dm crypt: introduce new format of cipher with "capi:" prefix

For the new authenticated encryption we have to support generic composed
modes (combination of encryption algorithm and authenticator) because
this is how the kernel crypto API accesses such algorithms.

To simplify the interface, we accept an algorithm directly in crypto API
format.  The new format is recognised by the "capi:" prefix.  The
dmcrypt internal IV specification is the same as for the old format.

The crypto API cipher specifications format is:
     capi:cipher_api_spec-ivmode[:ivopts]
Examples:
     capi:cbc(aes)-essiv:sha256 (equivalent to old aes-cbc-essiv:sha256)
     capi:xts(aes)-plain64      (equivalent to old aes-xts-plain64)
Examples of authenticated modes:
     capi:gcm(aes)-random
     capi:authenc(hmac(sha256),xts(aes))-random
     capi:rfc7539(chacha20,poly1305)-random

Authenticated modes can only be configured using the new cipher format.
Note that this format allows user to specify arbitrary combinations that
can be insecure. (Policy decision is done in cryptsetup userspace.)

Authenticated encryption algorithms can be of two types, either native
modes (like GCM) that performs both encryption and authentication
internally, or composed modes where user can compose AEAD with separate
specification of encryption algorithm and authenticator.

For composed mode with HMAC (length-preserving encryption mode like an
XTS and HMAC as an authenticator) we have to calculate HMAC digest size
(the separate authentication key is the same size as the HMAC digest).
Introduce crypt_ctr_auth_cipher() to parse the crypto API string to get
HMAC algorithm and retrieve digest size from it.

Also, for HMAC composed mode we need to parse the crypto API string to
get the cipher mode nested in the specification.  For native AEAD mode
(like GCM), we can use crypto_tfm_alg_name() API to get the cipher
specification.

Because the HMAC composed mode is not processed the same as the native
AEAD mode, the CRYPT_MODE_INTEGRITY_HMAC flag is no longer needed and
"hmac" specification for the table integrity argument is removed.

Signed-off-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

Documentation/device-mapper/dm-crypt.txt

@@ -11,14 +11,31 @@ Parameters: <cipher> <key> <iv_offset> <device path> \
 	      <offset> [<#opt_params> <opt_params>]
 
 <cipher>
-    Encryption cipher and an optional IV generation mode.
+    Encryption cipher, encryption mode and Initial Vector (IV) generator.
-    (In format cipher[:keycount]-chainmode-ivmode[:ivopts]).
-    Examples:
-       des
-       aes-cbc-essiv:sha256
-       twofish-ecb
 
-    /proc/crypto contains supported crypto modes
+    The cipher specifications format is:
+       cipher[:keycount]-chainmode-ivmode[:ivopts]
+    Examples:
+       aes-cbc-essiv:sha256
+       aes-xts-plain64
+       serpent-xts-plain64
+
+    Cipher format also supports direct specification with kernel crypt API
+    format (selected by capi: prefix). The IV specification is the same
+    as for the first format type.
+    This format is mainly used for specification of authenticated modes.
+
+    The crypto API cipher specifications format is:
+        capi:cipher_api_spec-ivmode[:ivopts]
+    Examples:
+        capi:cbc(aes)-essiv:sha256
+        capi:xts(aes)-plain64
+    Examples of authenticated modes:
+        capi:gcm(aes)-random
+        capi:authenc(hmac(sha256),xts(aes))-random
+        capi:rfc7539(chacha20,poly1305)-random
+
+    The /proc/crypto contains a list of curently loaded crypto modes.
 
 <key>
     Key used for encryption. It is encoded either as a hexadecimal number
@@ -94,20 +111,16 @@ submit_from_crypt_cpus
     same context.
 
 integrity:<bytes>:<type>
-    Calculates and verifies integrity for the encrypted device (uses
+    The device requires additional <bytes> metadata per-sector stored
-    authenticated encryption). This mode requires metadata stored in per-bio
+    in per-bio integrity structure. This metadata must by provided
-    integrity structure of <bytes> in size.
+    by underlying dm-integrity target.
 
