Received-SPF: pass (google.com: domain of linux-crypto+bounces-3728-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
From: Eric Biggers <ebiggers@kernel.org>
To: linux-crypto@vger.kernel.org
Cc: x86@kernel.org
Subject: [PATCH] crypto: x86/aes-xts - simplify loop in xts_crypt_slowpath()
Date: Fri, 19 Apr 2024 22:54:55 -0700
Message-ID: <20240420055455.25179-1-ebiggers@kernel.org>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

From: Eric Biggers <ebiggers@google.com>

Since the total length processed by the loop in xts_crypt_slowpath() is
a multiple of AES_BLOCK_SIZE, just round the length down to
AES_BLOCK_SIZE even on the last step.  This doesn't change behavior, as
the last step will process a multiple of AES_BLOCK_SIZE regardless.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 arch/x86/crypto/aesni-intel_glue.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/x86/crypto/aesni-intel_glue.c b/arch/x86/crypto/aesni-intel_glue.c
index 110b3282a1f2..02a4c0c276df 100644
--- a/arch/x86/crypto/aesni-intel_glue.c
+++ b/arch/x86/crypto/aesni-intel_glue.c
@@ -933,20 +933,17 @@ xts_crypt_slowpath(struct skcipher_request *req, xts_crypt_func crypt_func)
 	}
 
 	err = skcipher_walk_virt(&walk, req, false);
 
 	while (walk.nbytes) {
-		unsigned int nbytes = walk.nbytes;
-
-		if (nbytes < walk.total)
-			nbytes = round_down(nbytes, AES_BLOCK_SIZE);
-
 		kernel_fpu_begin();
-		(*crypt_func)(&ctx->crypt_ctx, walk.src.virt.addr,
-			      walk.dst.virt.addr, nbytes, req->iv);
+		(*crypt_func)(&ctx->crypt_ctx,
+			      walk.src.virt.addr, walk.dst.virt.addr,
+			      walk.nbytes & ~(AES_BLOCK_SIZE - 1), req->iv);
 		kernel_fpu_end();
-		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
+		err = skcipher_walk_done(&walk,
+					 walk.nbytes & (AES_BLOCK_SIZE - 1));
 	}
 
 	if (err || !tail)
 		return err;
 

base-commit: 543ea178fbfadeaf79e15766ac989f3351349f02
-- 
2.44.0