Add warnings to documentation stating that p256-m code may be out of date with upstream, plus other minor grammatical fixes.

Signed-off-by: Aditya Deshpande <aditya.deshpande@arm.com>

3rdparty/p256-m/README.md

@@ -1,4 +1,4 @@
-The files within the `p256-m/` subdirectory originate from the [p256-m GitHub repository](https://github.com/mpg/p256-m), which is distributed under the Apache 2.0 license. They are authored by Manuel Pégourié-Gonnard. p256-m is a minimalistic implementation of ECDH and ECDSA on NIST P-256, especially suited to constrained 32-bit environments. Mbed TLS documentation for integrating drivers uses p256-m as an example of a software accelerator, and describes how it can be integrated alongside Mbed TLS.
+The files within the `p256-m/` subdirectory originate from the [p256-m GitHub repository](https://github.com/mpg/p256-m), which is distributed under the Apache 2.0 license. They are authored by Manuel Pégourié-Gonnard. p256-m is a minimalistic implementation of ECDH and ECDSA on NIST P-256, especially suited to constrained 32-bit environments. Mbed TLS documentation for integrating drivers uses p256-m as an example of a software accelerator, and describes how it can be integrated alongside Mbed TLS. It should be noted that p256-m files in the Mbed TLS repo will not be updated regularly, so they may not have fixes and improvements present in the upstream project.
 
 The files `p256-m.c` and `.h`, along with the license, have been taken from the `p256-m` repository.
-It should be noted that p256-m deliberately does not supply its own cryptographically secure RNG function. As a result, an RNG function using `mbedtls_ctr_dbrg` has been implemented and added to `p256m.c`.
+It should be noted that p256-m deliberately does not supply its own cryptographically secure RNG function. As a result, the PSA RNG is used, with `p256_generate_random()` wrapping `psa_generate_random()`.

3rdparty/p256-m/p256-m/README.md

@@ -1,3 +1,7 @@
+*This is the original README for the p256-m repository. Please note that as
+only a subset of p256-m's files are present in Mbed TLS, this README may refer
+to files that are not present/relevant here.*
+
 p256-m is a minimalistic implementation of ECDH and ECDSA on NIST P-256,
 especially suited to constrained 32-bit environments. It's written in standard
 C, with optional bits of assembly for Arm Cortex-M and Cortex-A CPUs.

README.md

@@ -307,11 +307,11 @@ License
 
 Unless specifically indicated otherwise in a file, Mbed TLS files are provided under the [Apache-2.0](https://spdx.org/licenses/Apache-2.0.html) license. See the [LICENSE](LICENSE) file for the full text of this license. Contributors must accept that their contributions are made under both the Apache-2.0 AND [GPL-2.0-or-later](https://spdx.org/licenses/GPL-2.0-or-later.html) licenses. This enables LTS (Long Term Support) branches of the software to be provided under either the Apache-2.0 OR GPL-2.0-or-later licenses.
 
-### Other Projects
+### Third-party code included in Mbed TLS
 This project contains code from other projects. This code is located within the `3rdparty/` directory. The original license text is included within project subdirectories, and in source files. The projects are listed below:
 
 * `3rdparty/everest/`: Files stem from [Project Everest](https://project-everest.github.io/) and are distributed under the Apache 2.0 license.
-* `3rdparty/p256-m/p256-m/`: Files have been taken from the [p256-m](https://github.com/mpg/p256-m) repository. The code in the original repository is distributed under the Apache 2.0 license. It is also used by the project under the Apache 2.0 license.
+* `3rdparty/p256-m/p256-m/`: Files have been taken from the [p256-m](https://github.com/mpg/p256-m) repository. The code in the original repository is distributed under the Apache 2.0 license. It is also used by the project under the Apache 2.0 license. We do not plan to regularly update these files, so they may not contain fixes and improvements present in the upstream project.
 
 Contributing
 ------------

include/mbedtls/mbedtls_config.h

@@ -3927,7 +3927,8 @@
  *
  * \warning p256-m has only been included to serve as a sample implementation
  * of how a driver/accelerator can be integrated alongside Mbed TLS. It is not
- * intented for use in production.
+ * intended for use in production. p256-m files in Mbed TLS are not updated
+ * regularly, so they may not contain upstream fixes/improvements.
  * DO NOT ENABLE/USE THIS MACRO IN PRODUCTION BUILDS!
  */
 //#define MBEDTLS_P256M_EXAMPLE_DRIVER_ENABLED