Porting tock to open titan
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Porting tock to open titan
- 1. © 2020 Western Digital Corporation or its affiliates. All rights reserved. 4/19/2021 Porting Tock to OpenTitan Alistair Francis <alistair.francis@wdc.com> December 2020
- 2. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 2 Todays Talk • What is OpenTitan? • What is Tock? • What do Tock apps look like? • Status of Tock on OpenTitan • Deep dive into USB/CTAP support in Tock on OpenTitan
- 3. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 3 OpenTitan • OpenTitan is an open source silicon Root of Trust (RoT) project • Backed by lowRISC, ETH, Google, Nuvoton, Western Digital and others • OpenTitan uses the Ibex RV32 core as its main processor – Includes a variety of IP blocks for security, including AES, HMAC
- 4. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 4 Tock • Tock is an embedded operating system written in Rust • It’s designed for small platforms without an MMU – Tock's design centers around protection, both from potentially malicious applications and from device drivers • Tock uses the Rust language to enforce security and safety protections in the kernel
- 5. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 5 Tock Apps • Apps can be written in C (libtock-c) or Rust (libtock-rs) – C apps have better support – OpenTitan likes Rust as it provides more safety – Other languages are possible as well • Tock uses the ARM® MPU or RISC-V PMP to isolate apps • Apps only have access to their own memory and can’t interfere with the kernel or other apps – There are kernel calls and IPC to allow communication between apps OpenTitan Hardware OpenTitan Boot ROM Tock U2F App RNG App Other App
- 6. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 6 App interface to kernel • Four main system call categories – allow – subscribe – command – yield
- 7. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 7 Tock on OpenTitan • The majority of work happens on mainline Tock • Mainline Tock supports: – AES – Flash Controller – GPIOs – HMAC – I2C – Power Manager – Timers – UART – USB/CTAP • Upcoming work – ePMP – Key/Value filesystem – System call (syscall) Filtering – Storage ACLs
- 8. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8 CTAP2 Client To Authenticator Protocol • CTAP is a spec developed by the FIDO Alliance that specifies the protocol for a host to communicate with a cryptographic authenticator device. – Is used by browsers and Yubikeys for WebAuthn • Ctap Rust crate already exists: https://crates.io/crates/ctap2- authenticator This Photo by MesserWoland is licensed under CC BY-SA
- 9. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 9 Tock Kernel Changes for USB
- 10. 4/19/2021 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 10 Demo
- 11. © 2019 Western Digital Corporation or its affiliates. All rights reserved. 4/19/2021
Notes de l'éditeur
- Tock is asynchronous and all operations are non-blocking The core kernel has access to the entire system and can use the Rust unsafe keyword The peripheral devices can use the unsafe keyword and can directly access hardware Capsules (where a lot of functionality is implemented) must be safe Rust No access to hardware or core kernel features Currently no hardware isolation in the kernel, just code design isolation (WD is working on improving this)
- Allow marks a region of memory as shared between the kernel and application. Passing a null pointer requests the corresponding driver to stop accessing the shared memory region. Subscribe assigns callback functions to be executed in response to various events. Command instructs the driver to perform a specific action. Yield transitions the current process from the Running to the Yielded state, and the process will not execute again until another callback re-schedules the process. All except for yield are non-blocking
- Setup Tock drivers and register callbacks Read bytes from USB and pass to CTAP library Send data returned from library after processing Crypto sign and attest operations. Currently done in software in userspace, eventually wan to offload to the Tock kernel and hardware accelerators HMAC is off loaded to Tock and HMAC hardware Currently no TRGN, so nonce is hardcoded Also no flash storage, so data is lost on reboot