Re: [PATCH 12/12] RISC-V: crypto: add Zvkb accelerated ChaCha20 implementation

[Eric Biggers]

On Thu, Oct 26, 2023 at 02:36:44AM +0800, Jerry Shih wrote:
> diff --git a/arch/riscv/crypto/chacha-riscv64-glue.c b/arch/riscv/crypto/chacha-riscv64-glue.c
> new file mode 100644
> index 000000000000..72011949f705
> --- /dev/null
> +++ b/arch/riscv/crypto/chacha-riscv64-glue.c
> @@ -0,0 +1,120 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Port of the OpenSSL ChaCha20 implementation for RISC-V 64
> + *
> + * Copyright (C) 2023 SiFive, Inc.
> + * Author: Jerry Shih <jerry.shih@xxxxxxxxxx>
> + */
> +
> +#include <asm/simd.h>
> +#include <asm/vector.h>
> +#include <crypto/internal/chacha.h>
> +#include <crypto/internal/simd.h>
> +#include <crypto/internal/skcipher.h>
> +#include <linux/crypto.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +
> +#define CHACHA_BLOCK_VALID_SIZE_MASK (~(CHACHA_BLOCK_SIZE - 1))
> +#define CHACHA_BLOCK_REMAINING_SIZE_MASK (CHACHA_BLOCK_SIZE - 1)
> +#define CHACHA_KEY_OFFSET 4
> +#define CHACHA_IV_OFFSET 12
> +
> +/* chacha20 using zvkb vector crypto extension */
> +void ChaCha20_ctr32_zvkb(u8 *out, const u8 *input, size_t len, const u32 *key,
> +			 const u32 *counter);
> +
> +static int chacha20_encrypt(struct skcipher_request *req)
> +{
> +	u32 state[CHACHA_STATE_WORDS];

This function doesn't need to create the whole state matrix on the stack, since
the underlying assembly function takes as input the key and counter, not the
state matrix.  I recommend something like the following:

diff --git a/arch/riscv/crypto/chacha-riscv64-glue.c b/arch/riscv/crypto/chacha-riscv64-glue.c
index df185d0663fcc..216b4cd9d1e01 100644
--- a/arch/riscv/crypto/chacha-riscv64-glue.c
+++ b/arch/riscv/crypto/chacha-riscv64-glue.c
@@ -16,45 +16,42 @@
 #include <linux/module.h>
 #include <linux/types.h>
 
-#define CHACHA_KEY_OFFSET 4
-#define CHACHA_IV_OFFSET 12
-
 /* chacha20 using zvkb vector crypto extension */
 asmlinkage void ChaCha20_ctr32_zvkb(u8 *out, const u8 *input, size_t len,
 				    const u32 *key, const u32 *counter);
 
 static int chacha20_encrypt(struct skcipher_request *req)
 {
-	u32 state[CHACHA_STATE_WORDS];
 	u8 block_buffer[CHACHA_BLOCK_SIZE];
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	const struct chacha_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct skcipher_walk walk;
 	unsigned int nbytes;
 	unsigned int tail_bytes;
+	u32 iv[4];
 	int err;
 
-	chacha_init_generic(state, ctx->key, req->iv);
+	iv[0] = get_unaligned_le32(req->iv);
+	iv[1] = get_unaligned_le32(req->iv + 4);
+	iv[2] = get_unaligned_le32(req->iv + 8);
+	iv[3] = get_unaligned_le32(req->iv + 12);
 
 	err = skcipher_walk_virt(&walk, req, false);
 	while (walk.nbytes) {
-		nbytes = walk.nbytes & (~(CHACHA_BLOCK_SIZE - 1));
+		nbytes = walk.nbytes & ~(CHACHA_BLOCK_SIZE - 1);
 		tail_bytes = walk.nbytes & (CHACHA_BLOCK_SIZE - 1);
 		kernel_vector_begin();
 		if (nbytes) {
 			ChaCha20_ctr32_zvkb(walk.dst.virt.addr,
 					    walk.src.virt.addr, nbytes,
-					    state + CHACHA_KEY_OFFSET,
-					    state + CHACHA_IV_OFFSET);
-			state[CHACHA_IV_OFFSET] += nbytes / CHACHA_BLOCK_SIZE;
+					    ctx->key, iv);
+			iv[0] += nbytes / CHACHA_BLOCK_SIZE;
 		}
 		if (walk.nbytes == walk.total && tail_bytes > 0) {
 			memcpy(block_buffer, walk.src.virt.addr + nbytes,
 			       tail_bytes);
 			ChaCha20_ctr32_zvkb(block_buffer, block_buffer,
-					    CHACHA_BLOCK_SIZE,
-					    state + CHACHA_KEY_OFFSET,
-					    state + CHACHA_IV_OFFSET);
+					    CHACHA_BLOCK_SIZE, ctx->key, iv);
 			memcpy(walk.dst.virt.addr + nbytes, block_buffer,
 			       tail_bytes);
 			tail_bytes = 0;