TEE Containers: Secure Middleware for Enclaves

• TEE Containers are middleware that secure application code using hardware TEEs like Intel SGX and AMD SEV-SNP, ensuring confidentiality, integrity, and controlled availability.
• They employ layered isolation at application, OS, and orchestration interfaces to enable lift-and-shift migration of unmodified binaries while managing boundary vulnerabilities.
• Modern designs integrate LibOS, WASM, and VM techniques, enhancing performance, usability, and security through automated analysis and resource optimization.

Trusted Execution Environment (TEE) containers are middleware solutions designed to facilitate the secure development, deployment, and execution of applications within hardware-protected enclaves. By leveraging TEEs, these containers shield application code from potentially malicious operating systems and cloud orchestration platforms, aiming to preserve confidentiality, integrity, and—where possible—availability for sensitive workloads. TEE containerization builds on modern CPU TEE features (e.g., Intel SGX, AMD SEV-SNP, ARM TrustZone) and refines their service models, boundary isolation, and operational usability for a broad range of cloud and edge scenarios.

1. Isolation Architectures in TEE Containers

TEE containers employ multi-layered isolation to mediate interactions between trusted applications and untrusted environments. Common architectural boundaries include:

• Application Interfaces: Containers often implement wrapper layers (LibOS, modified libc, or WASI) that intercept system calls from the application, implementing "squash" semantics—only a select subset of calls reach the host OS, and many are processed or emulated inside the enclave.
• OS (I/O) Interfaces: TEE containers utilize Ocall stubs (or analogues such as Tcall) for host interactions, encrypting/decrypting I/O when necessary (e.g., disk, network).
• Orchestration Interfaces: Container orchestrators (e.g., Kubernetes) integrate operators or shims to mediate the deployment/configuration of TEE containers, isolating the control plane and metadata.
• Internal Isolation: Some solutions, particularly those designed for multi-tenant scenarios, integrate intra-enclave compartmentalization—using Software Fault Isolation (SFI) or WASM-based sandboxing to segregate multiple workloads.

This layered structure is depicted in Figure "Interface Design of Tcons" (Liu et al., 28 Aug 2025), which illustrates application, runtime, and orchestration boundaries. Formally, each system call or I/O operation from the application undergoes encapsulated processing:

$$\text{{Application}} \xrightarrow{\text{Encapsulated Syscall}} \text{TEE Container (Enclave)} \xrightarrow{\text{Ocall/Tcall}} \text{Host OS}$$

This multi-boundary approach enables "lift-and-shift" of unmodified binaries (as in Parma (Johnson et al., 2023)) and supports direct migration of applications from standard environments into TEEs.

2. Security Properties and Vulnerabilities

While TEE containers offer robust hardware-enforced protection, papers (Liu et al., 28 Aug 2025, Liu et al., 2021) identify numerous boundary vulnerabilities:

• Memory Management Issues: Partial emulation of Linux syscalls (e.g., mmap, mprotect, mremap) can result in incorrect region allocation, overprivileged permissions, or insufficient zero-filling, enabling unintended data modifications.
• File I/O / Filesystem Weaknesses: Inconsistent error handling (e.g., readlinkat, sendfile), incomplete persistence, and file caches may be subject to rollback/replay attacks, breaking atomicity and freshness.
• IPC/I/O Multiplexing Flaws: Defective semaphore or shared memory implementations can cause deadlocks or cross-process leakage.
• Iago Attacks: Unsanitized syscall return values from the untrusted host can subvert enclave invariants by maliciously manipulating return data, exposing in-enclave memory or breaching access controls.
• Privilege Reduction: Emerging architectures such as ReZone (Cerdeira et al., 2022) use hardware primitives (e.g., Platform Partition Controller (PPC), Auxiliary Control Unit (ACU)) to isolate and restrict zone-level privileges, mitigating privilege escalation and confining compromised OS kernels.
• Incomplete Internal Isolation: Partial SFI or sandboxing often fails to fully protect against intra-enclave threats, particularly when direct jumps bypass instrumentation.

