crypto: arm64/aes-neonbs-ctr - fallback to plain NEON for final chunk

Instead of processing the entire input with the 8-way bit sliced
algorithm, which is sub-optimal for inputs that are not a multiple of
128 bytes in size, invoke the plain NEON version of CTR for the
remainder of the input after processing the bulk using 128 byte strides.

This allows us to greatly simplify the asm code that implements CTR, and
get rid of all the branches and special code paths. It also gains us a
couple of percent of performance.

Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

arch/arm64/crypto/aes-glue.c

···
 module_init(aes_init);
 EXPORT_SYMBOL(neon_aes_ecb_encrypt);
 EXPORT_SYMBOL(neon_aes_cbc_encrypt);
+EXPORT_SYMBOL(neon_aes_ctr_encrypt);
 EXPORT_SYMBOL(neon_aes_xts_encrypt);
 EXPORT_SYMBOL(neon_aes_xts_decrypt);
 #endif

arch/arm64/crypto/aes-neonbs-core.S

···
 
 	/*
 	 * aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
-	 *		     int rounds, int blocks, u8 iv[], u8 final[])
+	 *		     int rounds, int blocks, u8 iv[])
 	 */
 SYM_FUNC_START(aesbs_ctr_encrypt)
-	frame_push	8
+	stp		x29, x30, [sp, #-16]!
+	mov		x29, sp
 
-	mov		x19, x0
-	mov		x20, x1
-	mov		x21, x2
-	mov		x22, x3
-	mov		x23, x4
-	mov		x24, x5
-	mov		x25, x6
-
-	cmp		x25, #0
-	cset		x26, ne
-	add		x23, x23, x26		// do one extra block if final
-
-	ldp		x7, x8, [x24]
-	ld1		{v0.16b}, [x24]
+	ldp		x7, x8, [x5]
+	ld1		{v0.16b}, [x5]
 CPU_LE(	rev		x7, x7		)
 CPU_LE(	rev		x8, x8		)
 	adds		x8, x8, #1
 	adc		x7, x7, xzr
 
-99:	mov		x9, #1
-	lsl		x9, x9, x23
-	subs		w23, w23, #8
-	csel		x23, x23, xzr, pl
-	csel		x9, x9, xzr, le
-
-	tbnz		x9, #1, 0f
-	next_ctr	v1
-	tbnz		x9, #2, 0f
+0:	next_ctr	v1
 	next_ctr	v2
-	tbnz		x9, #3, 0f
 	next_ctr	v3
-	tbnz		x9, #4, 0f
 	next_ctr	v4
-	tbnz		x9, #5, 0f
 	next_ctr	v5
-	tbnz		x9, #6, 0f
 	next_ctr	v6
-	tbnz		x9, #7, 0f
 	next_ctr	v7
 
-0:	mov		bskey, x21
-	mov		rounds, x22
+	mov		bskey, x2
+	mov		rounds, x3
 	bl		aesbs_encrypt8
 
-	lsr		x9, x9, x26		// disregard the extra block
-	tbnz		x9, #0, 0f
+	ld1		{ v8.16b-v11.16b}, [x1], #64
+	ld1		{v12.16b-v15.16b}, [x1], #64
 
-	ld1		{v8.16b}, [x20], #16
-	eor		v0.16b, v0.16b, v8.16b
-	st1		{v0.16b}, [x19], #16
-	tbnz		x9, #1, 1f
+	eor		v8.16b, v0.16b, v8.16b
+	eor		v9.16b, v1.16b, v9.16b
+	eor		v10.16b, v4.16b, v10.16b
+	eor		v11.16b, v6.16b, v11.16b
+	eor		v12.16b, v3.16b, v12.16b
+	eor		v13.16b, v7.16b, v13.16b
+	eor		v14.16b, v2.16b, v14.16b
+	eor		v15.16b, v5.16b, v15.16b
 
-	ld1		{v9.16b}, [x20], #16
-	eor		v1.16b, v1.16b, v9.16b
-	st1		{v1.16b}, [x19], #16
-	tbnz		x9, #2, 2f
+	st1		{ v8.16b-v11.16b}, [x0], #64
+	st1		{v12.16b-v15.16b}, [x0], #64
 
-	ld1		{v10.16b}, [x20], #16
-	eor		v4.16b, v4.16b, v10.16b
-	st1		{v4.16b}, [x19], #16
-	tbnz		x9, #3, 3f
+	next_ctr	v0
+	subs		x4, x4, #8
+	b.gt		0b
 
