusted path architecture for SGX, allowing user applications to run securely on top of an untrusted OS, while at the same time supporting trusted paths to generic I O devices. To achieve this, SGXIO combines the benefits of SGX's easy programming model with traditional hypervisor-based trusted path architectures. Moreover, SGXIO can tweak insecure debug enclaves to behave like secure production enclaves. SGXIO surpasses traditional use cases in cloud computing and digital rights management and makes SGX technology usable for protecting user-centric, local applications against kernel-level keyloggers and likewise. It is compatible to unmodified operating systems and works on a modern commodity notebook out of the box. Hence, SGXIO is particularly promising for the broad x86 community to which SGX is readily available.
Complete formal verification is the only known way to guarantee that a system is free of programming errors. We present our experience in performing the formal, machine-checked verification of the seL4 microkernel from an abstract specification down to its C implementation. We assume correctness of compiler, assembly code, and hardware, and we used a unique design approach that fuses formal and operating systems techniques. To our knowledge, this is the first formal proof of functional correctness of a complete, general-purpose operating-system kernel. Functional correctness means here that the implementation always strictly follows our high-level abstract specification of kernel behaviour. This encompasses traditional design and implementation safety properties such as the kernel will never crash, and it will never perform an unsafe operation. It also proves much more: we can predict precisely how the kernel will behave in every possible situation. seL4, a third-generation microkernel of L4 provenance, comprises 8,700 lines of C code and 600 lines of assembler. Its performance is comparable to other high-performance L4 kernels. Despite a number of radical changes in how computer systems are used, the design principles behind the very core of the systems stack---an operating system kernel---has remained unchanged for decades. We run monolithic kernels developed with a combination of an unsafe programming language, global sharing of data structures, opaque interfaces, and no explicit knowledge of kernel protocols. Today, the monolithic architecture of a kernel is the main factor undermining its security, and even worse, limiting its evolution towards a safer, more secure environment. Lack of isolation across kernel subsystems allows attackers to take control over the entire machine with a single kernel vulnerability. Furthermore, complex, semantically rich monolithic code with globally shared data structures and no explicit interfaces is not amenable to formal analysis and verification tools. Even after decades of work to make monolithic kernels more secure, over a hundred serious kernel vulnerabilities are still reported every year. Modern kernels need decomposition as a practical means of confining the effects of individual attacks. Historically, decomposed kernels were prohibitively slow. Today, the complexity of a modern kernel prevents a trivial decomposition effort. We argue, however, that despite all odds modern kernels can be decomposed. Careful choice of communication abstractions and execution model, a general approach to decomposition, a path for incremental adoption, and automation through proper language tools can address complexity of decomposition and performance overheads of decomposed kernels. Our work on lightweight capability domains (LCDs) develops principles, mechanisms, and tools that enable incremental, practical decomposition of a modern operating system kernel.