crypto: arm64/chacha20 - implement NEON version based on SSE3 code

This is a straight port to arm64/NEON of the x86 SSE3 implementation
of the ChaCha20 stream cipher. It uses the new skcipher walksize
attribute to process the input in strides of 4x the block size.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

arch/arm64/crypto/Kconfig

@@ -72,4 +72,10 @@ config CRYPTO_CRC32_ARM64
 	depends on ARM64
 	select CRYPTO_HASH
 
+config CRYPTO_CHACHA20_NEON
+	tristate "NEON accelerated ChaCha20 symmetric cipher"
+	depends on KERNEL_MODE_NEON
+	select CRYPTO_BLKCIPHER
+	select CRYPTO_CHACHA20
+
 endif

arch/arm64/crypto/Makefile

@@ -41,6 +41,9 @@ sha256-arm64-y := sha256-glue.o sha256-core.o
 obj-$(CONFIG_CRYPTO_SHA512_ARM64) += sha512-arm64.o
 sha512-arm64-y := sha512-glue.o sha512-core.o
 
+obj-$(CONFIG_CRYPTO_CHACHA20_NEON) += chacha20-neon.o
+chacha20-neon-y := chacha20-neon-core.o chacha20-neon-glue.o
+
 AFLAGS_aes-ce.o		:= -DINTERLEAVE=4
 AFLAGS_aes-neon.o	:= -DINTERLEAVE=4
 

