crypto: arm64/aes-xctr - Improve readability of XCTR and CTR modes

Added some clarifying comments, changed the register allocations to make
the code clearer, and added register aliases.

Signed-off-by: Nathan Huckleberry <nhuck@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 16 insertions, 0 deletions

diff --git a/arch/arm64/crypto/aes-glue.c b/arch/arm64/crypto/aes-glue.c
index b6883288234c..162787c7aa86 100644
--- a/arch/arm64/crypto/aes-glue.c
+++ b/arch/arm64/crypto/aes-glue.c
@@ -464,6 +464,14 @@ static int __maybe_unused xctr_encrypt(struct skcipher_request *req)
 		u8 *dst = walk.dst.virt.addr;
 		u8 buf[AES_BLOCK_SIZE];
 
+		/*
+		 * If given less than 16 bytes, we must copy the partial block
+		 * into a temporary buffer of 16 bytes to avoid out of bounds
+		 * reads and writes.  Furthermore, this code is somewhat unusual
+		 * in that it expects the end of the data to be at the end of
+		 * the temporary buffer, rather than the start of the data at
+		 * the start of the temporary buffer.
+		 */
 		if (unlikely(nbytes < AES_BLOCK_SIZE))
 			src = dst = memcpy(buf + sizeof(buf) - nbytes,
 					   src, nbytes);
@@ -501,6 +509,14 @@ static int __maybe_unused ctr_encrypt(struct skcipher_request *req)
 		u8 *dst = walk.dst.virt.addr;
 		u8 buf[AES_BLOCK_SIZE];
 
+		/*
+		 * If given less than 16 bytes, we must copy the partial block
+		 * into a temporary buffer of 16 bytes to avoid out of bounds
+		 * reads and writes.  Furthermore, this code is somewhat unusual
+		 * in that it expects the end of the data to be at the end of
+		 * the temporary buffer, rather than the start of the data at
+		 * the start of the temporary buffer.
+		 */
 		if (unlikely(nbytes < AES_BLOCK_SIZE))
 			src = dst = memcpy(buf + sizeof(buf) - nbytes,
 					   src, nbytes);