crypto: it51xxx: Fix SHA-256 padding length field to 64-bi

The SHA-256 standard (FIPS 180-4) requires the total message length (L) in
bits to be appended as a **64-bit big-endian integer**.

The previous implementation incorrectly calculated and wrote only the
lower **32 bits** of the length field (to W[15]), implicitly assuming
the upper 32 bits (W[14]) were correctly zeroed.

This commit updates `it51xxx_hash_handler()` to explicitly calculate the
length using `uint64_t` and writes both the MSB (W[14]) and LSB (W[15])
words in big-endian format. This ensures standard compliance and correct
hashing for all message lengths.

Signed-off-by: Badr Bacem KAABIA <[email protected]>

Author: kaabia

drivers/crypto/crypto_it51xxx_sha.c

@@ -183,11 +183,17 @@ static int it51xxx_hash_handler(struct hash_ctx *ctx, struct hash_pkt *pkt, bool
 		}
 
 		/*
-		 * Since input data (big-endian) are copied 1byte by 1byte to
-		 * it51xxx memory (little-endian), so the bit length needs to
-		 * be transformed into big-endian format and then write to memory.
+		 * SHA-256 requires the message length (in bits) as a 64-bit big-endian
+		 * integer in the final 8 bytes (words 14 and 15). The message is stored
+		 * in little-endian memory, so conversion is necessary.
 		 */
-		chip_ctx.w_sha[15] = sys_cpu_to_be32(chip_ctx.total_len * 8);
+		uint64_t bit_len = (uint64_t)chip_ctx.total_len * 8;
+
+		// Word 14: Most Significant 32 bits
+		chip_ctx.w_sha[14] = sys_cpu_to_be32((uint32_t)(bit_len >> 32));
+
+		// Word 15: Least Significant 32 bits
+		chip_ctx.w_sha[15] = sys_cpu_to_be32((uint32_t)(bit_len & 0xFFFFFFFFUL));
 
 		/* HW automatically load 64Bytes data from DLM */
 		sys_write8(IT51XXX_SHAEXEC_64_BYTE, IT51XXX_SHAECR);