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