[PATCH 2/4] crypto: xts - support multiple data units per request in template

[Leonid Ravich <lravich@amazon.com>]

Teach the generic xts() template to consume cryptlen larger than one
data unit when the caller has configured a non-zero data_unit_size on
the tfm.  Each data unit is processed with its own IV, derived from
the caller-supplied IV by treating it as a 128-bit little-endian
counter and adding the data-unit index.  This matches the
sector-indexed XTS used by dm-crypt's plain64 IV mode and by typical
inline-encryption hardware.

The single-data-unit body is unchanged and is now reached via a thin
xts_crypt_multi() dispatcher that skips straight to the body when
data_unit_size is zero (the legacy default), so existing users see
no extra cost.

Advertise CRYPTO_ALG_SKCIPHER_MULTI_DATA_UNIT in cra_flags only when
the inner cipher is synchronous.  An async inner cipher would require
a per-DU completion chain which is out of scope for the slow software
template; consumers that need multi-DU on async hardware will use one
of the arch-specific drivers added later in this series.

Signed-off-by: Leonid Ravich <lravich@amazon.com>
---
 crypto/xts.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/crypto/xts.c b/crypto/xts.c
index 3da8f5e053d6..2b7233311dad 100644
--- a/crypto/xts.c
+++ b/crypto/xts.c
@@ -258,7 +258,7 @@ static int xts_init_crypt(struct skcipher_request *req,
 	return 0;
 }
 
-static int xts_encrypt(struct skcipher_request *req)
+static int xts_encrypt_one(struct skcipher_request *req)
 {
 	struct xts_request_ctx *rctx = skcipher_request_ctx(req);
 	struct skcipher_request *subreq = &rctx->subreq;
@@ -275,7 +275,7 @@ static int xts_encrypt(struct skcipher_request *req)
 	return xts_cts_final(req, crypto_skcipher_encrypt);
 }
 
-static int xts_decrypt(struct skcipher_request *req)
+static int xts_decrypt_one(struct skcipher_request *req)
 {
 	struct xts_request_ctx *rctx = skcipher_request_ctx(req);
 	struct skcipher_request *subreq = &rctx->subreq;
@@ -292,6 +292,16 @@ static int xts_decrypt(struct skcipher_request *req)
 	return xts_cts_final(req, crypto_skcipher_decrypt);
 }
 
+static int xts_encrypt(struct skcipher_request *req)
+{
+	return skcipher_walk_data_units(req, xts_encrypt_one);
+}
+
+static int xts_decrypt(struct skcipher_request *req)
+{
+	return skcipher_walk_data_units(req, xts_decrypt_one);
+}
+
 static int xts_init_tfm(struct crypto_skcipher *tfm)
 {
 	struct skcipher_instance *inst = skcipher_alg_instance(tfm);
@@ -427,6 +437,17 @@ static int xts_create(struct crypto_template *tmpl, struct rtattr **tb)
 	inst->alg.base.cra_alignmask = alg->base.cra_alignmask |
 				       (__alignof__(u64) - 1);
 
+	/*
+	 * Advertise multi-data-unit support only when the inner cipher is
+	 * synchronous.  The dispatcher in skcipher_walk_data_units() calls
+	 * the single-DU body in a loop and assumes synchronous completion;
+	 * supporting async would require a per-DU callback chain, which
+	 * the slow software template does not need.
+	 */
+	if (!(alg->base.cra_flags & CRYPTO_ALG_ASYNC))
+		inst->alg.base.cra_flags |=
+			CRYPTO_ALG_SKCIPHER_MULTI_DATA_UNIT;
+
 	inst->alg.ivsize = XTS_BLOCK_SIZE;
 	inst->alg.min_keysize = alg->min_keysize * 2;
 	inst->alg.max_keysize = alg->max_keysize * 2;
-- 
2.47.3