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From: David Horstmann via mbed-tls <mbed-tls@lists.trustedfirmware.org>
Sent: Tuesday, September 24, 2024 5:14 PM
To: mbed-tls@lists.trustedfirmware.org; Lee, William <William.Lee@garmin.com>
Subject: [mbed-tls] Re: Looking for suggestions about make Mbed TLS APIs non-secure callable APIs on armv8m

 

Hi William,

 

Since Mbed TLS is a cross-platform library, we don't deal directly with TrustZone-M.

 

However, if I have understood correctly, I think your usecase is solved by the Trusted Firmware M (TF-M) project[1], which is an implementation of secure firmware that provides cryptography services via non-secure-callable APIs.

 

TF-M uses Mbed TLS internally and implements the PSA Certified Cryptography API[2]. The Crypto Service Integration Guide[3] in the documentation should be a good starting point for what you are trying to do.

 

I hope that helps,

David Horstmann
Mbed TLS developer

 

[1] https://www.trustedfirmware.org/projects/tf-m

[2] https://www.psacertified.org/getting-certified/crypto-api-compliance/

[3] https://trustedfirmware-m.readthedocs.io/en/latest/integration_guide/services/tfm_crypto_integration_guide.html

TrustedFirmware-M (TF-M) implements the Secure Processing Environment (SPE) for Armv8-M, Armv8.1-M architectures or dual-core platforms.

 

From: Lee, William via mbed-tls <mbed-tls@lists.trustedfirmware.org>
Sent: 24 September 2024 15:08
To: mbed-tls@lists.trustedfirmware.org <mbed-tls@lists.trustedfirmware.org>
Subject: [mbed-tls] Looking for suggestions about make Mbed TLS APIs non-secure callable APIs on armv8m

 

Hi Mbed TLS,

 

I am looking for some suggestions about make some (or all) Mbed TLS APIs non-secure callable APIs on armv8m.

 

The background is that I am going to have a secure firmware that provides encryption services by building part (or whole) of Mbed TLS into that firmware and make those original mbedtls_x APIs non-secure callable, so the existing non-secure firmware could link those non-secure callable APIs and use them.

 

Some of my thoughts:

(1) The easiest way to do it I can think of is just add the attribute "cmse_nonsecure_call" to those APIs' declaration (or use a macro to wrap the attribute for conditional build to not impact others don't want it), but I do not think this modification could be accepted by upstream 🙂.

(2) So my another thought is duplicate all header files and put them under another folder, assuming it is my-include folder, then I can do whatever I want to my-include folder, but there is also a problem I can think of: a merge/compare burden between include and my-include folder after I have updated Mbed TLS.

 

I really appreciate other suggestions!

 

Thanks,

William