-    This option requires that the underlying device is created by dm-integrity
+    The <type> can be "none" if metadata is used only for persistent IV.
-    target and provides exactly <bytes> of per-sector metadata.
 
-    There can by two options for <type>. The first one is used when encryption
+    For Authenticated Encryption with Additional Data (AEAD)
-    mode is Authenticated mode (AEAD mode), then type must be just "aead".
+    the <type> is "aead". An AEAD mode additionally calculates and verifies
-    The second option is integrity calculated by keyed hash (HMAC), then
+    integrity for the encrypted device. The additional space is then
-    <type> is for example "hmac(sha256)".
+    used for storing authentication tag (and persistent IV if needed).
-
-    If random IV is used (persistently stored IV in metadata per-sector),
-    then <bytes> includes both space for random IV and authentication tag.
 
 Example scripts
 ===============

drivers/md/dm-crypt.c

@@ -129,7 +129,6 @@ enum flags { DM_CRYPT_SUSPENDED, DM_CRYPT_KEY_VALID,
 
 enum cipher_flags {
 	CRYPT_MODE_INTEGRITY_AEAD,	/* Use authenticated mode for cihper */
-	CRYPT_MODE_INTEGRITY_HMAC,	/* Compose authenticated mode from normal mode and HMAC */
 };
 
 /*
@@ -873,19 +872,14 @@ static bool crypt_integrity_aead(struct crypt_config *cc)
 
 static bool crypt_integrity_hmac(struct crypt_config *cc)
 {
-	return test_bit(CRYPT_MODE_INTEGRITY_HMAC, &cc->cipher_flags);
+	return crypt_integrity_aead(cc) && cc->key_mac_size;
-}
-
-static bool crypt_integrity_mode(struct crypt_config *cc)
-{
-	return crypt_integrity_aead(cc) || crypt_integrity_hmac(cc);
 }
 
 /* Get sg containing data */
 static struct scatterlist *crypt_get_sg_data(struct crypt_config *cc,
 					     struct scatterlist *sg)
 {
-	if (unlikely(crypt_integrity_mode(cc)))
+	if (unlikely(crypt_integrity_aead(cc)))
 		return &sg[2];
 
 	return sg;
@@ -936,7 +930,7 @@ static int crypt_integrity_ctr(struct crypt_config *cc, struct dm_target *ti)
 		return -EINVAL;
 	}
 
-	if (crypt_integrity_mode(cc)) {
+	if (crypt_integrity_aead(cc)) {
 		cc->integrity_tag_size = cc->on_disk_tag_size - cc->integrity_iv_size;
 		DMINFO("Integrity AEAD, tag size %u, IV size %u.",
 		       cc->integrity_tag_size, cc->integrity_iv_size);
@@ -990,7 +984,7 @@ static void *req_of_dmreq(struct crypt_config *cc, struct dm_crypt_request *dmre
 static u8 *iv_of_dmreq(struct crypt_config *cc,
 		       struct dm_crypt_request *dmreq)
 {
-	if (crypt_integrity_mode(cc))
+	if (crypt_integrity_aead(cc))
 		return (u8 *)ALIGN((unsigned long)(dmreq + 1),
 			crypto_aead_alignmask(any_tfm_aead(cc)) + 1);
 	else
@@ -1235,7 +1229,7 @@ static void crypt_alloc_req_aead(struct crypt_config *cc,
 static void crypt_alloc_req(struct crypt_config *cc,
 			    struct convert_context *ctx)
 {
-	if (crypt_integrity_mode(cc))
+	if (crypt_integrity_aead(cc))
 		crypt_alloc_req_aead(cc, ctx);
 	else
 		crypt_alloc_req_skcipher(cc, ctx);
@@ -1261,7 +1255,7 @@ static void crypt_free_req_aead(struct crypt_config *cc,
 
 static void crypt_free_req(struct crypt_config *cc, void *req, struct bio *base_bio)
 {
-	if (crypt_integrity_mode(cc))
+	if (crypt_integrity_aead(cc))
 		crypt_free_req_aead(cc, req, base_bio);
 	else
 		crypt_free_req_skcipher(cc, req, base_bio);
@@ -1284,7 +1278,7 @@ static int crypt_convert(struct crypt_config *cc,
 
 		atomic_inc(&ctx->cc_pending);
 