arch/arm64/crypto/chacha20-neon-core.S

+/*
+ * ChaCha20 256-bit cipher algorithm, RFC7539, arm64 NEON functions
+ *
+ * Copyright (C) 2016 Linaro, Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Based on:
+ * ChaCha20 256-bit cipher algorithm, RFC7539, x64 SSSE3 functions
+ *
+ * Copyright (C) 2015 Martin Willi
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <linux/linkage.h>
+
+	.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]
+
+	mov		x3, #10
+
+.Ldoubleround:
+	// x0 += x1, x3 = rotl32(x3 ^ x0, 16)
+	add		v0.4s, v0.4s, v1.4s
+	eor		v3.16b, v3.16b, v0.16b
+	rev32		v3.8h, v3.8h
+
+	// x2 += x3, x1 = rotl32(x1 ^ x2, 12)
+	add		v2.4s, v2.4s, v3.4s
+	eor		v4.16b, v1.16b, v2.16b
+	shl		v1.4s, v4.4s, #12
+	sri		v1.4s, v4.4s, #20
+
+	// x0 += x1, x3 = rotl32(x3 ^ x0, 8)
+	add		v0.4s, v0.4s, v1.4s
+	eor		v3.16b, v3.16b, v0.16b
+	tbl		v3.16b, {v3.16b}, v12.16b
+
+	// x2 += x3, x1 = rotl32(x1 ^ x2, 7)
+	add		v2.4s, v2.4s, v3.4s
+	eor		v4.16b, v1.16b, v2.16b
+	shl		v1.4s, v4.4s, #7
+	sri		v1.4s, v4.4s, #25
+
+	// x1 = shuffle32(x1, MASK(0, 3, 2, 1))
+	ext		v1.16b, v1.16b, v1.16b, #4
+	// x2 = shuffle32(x2, MASK(1, 0, 3, 2))
+	ext		v2.16b, v2.16b, v2.16b, #8
+	// x3 = shuffle32(x3, MASK(2, 1, 0, 3))
+	ext		v3.16b, v3.16b, v3.16b, #12
+
+	// x0 += x1, x3 = rotl32(x3 ^ x0, 16)
+	add		v0.4s, v0.4s, v1.4s
+	eor		v3.16b, v3.16b, v0.16b
+	rev32		v3.8h, v3.8h
+
+	// x2 += x3, x1 = rotl32(x1 ^ x2, 12)
+	add		v2.4s, v2.4s, v3.4s
+	eor		v4.16b, v1.16b, v2.16b
+	shl		v1.4s, v4.4s, #12
+	sri		v1.4s, v4.4s, #20
+
+	// x0 += x1, x3 = rotl32(x3 ^ x0, 8)
+	add		v0.4s, v0.4s, v1.4s
+	eor		v3.16b, v3.16b, v0.16b
+	tbl		v3.16b, {v3.16b}, v12.16b
+
+	// x2 += x3, x1 = rotl32(x1 ^ x2, 7)
+	add		v2.4s, v2.4s, v3.4s
+	eor		v4.16b, v1.16b, v2.16b
+	shl		v1.4s, v4.4s, #7
+	sri		v1.4s, v4.4s, #25
+
+	// x1 = shuffle32(x1, MASK(2, 1, 0, 3))
+	ext		v1.16b, v1.16b, v1.16b, #12
+	// x2 = shuffle32(x2, MASK(1, 0, 3, 2))
+	ext		v2.16b, v2.16b, v2.16b, #8
+	// x3 = shuffle32(x3, MASK(0, 3, 2, 1))
+	ext		v3.16b, v3.16b, v3.16b, #4
+
+	subs		x3, x3, #1
+	b.ne		.Ldoubleround
+
+	ld1		{v4.16b-v7.16b}, [x2]
+
+	// o0 = i0 ^ (x0 + s0)
+	add		v0.4s, v0.4s, v8.4s
+	eor		v0.16b, v0.16b, v4.16b
+
+	// o1 = i1 ^ (x1 + s1)
+	add		v1.4s, v1.4s, v9.4s
+	eor		v1.16b, v1.16b, v5.16b
+
+	// o2 = i2 ^ (x2 + s2)
+	add		v2.4s, v2.4s, v10.4s
+	eor		v2.16b, v2.16b, v6.16b
+
+	// o3 = i3 ^ (x3 + s3)
+	add		v3.4s, v3.4s, v11.4s
+	eor		v3.16b, v3.16b, v7.16b
+
+	st1		{v0.16b-v3.16b}, [x1]
+
+	ret
+ENDPROC(chacha20_block_xor_neon)
+
+	.align		6
+ENTRY(chacha20_4block_xor_neon)
+	// x0: Input state matrix, s
+	// x1: 4 data blocks output, o
+	// x2: 4 data blocks input, i
+
+	//
+	// This function encrypts four consecutive ChaCha20 blocks by loading