-	ld1		{v11.16b}, [x20], #16
-	eor		v6.16b, v6.16b, v11.16b
-	st1		{v6.16b}, [x19], #16
-	tbnz		x9, #4, 4f
-
-	ld1		{v12.16b}, [x20], #16
-	eor		v3.16b, v3.16b, v12.16b
-	st1		{v3.16b}, [x19], #16
-	tbnz		x9, #5, 5f
-
-	ld1		{v13.16b}, [x20], #16
-	eor		v7.16b, v7.16b, v13.16b
-	st1		{v7.16b}, [x19], #16
-	tbnz		x9, #6, 6f
-
-	ld1		{v14.16b}, [x20], #16
-	eor		v2.16b, v2.16b, v14.16b
-	st1		{v2.16b}, [x19], #16
-	tbnz		x9, #7, 7f
-
-	ld1		{v15.16b}, [x20], #16
-	eor		v5.16b, v5.16b, v15.16b
-	st1		{v5.16b}, [x19], #16
-
-8:	next_ctr	v0
-	st1		{v0.16b}, [x24]
-	cbz		x23, .Lctr_done
-
-	b		99b
-
-.Lctr_done:
-	frame_pop
+	st1		{v0.16b}, [x5]
+	ldp		x29, x30, [sp], #16
 	ret
-
-	/*
-	 * If we are handling the tail of the input (x6 != NULL), return the
-	 * final keystream block back to the caller.
-	 */
-0:	cbz		x25, 8b
-	st1		{v0.16b}, [x25]
-	b		8b
-1:	cbz		x25, 8b
-	st1		{v1.16b}, [x25]
-	b		8b
-2:	cbz		x25, 8b
-	st1		{v4.16b}, [x25]
-	b		8b
-3:	cbz		x25, 8b
-	st1		{v6.16b}, [x25]
-	b		8b
-4:	cbz		x25, 8b
-	st1		{v3.16b}, [x25]
-	b		8b
-5:	cbz		x25, 8b
-	st1		{v7.16b}, [x25]
-	b		8b
-6:	cbz		x25, 8b
-	st1		{v2.16b}, [x25]
-	b		8b
-7:	cbz		x25, 8b
-	st1		{v5.16b}, [x25]
-	b		8b
 SYM_FUNC_END(aesbs_ctr_encrypt)

arch/arm64/crypto/aes-neonbs-glue.c

···
 				  int rounds, int blocks, u8 iv[]);
 
 asmlinkage void aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
-				  int rounds, int blocks, u8 iv[], u8 final[]);
+				  int rounds, int blocks, u8 iv[]);
 
 asmlinkage void aesbs_xts_encrypt(u8 out[], u8 const in[], u8 const rk[],
 				  int rounds, int blocks, u8 iv[]);
···
 				     int rounds, int blocks);
 asmlinkage void neon_aes_cbc_encrypt(u8 out[], u8 const in[], u32 const rk[],
 				     int rounds, int blocks, u8 iv[]);
+asmlinkage void neon_aes_ctr_encrypt(u8 out[], u8 const in[], u32 const rk[],
+				     int rounds, int bytes, u8 ctr[]);
 asmlinkage void neon_aes_xts_encrypt(u8 out[], u8 const in[],
 				     u32 const rk1[], int rounds, int bytes,
 				     u32 const rk2[], u8 iv[], int first);
···
 	int	rounds;
 } __aligned(AES_BLOCK_SIZE);
 
-struct aesbs_cbc_ctx {
+struct aesbs_cbc_ctr_ctx {
 	struct aesbs_ctx	key;
 	u32			enc[AES_MAX_KEYLENGTH_U32];
 };
···
 	return __ecb_crypt(req, aesbs_ecb_decrypt);
 }
 
-static int aesbs_cbc_setkey(struct crypto_skcipher *tfm, const u8 *in_key,
+static int aesbs_cbc_ctr_setkey(struct crypto_skcipher *tfm, const u8 *in_key,
 			    unsigned int key_len)
 {
-	struct aesbs_cbc_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct aesbs_cbc_ctr_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct crypto_aes_ctx rk;
 	int err;
 
···
 static int cbc_encrypt(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
-	struct aesbs_cbc_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct aesbs_cbc_ctr_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct skcipher_walk walk;
 	int err;
 
