[dm-devel] [PATCH v2 3/3] dm-crypt: Implement eboiv - encrypted byte-offset initialization vector.

[Milan Broz]

This IV is used in some BitLocker devices with CBC encryption mode.

IV is encrypted little-endian byte-offset (with the same key and cipher
as the volume).

Signed-off-by: Milan Broz <gmazyland at gmail.com>
---
 drivers/md/dm-crypt.c | 82 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 81 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index c567e13a0e5f..0443a925840b 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -120,6 +120,10 @@ struct iv_tcw_private {
 	u8 *whitening;
 };
 
+struct iv_eboiv_private {
+	struct crypto_cipher *tfm;
+};
+
 /*
  * Crypt: maps a linear range of a block device
  * and encrypts / decrypts at the same time.
@@ -159,6 +163,7 @@ struct crypt_config {
 		struct iv_benbi_private benbi;
 		struct iv_lmk_private lmk;
 		struct iv_tcw_private tcw;
+		struct iv_eboiv_private eboiv;
 	} iv_gen_private;
 	u64 iv_offset;
 	unsigned int iv_size;
@@ -290,6 +295,10 @@ static struct crypto_aead *any_tfm_aead(struct crypt_config *cc)
  *       is calculated from initial key, sector number and mixed using CRC32.
  *       Note that this encryption scheme is vulnerable to watermarking attacks
  *       and should be used for old compatible containers access only.
+ *
+ * eboiv: Encrypted byte-offset IV (used in Bitlocker in CBC mode)
+ *        The IV is encrypted little-endian byte-offset (with the same key
+ *        and cipher as the volume).
  */
 
 static int crypt_iv_plain_gen(struct crypt_config *cc, u8 *iv,
@@ -838,6 +847,67 @@ static int crypt_iv_random_gen(struct crypt_config *cc, u8 *iv,
 	return 0;
 }
 
+static void crypt_iv_eboiv_dtr(struct crypt_config *cc)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+
+	crypto_free_cipher(eboiv->tfm);
+	eboiv->tfm = NULL;
+}
+
+static int crypt_iv_eboiv_ctr(struct crypt_config *cc, struct dm_target *ti,
+			    const char *opts)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+	struct crypto_cipher *tfm;
+
+	tfm = crypto_alloc_cipher(cc->cipher, 0, 0);
+	if (IS_ERR(tfm)) {
+		ti->error = "Error allocating crypto tfm for EBOIV";
+		return PTR_ERR(tfm);
+	}
+
+	if (crypto_cipher_blocksize(tfm) != cc->iv_size) {
+		ti->error = "Block size of EBOIV cipher does "
+			    "not match IV size of block cipher";
+		crypto_free_cipher(tfm);
+		return -EINVAL;
+	}
+
+	eboiv->tfm = tfm;
+	return 0;
+}
+
+static int crypt_iv_eboiv_init(struct crypt_config *cc)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+	int err;
+
+	err = crypto_cipher_setkey(eboiv->tfm, cc->key, cc->key_size);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static int crypt_iv_eboiv_wipe(struct crypt_config *cc)
+{
+	/* Called after cc->key is set to random key in crypt_wipe() */
+	return crypt_iv_eboiv_init(cc);
+}
+
+static int crypt_iv_eboiv_gen(struct crypt_config *cc, u8 *iv,
+			    struct dm_crypt_request *dmreq)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+
+	memset(iv, 0, cc->iv_size);
+	*(__le64 *)iv = cpu_to_le64(dmreq->iv_sector * cc->sector_size);
+	crypto_cipher_encrypt_one(eboiv->tfm, iv, iv);
+
+	return 0;
+}
+
 static const struct crypt_iv_operations crypt_iv_plain_ops = {
 	.generator = crypt_iv_plain_gen
 };
@@ -890,6 +960,14 @@ static struct crypt_iv_operations crypt_iv_random_ops = {
 	.generator = crypt_iv_random_gen
 };
 
+static struct crypt_iv_operations crypt_iv_eboiv_ops = {
+	.ctr	   = crypt_iv_eboiv_ctr,
+	.dtr	   = crypt_iv_eboiv_dtr,
+	.init	   = crypt_iv_eboiv_init,
+	.wipe	   = crypt_iv_eboiv_wipe,
+	.generator = crypt_iv_eboiv_gen
+};
+
 /*
  * Integrity extensions
  */
@@ -2293,6 +2371,8 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 		cc->iv_gen_ops = &crypt_iv_benbi_ops;
 	else if (strcmp(ivmode, "null") == 0)
 		cc->iv_gen_ops = &crypt_iv_null_ops;
+	else if (strcmp(ivmode, "eboiv") == 0)
+		cc->iv_gen_ops = &crypt_iv_eboiv_ops;
 	else if (strcmp(ivmode, "lmk") == 0) {
 		cc->iv_gen_ops = &crypt_iv_lmk_ops;
 		/*
@@ -3093,7 +3173,7 @@ static void crypt_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 static struct target_type crypt_target = {
 	.name   = "crypt",
-	.version = {1, 18, 1},
+	.version = {1, 19, 0},
 	.module = THIS_MODULE,
 	.ctr    = crypt_ctr,
 	.dtr    = crypt_dtr,
-- 
2.20.1