+	// the state matrix in NEON registers four times. The algorithm performs
+	// each operation on the corresponding word of each state matrix, hence
+	// requires no word shuffling. For final XORing step we transpose the
+	// matrix by interleaving 32- and then 64-bit words, which allows us to
+	// do XOR in NEON registers.
+	//
+	adr		x3, CTRINC		// ... and ROT8
+	ld1		{v30.4s-v31.4s}, [x3]
+
+	// x0..15[0-3] = s0..3[0..3]
+	mov		x4, x0
+	ld4r		{ v0.4s- v3.4s}, [x4], #16
+	ld4r		{ v4.4s- v7.4s}, [x4], #16
+	ld4r		{ v8.4s-v11.4s}, [x4], #16
+	ld4r		{v12.4s-v15.4s}, [x4]
+
+	// x12 += counter values 0-3
+	add		v12.4s, v12.4s, v30.4s
+
+	mov		x3, #10
+
+.Ldoubleround4:
+	// x0 += x4, x12 = rotl32(x12 ^ x0, 16)
+	// x1 += x5, x13 = rotl32(x13 ^ x1, 16)
+	// x2 += x6, x14 = rotl32(x14 ^ x2, 16)
+	// x3 += x7, x15 = rotl32(x15 ^ x3, 16)
+	add		v0.4s, v0.4s, v4.4s
+	add		v1.4s, v1.4s, v5.4s
+	add		v2.4s, v2.4s, v6.4s
+	add		v3.4s, v3.4s, v7.4s
+
+	eor		v12.16b, v12.16b, v0.16b
+	eor		v13.16b, v13.16b, v1.16b
+	eor		v14.16b, v14.16b, v2.16b
+	eor		v15.16b, v15.16b, v3.16b
+
+	rev32		v12.8h, v12.8h
+	rev32		v13.8h, v13.8h
+	rev32		v14.8h, v14.8h
+	rev32		v15.8h, v15.8h
+
+	// x8 += x12, x4 = rotl32(x4 ^ x8, 12)
+	// x9 += x13, x5 = rotl32(x5 ^ x9, 12)
+	// x10 += x14, x6 = rotl32(x6 ^ x10, 12)
+	// x11 += x15, x7 = rotl32(x7 ^ x11, 12)
+	add		v8.4s, v8.4s, v12.4s
+	add		v9.4s, v9.4s, v13.4s
+	add		v10.4s, v10.4s, v14.4s
+	add		v11.4s, v11.4s, v15.4s
+
+	eor		v16.16b, v4.16b, v8.16b
+	eor		v17.16b, v5.16b, v9.16b
+	eor		v18.16b, v6.16b, v10.16b
+	eor		v19.16b, v7.16b, v11.16b
+
+	shl		v4.4s, v16.4s, #12
+	shl		v5.4s, v17.4s, #12
+	shl		v6.4s, v18.4s, #12
+	shl		v7.4s, v19.4s, #12
+
+	sri		v4.4s, v16.4s, #20
+	sri		v5.4s, v17.4s, #20
+	sri		v6.4s, v18.4s, #20
+	sri		v7.4s, v19.4s, #20
+
+	// x0 += x4, x12 = rotl32(x12 ^ x0, 8)
+	// x1 += x5, x13 = rotl32(x13 ^ x1, 8)
+	// x2 += x6, x14 = rotl32(x14 ^ x2, 8)
+	// x3 += x7, x15 = rotl32(x15 ^ x3, 8)
+	add		v0.4s, v0.4s, v4.4s
+	add		v1.4s, v1.4s, v5.4s
+	add		v2.4s, v2.4s, v6.4s
+	add		v3.4s, v3.4s, v7.4s
+
+	eor		v12.16b, v12.16b, v0.16b
+	eor		v13.16b, v13.16b, v1.16b
+	eor		v14.16b, v14.16b, v2.16b
+	eor		v15.16b, v15.16b, v3.16b
+
+	tbl		v12.16b, {v12.16b}, v31.16b
+	tbl		v13.16b, {v13.16b}, v31.16b
+	tbl		v14.16b, {v14.16b}, v31.16b
+	tbl		v15.16b, {v15.16b}, v31.16b
+
+	// x8 += x12, x4 = rotl32(x4 ^ x8, 7)
+	// x9 += x13, x5 = rotl32(x5 ^ x9, 7)
+	// x10 += x14, x6 = rotl32(x6 ^ x10, 7)
+	// x11 += x15, x7 = rotl32(x7 ^ x11, 7)
+	add		v8.4s, v8.4s, v12.4s
+	add		v9.4s, v9.4s, v13.4s
+	add		v10.4s, v10.4s, v14.4s
+	add		v11.4s, v11.4s, v15.4s
+
+	eor		v16.16b, v4.16b, v8.16b
+	eor		v17.16b, v5.16b, v9.16b
+	eor		v18.16b, v6.16b, v10.16b
+	eor		v19.16b, v7.16b, v11.16b
+
+	shl		v4.4s, v16.4s, #7
+	shl		v5.4s, v17.4s, #7