Tbouncer and TECUZZER, automated analyzers (Liu et al., 28 Aug 2025, Liu et al., 2021), systematically probe these boundaries, revealing subtle cross-layer vulnerabilities. For example, improper handling of VirtIO driver parameters or shared DMA buffers may inadvertently leak enclave memory addresses. Rollback and replay are typically mitigated using persistent integrity structures such as Merkle Trees. However, file and resource protection remain inconsistent among existing TEE containers.

3. Containerization Strategies and System Designs

TEE containers support diverse strategies for lifting and securing workloads:

• LibOS-based Migration: Containers like Graphene-SGX, Occlum, Mystikos intercept system calls via a wrapped LibOS, enabling direct execution of unmodified binaries. Only a subset of Linux syscalls (often 31–166 out of >450) are available in such environments (Paju et al., 2023), reducing attack surface and optimizing performance.
• WASM-based Sandboxing: Twine, Enarx, AccTee encapsulate legacy binaries using WASM runtimes, leveraging structured control flow and well-defined stack semantics for sandboxing. While promising, WASM-based containers impose significant restrictions on threading, I/O, and require substantial porting/adaptation.
• VM-based TEE Containers: Systems like Parma (Johnson et al., 2023), CoCo, leverage hardware-virtualized TEEs (e.g., AMD SEV-SNP, Intel TDX) for strong isolation. Attested execution policies enforce inductive proof over future container group states, and policy measurements are encoded in attestation reports.
• Microarchitecture Partitioning: MicroTEE (Ji et al., 2019) implements a microkernel architecture, migrating crypto and key management services to user-layer processes. The kernel focuses on minimal functions (address space, thread management, IPC), substantially reducing the Trusted Computing Base and improving resilience.
• Dynamic Customization and TPM 2.0 Support: FPGA-vTPM architectures (Mao et al., 18 May 2025) provide runtime customizable TEEs, leveraging TPM 2.0 for dynamic IP deployment and invocation on FPGA-SoCs.

Table: Example Containerization Mechanisms

Mechanism	Typical Projects	Migration Approach
LibOS / Wrapped libc	Graphene, Occlum	Direct binary execution
WASM Runtime	Twine, Enarx	Source/binary porting
VM-Level TEE Container	Parma, CoCo	VM-guest isolation

4. Performance, Usability, and Developer Tooling

Performance and usability are critical factors in the adoption of TEE containers:

• Performance Overheads: Runtime measurements for enclave operations vary widely (e.g., mean overheads 0–26% in Parma (Johnson et al., 2023); enclave execution startup time ~430.5 μs in Open-TEE (McGillion et al., 2015); microkernel IPC <1 μs for short messages in MicroTEE (Ji et al., 2019)).
• Resource Management: Memory footprints are optimized via extensive use of shared libraries/process zygote patterns (as in Open-TEE (McGillion et al., 2015)). However, secure memory limitations (e.g., SGX EPC 128 MB) require partitioning strategies, offloading bulk data to encrypted storage and caching with integrity via Merkle Hash Trees (Messaoud et al., 6 Jan 2025).
• Usability Studies: Open-TEE (McGillion et al., 2015) demonstrated significant improvements in developer usability (SUS scores increase from ~52 to ~74), highlighting the impact of hardware-independent, open-source debugging environments.
• Developer Tooling: Migration and protection automation (e.g., AutoTEE (Han et al., 19 Feb 2025)) leverages LLM-enabled source analysis and transformation with high F1 scores (0.91), enabling partitioning and secure runtime transformation with minimal manual intervention across various languages and TEE platforms.
• Partitioning Analysis: Static analyzers such as DITING (Ma et al., 21 Feb 2025) can detect insecure partitioning (unencrypted outputs, unchecked inputs, shallow shared memory) with high accuracy (overall F1 ~0.90).

