dm crypt: Implement Elephant diffuser for Bitlocker compatibility

Add experimental support for BitLocker encryption with CBC mode and
additional Elephant diffuser.

The mode was used in older Windows systems and it is provided mainly
for compatibility reasons. The userspace support to activate these
devices is being added to cryptsetup utility.

Read-write activation of such a device is very simple, for example:
  echo <password> | cryptsetup bitlkOpen bitlk_image.img test

The Elephant diffuser uses two rotations in opposite direction for
data (Diffuser A and B) and also XOR operation with Sector key over
the sector data; Sector key is derived from additional key data. The
original public documentation is available here:
  http://download.microsoft.com/download/0/2/3/0238acaf-d3bf-4a6d-b3d6-0a0be4bbb36e/bitlockercipher200608.pdf

The dm-crypt implementation is embedded to "elephant" IV (similar to
tcw IV construction).

Because we cannot modify original bio data for write (before
encryption), an additional internal flag to pre-process data is
added.
Signed-off-by: Milan Broz <gmazyland@gmail.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-crypt.c

 /*
  * Copyright (C) 2003 Jana Saout <jana@saout.de>
  * Copyright (C) 2004 Clemens Fruhwirth <clemens@endorphin.org>
- * Copyright (C) 2006-2017 Red Hat, Inc. All rights reserved.
- * Copyright (C) 2013-2017 Milan Broz <gmazyland@gmail.com>
+ * Copyright (C) 2006-2020 Red Hat, Inc. All rights reserved.
+ * Copyright (C) 2013-2020 Milan Broz <gmazyland@gmail.com>
  *
  * This file is released under the GPL.
  */
@@ -115,6 +115,11 @@ struct iv_tcw_private {
 	u8 *whitening;
 };
 
+#define ELEPHANT_MAX_KEY_SIZE 32
+struct iv_elephant_private {
+	struct crypto_skcipher *tfm;
+};
+
 /*
  * Crypt: maps a linear range of a block device
  * and encrypts / decrypts at the same time.
@@ -125,6 +130,7 @@ enum flags { DM_CRYPT_SUSPENDED, DM_CRYPT_KEY_VALID,
 enum cipher_flags {
 	CRYPT_MODE_INTEGRITY_AEAD,	/* Use authenticated mode for cihper */
 	CRYPT_IV_LARGE_SECTORS,		/* Calculate IV from sector_size, not 512B sectors */
+	CRYPT_ENCRYPT_PREPROCESS,	/* Must preprocess data for encryption (elephant) */
 };
 
 /*
@@ -152,6 +158,7 @@ struct crypt_config {
 		struct iv_benbi_private benbi;
 		struct iv_lmk_private lmk;
 		struct iv_tcw_private tcw;
+		struct iv_elephant_private elephant;
 	} iv_gen_private;
 	u64 iv_offset;
 	unsigned int iv_size;
@@ -285,6 +292,11 @@ static struct crypto_aead *any_tfm_aead(struct crypt_config *cc)
  * 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).
+ *
+ * elephant: The extended version of eboiv with additional Elephant diffuser
+ *           used with Bitlocker CBC mode.
+ *           This mode was used in older Windows systems
+ *           http://download.microsoft.com/download/0/2/3/0238acaf-d3bf-4a6d-b3d6-0a0be4bbb36e/bitlockercipher200608.pdf
  */
 
 static int crypt_iv_plain_gen(struct crypt_config *cc, u8 *iv,
@@ -734,6 +746,290 @@ static int crypt_iv_eboiv_gen(struct crypt_config *cc, u8 *iv,
 	return err;
 }
 