···
 static int cbc_decrypt(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
-	struct aesbs_cbc_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct aesbs_cbc_ctr_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct skcipher_walk walk;
 	int err;
 
···
 static int ctr_encrypt(struct skcipher_request *req)
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
-	struct aesbs_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct aesbs_cbc_ctr_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct skcipher_walk walk;
-	u8 buf[AES_BLOCK_SIZE];
 	int err;
 
 	err = skcipher_walk_virt(&walk, req, false);
 
 	while (walk.nbytes > 0) {
-		unsigned int blocks = walk.nbytes / AES_BLOCK_SIZE;
-		u8 *final = (walk.total % AES_BLOCK_SIZE) ? buf : NULL;
-
-		if (walk.nbytes < walk.total) {
-			blocks = round_down(blocks,
-					    walk.stride / AES_BLOCK_SIZE);
-			final = NULL;
-		}
+		int blocks = (walk.nbytes / AES_BLOCK_SIZE) & ~7;
+		int nbytes = walk.nbytes % (8 * AES_BLOCK_SIZE);
+		const u8 *src = walk.src.virt.addr;
+		u8 *dst = walk.dst.virt.addr;
 
 		kernel_neon_begin();
-		aesbs_ctr_encrypt(walk.dst.virt.addr, walk.src.virt.addr,
-				  ctx->rk, ctx->rounds, blocks, walk.iv, final);
-		kernel_neon_end();
-
-		if (final) {
-			u8 *dst = walk.dst.virt.addr + blocks * AES_BLOCK_SIZE;
-			u8 *src = walk.src.virt.addr + blocks * AES_BLOCK_SIZE;
-
-			crypto_xor_cpy(dst, src, final,
-				       walk.total % AES_BLOCK_SIZE);
-
-			err = skcipher_walk_done(&walk, 0);
-			break;
+		if (blocks >= 8) {
+			aesbs_ctr_encrypt(dst, src, ctx->key.rk, ctx->key.rounds,
+					  blocks, walk.iv);
+			dst += blocks * AES_BLOCK_SIZE;
+			src += blocks * AES_BLOCK_SIZE;
 		}
-		err = skcipher_walk_done(&walk,
-					 walk.nbytes - blocks * AES_BLOCK_SIZE);
+		if (nbytes && walk.nbytes == walk.total) {
+			neon_aes_ctr_encrypt(dst, src, ctx->enc, ctx->key.rounds,
+					     nbytes, walk.iv);
+			nbytes = 0;
+		}
+		kernel_neon_end();
+		err = skcipher_walk_done(&walk, nbytes);
 	}
 	return err;
 }
···
 	.base.cra_driver_name	= "cbc-aes-neonbs",
 	.base.cra_priority	= 250,
 	.base.cra_blocksize	= AES_BLOCK_SIZE,
-	.base.cra_ctxsize	= sizeof(struct aesbs_cbc_ctx),
+	.base.cra_ctxsize	= sizeof(struct aesbs_cbc_ctr_ctx),
 	.base.cra_module	= THIS_MODULE,
 
 	.min_keysize		= AES_MIN_KEY_SIZE,
 	.max_keysize		= AES_MAX_KEY_SIZE,
 	.walksize		= 8 * AES_BLOCK_SIZE,
 	.ivsize			= AES_BLOCK_SIZE,
-	.setkey			= aesbs_cbc_setkey,
+	.setkey			= aesbs_cbc_ctr_setkey,
 	.encrypt		= cbc_encrypt,
 	.decrypt		= cbc_decrypt,
 }, {
···
 	.base.cra_driver_name	= "ctr-aes-neonbs",
 	.base.cra_priority	= 250,
 	.base.cra_blocksize	= 1,
-	.base.cra_ctxsize	= sizeof(struct aesbs_ctx),
+	.base.cra_ctxsize	= sizeof(struct aesbs_cbc_ctr_ctx),
 	.base.cra_module	= THIS_MODULE,
 
 	.min_keysize		= AES_MIN_KEY_SIZE,
···
 	.chunksize		= AES_BLOCK_SIZE,
 	.walksize		= 8 * AES_BLOCK_SIZE,
 	.ivsize			= AES_BLOCK_SIZE,
-	.setkey			= aesbs_setkey,
+	.setkey			= aesbs_cbc_ctr_setkey,
 	.encrypt		= ctr_encrypt,
 	.decrypt		= ctr_encrypt,
 }, {