nrf_security: cracen: add support for l09/l20 to ctr_drbg

l09/l20 only supports a 16 bit ctr counter. As such
we must reseed before this counter overflows, to avoid
repeating blocks.
Limited the max output for cracen lite boards and
changed the reseed counter to depend on the amount of
blocks given as input to support this

Signed-off-by: Dag Erik Gjørvad <[email protected]>

Author: degjorva

subsys/nrf_security/src/drivers/cracen/cracenpsa/src/ctr_drbg.c

@@ -20,12 +20,17 @@
 #include <sxsymcrypt/trng.h>
 #include <sxsymcrypt/aes.h>
 #include <sxsymcrypt/keyref.h>
-
 #include <zephyr/kernel.h>
 #include <nrf_security_mutexes.h>
 
-#define MAX_BITS_PER_REQUEST (1 << 19)		 /* NIST.SP.800-90Ar1:Table 3 */
-#define RESEED_INTERVAL	     ((uint64_t)1 << 48) /* 2^48 as per NIST spec */
+#ifdef CONFIG_CRACEN_HW_VERSION_LITE
+#define MAX_BITS_PER_REQUEST (1 << 16) /* Cracen Lite only supports 2^16 ctr size */
+/* Cracen Lite only supports 2^16 ctr size so will need to reseed before it overflows */
+#define RESEED_INTERVAL ((uint64_t)1 << 16)
+#else
+#define MAX_BITS_PER_REQUEST (1 << 19) /* NIST.SP.800-90Ar1:Table 3 */
+#define RESEED_INTERVAL ((uint64_t)1 << 48) /* 2^48 as per NIST spec */
+#endif
 
 /** @brief Magic number to signal that PRNG context is initialized */
 #define CRACEN_PRNG_INITIALIZED (0xA5B4A5B4)
@@ -103,6 +108,7 @@ static psa_status_t ctr_drbg_update(uint8_t *data)
 			return status;
 		}
 		temp_length += SX_BLKCIPHER_AES_BLK_SZ;
+		prng.reseed_counter++;
 	}
 
 	if (data) {
@@ -158,12 +164,33 @@ psa_status_t cracen_init_random(cracen_prng_context_t *context)
 	return silex_statuscodes_to_psa(sx_err);
 }
 
+static psa_status_t cracen_reseed(void)
+{
+	psa_status_t status;
+
+	/* DRBG entropy + nonce buffer. */
+	char entropy[CRACEN_PRNG_ENTROPY_SIZE + CRACEN_PRNG_NONCE_SIZE];
+	int sx_err = trng_get_seed(entropy, sizeof(entropy));
+
+	if (sx_err) {
+		return PSA_ERROR_HARDWARE_FAILURE;
+	}
+	status = ctr_drbg_update(entropy);
+	if (status != PSA_SUCCESS) {
+		return status;
+	}
+	safe_memset(entropy, sizeof(entropy), 0, CRACEN_PRNG_ENTROPY_SIZE + CRACEN_PRNG_NONCE_SIZE);
+	prng.reseed_counter = 0;
+	return PSA_SUCCESS;
+}
+
 psa_status_t cracen_get_random(cracen_prng_context_t *context, uint8_t *output, size_t output_size)
 {
 	(void)context;
 
 	psa_status_t status = PSA_SUCCESS;
 	size_t len_left = output_size;
+	size_t number_of_blocks = DIV_ROUND_UP(output_size, SX_BLKCIPHER_AES_BLK_SZ);
 
 	if (output_size > 0 && output == NULL) {
 		return PSA_ERROR_INVALID_ARGUMENT;
@@ -181,29 +208,18 @@ psa_status_t cracen_get_random(cracen_prng_context_t *context, uint8_t *output,
 		 * here even though we hold the mutex.
 		 */
 		status = cracen_init_random(context);
-
 		if (status != PSA_SUCCESS) {
-			goto exit;
+			nrf_security_mutex_unlock(cracen_prng_context_mutex);
+			return status;
 		}
 	}
 
-	if (prng.reseed_counter >= RESEED_INTERVAL) {
-		char entropy[CRACEN_PRNG_ENTROPY_SIZE +
-			     CRACEN_PRNG_NONCE_SIZE]; /* DRBG entropy + nonce buffer. */
-		int sx_err = trng_get_seed(entropy, sizeof(entropy));
-
-		if (sx_err) {
-			status = PSA_ERROR_HARDWARE_FAILURE;
-			goto exit;
-		}
-		status = ctr_drbg_update(entropy);
+	if (prng.reseed_counter + number_of_blocks >= RESEED_INTERVAL) {
+		status = cracen_reseed();
 		if (status != PSA_SUCCESS) {
-			goto exit;
+			nrf_security_mutex_unlock(cracen_prng_context_mutex);
+			return status;
 		}
-		safe_memset(entropy, sizeof(entropy), 0,
-			    CRACEN_PRNG_ENTROPY_SIZE + CRACEN_PRNG_NONCE_SIZE);
-
-		prng.reseed_counter = 0;
 	}
 
 	psa_key_attributes_t attr = PSA_KEY_ATTRIBUTES_INIT;
@@ -212,10 +228,6 @@ psa_status_t cracen_get_random(cracen_prng_context_t *context, uint8_t *output,
 	psa_set_key_bits(&attr, PSA_BYTES_TO_BITS(sizeof(prng.key)));
 	psa_set_key_usage_flags(&attr, PSA_KEY_USAGE_ENCRYPT);
 
-	if (status != PSA_SUCCESS) {
-		return status;
-	}
-
 	while (len_left > 0) {
 		size_t cur_len = MIN(len_left, SX_BLKCIPHER_AES_BLK_SZ);
 		char temp[SX_BLKCIPHER_AES_BLK_SZ] __aligned(CONFIG_DCACHE_LINE_SIZE);
@@ -225,7 +237,8 @@ psa_status_t cracen_get_random(cracen_prng_context_t *context, uint8_t *output,
 						 temp, sizeof(temp));
 
 		if (status != PSA_SUCCESS) {
-			goto exit;
+			nrf_security_mutex_unlock(cracen_prng_context_mutex);
+			return status;
 		}
 
 		for (int i = 0; i < cur_len; i++) {
@@ -234,16 +247,10 @@ psa_status_t cracen_get_random(cracen_prng_context_t *context, uint8_t *output,
 
 		len_left -= cur_len;
 		output += cur_len;
+		prng.reseed_counter++;
 	}
 
 	status = ctr_drbg_update(NULL);
-	if (status != PSA_SUCCESS) {
-		goto exit;
-	}
-
-	prng.reseed_counter += 1;
-
-exit:
 	nrf_security_mutex_unlock(cracen_prng_context_mutex);
 	return status;
 }