+static void crypt_iv_elephant_dtr(struct crypt_config *cc)
+{
+	struct iv_elephant_private *elephant = &cc->iv_gen_private.elephant;
+
+	crypto_free_skcipher(elephant->tfm);
+	elephant->tfm = NULL;
+}
+
+static int crypt_iv_elephant_ctr(struct crypt_config *cc, struct dm_target *ti,
+			    const char *opts)
+{
+	struct iv_elephant_private *elephant = &cc->iv_gen_private.elephant;
+	int r;
+
+	elephant->tfm = crypto_alloc_skcipher("ecb(aes)", 0, 0);
+	if (IS_ERR(elephant->tfm)) {
+		r = PTR_ERR(elephant->tfm);
+		elephant->tfm = NULL;
+		return r;
+	}
+
+	r = crypt_iv_eboiv_ctr(cc, ti, NULL);
+	if (r)
+		crypt_iv_elephant_dtr(cc);
+	return r;
+}
+
+static void diffuser_disk_to_cpu(u32 *d, size_t n)
+{
+#ifndef __LITTLE_ENDIAN
+	int i;
+
+	for (i = 0; i < n; i++)
+		d[i] = le32_to_cpu((__le32)d[i]);
+#endif
+}
+
+static void diffuser_cpu_to_disk(__le32 *d, size_t n)
+{
+#ifndef __LITTLE_ENDIAN
+	int i;
+
+	for (i = 0; i < n; i++)
+		d[i] = cpu_to_le32((u32)d[i]);
+#endif
+}
+
+static void diffuser_a_decrypt(u32 *d, size_t n)
+{
+	int i, i1, i2, i3;
+
+	for (i = 0; i < 5; i++) {
+		i1 = 0;
+		i2 = n - 2;
+		i3 = n - 5;
+
+		while (i1 < (n - 1)) {
+			d[i1] += d[i2] ^ (d[i3] << 9 | d[i3] >> 23);
+			i1++; i2++; i3++;
+
+			if (i3 >= n)
+				i3 -= n;
+
+			d[i1] += d[i2] ^ d[i3];
+			i1++; i2++; i3++;
+
+			if (i2 >= n)
+				i2 -= n;
+
+			d[i1] += d[i2] ^ (d[i3] << 13 | d[i3] >> 19);
+			i1++; i2++; i3++;
+
+			d[i1] += d[i2] ^ d[i3];
+			i1++; i2++; i3++;
+		}
+	}
+}
+
+static void diffuser_a_encrypt(u32 *d, size_t n)
+{
+	int i, i1, i2, i3;
+
+	for (i = 0; i < 5; i++) {
+		i1 = n - 1;
+		i2 = n - 2 - 1;
+		i3 = n - 5 - 1;
+
+		while (i1 > 0) {
+			d[i1] -= d[i2] ^ d[i3];
+			i1--; i2--; i3--;
+
+			d[i1] -= d[i2] ^ (d[i3] << 13 | d[i3] >> 19);
+			i1--; i2--; i3--;
+
+			if (i2 < 0)
+				i2 += n;
+
+			d[i1] -= d[i2] ^ d[i3];
+			i1--; i2--; i3--;
+
+			if (i3 < 0)
+				i3 += n;
+
+			d[i1] -= d[i2] ^ (d[i3] << 9 | d[i3] >> 23);
+			i1--; i2--; i3--;
+		}
+	}
+}
+
+static void diffuser_b_decrypt(u32 *d, size_t n)
+{
+	int i, i1, i2, i3;
+
+	for (i = 0; i < 3; i++) {
+		i1 = 0;
+		i2 = 2;
+		i3 = 5;
+
+		while (i1 < (n - 1)) {
+			d[i1] += d[i2] ^ d[i3];
+			i1++; i2++; i3++;
+
+			d[i1] += d[i2] ^ (d[i3] << 10 | d[i3] >> 22);
+			i1++; i2++; i3++;
+
+			if (i2 >= n)
+				i2 -= n;
+
+			d[i1] += d[i2] ^ d[i3];
+			i1++; i2++; i3++;
+
+			if (i3 >= n)
+				i3 -= n;
+
+			d[i1] += d[i2] ^ (d[i3] << 25 | d[i3] >> 7);
+			i1++; i2++; i3++;
+		}
+	}
+}
+
+static void diffuser_b_encrypt(u32 *d, size_t n)
+{
+	int i, i1, i2, i3;
+
+	for (i = 0; i < 3; i++) {
+		i1 = n - 1;
+		i2 = 2 - 1;
+		i3 = 5 - 1;
+
+		while (i1 > 0) {
+			d[i1] -= d[i2] ^ (d[i3] << 25 | d[i3] >> 7);
+			i1--; i2--; i3--;
+
+			if (i3 < 0)
+				i3 += n;
+
+			d[i1] -= d[i2] ^ d[i3];
+			i1--; i2--; i3--;
+
+			if (i2 < 0)
+				i2 += n;
+
+			d[i1] -= d[i2] ^ (d[i3] << 10 | d[i3] >> 22);
+			i1--; i2--; i3--;
+
+			d[i1] -= d[i2] ^ d[i3];
+			i1--; i2--; i3--;
+		}
+	}
+}
+
+static int crypt_iv_elephant(struct crypt_config *cc, struct dm_crypt_request *dmreq)
+{
+	struct iv_elephant_private *elephant = &cc->iv_gen_private.elephant;
+	u8 *es, *ks, *data, *data2, *data_offset;
+	struct skcipher_request *req;
+	struct scatterlist *sg, *sg2, src, dst;
+	struct crypto_wait wait;
+	int i, r;
+
