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1. TruZ-Droid: Integrating TrustZone with Mobile Operating System

   Ying, Kailiang; Ahlawat, Amit; Alsharifi, Bilal; Jiang, Yuexin; Thavai, Priyank; Du, Wenliang (June 2018, The 16th ACM International Conference on Mobile Systems, Applications, and Services (MobiSys 2018))

   Mobile devices today provide a hardware-protected mode called Trusted Execution Environment (TEE) to help protect users from a compromised OS and hypervisor. Today TEE can only be leveraged either by vendor apps or by developers who work with the vendor. Since vendors consider third-party app code untrusted inside the TEE, to allow an app to leverage TEE, app developers have to write the app code in a tailored way to work with the vendor’s SDK. We proposed a novel design to integrate TEE with mobile OS to allow any app to leverage the TEE. Our design incorporates TEE support at the OS level, allowing apps to leverage the TEE without adding app-specific code into the TEE, and while using existing interface to interact with the mobile OS. We implemented our design, called TruZ-Droid, by integrating TrustZone TEE with the Android OS. TruZ-Droid allows apps to leverage the TEE to protect the following: (i) user’s secret input and confirmation, and (ii) sending of user’s secrets to the authorized server. We built a prototype using the TrustZone-enabled HiKey board to evaluate our design. We demonstrated TruZ-Droid’s effectiveness by adding new security features to existing apps to protect user’s sensitive information and attest user’s confirmation. TruZ-Droid’s real-world use case evaluation shows that apps can leverage TrustZone while using existing OS APIs. Our usability study proves that users can correctly interact with TruZ-Droid to protect their security sensitive activities and data. 

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2. Information Flow Control for Distributed Trusted Execution Environments

   https://doi.org/10.1109/CSF.2019.00028  

   Gollamudi, Anitha; Chong, Stephen; Arden, Owen (June 2019, 2019 IEEE 32nd Computer Security Foundations Symposium (CSF))

   null (Ed.)

   Distributed applications cannot assume that their security policies will be enforced on untrusted hosts. Trusted execution environments (TEEs) combined with cryptographic mechanisms enable execution of known code on an untrusted host and the exchange of confidential and authenticated messages with it. TEEs do not, however, establish the trustworthiness of code executing in a TEE. Thus, developing secure applications using TEEs requires specialized expertise and careful auditing. This paper presents DFLATE, a core security calculus for distributed applications with TEEs. DFLATE offers high-level abstractions that reflect both the guarantees and limitations of the underlying security mechanisms they are based on. The accuracy of these abstractions is exhibited by asymmetry between confidentiality and integrity in our formal results: DFLATE enforces a strong form of noninterference for confidentiality, but only a weak form for integrity. This reflects the asymmetry of the security guarantees of a TEE: a malicious host cannot access secrets in the TEE or modify its contents, but they can suppress or manipulate the sequence of its inputs and outputs. Therefore DFLATE cannot protect against the suppression of high-integrity messages, but when these messages are delivered, their contents cannot have been influenced by an attacker. 

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3. Running Language Interpreters Inside SGX: A Lightweight,Legacy-Compatible Script Code Hardening Approach

   https://doi.org/10.1145/3321705.3329848  

   Wang, Huibo; Bauman, Erick; Karande, Vishal; Lin, Zhiqiang; Cheng, Yueqiang; Zhang, Yinqian (January 2019, Proceedings of the 2019 ACM Asia Conference on Computer and Communications Security)

   Recent advances in trusted execution environments, specifically with Intel's introduction of SGX on consumer processors, have provided unprecedented opportunities to create secure applications with a small TCB. While a large number of SGX solutions have been proposed, nearly all of them focus on protecting native code applications, leaving scripting languages unprotected. To fill this gap, this paper presents SCRIPTSHIELD, a framework capable of running legacy script code while simultaneously providing confidentiality and integrity for scripting code and data. In contrast to the existing schemes that either require tedious and time-consuming re-development or result in a large TCB by importing an entire library OS or container, SCRIPTSHIELD keeps the TCB small and provides backwards compatibility (i.e., no changes needed to the scripting code itself). The core idea is to customize the script interpreter to run inside an SGX enclave and pass scripts to it. We have implemented SCRIPTSHIELD and tested with three popular scripting languages: Lua, JavaScript, and Squirrel. Our experimental results show that SCRIPTSHIELD does not cause noticeable overhead. The source code of SCRIPTSHIELD has been made publicly available as an open source project. 

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4. Secure and Timely GPU Execution in Cyber-physical Systems

   https://doi.org/10.1145/3576915.3623197  

   Wang, Jinwen; Wang, Yujie; Zhang, Ning (November 2023, ACM Conference on Computer and Communications Security)

   Graphics Processing Units (GPU) are increasingly deployed on Cyber-physical Systems (CPSs), frequently used to perform real-time safety-critical functions, such as object detection on autonomous vehicles. As a result, availability is important for GPU tasks in CPS platforms. However, existing Trusted Execution Environments (TEE) solutions with availability guarantees focus only on CPU computing.To bridge this gap, we propose AvaGPU, a TEE that guarantees real-time availability for CPU tasks involving GPU execution under compromised OS. There are three technical challenges. First, to prevent malicious resource contention due to separate scheduling of CPU and GPU tasks, we proposed a CPU-GPU co-scheduling framework that couples the priority of CPU and GPU tasks. Second, we propose software-based secure preemption on GPU tasks to bound the degree of priority inversion on GPU. Third, we propose a new split design of GPU driver with minimized Trusted Computing Base (TCB) to achieve secure and efficient GPU management for CPS. We implement a prototype of AvaGPU on the Jetson AGX Orin platform. The system is evaluated on benchmark, synthetic tasks, and real-world applications with 15.87% runtime overhead on average. 

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5. TruzCall: Secure VoIP Calling on Android using ARM TrustZone

   https://doi.org/10.1109/MobiSecServ48690.2020.9042945  

   Ahlawat, A; Du, W (February 2020, 2020 Sixth International Conference on Mobile And Secure Services)

   Use of mobile phones today has become pervasive throughout society. A common use of a phone involves calling another person using VoIP apps. However the OSes on mobile devices are prone to compromise creating a risk for users who want to have private conversations when calling someone. Mobile devices today provide a hardware-protected mode called trusted execution environment (TEE) to protect users from a compromised OS. In this paper we propose a design to allow a user to make a secure end-to-end protected VoIP call from a compromised mobile phone. We implemented our design, TruzCall using Android OS and TrustZone TEE running OP-TEE OS. We built a prototype using the TrustZone-enabled Hikey development board and tested our design using the open source VoIP app Linphone. Our testing utilizes a simulation based environment that allows a Hikey board to use a real phone for audio hardware. 

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