-		if (crypt_integrity_mode(cc))
+		if (crypt_integrity_aead(cc))
 			r = crypt_convert_block_aead(cc, ctx, ctx->r.req_aead, tag_offset);
 		else
 			r = crypt_convert_block_skcipher(cc, ctx, ctx->r.req, tag_offset);
@@ -1849,7 +1843,7 @@ static void crypt_free_tfms_skcipher(struct crypt_config *cc)
 
 static void crypt_free_tfms(struct crypt_config *cc)
 {
-	if (crypt_integrity_mode(cc))
+	if (crypt_integrity_aead(cc))
 		crypt_free_tfms_aead(cc);
 	else
 		crypt_free_tfms_skcipher(cc);
@@ -1879,27 +1873,12 @@ static int crypt_alloc_tfms_skcipher(struct crypt_config *cc, char *ciphermode)
 
 static int crypt_alloc_tfms_aead(struct crypt_config *cc, char *ciphermode)
 {
-	char *authenc = NULL;
 	int err;
 
 	cc->cipher_tfm.tfms = kmalloc(sizeof(struct crypto_aead *), GFP_KERNEL);
 	if (!cc->cipher_tfm.tfms)
 		return -ENOMEM;
 
-	/* Compose AEAD cipher with autenc(authenticator,cipher) structure */
-	if (crypt_integrity_hmac(cc)) {
-		authenc = kmalloc(CRYPTO_MAX_ALG_NAME, GFP_KERNEL);
-		if (!authenc)
-			return -ENOMEM;
-		err = snprintf(authenc, CRYPTO_MAX_ALG_NAME,
-		       "authenc(%s,%s)", cc->cipher_auth, ciphermode);
-		if (err < 0) {
-			kzfree(authenc);
-			return err;
-		}
-		ciphermode = authenc;
-	}
-
 	cc->cipher_tfm.tfms_aead[0] = crypto_alloc_aead(ciphermode, 0, 0);
 	if (IS_ERR(cc->cipher_tfm.tfms_aead[0])) {
 		err = PTR_ERR(cc->cipher_tfm.tfms_aead[0]);
@@ -1907,13 +1886,12 @@ static int crypt_alloc_tfms_aead(struct crypt_config *cc, char *ciphermode)
 		return err;
 	}
 
-	kzfree(authenc);
 	return 0;
 }
 
 static int crypt_alloc_tfms(struct crypt_config *cc, char *ciphermode)
 {
-	if (crypt_integrity_mode(cc))
+	if (crypt_integrity_aead(cc))
 		return crypt_alloc_tfms_aead(cc, ciphermode);
 	else
 		return crypt_alloc_tfms_skcipher(cc, ciphermode);
@@ -1964,13 +1942,13 @@ static int crypt_setkey(struct crypt_config *cc)
 				      subkey_size - cc->key_mac_size,
 				      cc->key_mac_size);
 	for (i = 0; i < cc->tfms_count; i++) {
-		if (crypt_integrity_aead(cc))
+		if (crypt_integrity_hmac(cc))
-			r = crypto_aead_setkey(cc->cipher_tfm.tfms_aead[i],
-						   cc->key + (i * subkey_size),
-						   subkey_size);
-		else if (crypt_integrity_hmac(cc))
 			r = crypto_aead_setkey(cc->cipher_tfm.tfms_aead[i],
 				cc->authenc_key, crypt_authenckey_size(cc));
+		else if (crypt_integrity_aead(cc))
+			r = crypto_aead_setkey(cc->cipher_tfm.tfms_aead[i],
+					       cc->key + (i * subkey_size),
+					       subkey_size);
 		else
 			r = crypto_skcipher_setkey(cc->cipher_tfm.tfms[i],
 						   cc->key + (i * subkey_size),
@@ -2200,19 +2178,11 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 {
 	struct crypt_config *cc = ti->private;
 
-	if (crypt_integrity_mode(cc))
+	if (crypt_integrity_aead(cc))
 		cc->iv_size = crypto_aead_ivsize(any_tfm_aead(cc));
 	else
 		cc->iv_size = crypto_skcipher_ivsize(any_tfm(cc));
 
