mbedtls: improve debug output and fix AES-ICM issues

[seyednasermoravej]

• aes_gcm: Add debug print when PSA status fails.
• aes_icm: Destroy previous key before importing new key.
• aes_icm: Add missing destination buffer argument to encrypt function.

After testing the new libSRTP on a microcontroller with a limited resources (RAM = 256KB), I faced two issues:

1. We need to check if the key is available, first we need to destroy it, after that we can address its pointer to the NULL pointer.
2. When performing in-place encryption/decryption (input buffer == output buffer), the input length must be divisible by the cipher block size. Please check this:
   https://github.com/Mbed-TLS/TF-PSA-Crypto/blob/76920edddcad00ac41b248e12d937b845df7bedb/drivers/builtin/src/cipher.c#L641

[pabuhler]

I am still unsure if you would like to try and merge this or have it as a local fix only?

[seyednasermoravej]

I am still unsure if you would like to try and merge this or have it as a local fix only?

Based on this comment Mbed-TLS/TF-PSA-Crypto#711 (comment) the bug is on the MbedTLS side. I figured it out why the code works on Ubuntu while doesn't on Zephyr and fixed the issue. The fact is somewhere in the code two micros are defined differently for Zephyr and Ubuntu. For example, LOCAL_INPUT_ALLOC by default is defined
https://github.com/Mbed-TLS/TF-PSA-Crypto/blob/8c29e401e9c1a3180a1eca6aed13958453276550/core/psa_crypto.c#L291
in Zephyr RTOS and is defined
https://github.com/Mbed-TLS/TF-PSA-Crypto/blob/8c29e401e9c1a3180a1eca6aed13958453276550/core/psa_crypto.c#L218
in the Ubuntu. I changed the configurations for Zephyr to works like the Ubuntu. The point is in the deep inside with Ubuntu configurations, the function is NOT in-place at all. It seems to be in-place but in the background it allocates another buffer for the input and a another buffer for the output. In summery.
Ubuntu way:
input -> copy to new buffer, allocates a new output buffer -> three buffers + 1 copy at least.
So, the current code (this modified aes_icm_mbedtls.c) is more optimized.

So, we have two options

1. Merging the current code to the main (better for optimization, Also MBEDTLS_PSA_ASSUME_EXCLUSIVE_BUFFERS should be enabled for Ubuntu).
2. Removing the code added to aes_icm_mbedtls.c (cleaner code, maybe some day MbedTLS fixes this bug).
   What do you suggest? @pabuhler

[pabuhler]

I would personally go for option 2 if there is no actual need for this code now, mostly to avoid maintaining special case handling.
But that said I do not use this back end and so will not block it from being merge if it serves a purpose for some one.

[seyednasermoravej]

I would personally go for option 2 if there is no actual need for this code now, mostly to avoid maintaining special case handling. But that said I do not use this back end and so will not block it from being merge if it serves a purpose for some one.

I applied the option 2. I'm handling the issue on Zephyr side with the same configurations like PC. zephyrproject-rtos/zephyr#108519
Now I think the code is more cleaner. The only important issue with the current main branch is the problem with not deleting keys which this commit fix it.