[BLOCK] dm-crypt: benbi IV, big endian narrow block count for LRW-32-AES

LRW-32-AES needs a certain IV. This IV should be provided dm-crypt.
The block cipher mode could, in principle generate the correct IV from
the plain IV, but I think that it is cleaner to supply the right IV
directly.

The sector -> narrow block calculation uses a shift for performance reasons.
This shift is computed in .ctr and stored in cc->iv_gen_private (as a void *).
Signed-off-by: Rik Snel <rsnel@cube.dyndns.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/md/dm-crypt.c

@@ -20,6 +20,7 @@
 #include <asm/atomic.h>
 #include <linux/scatterlist.h>
 #include <asm/page.h>
+#include <asm/unaligned.h>
 
 #include "dm.h"
 
@@ -113,6 +114,9 @@ static kmem_cache_t *_crypt_io_pool;
  *        encrypted with the bulk cipher using a salt as key. The salt
  *        should be derived from the bulk cipher's key via hashing.
  *
+ * benbi: the 64-bit "big-endian 'narrow block'-count", starting at 1
+ *        (needed for LRW-32-AES and possible other narrow block modes)
+ *
  * plumb: unimplemented, see:
  * http://article.gmane.org/gmane.linux.kernel.device-mapper.dm-crypt/454
  */
@@ -209,6 +213,44 @@ static int crypt_iv_essiv_gen(struct crypt_config *cc, u8 *iv, sector_t sector)
 	return 0;
 }
 
+static int crypt_iv_benbi_ctr(struct crypt_config *cc, struct dm_target *ti,
+			      const char *opts)
+{
+	unsigned int bs = crypto_blkcipher_blocksize(cc->tfm);
+	int log = long_log2(bs);
+
+	/* we need to calculate how far we must shift the sector count
+	 * to get the cipher block count, we use this shift in _gen */
+
+	if (1 << log != bs) {
+		ti->error = "cypher blocksize is not a power of 2";
+		return -EINVAL;
+	}
+
+	if (log > 9) {
+		ti->error = "cypher blocksize is > 512";
+		return -EINVAL;
+	}
+
+	cc->iv_gen_private = (void *)(9 - log);
+
+	return 0;
+}
+
+static void crypt_iv_benbi_dtr(struct crypt_config *cc)
+{
+	cc->iv_gen_private = NULL;
+}
+
+static int crypt_iv_benbi_gen(struct crypt_config *cc, u8 *iv, sector_t sector)
+{
+	memset(iv, 0, cc->iv_size - sizeof(u64)); /* rest is cleared below */
+	put_unaligned(cpu_to_be64(((u64)sector << (u32)cc->iv_gen_private) + 1),
+		      (__be64 *)(iv + cc->iv_size - sizeof(u64)));
+
+	return 0;
+}
+
 static struct crypt_iv_operations crypt_iv_plain_ops = {
 	.generator = crypt_iv_plain_gen
 };
@@ -219,6 +261,11 @@ static struct crypt_iv_operations crypt_iv_essiv_ops = {
 	.generator = crypt_iv_essiv_gen
 };
 
+static struct crypt_iv_operations crypt_iv_benbi_ops = {
+	.ctr	   = crypt_iv_benbi_ctr,
+	.dtr	   = crypt_iv_benbi_dtr,
+	.generator = crypt_iv_benbi_gen
+};
 
 static int
 crypt_convert_scatterlist(struct crypt_config *cc, struct scatterlist *out,
@@ -768,7 +815,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	cc->tfm = tfm;
 
 	/*
-	 * Choose ivmode. Valid modes: "plain", "essiv:<esshash>".
+	 * Choose ivmode. Valid modes: "plain", "essiv:<esshash>", "benbi".
 	 * See comments at iv code
 	 */
 
@@ -778,6 +825,8 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		cc->iv_gen_ops = &crypt_iv_plain_ops;
 	else if (strcmp(ivmode, "essiv") == 0)
 		cc->iv_gen_ops = &crypt_iv_essiv_ops;
+	else if (strcmp(ivmode, "benbi") == 0)
+		cc->iv_gen_ops = &crypt_iv_benbi_ops;
 	else {
 		ti->error = "Invalid IV mode";
 		goto bad2;