BlackBox: A Container Security Monitor for Protecting Containers on Untrusted Operating Systems

Containers are widely deployed to package, isolate, and multiplex applications on shared computing infrastructure, but rely on the operating system to enforce their security guarantees. This poses a significant security risk as large operating system codebases contain many vulnerabilities. We have created BlackBox, a new container architecture that provides fine-grain protection of application data confidentiality and integrity without trusting the operating system. BlackBox introduces a container security monitor, a small trusted computing base that creates protected physical address spaces (PPASes) for each container such that there is no direct information flow from container to operating system or other container PPASes. Indirect information flow can only happen through the monitor, which only copies data between container PPASes and the operating system as system call arguments, encrypting data as needed to protect interprocess communication through the operating system. Containerized applications do not need to be modified, can still make use of operating system services via system calls, yet their CPU and memory state are isolated and protected from other containers and the operating system. We have implemented BlackBox by leveraging Arm hardware virtualization support, using nested paging to enforce PPASes. The trusted computing base is a few thousand lines of code, many orders of magnitude less than Linux, yet supports widely-used Linux containers with only modest modifications to the Linux kernel. We show that BlackBox provides superior security guarantees over traditional hypervisor and container architectures with only modest performance overhead on real application workloads.