Memory allocation failure in benchmark example IAR + KW24D

[mazimkhan]

Error:

RSA-4096                 :  FAILED: RSA - The private key operation failed : BIGNUM - Memory allocation failed

IAR 7.8
KW24D
CI log https://jenkins-internal.mbed.com/job/mbedtls-mbed-os-examples-pr/75/execution/node/592/log/
mbed-os 5.7

@MarceloSalazar please check.

[MarceloSalazar]

@maclobdell would you like to review this for the KW24D platform?

[maclobdell]

@bentcooke - did you recently make a heap size change to get KW24D working in another example? Perhaps that could be relevant to this issue. Please share any details you have.

[bentcooke]

@maclobdell I had to reduce the heap size (20k->15k) and move the nanostack heap into the system heap ("mbed-mesh-api.use-malloc-for-heap": true,) in order to get the mesh minimal example working on the KW24D.

[ciarmcom]

ARM Internal Ref: IOTSSL-2427

[k-stachowiak]

The impact of this issue has increased by one more test failing to allocate memory on the heap. Currently there are two allocation failures in the BIGNUM module:

...
RSA - The private key operation failed : BIGNUM - Memory allocation failed
...
DHM - Making of the public value failed : BIGNUM - Memory allocation failed
...

[simonbutcher]

I understand the underlying issue is there's not enough heap available on this target for the test, which has been raised as issue #8306.

We've got no way of externally determining if the target can support the test or not, so I'd like to propose we change the benchmark to only test RSA-2048, and skip RSA-4096. RSA-4096 is demanding in memory and in my view it's better to disable the test until #8306 is fixed, which is open ended and has no immediate resolution.

Equally, I suggest we disable the Diffie-Hellman tests. They're not part of the default configuration of Mbed TLS in Mbed OS, so why run them? The lines enabling them in the config.h file, can just be removed.