As computer system software stacks become increasingly complex, the associated security risks also escalate. Trusted Execution Environments (TEEs) have emerged as a mainstream security solution to enhance system security. TEEs can be categorized into user-level TEEs, OS-level TEEs, and hybrid TEEs. However, these TEEs typically possess fixed security boundaries and isolation domains, limiting their adaptability to varying security requirements and dynamic scenarios. Moreover, the design of Trusted Computing Base (TCB) components in TEE frameworks often operates at the highest privilege levels of the architecture. This concentration of critical code at the highest privilege level increases the whole platform’s security risk due to the growing amount of code as more security functions are added. In this paper, we propose FlexClave, an extensible and secure TEE framework designed to address these issues. FlexClave leverages hardware primitives to create secure isolation boundaries tailored to different use cases. Additionally, our framework distributes TCB components across various privilege levels, reducing the concentration of security functions at the highest privilege levels and mitigating the risks associated with running extensive code in a single, highly privileged context. We implement two prototypes on ARMv9-A Fixed Virtual Platform and ARMv8 RK3399 SoC, each with two use cases (container and virtual machine), to evaluate the system’s security and performance.

TrustZone-assisted Trusted Execution Environment (TEE) has been widely employed in mobile devices to protect sensitive applications. With increased customization demands, Trusted Applications (TAs) have become more flexible and complex, exposing numerous vulnerabilities within the TEE. Furthermore, due to the unrestricted Trusted Operating System (TOS) services provided to TA, an attacker can exploit vulnerabilities to compromise the whole TEE system. In this paper, we propose a novel customized TOS partition approach, called Chameleon, to enhance the security of the TrustZone-assisted TEE system. Inspired by the principle of least privilege and our TEE vulnerability analysis, we first categorize the TOS into TOS service modules and basic kernel modules. Then, we selectively encapsulate these modules into distinct Capsules based on the TA's functional requirements, providing each TA with a separate execution environment (TA-entity). To enforce access control and confine vulnerable modules within a TA-entity, we introduce T-Visor, which serves as our Trusted Computing Base. Our prototype implementation, built upon Linaro's OP-TEE, requires only 2.9K Lines of Code (LoC) modifications. Evaluation on a Hikey960 board demonstrates that Chameleon reduces the attack surface of TOS services to 51% and mitigates 122 out of 138 CVEs (88.41%) with negligible performance overhead.

Cloud computing nowadays provides flexible and scalable computing services, using different hardware platforms, including ARM. Virtualization allows multiple virtual machines (VMs) to share the physical resources of a host machine. However, these technologies have security risks. The hypervisor is the software that controls VMs, and it can be exploited or manipulated by hackers or untrusted providers. ARM CCA, a novel feature of ARMv9-A, allows confidential VMs to run in a new security state called realm. However, the current CCA prototype still has some problems, including risks brought by external libraries, single point of failure, highly privileged TF-RMM and costly world switch. In this paper, we introduce CubeVisor, a new secure virtualization architecture based on ARM CCA. It uses the idea of the Cube, which is a combination of a hypervisor and a VM, protecting each Cube from other Cubes or components. The CubeVisor also improves performance by optimizing memory allocation and world-switching processes. We implement prototypes on both software-based ARM FVP platform and hardware-based ARM Cortex-A platform for evaluations. The results show that the CubeVisor can protect VMs well and has very low overhead compared to the CCA based virtualization methods.

Cloud computing has been applied on a large scale due to its competitive advantages. However, the introduction of virtualization brings new risks, which can come from within the VM and the host. Due to the abstraction of hardware resources by the hypervisor, traditional trusted computing methods, such as TPM and ASP, are no longer available in cloud environments. Existing work focusing on enabling trusted computing in cloud computing is primarily based on TPM and vTPM, but there are still issues such as the trusted chain not covering all stages of the VM life cycle and the integrity measurement operation potentially causing high overhead. In this paper, we present the vASP architecture, which solves the limitation of the ASP architecture in a cloud environment. Using customization features provided by the ASP, we customize interfaces for the vASP architecture and pass the trusted relationship to the upper layer to form a complete chain of trust. The vASP front-end plugs into the hypervisor actively and regularly operates the dynamic measurement process of the guest to ensure that data from the guest machine are not tampered with. With the introduction of vASP in the cloud computing platform, the security of vASP components during VM operation is also a concern. As a result, we propose a full VM life-cycle protection method through verification and measurement mechanisms that cannot be bypassed to ensure that vASP maintains a match with specific VMs. We have implemented the vASP architecture on a commercial platform deployed with ASP architecture and evaluated it. The result shows that the vASP architecture can protect VM integrity well during full life-cycle and has very low overhead compared to the native virtualization architecture.

Virtualization is the corner stone of cloud computing, but the hypervisor, the crucial software component that enables virtualization, is known to suffer from various attacks. It is challenging to secure the hypervisor due to at least two reasons. On one hand, commercial hypervisors are usually integrated into a privileged Operating System (OS), which brings in a larger attack surface. On the other hand, multiple Virtual Machines (VM) share a single hypervisor, thus a malicious VM could leverage the hypervisor as a bridge to launch “cross-VM” attacks. In this work, we propose SecFortress, a dependable hypervisor design that decouples the virtualization layer into a mediator, an outerOS, and multiple HypBoxes through a cross-layer isolation approach. SecFortress extends the nested kernel approach to de-privilege the outerOS from accessing the mediator's memory and creates an isolated hypervisor instance, HypBox, to confine the impacts from the untrusted VMs. We implemented SecFortress based on KVM and evaluated its effectiveness and efficiency through case studies and performance evaluation. Experimental results show that SecFortress can significantly improve the security of the hypervisor with negligible runtime overhead.