[PATCH v2 2/4] crypto: arm64/chacha20 - add XChaCha20 support

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

Add an XChaCha20 implementation that is hooked up to the ARM64 NEON
implementation of ChaCha20.  This can be used by Adiantum.

A NEON implementation of single-block HChaCha20 is also added so that
XChaCha20 can use it rather than the generic implementation.  This
required refactoring the ChaCha20 permutation into its own function.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 arch/arm64/crypto/Kconfig              |   2 +-
 arch/arm64/crypto/chacha20-neon-core.S |  65 +++++++++++-----
 arch/arm64/crypto/chacha20-neon-glue.c | 101 +++++++++++++++++++------
 3 files changed, 125 insertions(+), 43 deletions(-)

diff --git a/arch/arm64/crypto/Kconfig b/arch/arm64/crypto/Kconfig
index 3f5aeb786192..d54ddb8468ef 100644
--- a/arch/arm64/crypto/Kconfig
+++ b/arch/arm64/crypto/Kconfig
@@ -101,7 +101,7 @@ config CRYPTO_AES_ARM64_NEON_BLK
 	select CRYPTO_SIMD
 
 config CRYPTO_CHACHA20_NEON
-	tristate "NEON accelerated ChaCha20 symmetric cipher"
+	tristate "ChaCha20 and XChaCha20 stream ciphers using NEON instructions"
 	depends on KERNEL_MODE_NEON
 	select CRYPTO_BLKCIPHER
 	select CRYPTO_CHACHA20
diff --git a/arch/arm64/crypto/chacha20-neon-core.S b/arch/arm64/crypto/chacha20-neon-core.S
index 13c85e272c2a..0571e45a1a0a 100644
--- a/arch/arm64/crypto/chacha20-neon-core.S
+++ b/arch/arm64/crypto/chacha20-neon-core.S
@@ -23,25 +23,20 @@
 	.text
 	.align		6
 
-ENTRY(chacha20_block_xor_neon)
-	// x0: Input state matrix, s
-	// x1: 1 data block output, o
-	// x2: 1 data block input, i
-
-	//
-	// This function encrypts one ChaCha20 block by loading the state matrix
-	// in four NEON registers. It performs matrix operation on four words in
-	// parallel, but requires shuffling to rearrange the words after each
-	// round.
-	//
-
-	// x0..3 = s0..3
-	adr		x3, ROT8
-	ld1		{v0.4s-v3.4s}, [x0]
-	ld1		{v8.4s-v11.4s}, [x0]
-	ld1		{v12.4s}, [x3]
+/*
+ * chacha20_permute - permute one block
+ *
+ * Permute one 64-byte block where the state matrix is stored in the four NEON
+ * registers v0-v3.  It performs matrix operations on four words in parallel,
+ * but requires shuffling to rearrange the words after each round.
+ *
+ * Clobbers: x3, x10, v4, v12
+ */
+chacha20_permute:
 
 	mov		x3, #10
+	adr		x10, ROT8
+	ld1		{v12.4s}, [x10]
 
 .Ldoubleround:
 	// x0 += x1, x3 = rotl32(x3 ^ x0, 16)
@@ -105,6 +100,23 @@ ENTRY(chacha20_block_xor_neon)
 	subs		x3, x3, #1
 	b.ne		.Ldoubleround
 
+	ret
+ENDPROC(chacha20_permute)
+
+ENTRY(chacha20_block_xor_neon)
+	// x0: Input state matrix, s
+	// x1: 1 data block output, o
+	// x2: 1 data block input, i
+
+	stp		x29, x30, [sp, #-16]!
+	mov		x29, sp
+
+	// x0..3 = s0..3
+	ld1		{v0.4s-v3.4s}, [x0]
+	ld1		{v8.4s-v11.4s}, [x0]
+
+	bl		chacha20_permute
+
 	ld1		{v4.16b-v7.16b}, [x2]
 
 	// o0 = i0 ^ (x0 + s0)
@@ -125,9 +137,28 @@ ENTRY(chacha20_block_xor_neon)
 
 	st1		{v0.16b-v3.16b}, [x1]
 
+	ldp		x29, x30, [sp], #16
 	ret
 ENDPROC(chacha20_block_xor_neon)
 
+ENTRY(hchacha20_block_neon)
+	// x0: Input state matrix, s
+	// x1: output (8 32-bit words)
+
+	stp		x29, x30, [sp, #-16]!
+	mov		x29, sp
+
+	ld1		{v0.4s-v3.4s}, [x0]
+
+	bl		chacha20_permute
+
+	st1		{v0.16b}, [x1], #16
+	st1		{v3.16b}, [x1]
+
+	ldp		x29, x30, [sp], #16
+	ret
+ENDPROC(hchacha20_block_neon)
+
 	.align		6
 ENTRY(chacha20_4block_xor_neon)
 	// x0: Input state matrix, s
diff --git a/arch/arm64/crypto/chacha20-neon-glue.c b/arch/arm64/crypto/chacha20-neon-glue.c
index 96e0cfb8c3f5..a5b9cbc0c4de 100644
--- a/arch/arm64/crypto/chacha20-neon-glue.c
+++ b/arch/arm64/crypto/chacha20-neon-glue.c
@@ -30,6 +30,7 @@
 
 asmlinkage void chacha20_block_xor_neon(u32 *state, u8 *dst, const u8 *src);
 asmlinkage void chacha20_4block_xor_neon(u32 *state, u8 *dst, const u8 *src);
+asmlinkage void hchacha20_block_neon(const u32 *state, u32 *out);
 
 static void chacha20_doneon(u32 *state, u8 *dst, const u8 *src,
 			    unsigned int bytes)
@@ -65,20 +66,16 @@ static void chacha20_doneon(u32 *state, u8 *dst, const u8 *src,
 	kernel_neon_end();
 }
 
