Hi,

Sorry the image did not got trough. One way to share the image could be to create a ticket here https://developer.trustedfirmware.org/maniphest/ where the image can be uploaded.

/George

-----Original Message----- From: TF-M tf-m-bounces@lists.trustedfirmware.org On Behalf Of Reinhard Keil via TF-M Sent: 12 December 2019 13:13 To: tf-m@lists.trustedfirmware.org Cc: Bruno Mendes Bruno.Mendes@arm.com Subject: [TF-M] Simplify RTOS / TF-M interface (single thread execution)

When using TF-M on v8-M with Secure Function Call SFC (aka Library) mode, the entry to the secure side is protected by a Mutex. Thus only one thread at the time is calling a secure service. The picture below should therefore represent the execution flow (Level 1 isolation). [cid:image003.jpg@01D5B0ED.DEEA6A60]

Under this assumption there is no need to implement TZ_context management in the RTOS (https://arm-software.github.io/CMSIS_5/Core/html/using_TrustZone_pg.html#RTO...). Any RTOS could be used, provided that the Mutex capability is sufficient.

Moreover this design should create a really simple secure side:

* Only one stack is needed on the secure side for Thread mode execution * No multi-threading issues that need to be resolved (i.e. with access of hardware crypto accelerators)

The drawback of course is that only one task at a time can use a secure service. However an RTOS with priority inversion will ensure that the Secure service is executed as fast as possible, once a scheduling conflict arises.

I would like to gather feedback on that approach. Let me know what you think.

Reinhard

IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.