-	if (crypt_integrity_hmac(cc)) {
-		cc->authenc_key = kmalloc(crypt_authenckey_size(cc), GFP_KERNEL);
-		if (!cc->authenc_key) {
-			ti->error = "Error allocating authenc key space";
-			return -ENOMEM;
-		}
-	}
-
 	if (cc->iv_size)
 		/* at least a 64 bit sector number should fit in our buffer */
 		cc->iv_size = max(cc->iv_size,
@@ -2263,24 +2233,155 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 	return 0;
 }
 
-static int crypt_ctr_cipher(struct dm_target *ti,
+/*
-			    char *cipher_in, char *key)
+ * Workaround to parse cipher algorithm from crypto API spec.
+ * The cc->cipher is currently used only in ESSIV.
+ * This should be probably done by crypto-api calls (once available...)
+ */
+static int crypt_ctr_blkdev_cipher(struct crypt_config *cc)
+{
+	const char *alg_name = NULL;
+	char *start, *end;
+
+	if (crypt_integrity_aead(cc)) {
+		alg_name = crypto_tfm_alg_name(crypto_aead_tfm(any_tfm_aead(cc)));
+		if (!alg_name)
+			return -EINVAL;
+		if (crypt_integrity_hmac(cc)) {
+			alg_name = strchr(alg_name, ',');
+			if (!alg_name)
+				return -EINVAL;
+		}
+		alg_name++;
+	} else {
+		alg_name = crypto_tfm_alg_name(crypto_skcipher_tfm(any_tfm(cc)));
+		if (!alg_name)
+			return -EINVAL;
+	}
+
+	start = strchr(alg_name, '(');
+	end = strchr(alg_name, ')');
+
+	if (!start && !end) {
+		cc->cipher = kstrdup(alg_name, GFP_KERNEL);
+		return cc->cipher ? 0 : -ENOMEM;
+	}
+
+	if (!start || !end || ++start >= end)
+		return -EINVAL;
+
+	cc->cipher = kzalloc(end - start + 1, GFP_KERNEL);
+	if (!cc->cipher)
+		return -ENOMEM;
+
+	strncpy(cc->cipher, start, end - start);
+
+	return 0;
+}
+
+/*
+ * Workaround to parse HMAC algorithm from AEAD crypto API spec.
+ * The HMAC is needed to calculate tag size (HMAC digest size).
+ * This should be probably done by crypto-api calls (once available...)
+ */
+static int crypt_ctr_auth_cipher(struct crypt_config *cc, char *cipher_api)
+{
+	char *start, *end, *mac_alg = NULL;
+	struct crypto_ahash *mac;
+
+	if (!strstarts(cipher_api, "authenc("))
+		return 0;
+
+	start = strchr(cipher_api, '(');
+	end = strchr(cipher_api, ',');
+	if (!start || !end || ++start > end)
+		return -EINVAL;
+
+	mac_alg = kzalloc(end - start + 1, GFP_KERNEL);
+	if (!mac_alg)
+		return -ENOMEM;
+	strncpy(mac_alg, start, end - start);
+
+	mac = crypto_alloc_ahash(mac_alg, 0, 0);
+	kfree(mac_alg);
+
+	if (IS_ERR(mac))
+		return PTR_ERR(mac);
+
+	cc->key_mac_size = crypto_ahash_digestsize(mac);
+	crypto_free_ahash(mac);
+
+	cc->authenc_key = kmalloc(crypt_authenckey_size(cc), GFP_KERNEL);
+	if (!cc->authenc_key)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static int crypt_ctr_cipher_new(struct dm_target *ti, char *cipher_in, char *key,
+				char **ivmode, char **ivopts)
 {
 	struct crypt_config *cc = ti->private;
-	char *tmp, *cipher, *chainmode, *ivmode, *ivopts, *keycount;
+	char *tmp, *cipher_api;
+	int ret = -EINVAL;
+
+	cc->tfms_count = 1;
+
+	/*
+	 * New format (capi: prefix)
+	 * capi:cipher_api_spec-iv:ivopts
+	 */
+	tmp = &cipher_in[strlen("capi:")];
+	cipher_api = strsep(&tmp, "-");
+	*ivmode = strsep(&tmp, ":");
+	*ivopts = tmp;
+
+	if (*ivmode && !strcmp(*ivmode, "lmk"))
+		cc->tfms_count = 64;
+
+	cc->key_parts = cc->tfms_count;
+
+	/* Allocate cipher */
+	ret = crypt_alloc_tfms(cc, cipher_api);
+	if (ret < 0) {
+		ti->error = "Error allocating crypto tfm";
+		return ret;
+	}
+
+	/* Alloc AEAD, can be used only in new format. */
+	if (crypt_integrity_aead(cc)) {
+		ret = crypt_ctr_auth_cipher(cc, cipher_api);
+		if (ret < 0) {
+			ti->error = "Invalid AEAD cipher spec";
+			return -ENOMEM;
+		}
+		cc->iv_size = crypto_aead_ivsize(any_tfm_aead(cc));
+	} else
+		cc->iv_size = crypto_skcipher_ivsize(any_tfm(cc));
+
+	ret = crypt_ctr_blkdev_cipher(cc);
+	if (ret < 0) {
+		ti->error = "Cannot allocate cipher string";
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static int crypt_ctr_cipher_old(struct dm_target *ti, char *cipher_in, char *key,
+				char **ivmode, char **ivopts)
+{
+	struct crypt_config *cc = ti->private;
+	char *tmp, *cipher, *chainmode, *keycount;
 	char *cipher_api = NULL;
 	int ret = -EINVAL;
 	char dummy;
 
