nrf_security: Use static variables in sx_blkcipher_ecb_simple

The in and out dma descriptors variables in sx_blkcipher_ecb_simple
takes up around 80 bytes of space in the stack.
To optimize the stack usage these variables are now static, the
mutex locking was moved before there variables are set so that
accessing these from multiple threads is not an issue.

Signed-off-by: Georgios Vasilakis <[email protected]>

Author: Vge0rge

subsys/nrf_security/src/drivers/cracen/sxsymcrypt/src/blkcipher.c

@@ -408,7 +408,14 @@ int sx_blkcipher_ecb_simple(uint8_t *key, size_t key_size, uint8_t *input, size_
 	int status = SX_ERR_HW_PROCESSING;
 
 	uint32_t cmd = CMDMA_BLKCIPHER_MODE_SET(BLKCIPHER_MODEID_ECB);
-	struct sxdesc in_descs[3] = {};
+	/* Both out_desc and in_descs are used after sx_hw_reserve which locks
+	 * the symmetric mutex, so it is safe to have them as static.
+	 */
+	static struct sxdesc out_desc;
+	static struct sxdesc in_descs[3];
+
+	/* This guards the static variables out_desc and in_descs */
+	sx_hw_reserve(NULL);
 
 	in_descs[0].addr = (char *)&cmd;
 	in_descs[0].sz = DMA_REALIGN | sizeof(cmd);
@@ -425,15 +432,11 @@ int sx_blkcipher_ecb_simple(uint8_t *key, size_t key_size, uint8_t *input, size_
 	in_descs[2].dmatag = DMATAG_LAST | ba411tags.data;
 	in_descs[2].next = (void *)1;
 
-	struct sxdesc out_desc = {};
-
 	out_desc.addr = output;
 	out_desc.sz = DMA_REALIGN | output_size;
 	out_desc.next = (void *)1;
 	out_desc.dmatag = DMATAG_LAST;
 
-	sx_hw_reserve(NULL);
-
 #if CONFIG_DCACHE
 	sys_cache_data_flush_range(in_descs, sizeof(in_descs));
 	sys_cache_data_flush_range(&out_desc, sizeof(out_desc));