crypto: xts - Convert to skcipher

This patch converts xts over to the skcipher interface.  It also
optimises the implementation to be based on ECB instead of the
underlying cipher.  For compatibility the existing naming scheme
of xts(aes) is maintained as opposed to the more obvious one of
xts(ecb(aes)).
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/xts.h

@@ -2,8 +2,7 @@
 #define _CRYPTO_XTS_H
 
 #include <crypto/b128ops.h>
-#include <linux/crypto.h>
-#include <crypto/algapi.h>
+#include <crypto/internal/skcipher.h>
 #include <linux/fips.h>
 
 struct scatterlist;
@@ -51,4 +50,27 @@ static inline int xts_check_key(struct crypto_tfm *tfm,
 	return 0;
 }
 
+static inline int xts_verify_key(struct crypto_skcipher *tfm,
+				 const u8 *key, unsigned int keylen)
+{
+	/*
+	 * key consists of keys of equal size concatenated, therefore
+	 * the length must be even.
+	 */
+	if (keylen % 2) {
+		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
+		return -EINVAL;
+	}
+
+	/* ensure that the AES and tweak key are not identical */
+	if ((fips_enabled || crypto_skcipher_get_flags(tfm) &
+			     CRYPTO_TFM_REQ_WEAK_KEY) &&
+	    !crypto_memneq(key, key + (keylen / 2), keylen / 2)) {
+		crypto_skcipher_set_flags(tfm, CRYPTO_TFM_RES_WEAK_KEY);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 #endif  /* _CRYPTO_XTS_H */