-	if (strchr(cipher_in, '(')) {
+	if (strchr(cipher_in, '(') || crypt_integrity_aead(cc)) {
 		ti->error = "Bad cipher specification";
 		return -EINVAL;
 	}
 
-	cc->cipher_string = kstrdup(cipher_in, GFP_KERNEL);
-	if (!cc->cipher_string)
-		goto bad_mem;
-
 	/*
 	 * Legacy dm-crypt cipher specification
 	 * cipher[:keycount]-mode-iv:ivopts
@@ -2303,8 +2404,8 @@ static int crypt_ctr_cipher(struct dm_target *ti,
 		goto bad_mem;
 
 	chainmode = strsep(&tmp, "-");
-	ivopts = strsep(&tmp, "-");
+	*ivopts = strsep(&tmp, "-");
-	ivmode = strsep(&ivopts, ":");
+	*ivmode = strsep(&*ivopts, ":");
 
 	if (tmp)
 		DMWARN("Ignoring unexpected additional cipher options");
@@ -2313,12 +2414,12 @@ static int crypt_ctr_cipher(struct dm_target *ti,
 	 * For compatibility with the original dm-crypt mapping format, if
 	 * only the cipher name is supplied, use cbc-plain.
 	 */
-	if (!chainmode || (!strcmp(chainmode, "plain") && !ivmode)) {
+	if (!chainmode || (!strcmp(chainmode, "plain") && !*ivmode)) {
 		chainmode = "cbc";
-		ivmode = "plain";
+		*ivmode = "plain";
 	}
 
-	if (strcmp(chainmode, "ecb") && !ivmode) {
+	if (strcmp(chainmode, "ecb") && !*ivmode) {
 		ti->error = "IV mechanism required";
 		return -EINVAL;
 	}
@@ -2338,19 +2439,45 @@ static int crypt_ctr_cipher(struct dm_target *ti,
 	ret = crypt_alloc_tfms(cc, cipher_api);
 	if (ret < 0) {
 		ti->error = "Error allocating crypto tfm";
-		goto bad;
+		kfree(cipher_api);
+		return ret;
 	}
 