+	req = skcipher_request_alloc(elephant->tfm, GFP_NOIO);
+	es = kzalloc(16, GFP_NOIO); /* Key for AES */
+	ks = kzalloc(32, GFP_NOIO); /* Elephant sector key */
+
+	if (!req || !es || !ks) {
+		r = -ENOMEM;
+		goto out;
+	}
+
+	*(__le64 *)es = cpu_to_le64(dmreq->iv_sector * cc->sector_size);
+
+	/* E(Ks, e(s)) */
+	sg_init_one(&src, es, 16);
+	sg_init_one(&dst, ks, 16);
+	skcipher_request_set_crypt(req, &src, &dst, 16, NULL);
+	skcipher_request_set_callback(req, 0, crypto_req_done, &wait);
+	r = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
+	if (r)
+		goto out;
+
+	/* E(Ks, e'(s)) */
+	es[15] = 0x80;
+	sg_init_one(&dst, &ks[16], 16);
+	r = crypto_wait_req(crypto_skcipher_encrypt(req), &wait);
+	if (r)
+		goto out;
+
+	sg = crypt_get_sg_data(cc, dmreq->sg_out);
+	data = kmap_atomic(sg_page(sg));
+	data_offset = data + sg->offset;
+
+	/* Cannot modify original bio, copy to sg_out and apply Elephant to it */
+	if (bio_data_dir(dmreq->ctx->bio_in) == WRITE) {
+		sg2 = crypt_get_sg_data(cc, dmreq->sg_in);
+		data2 = kmap_atomic(sg_page(sg2));
+		memcpy(data_offset, data2 + sg2->offset, cc->sector_size);
+		kunmap_atomic(data2);
+	}
+
+	if (bio_data_dir(dmreq->ctx->bio_in) != WRITE) {
+		diffuser_disk_to_cpu((u32*)data_offset, cc->sector_size / sizeof(u32));
+		diffuser_b_decrypt((u32*)data_offset, cc->sector_size / sizeof(u32));
+		diffuser_a_decrypt((u32*)data_offset, cc->sector_size / sizeof(u32));
+		diffuser_cpu_to_disk((__le32*)data_offset, cc->sector_size / sizeof(u32));
+	}
+
+	for (i = 0; i < (cc->sector_size / 32); i++)
+		crypto_xor(data_offset + i * 32, ks, 32);
+
+	if (bio_data_dir(dmreq->ctx->bio_in) == WRITE) {
+		diffuser_disk_to_cpu((u32*)data_offset, cc->sector_size / sizeof(u32));
+		diffuser_a_encrypt((u32*)data_offset, cc->sector_size / sizeof(u32));
+		diffuser_b_encrypt((u32*)data_offset, cc->sector_size / sizeof(u32));
+		diffuser_cpu_to_disk((__le32*)data_offset, cc->sector_size / sizeof(u32));
+	}
+
+	kunmap_atomic(data);
+out:
+	kzfree(ks);
+	kzfree(es);
+	skcipher_request_free(req);
+	return r;
+}
+
+static int crypt_iv_elephant_gen(struct crypt_config *cc, u8 *iv,
+			    struct dm_crypt_request *dmreq)
+{
+	int r;
+
+	if (bio_data_dir(dmreq->ctx->bio_in) == WRITE) {
+		r = crypt_iv_elephant(cc, dmreq);
+		if (r)
+			return r;
+	}
+
+	return crypt_iv_eboiv_gen(cc, iv, dmreq);
+}
+
+static int crypt_iv_elephant_post(struct crypt_config *cc, u8 *iv,
+				  struct dm_crypt_request *dmreq)
+{
+	if (bio_data_dir(dmreq->ctx->bio_in) != WRITE)
+		return crypt_iv_elephant(cc, dmreq);
+
+	return 0;
+}
+
+static int crypt_iv_elephant_init(struct crypt_config *cc)
+{
+	struct iv_elephant_private *elephant = &cc->iv_gen_private.elephant;
+	int key_offset = cc->key_size - cc->key_extra_size;
+
+	return crypto_skcipher_setkey(elephant->tfm, &cc->key[key_offset], cc->key_extra_size);
+}
+
+static int crypt_iv_elephant_wipe(struct crypt_config *cc)
+{
+	struct iv_elephant_private *elephant = &cc->iv_gen_private.elephant;
+	u8 key[ELEPHANT_MAX_KEY_SIZE];
+
+	memset(key, 0, cc->key_extra_size);
+	return crypto_skcipher_setkey(elephant->tfm, key, cc->key_extra_size);
+}
+
 static const struct crypt_iv_operations crypt_iv_plain_ops = {
 	.generator = crypt_iv_plain_gen
 };
@@ -787,6 +1083,15 @@ static struct crypt_iv_operations crypt_iv_eboiv_ops = {
 	.generator = crypt_iv_eboiv_gen
 };
 
