The document outlines future enhancements for OP-TEE, focusing on improvements in cryptographic services, secure storage, and memory management. Key enhancements include defining an API for implementing various cryptographic algorithms, ensuring secure storage encryption by default, and enabling multiple Trusted Applications (TAs) to run in parallel. Additionally, it discusses the aim to support power state coordination interface (PSCI) and integrate address space layout randomization (ASLR) to enhance security.

1. LCU14-306: OP-TEE Future Enhancements
Joakim Bech, Jens Wiklander and Pascal Brand, LCU14
LCU14 BURLINGAME

2. Cryptographic Layer in OP-TEE
● Aim and problem
● Interaction between TA and Cryptographic Services
● Does not define how the services are implemented / data structures
● Current Status
● LibTomCrypt is the cryptographic library in OP-TEE
● End user may want to switch to ...
- OpenSSL
- Using ARMv8-A cryptographic extensions
- Dedicated cryptographic IP
● Enhancement
● Define a low level API to easily switch from one implementation to another one.

3. GlobalPlatform Internal Core API 1.1
● Current Status
● Internal API 1.0 is supported
● Enhancement
● Add support for GP Internal API 1.1 released in June 2014
● Main updates are:
- Elliptic Curve Digital Signature Algorithm (ECDSA)
- Elliptic Curve Cryptography Cofactor Diffie-Hellman (ECDH)
- Some errata with new error cause
- Few deprecated features (object)

4. Secure Storage
● Current Status
● File storage is implemented (using a daemon running normal world)
● Data isn’t encrypted by default
● No persistent storage
● Enhancement
● Making Secure Storage … more secure
● Enable encryption by default
● Key provisioning
● Streaming to be taken into account
● Replay Protected Memory Block (RPMB) support
Secure World
Trusted
Application
Normal World
TEE supplicant
Linux kernel Trusted OS
Secure monitor
RPMB

5. Secure Time
● Aim and problem
● GlobalPlatform TEE Internal API defines support of the Clock
● Secure clock will be needed in DRM use cases
● Secure IP usage is specific to a given platform
● Current Status
● Only based on REE using RPC NOT Secure!
● Enhancement
● Enable clocks from both REE and Secure IP
● Create a Time API to access the Secure IP
● Fulfill TEE Internal API 1.1 requirements of maximum 15% deviation from real time

6. Reduce Memory Footprint
● Aim and problem
● Memory footprint of the Trusted OS part is critical
● OP-TEE enables all GlobalPlatform features by default
● Enhancement
● Make it possible to select functionality at compile time
● All cryptographic algorithms are probably not needed …
● Some functionality may not be needed (Big Number arithmetic, ...)

7. Multiple TA Support
● Aim
● Enable multiple TA functions to be called at the same time
● Current Status
● Threading model of the Trusted OS is ready, but not activated
● Enhancement
● Will enable multiple-TA’s running in parallel

8. Paging
● Aim
● Trusted OS may run on embedded memory which is small
● Enhancement
● Paging the Trusted OS would solve memory constraint
● some parts would never be paged out (mmu management,...)
● some parts could be paged in DDR (secured or encrypted)

9. PSCI - Power State Coordination Interface
● Aim
● Make OP-TEE aware of PSCI functions.
● Current Status
● OP-TEE aware of: CPU_ON, CPU_OFF,
CPU_SUSPEND and CPU_RESUME (as stubbed functions)
● ARM-Trusted-Firmware handles
● Implemented: PSCI_VERSION, AFFINITY_INFO
● Not implemented: MIGRATE, MIGRATE_INFO_TYPE,
MIGRATE_INFO_UP_CPU, SYSTEM_OFF and SYSTEM_RESET

10. ASLR - Address Space Layout Randomization
● Aim and problem
● Already exists in normal world (user space and kernel)
● To avoid attack like return-to-libc-attack for example
● Make it random enough!
● Enhancement
● This feature could be part of Trusted OS
● Current limitations
● We use pre-defined virtual addresses
● Trusted Applications are currently statically linked

11. Other Potential Enhancements
● GlobalPlatform Trusted UI 1.1
● API to display content and capture input
in a secure manner.
● User-mode TEE
● For early Trusted Applications development and debug
● Avoid the need for having a full TrustZone platform
● Support for OP-TEE in QEMU
● Virtualization team have patches enabling
TrustZone functionality

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