psa: simplify management of mbedtls_psa_drbg_context_t

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>

library/psa_crypto.c

@@ -101,11 +101,6 @@ typedef struct {
 
 static psa_global_data_t global_data;
 
-#if !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
-mbedtls_psa_drbg_context_t *const mbedtls_psa_drbg_ctx =
-    &global_data.rng.drbg;
-#endif
-
 #define GUARD_MODULE_INITIALIZED        \
     if (global_data.initialized == 0)  \
     return PSA_ERROR_BAD_STATE;
@@ -7322,7 +7317,7 @@ static void mbedtls_psa_random_init(mbedtls_psa_random_context_t *rng)
                                MBEDTLS_ENTROPY_SOURCE_STRONG);
 #endif
 
-    mbedtls_psa_drbg_init(MBEDTLS_PSA_DRBG_CTX);
+    mbedtls_psa_drbg_init(&rng->drbg);
 #endif /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
 }
 
@@ -7333,7 +7328,7 @@ static void mbedtls_psa_random_free(mbedtls_psa_random_context_t *rng)
 #if defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
     memset(rng, 0, sizeof(*rng));
 #else /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
-    mbedtls_psa_drbg_free(MBEDTLS_PSA_DRBG_CTX);
+    mbedtls_psa_drbg_free(&rng->drbg);
     rng->entropy_free(&rng->entropy);
 #endif /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
 }
@@ -7348,7 +7343,7 @@ static psa_status_t mbedtls_psa_random_seed(mbedtls_psa_random_context_t *rng)
     return PSA_SUCCESS;
 #else /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
     const unsigned char drbg_seed[] = "PSA";
-    int ret = mbedtls_psa_drbg_seed(&rng->entropy,
+    int ret = mbedtls_psa_drbg_seed(&rng->drbg, &rng->entropy,
                                     drbg_seed, sizeof(drbg_seed) - 1);
     return mbedtls_to_psa_error(ret);
 #endif /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
@@ -7382,7 +7377,7 @@ psa_status_t psa_generate_random(uint8_t *output,
             (output_size > MBEDTLS_PSA_RANDOM_MAX_REQUEST ?
              MBEDTLS_PSA_RANDOM_MAX_REQUEST :
              output_size);
-        int ret = mbedtls_psa_legacy_get_random(MBEDTLS_PSA_DRBG_CTX,
+        int ret = mbedtls_psa_legacy_get_random(&global_data.rng.drbg,
                                                 output, request_size);
         if (ret != 0) {
             return mbedtls_to_psa_error(ret);

library/psa_crypto_random_impl.h

@@ -118,14 +118,6 @@ typedef struct {
 #define MBEDTLS_PSA_RANDOM_MAX_REQUEST MBEDTLS_HMAC_DRBG_MAX_REQUEST
 #endif
 
-/** A pointer to the PSA DRBG context.
- *
- * This variable is only intended to be used through the macro
- * #MBEDTLS_PSA_DRBG_CTX.
- */
-extern mbedtls_psa_drbg_context_t *const mbedtls_psa_drbg_ctx;
-#define MBEDTLS_PSA_DRBG_CTX    mbedtls_psa_drbg_ctx
-
 /** Seed the PSA DRBG.
  *
  * \param entropy       An entropy context to read the seed from.
@@ -138,18 +130,19 @@ extern mbedtls_psa_drbg_context_t *const mbedtls_psa_drbg_ctx;
  * \return              An Mbed TLS error code (\c MBEDTLS_ERR_xxx) on failure.
  */
 static inline int mbedtls_psa_drbg_seed(
+    mbedtls_psa_drbg_context_t *drbg_ctx,
     mbedtls_entropy_context *entropy,
     const unsigned char *custom, size_t len)
 {
 #if defined(MBEDTLS_CTR_DRBG_C)
-    return mbedtls_ctr_drbg_seed(MBEDTLS_PSA_DRBG_CTX,
+    return mbedtls_ctr_drbg_seed(drbg_ctx,
                                  mbedtls_entropy_func,
                                  entropy,
                                  custom, len);
 #elif defined(MBEDTLS_HMAC_DRBG_C)
     const mbedtls_md_info_t *md_info =
         mbedtls_md_info_from_type(MBEDTLS_PSA_HMAC_DRBG_MD_TYPE);
-    return mbedtls_hmac_drbg_seed(MBEDTLS_PSA_DRBG_CTX,
+    return mbedtls_hmac_drbg_seed(drbg_ctx,
                                   md_info,
                                   mbedtls_entropy_func,
                                   entropy,