Fix warning in Crypto when using boot seed injection

[alzix]

Description

When enabling boot seed injection (e.g. FUTURE_SEQUANA_M0_PSA) entropy read & write callbacks are injected via macros and cause implicit declaration compilation warning.

Compile [ 37.1%]: entropy.c
[Warning] <command-line>@0,38: implicit declaration of function 'mbed_default_seed_write' [-Wimplicit-function-declaration]
...
Compile [ 37.1%]: entropy.c
[Warning] <command-line>@0,38: implicit declaration of function 'mbed_default_seed_write' [-Wimplicit-function-declaration]

This PR fixes the warning by adding include to a platfrom_mbed.h

In addition this PR suggests simplified and user friendly way of wiring NVSEED read/write callbacks.
MBEDTLS_ENTROPY_NV_SEED macro is sufficient since the callbacks have fixed values for all PSA targets.

The option for advanced user to inject custom version of MBEDTLS_PLATFORM_NV_SEED_READ_MACRO and MBEDTLS_PLATFORM_NV_SEED_WRITE_MACRO is preserved.

Pull request type

[x] Fix
[X] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

Reviewers

@netanelgonen @Patater @avolinski @sbutcher-arm

[ciarmcom]

@alzix, thank you for your changes.
@netanelgonen @Patater @avolinski @sbutcher-arm @ARMmbed/mbed-os-crypto @ARMmbed/mbed-os-tls @ARMmbed/mbed-os-maintainers please review.

[simonbutcher]

Why do we need to include this header?

There should be no "default random seed". That sounds really dangerous. (And not very random).

[yanesca]

This header contains the default read/write functions that supposed to be registered with the Mbed TLS NV_SEED feature.

[simonbutcher]

Maintainers - I'm too busy to approve this, so I'd like to delegate this to @andresag01. When he's approved it, it's fine by me.

[yanesca]

This default_random_seed.h seems to be TARGET_PSA specific. How will the compiler find it when the target is not TARGET_PSA?

[alzix]

fixed

[netanelgonen]

Is this possible to be in target PSA with NV_SEED but in the non-secure side?
If yes, we will have compilation error on default_random_seed.h file would not found

[alzix]

There are two use cases:

1. PSA target (with SPE and NSPE) and we are building for NSPE. e.g. FUTURE_SEQUANA_PSA for such a targets it is not expected to have MBEDTLS_ENTROPY_NV_SEED macro enabled.
2. PSA compliant target (NSPE only). e.g. K64F. IIRC you have tested it on such a target yourself :)

[alzix]

@0xc0170 can we proceed with it?

[NirSonnenschein]

@alzix martin is ooo today

[NirSonnenschein]

starting CI

[alekla01]

Restarted CI

[mbed-ci]

Test run: SUCCESS

Summary: 12 of 12 test jobs passed
Build number : 2
Build artifacts

[0xc0170]

Labeled for 5.12 (adding new config - stated as refactor above).

One additional question - this is changing mbedtls file, is this intentional (we do not accept changes besides doing version updates) and won't be overriden by next mbedtls update?

[yanesca]

The files in the features/mbedtls/platform, features/mbedtls/targets directories and the scripts in the features/mbedtls/importer directory are not (in the strict sense) part of Mbed TLS and are unaffected by the Mbed TLS update.