by Gal Beniamini, Project Zero

Mobile devices are becoming an increasingly privacy-sensitive platform. Nowadays, devices process a wide range of personal and private information of a sensitive nature, such as biometric identifiers, payment data and cryptographic keys. Additionally, modern content protection schemes demand a high degree of confidentiality, requiring stricter guarantees than those offered by the “regular” operating system. In response to these use-cases and more, mobile device manufacturers have opted for the creation of a “Trusted Execution Environment” (TEE), which can be used to safeguard the information processed within it. In the Android ecosystem, two major TEE implementations exist – Qualcomm’s QSEE and Trustonic’s Kinibi (formerly <t-base). Both of these implementations rely on ARM TrustZone security extensions in order to facilitate a small “secure” operating system, within which “Trusted Applications” (TAs) may be executed. In this blog post we’ll explore the security properties of the two major TEEs present on Android devices. We’ll see how, despite their highly sensitive vantage point, these operating systems currently lag behind modern operating systems in terms of security mitigations and practices. Additionally, we’ll discover and exploit a major design issue which affects the security of most devices utilising both platforms. Lastly, we’ll see why the integrity of TEEs is crucial to the overall security of the device, making a case for the need to increase their defences. […]

https://googleprojectzero.blogspot.com/2017/07/trust-issues-exploiting-trustzone-tees.html