+	return 0;
+bad_mem:
+	ti->error = "Cannot allocate cipher strings";
+	return -ENOMEM;
+}
+
+static int crypt_ctr_cipher(struct dm_target *ti, char *cipher_in, char *key)
+{
+	struct crypt_config *cc = ti->private;
+	char *ivmode = NULL, *ivopts = NULL;
+	int ret;
+
+	cc->cipher_string = kstrdup(cipher_in, GFP_KERNEL);
+	if (!cc->cipher_string) {
+		ti->error = "Cannot allocate cipher strings";
+		return -ENOMEM;
+	}
+
+	if (strstarts(cipher_in, "capi:"))
+		ret = crypt_ctr_cipher_new(ti, cipher_in, key, &ivmode, &ivopts);
+	else
+		ret = crypt_ctr_cipher_old(ti, cipher_in, key, &ivmode, &ivopts);
+	if (ret)
+		return ret;
+
 	/* Initialize IV */
 	ret = crypt_ctr_ivmode(ti, ivmode);
 	if (ret < 0)
-		goto bad;
+		return ret;
 
 	/* Initialize and set key */
 	ret = crypt_set_key(cc, key);
 	if (ret < 0) {
 		ti->error = "Error decoding and setting key";
-		goto bad;
+		return ret;
 	}
 
 	/* Allocate IV */
@@ -2358,7 +2485,7 @@ static int crypt_ctr_cipher(struct dm_target *ti,
 		ret = cc->iv_gen_ops->ctr(cc, ti, ivopts);
 		if (ret < 0) {
 			ti->error = "Error creating IV";
-			goto bad;
+			return ret;
 		}
 	}
 
@@ -2367,18 +2494,11 @@ static int crypt_ctr_cipher(struct dm_target *ti,
 		ret = cc->iv_gen_ops->init(cc);
 		if (ret < 0) {
 			ti->error = "Error initialising IV";
-			goto bad;
+			return ret;
 		}
 	}
 
-	ret = 0;
-bad:
-	kfree(cipher_api);
 	return ret;
-
-bad_mem:
-	ti->error = "Cannot allocate cipher strings";
-	return -ENOMEM;
 }
 
 static int crypt_ctr_optional(struct dm_target *ti, unsigned int argc, char **argv)
@@ -2424,15 +2544,6 @@ static int crypt_ctr_optional(struct dm_target *ti, unsigned int argc, char **ar
 			sval = strchr(opt_string + strlen("integrity:"), ':') + 1;
 			if (!strcasecmp(sval, "aead")) {
 				set_bit(CRYPT_MODE_INTEGRITY_AEAD, &cc->cipher_flags);
-			} else  if (!strncasecmp(sval, "hmac(", strlen("hmac("))) {
-				struct crypto_ahash *hmac_tfm = crypto_alloc_ahash(sval, 0, 0);
-				if (IS_ERR(hmac_tfm)) {
-					ti->error = "Error initializing HMAC integrity hash.";
-					return PTR_ERR(hmac_tfm);
-				}
-				cc->key_mac_size = crypto_ahash_digestsize(hmac_tfm);
-				crypto_free_ahash(hmac_tfm);
-				set_bit(CRYPT_MODE_INTEGRITY_HMAC, &cc->cipher_flags);
 			} else  if (strcasecmp(sval, "none")) {
 				ti->error = "Unknown integrity profile";
 				return -EINVAL;
@@ -2495,7 +2606,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	if (ret < 0)
 		goto bad;
 
-	if (crypt_integrity_mode(cc)) {
+	if (crypt_integrity_aead(cc)) {
 		cc->dmreq_start = sizeof(struct aead_request);
 		cc->dmreq_start += crypto_aead_reqsize(any_tfm_aead(cc));
 		align_mask = crypto_aead_alignmask(any_tfm_aead(cc));
@@ -2572,7 +2683,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	}
 	cc->start = tmpll;
 
-	if (crypt_integrity_mode(cc) || cc->integrity_iv_size) {
+	if (crypt_integrity_aead(cc) || cc->integrity_iv_size) {
 		ret = crypt_integrity_ctr(cc, ti);
 		if (ret)
 			goto bad;
@@ -2670,7 +2781,7 @@ static int crypt_map(struct dm_target *ti, struct bio *bio)
 		}
 	}
 
-	if (crypt_integrity_mode(cc))
+	if (crypt_integrity_aead(cc))
 		io->ctx.r.req_aead = (struct aead_request *)(io + 1);
 	else
 		io->ctx.r.req = (struct skcipher_request *)(io + 1);