crypto: xts - consolidate sanity check for keys

The patch centralizes the XTS key check logic into the service function
xts_check_key which is invoked from the different XTS implementations.
With this, the XTS implementations in ARM, ARM64, PPC and S390 have now
a sanity check for the XTS keys similar to the other arches.

In addition, this service function received a check to ensure that the
key != the tweak key which is mandated by FIPS 140-2 IG A.9. As the
check is not present in the standards defining XTS, it is only enforced
in FIPS mode of the kernel.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 27 insertions, 0 deletions

diff --git a/include/crypto/xts.h b/include/crypto/xts.h
index 72c09eb56437..ede6b97b24cc 100644
--- a/include/crypto/xts.h
+++ b/include/crypto/xts.h
@@ -2,6 +2,9 @@
 #define _CRYPTO_XTS_H
 
 #include <crypto/b128ops.h>
+#include <linux/crypto.h>
+#include <crypto/algapi.h>
+#include <linux/fips.h>
 
 struct scatterlist;
 struct blkcipher_desc;
@@ -24,4 +27,28 @@ int xts_crypt(struct blkcipher_desc *desc, struct scatterlist *dst,
 	      struct scatterlist *src, unsigned int nbytes,
 	      struct xts_crypt_req *req);
 
+static inline int xts_check_key(struct crypto_tfm *tfm,
+				const u8 *key, unsigned int keylen)
+{
+	u32 *flags = &tfm->crt_flags;
+
+	/*
+	 * key consists of keys of equal size concatenated, therefore
+	 * the length must be even.
+	 */
+	if (keylen % 2) {
+		*flags |= CRYPTO_TFM_RES_BAD_KEY_LEN;
+		return -EINVAL;
+	}
+
+	/* ensure that the AES and tweak key are not identical */
+	if (fips_enabled &&
+	    !crypto_memneq(key, key + (keylen / 2), keylen / 2)) {
+		*flags |= CRYPTO_TFM_RES_WEAK_KEY;
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 #endif  /* _CRYPTO_XTS_H */