+	shl		v6.4s, v18.4s, #7
+	shl		v7.4s, v19.4s, #7
+
+	sri		v4.4s, v16.4s, #25
+	sri		v5.4s, v17.4s, #25
+	sri		v6.4s, v18.4s, #25
+	sri		v7.4s, v19.4s, #25
+
+	// x0 += x5, x15 = rotl32(x15 ^ x0, 16)
+	// x1 += x6, x12 = rotl32(x12 ^ x1, 16)
+	// x2 += x7, x13 = rotl32(x13 ^ x2, 16)
+	// x3 += x4, x14 = rotl32(x14 ^ x3, 16)
+	add		v0.4s, v0.4s, v5.4s
+	add		v1.4s, v1.4s, v6.4s
+	add		v2.4s, v2.4s, v7.4s
+	add		v3.4s, v3.4s, v4.4s
+
+	eor		v15.16b, v15.16b, v0.16b
+	eor		v12.16b, v12.16b, v1.16b
+	eor		v13.16b, v13.16b, v2.16b
+	eor		v14.16b, v14.16b, v3.16b
+
+	rev32		v15.8h, v15.8h
+	rev32		v12.8h, v12.8h
+	rev32		v13.8h, v13.8h
+	rev32		v14.8h, v14.8h
+
+	// x10 += x15, x5 = rotl32(x5 ^ x10, 12)
+	// x11 += x12, x6 = rotl32(x6 ^ x11, 12)
+	// x8 += x13, x7 = rotl32(x7 ^ x8, 12)
+	// x9 += x14, x4 = rotl32(x4 ^ x9, 12)
+	add		v10.4s, v10.4s, v15.4s
+	add		v11.4s, v11.4s, v12.4s
+	add		v8.4s, v8.4s, v13.4s
+	add		v9.4s, v9.4s, v14.4s
+
+	eor		v16.16b, v5.16b, v10.16b
+	eor		v17.16b, v6.16b, v11.16b
+	eor		v18.16b, v7.16b, v8.16b
+	eor		v19.16b, v4.16b, v9.16b
+
+	shl		v5.4s, v16.4s, #12
+	shl		v6.4s, v17.4s, #12
+	shl		v7.4s, v18.4s, #12
+	shl		v4.4s, v19.4s, #12
+
+	sri		v5.4s, v16.4s, #20
+	sri		v6.4s, v17.4s, #20
+	sri		v7.4s, v18.4s, #20
+	sri		v4.4s, v19.4s, #20
+
+	// x0 += x5, x15 = rotl32(x15 ^ x0, 8)
+	// x1 += x6, x12 = rotl32(x12 ^ x1, 8)
+	// x2 += x7, x13 = rotl32(x13 ^ x2, 8)
+	// x3 += x4, x14 = rotl32(x14 ^ x3, 8)
+	add		v0.4s, v0.4s, v5.4s
+	add		v1.4s, v1.4s, v6.4s
+	add		v2.4s, v2.4s, v7.4s
+	add		v3.4s, v3.4s, v4.4s
+
+	eor		v15.16b, v15.16b, v0.16b
+	eor		v12.16b, v12.16b, v1.16b
+	eor		v13.16b, v13.16b, v2.16b
+	eor		v14.16b, v14.16b, v3.16b
+
+	tbl		v15.16b, {v15.16b}, v31.16b
+	tbl		v12.16b, {v12.16b}, v31.16b
+	tbl		v13.16b, {v13.16b}, v31.16b
+	tbl		v14.16b, {v14.16b}, v31.16b
+
+	// x10 += x15, x5 = rotl32(x5 ^ x10, 7)
+	// x11 += x12, x6 = rotl32(x6 ^ x11, 7)
+	// x8 += x13, x7 = rotl32(x7 ^ x8, 7)
+	// x9 += x14, x4 = rotl32(x4 ^ x9, 7)
+	add		v10.4s, v10.4s, v15.4s
+	add		v11.4s, v11.4s, v12.4s
+	add		v8.4s, v8.4s, v13.4s
+	add		v9.4s, v9.4s, v14.4s
+
+	eor		v16.16b, v5.16b, v10.16b
+	eor		v17.16b, v6.16b, v11.16b
+	eor		v18.16b, v7.16b, v8.16b
+	eor		v19.16b, v4.16b, v9.16b
+
+	shl		v5.4s, v16.4s, #7
+	shl		v6.4s, v17.4s, #7
+	shl		v7.4s, v18.4s, #7
+	shl		v4.4s, v19.4s, #7
+
+	sri		v5.4s, v16.4s, #25
+	sri		v6.4s, v17.4s, #25
+	sri		v7.4s, v18.4s, #25
+	sri		v4.4s, v19.4s, #25
+
+	subs		x3, x3, #1
+	b.ne		.Ldoubleround4
+
+	ld4r		{v16.4s-v19.4s}, [x0], #16
+	ld4r		{v20.4s-v23.4s}, [x0], #16
+
+	// x12 += counter values 0-3
+	add		v12.4s, v12.4s, v30.4s
+
+	// x0[0-3] += s0[0]
+	// x1[0-3] += s0[1]
+	// x2[0-3] += s0[2]
+	// x3[0-3] += s0[3]
+	add		v0.4s, v0.4s, v16.4s
+	add		v1.4s, v1.4s, v17.4s
