feat(mbedtls-psa): initialise mbedtls psa crypto
Initialised Mbedtls PSA cryto during Crypto init using
function call 'psa_crypto_init'.
MbedTLS currently requires a Random Number Generator (RNG) once
PSA Crypto support is enabled. However, TF-A itself doesn't engage
in cryptographic operations that demand randomness. Consequently,
we simulate the presence of an external TRNG (through the configuration
option 'MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG) while, in reality, we offer
a dummy implementation of mbedtls_psa_external_get_random() that always
returns an error.
Change-Id: Ife6d03909c0e6081438d2b2519ef500e5dcdb88f
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
diff --git a/include/drivers/auth/mbedtls/psa_mbedtls_config.h b/include/drivers/auth/mbedtls/psa_mbedtls_config.h
index 65df2d4..ad825f0 100644
--- a/include/drivers/auth/mbedtls/psa_mbedtls_config.h
+++ b/include/drivers/auth/mbedtls/psa_mbedtls_config.h
@@ -11,4 +11,18 @@
#define MBEDTLS_PSA_CRYPTO_C
+/*
+ * Using PSA crypto API requires an RNG right now. If we don't define the macro
+ * below then we get build errors.
+ *
+ * This is a functionality gap in mbedTLS. The technical limitation is that
+ * psa_crypto_init() is all-or-nothing, and fixing that would require separate
+ * initialization of the keystore, the RNG, etc.
+ *
+ * By defining MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG, we pretend using an external
+ * RNG. As a result, the PSA crypto init code does nothing when it comes to
+ * initializing the RNG, as we are supposed to take care of that ourselves.
+ */
+#define MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG
+
#endif /* PSA_MBEDTLS_CONFIG_H */