5. Security Evaluation, Analyzer Methodologies, and Attack Models

Automated security evaluation is increasingly central:

• Boundary Testing: Analyzers (TECUZZER, TBouncer) implement multi-part fuzzing frameworks—probing both from within the enclave and from the host—to identify boundary violations, parameter mismanagement, and unsanitized I/O (Liu et al., 2021, Liu et al., 28 Aug 2025).
• Control Flow Attestation & Runtime Auditing: TRACES (Caulfield et al., 27 Sep 2024) leverages TrustZone-M isolation to guarantee reliable delivery of periodic runtime reports (CFLogs), featuring time-based triggers and MAC-bound evidence even under active compromise. This enhances both detection and remediation, surpassing traditional CFA which lacks guaranteed delivery and active fixing.
• Attack Vectors: Evaluations consistently identify Iago attacks (malicious manipulation of syscall return values), rollback/replay (breaks data freshness), buffer overruns, and epistemic vulnerabilities in partitioning—where untrusted data or output leaks from TEE to non-secure domains.
• Cryptography, Remote Attestation, and Integrity: Encrypted storage, MAC-bound hash chains, and attestation protocols (e.g., AMD SEV-SNP or TPM 2.0 (Mao et al., 18 May 2025)) support integrity and remote proof of enclave state/configuration.

6. Emerging Trends and Future Directions in TEE Containerization

The evolution of TEE containerization is marked by several trends:

• VM-based TEEs and Confidential Orchestration: Adoption of hardware VM-based TEEs (SEV, TDX) is shifting the locus of isolation from process-level to guest-level, with Confidential Kubernetes and similar frameworks providing orchestrated deployment while preserving control plane confidentiality.
• WebAssembly Integration: The sandboxing potential of WASM is being explored for fine-grained intra-enclave isolation, though practical application currently forces substantial migration effort (Paju et al., 2023).
• Integration of Trusted Time Sources: Protocols that secure delay measurements and time synchronization (COoL-TEE (Bettinger et al., 24 Mar 2025)) mitigate host-induced bias and enhance fairness for distributed services, a crucial consideration for latency-sensitive container deployments.
• Automated Partitioning and Static Analysis: Tools like AutoTEE and DITING offer promising methods for automated identification, migration, and verification of sensitive code partitions and boundary management (Han et al., 19 Feb 2025, Ma et al., 21 Feb 2025).
• Performance Scalability and Secure Storage: Proposals to extend secure memory capacity (e.g., Scalable SGX) and to integrate efficient asynchronous I/O libraries (SPDK, DPDK) (Messaoud et al., 6 Jan 2025) target performance limitations, crucial for database, analytics, and real-time workloads.
• Unified Security Documentation and Guarantees: Multiple studies (Liu et al., 2021, Liu et al., 28 Aug 2025) reiterate the necessity of precise, transparent documentation of container interfaces, limitations, and security properties for effective risk management and developer adoption.

7. Application Domains and Use Cases

TEE containers are deployed in a wide array of domains:

• Cloud Confidentiality: Parma (Johnson et al., 2023) supports confidential containers with attested execution policies deployed in production on Azure.
• Secure Storage: TEE-based key-value stores run critical database logic inside enclaves, using partitioned architecture for scalable secure storage (Messaoud et al., 6 Jan 2025).
• Edge and Embedded Systems: TRACES (Caulfield et al., 27 Sep 2024), designed for ARM TrustZone-M on embedded MCUs, provides runtime control-flow attestation and enforced remediation in commodity devices.
• FPGA-SoC and Dynamic IP Protection: FPGA-vTPM enables runtime customization and secure IP deployment in cloud acceleration scenarios (Mao et al., 18 May 2025).
• Distributed Search and Marketplaces: COoL-TEE (Bettinger et al., 24 Mar 2025) ensures resilient, fair provider selection under adversarial conditions, minimizing information head-start and latency bias through close integration of trusted measurements.

Conclusion

TEE containers provide a middleware abstraction that integrates hardware-backed isolation, trusted runtime services, and orchestrated deployment for confidential computing. Their layered approach to system call and I/O interface mediation, automated migration, and robust performance optimization paves the way for broad adoption in cloud, edge, and specialized hardware domains. However, continued scrutiny is required, as design flaws, incomplete boundary management, and inconsistent partitioning practices present serious vulnerabilities, necessitating rigorous automated analysis, improved documentation, and innovative architectural evolution according to the lessons learned and future directions outlined in contemporary research (Liu et al., 28 Aug 2025, Liu et al., 2021, Johnson et al., 2023, Paju et al., 2023).