+	add		v2.4s, v2.4s, v18.4s
+	add		v3.4s, v3.4s, v19.4s
+
+	ld4r		{v24.4s-v27.4s}, [x0], #16
+	ld4r		{v28.4s-v31.4s}, [x0]
+
+	// x4[0-3] += s1[0]
+	// x5[0-3] += s1[1]
+	// x6[0-3] += s1[2]
+	// x7[0-3] += s1[3]
+	add		v4.4s, v4.4s, v20.4s
+	add		v5.4s, v5.4s, v21.4s
+	add		v6.4s, v6.4s, v22.4s
+	add		v7.4s, v7.4s, v23.4s
+
+	// x8[0-3] += s2[0]
+	// x9[0-3] += s2[1]
+	// x10[0-3] += s2[2]
+	// x11[0-3] += s2[3]
+	add		v8.4s, v8.4s, v24.4s
+	add		v9.4s, v9.4s, v25.4s
+	add		v10.4s, v10.4s, v26.4s
+	add		v11.4s, v11.4s, v27.4s
+
+	// x12[0-3] += s3[0]
+	// x13[0-3] += s3[1]
+	// x14[0-3] += s3[2]
+	// x15[0-3] += s3[3]
+	add		v12.4s, v12.4s, v28.4s
+	add		v13.4s, v13.4s, v29.4s
+	add		v14.4s, v14.4s, v30.4s
+	add		v15.4s, v15.4s, v31.4s
+
+	// interleave 32-bit words in state n, n+1
+	zip1		v16.4s, v0.4s, v1.4s
+	zip2		v17.4s, v0.4s, v1.4s
+	zip1		v18.4s, v2.4s, v3.4s
+	zip2		v19.4s, v2.4s, v3.4s
+	zip1		v20.4s, v4.4s, v5.4s
+	zip2		v21.4s, v4.4s, v5.4s
+	zip1		v22.4s, v6.4s, v7.4s
+	zip2		v23.4s, v6.4s, v7.4s
+	zip1		v24.4s, v8.4s, v9.4s
+	zip2		v25.4s, v8.4s, v9.4s
+	zip1		v26.4s, v10.4s, v11.4s
+	zip2		v27.4s, v10.4s, v11.4s
+	zip1		v28.4s, v12.4s, v13.4s
+	zip2		v29.4s, v12.4s, v13.4s
+	zip1		v30.4s, v14.4s, v15.4s
+	zip2		v31.4s, v14.4s, v15.4s
+
+	// interleave 64-bit words in state n, n+2
+	zip1		v0.2d, v16.2d, v18.2d
+	zip2		v4.2d, v16.2d, v18.2d
+	zip1		v8.2d, v17.2d, v19.2d
+	zip2		v12.2d, v17.2d, v19.2d
+	ld1		{v16.16b-v19.16b}, [x2], #64
+
+	zip1		v1.2d, v20.2d, v22.2d
+	zip2		v5.2d, v20.2d, v22.2d
+	zip1		v9.2d, v21.2d, v23.2d
+	zip2		v13.2d, v21.2d, v23.2d
+	ld1		{v20.16b-v23.16b}, [x2], #64
+
+	zip1		v2.2d, v24.2d, v26.2d
+	zip2		v6.2d, v24.2d, v26.2d
+	zip1		v10.2d, v25.2d, v27.2d
+	zip2		v14.2d, v25.2d, v27.2d
+	ld1		{v24.16b-v27.16b}, [x2], #64
+
+	zip1		v3.2d, v28.2d, v30.2d
+	zip2		v7.2d, v28.2d, v30.2d
+	zip1		v11.2d, v29.2d, v31.2d
+	zip2		v15.2d, v29.2d, v31.2d
+	ld1		{v28.16b-v31.16b}, [x2]
+
+	// xor with corresponding input, write to output
+	eor		v16.16b, v16.16b, v0.16b
+	eor		v17.16b, v17.16b, v1.16b
+	eor		v18.16b, v18.16b, v2.16b
+	eor		v19.16b, v19.16b, v3.16b
+	eor		v20.16b, v20.16b, v4.16b
+	eor		v21.16b, v21.16b, v5.16b
+	st1		{v16.16b-v19.16b}, [x1], #64
+	eor		v22.16b, v22.16b, v6.16b
+	eor		v23.16b, v23.16b, v7.16b
+	eor		v24.16b, v24.16b, v8.16b
+	eor		v25.16b, v25.16b, v9.16b
+	st1		{v20.16b-v23.16b}, [x1], #64
+	eor		v26.16b, v26.16b, v10.16b
+	eor		v27.16b, v27.16b, v11.16b
+	eor		v28.16b, v28.16b, v12.16b
+	st1		{v24.16b-v27.16b}, [x1], #64
+	eor		v29.16b, v29.16b, v13.16b
+	eor		v30.16b, v30.16b, v14.16b
+	eor		v31.16b, v31.16b, v15.16b
+	st1		{v28.16b-v31.16b}, [x1]
+
+	ret
+ENDPROC(chacha20_4block_xor_neon)
+
+CTRINC:	.word		0, 1, 2, 3
+ROT8:	.word		0x02010003, 0x06050407, 0x0a09080b, 0x0e0d0c0f