+static struct crypt_iv_operations crypt_iv_elephant_ops = {
+	.ctr	   = crypt_iv_elephant_ctr,
+	.dtr	   = crypt_iv_elephant_dtr,
+	.init	   = crypt_iv_elephant_init,
+	.wipe	   = crypt_iv_elephant_wipe,
+	.generator = crypt_iv_elephant_gen,
+	.post	   = crypt_iv_elephant_post
+};
+
 /*
  * Integrity extensions
  */
@@ -1103,6 +1408,9 @@ static int crypt_convert_block_skcipher(struct crypt_config *cc,
 			r = cc->iv_gen_ops->generator(cc, org_iv, dmreq);
 			if (r < 0)
 				return r;
+			/* Data can be already preprocessed in generator */
+			if (test_bit(CRYPT_ENCRYPT_PREPROCESS, &cc->cipher_flags))
+				sg_in = sg_out;
 			/* Store generated IV in integrity metadata */
 			if (cc->integrity_iv_size)
 				memcpy(tag_iv, org_iv, cc->integrity_iv_size);
@@ -2191,7 +2499,14 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 		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) {
+	else if (strcmp(ivmode, "elephant") == 0) {
+		cc->iv_gen_ops = &crypt_iv_elephant_ops;
+		cc->key_parts = 2;
+		cc->key_extra_size = cc->key_size / 2;
+		if (cc->key_extra_size > ELEPHANT_MAX_KEY_SIZE)
+			return -EINVAL;
+		set_bit(CRYPT_ENCRYPT_PREPROCESS, &cc->cipher_flags);
+	} else if (strcmp(ivmode, "lmk") == 0) {
 		cc->iv_gen_ops = &crypt_iv_lmk_ops;
 		/*
 		 * Version 2 and 3 is recognised according
@@ -2959,7 +3274,7 @@ static void crypt_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 static struct target_type crypt_target = {
 	.name   = "crypt",
-	.version = {1, 19, 0},
+	.version = {1, 20, 0},
 	.module = THIS_MODULE,
 	.ctr    = crypt_ctr,
 	.dtr    = crypt_dtr,