-static int chacha20_neon(struct skcipher_request *req)
+static int chacha20_neon_stream_xor(struct skcipher_request *req,
+				    struct chacha_ctx *ctx, u8 *iv)
 {
-	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
-	struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct skcipher_walk walk;
 	u32 state[16];
 	int err;
 
-	if (!may_use_simd() || req->cryptlen <= CHACHA_BLOCK_SIZE)
-		return crypto_chacha_crypt(req);
-
 	err = skcipher_walk_virt(&walk, req, false);
 
-	crypto_chacha_init(state, ctx, walk.iv);
+	crypto_chacha_init(state, ctx, iv);
 
 	while (walk.nbytes > 0) {
 		unsigned int nbytes = walk.nbytes;
@@ -94,22 +91,73 @@ static int chacha20_neon(struct skcipher_request *req)
 	return err;
 }
 
-static struct skcipher_alg alg = {
-	.base.cra_name		= "chacha20",
-	.base.cra_driver_name	= "chacha20-neon",
-	.base.cra_priority	= 300,
-	.base.cra_blocksize	= 1,
-	.base.cra_ctxsize	= sizeof(struct chacha_ctx),
-	.base.cra_module	= THIS_MODULE,
-
-	.min_keysize		= CHACHA_KEY_SIZE,
-	.max_keysize		= CHACHA_KEY_SIZE,
-	.ivsize			= CHACHA_IV_SIZE,
-	.chunksize		= CHACHA_BLOCK_SIZE,
-	.walksize		= 4 * CHACHA_BLOCK_SIZE,
-	.setkey			= crypto_chacha20_setkey,
-	.encrypt		= chacha20_neon,
-	.decrypt		= chacha20_neon,
+static int chacha20_neon(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
+
+	if (req->cryptlen <= CHACHA_BLOCK_SIZE || !may_use_simd())
+		return crypto_chacha_crypt(req);
+
+	return chacha20_neon_stream_xor(req, ctx, req->iv);
+}
+
+static int xchacha20_neon(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct chacha_ctx subctx;
+	u32 state[16];
+	u8 real_iv[16];
+
+	if (req->cryptlen <= CHACHA_BLOCK_SIZE || !may_use_simd())
+		return crypto_xchacha_crypt(req);
+
+	crypto_chacha_init(state, ctx, req->iv);
+
+	kernel_neon_begin();
+	hchacha20_block_neon(state, subctx.key);
+	kernel_neon_end();
+
+	memcpy(&real_iv[0], req->iv + 24, 8);
+	memcpy(&real_iv[8], req->iv + 16, 8);
+	return chacha20_neon_stream_xor(req, &subctx, real_iv);
+}
+
+static struct skcipher_alg algs[] = {
+	{
+		.base.cra_name		= "chacha20",
+		.base.cra_driver_name	= "chacha20-neon",
+		.base.cra_priority	= 300,
+		.base.cra_blocksize	= 1,
+		.base.cra_ctxsize	= sizeof(struct chacha_ctx),
+		.base.cra_module	= THIS_MODULE,
+
+		.min_keysize		= CHACHA_KEY_SIZE,
+		.max_keysize		= CHACHA_KEY_SIZE,
+		.ivsize			= CHACHA_IV_SIZE,
+		.chunksize		= CHACHA_BLOCK_SIZE,
+		.walksize		= 4 * CHACHA_BLOCK_SIZE,
+		.setkey			= crypto_chacha20_setkey,
+		.encrypt		= chacha20_neon,
+		.decrypt		= chacha20_neon,
+	}, {
+		.base.cra_name		= "xchacha20",
+		.base.cra_driver_name	= "xchacha20-neon",
+		.base.cra_priority	= 300,
+		.base.cra_blocksize	= 1,
+		.base.cra_ctxsize	= sizeof(struct chacha_ctx),
+		.base.cra_module	= THIS_MODULE,
+
+		.min_keysize		= CHACHA_KEY_SIZE,
+		.max_keysize		= CHACHA_KEY_SIZE,
+		.ivsize			= XCHACHA_IV_SIZE,
+		.chunksize		= CHACHA_BLOCK_SIZE,
+		.walksize		= 4 * CHACHA_BLOCK_SIZE,
+		.setkey			= crypto_chacha20_setkey,
+		.encrypt		= xchacha20_neon,
+		.decrypt		= xchacha20_neon,
+	}
 };
 
 static int __init chacha20_simd_mod_init(void)
@@ -117,12 +165,12 @@ static int __init chacha20_simd_mod_init(void)
 	if (!(elf_hwcap & HWCAP_ASIMD))
 		return -ENODEV;
 
-	return crypto_register_skcipher(&alg);
+	return crypto_register_skciphers(algs, ARRAY_SIZE(algs));
 }
 
 static void __exit chacha20_simd_mod_fini(void)
 {
-	crypto_unregister_skcipher(&alg);
+	crypto_unregister_skciphers(algs, ARRAY_SIZE(algs));
 }
 
 module_init(chacha20_simd_mod_init);
@@ -131,3 +179,6 @@ module_exit(chacha20_simd_mod_fini);
 MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
 MODULE_LICENSE("GPL v2");
 MODULE_ALIAS_CRYPTO("chacha20");
+MODULE_ALIAS_CRYPTO("chacha20-neon");
+MODULE_ALIAS_CRYPTO("xchacha20");
+MODULE_ALIAS_CRYPTO("xchacha20-neon");
-- 
2.19.2