psa: Add NV seed as an entropy source when needed

When MBEDTLS_PSA_INJECT_ENTROPY is used, we now require also defining
MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES. When
MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES is defined, we do not add entropy
sources by default. This includes the NV seed entropy source, which the
PSA entropy injection API is built upon.

The PSA entropy injection feature depends on using NV seed as an entropy
source. Add NV seed as an entropy source for PSA entropy injection.

Fixes e3dbdd8 ("Gate entropy injection through a dedicated configuration option")

Author: Patater

library/psa_crypto.c

@@ -4639,6 +4639,15 @@ psa_status_t psa_crypto_init( void )
 
     /* Initialize the random generator. */
     global_data.entropy_init( &global_data.entropy );
+#if defined(MBEDTLS_PSA_INJECT_ENTROPY) && \
+    defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
+    /* The PSA entropy injection feature depends on using NV seed as an entropy
+     * source. Add NV seed as an entropy source for PSA entropy injection. */
+    mbedtls_entropy_add_source( &global_data.entropy,
+                                mbedtls_nv_seed_poll, NULL,
+                                MBEDTLS_ENTROPY_BLOCK_SIZE,
+                                MBEDTLS_ENTROPY_SOURCE_STRONG );
+#endif
     mbedtls_ctr_drbg_init( &global_data.ctr_drbg );
     global_data.rng_state = RNG_INITIALIZED;
     status = mbedtls_to_psa_error(