arch/arm64/crypto/chacha20-neon-glue.c

+/*
+ * ChaCha20 256-bit cipher algorithm, RFC7539, arm64 NEON functions
+ *
+ * Copyright (C) 2016 Linaro, Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * Based on:
+ * ChaCha20 256-bit cipher algorithm, RFC7539, SIMD glue code
+ *
+ * Copyright (C) 2015 Martin Willi
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <crypto/algapi.h>
+#include <crypto/chacha20.h>
+#include <crypto/internal/skcipher.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+#include <asm/hwcap.h>
+#include <asm/neon.h>
+
+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);
+
+static void chacha20_doneon(u32 *state, u8 *dst, const u8 *src,
+			    unsigned int bytes)
+{
+	u8 buf[CHACHA20_BLOCK_SIZE];
+
+	while (bytes >= CHACHA20_BLOCK_SIZE * 4) {
+		chacha20_4block_xor_neon(state, dst, src);
+		bytes -= CHACHA20_BLOCK_SIZE * 4;
+		src += CHACHA20_BLOCK_SIZE * 4;
+		dst += CHACHA20_BLOCK_SIZE * 4;
+		state[12] += 4;
+	}
+	while (bytes >= CHACHA20_BLOCK_SIZE) {
+		chacha20_block_xor_neon(state, dst, src);
+		bytes -= CHACHA20_BLOCK_SIZE;
+		src += CHACHA20_BLOCK_SIZE;
+		dst += CHACHA20_BLOCK_SIZE;
+		state[12]++;
+	}
+	if (bytes) {
+		memcpy(buf, src, bytes);
+		chacha20_block_xor_neon(state, buf, buf);
+		memcpy(dst, buf, bytes);
+	}
+}
+
+static int chacha20_neon(struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+	struct chacha20_ctx *ctx = crypto_skcipher_ctx(tfm);
+	struct skcipher_walk walk;
+	u32 state[16];
+	int err;
+
+	if (req->cryptlen <= CHACHA20_BLOCK_SIZE)
+		return crypto_chacha20_crypt(req);
+
+	err = skcipher_walk_virt(&walk, req, true);
+
+	crypto_chacha20_init(state, ctx, walk.iv);
+
+	kernel_neon_begin();
+	while (walk.nbytes > 0) {
+		unsigned int nbytes = walk.nbytes;
+
+		if (nbytes < walk.total)
+			nbytes = round_down(nbytes, walk.stride);
+
+		chacha20_doneon(state, walk.dst.virt.addr, walk.src.virt.addr,
+				nbytes);
+		err = skcipher_walk_done(&walk, walk.nbytes - nbytes);
+	}
+	kernel_neon_end();
+
+	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 chacha20_ctx),
+	.base.cra_alignmask	= 1,
+	.base.cra_module	= THIS_MODULE,
+
+	.min_keysize		= CHACHA20_KEY_SIZE,
+	.max_keysize		= CHACHA20_KEY_SIZE,
+	.ivsize			= CHACHA20_IV_SIZE,
+	.chunksize		= CHACHA20_BLOCK_SIZE,
+	.walksize		= 4 * CHACHA20_BLOCK_SIZE,
+	.setkey			= crypto_chacha20_setkey,
+	.encrypt		= chacha20_neon,
+	.decrypt		= chacha20_neon,
+};
+
+static int __init chacha20_simd_mod_init(void)
+{
+	if (!(elf_hwcap & HWCAP_ASIMD))
+		return -ENODEV;
+
+	return crypto_register_skcipher(&alg);
+}
+
+static void __exit chacha20_simd_mod_fini(void)
+{
+	crypto_unregister_skcipher(&alg);
+}
+
+module_init(chacha20_simd_mod_init);
+module_exit(chacha20_simd_mod_fini);
+
+MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS_CRYPTO("chacha20");