crypto: riscv - add vector crypto accelerated ChaCha20

Add an implementation of ChaCha20 using the Zvkb extension.  The
assembly code is derived from OpenSSL code (openssl/openssl#21923) that
was dual-licensed so that it could be reused in the kernel.
Nevertheless, the assembly has been significantly reworked for
integration with the kernel, for example by using a regular .S file
instead of the so-called perlasm, using the assembler instead of bare
'.inst', and reducing code duplication.

Signed-off-by: Jerry Shih <jerry.shih@sifive.com>
Co-developed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>

arch/riscv/crypto/Kconfig

@@ -18,4 +18,15 @@ config CRYPTO_AES_RISCV64
 	  - Zvkb vector crypto extension (CTR)
 	  - Zvkg vector crypto extension (XTS)
 
+config CRYPTO_CHACHA_RISCV64
+	tristate "Ciphers: ChaCha"
+	depends on 64BIT && RISCV_ISA_V && TOOLCHAIN_HAS_VECTOR_CRYPTO
+	select CRYPTO_SKCIPHER
+	select CRYPTO_LIB_CHACHA_GENERIC
+	help
+	  Length-preserving ciphers: ChaCha20 stream cipher algorithm
+
+	  Architecture: riscv64 using:
+	  - Zvkb vector crypto extension
+
 endmenu

arch/riscv/crypto/Makefile

@@ -3,3 +3,6 @@
 obj-$(CONFIG_CRYPTO_AES_RISCV64) += aes-riscv64.o
 aes-riscv64-y := aes-riscv64-glue.o aes-riscv64-zvkned.o \
 		 aes-riscv64-zvkned-zvbb-zvkg.o aes-riscv64-zvkned-zvkb.o
+
+obj-$(CONFIG_CRYPTO_CHACHA_RISCV64) += chacha-riscv64.o
+chacha-riscv64-y := chacha-riscv64-glue.o chacha-riscv64-zvkb.o

arch/riscv/crypto/chacha-riscv64-glue.c

@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ChaCha20 using the RISC-V vector crypto extensions
+ *
+ * Copyright (C) 2023 SiFive, Inc.
+ * Author: Jerry Shih <jerry.shih@sifive.com>
+ */
+
+#include <asm/simd.h>
+#include <asm/vector.h>
+#include <crypto/internal/chacha.h>
+#include <crypto/internal/skcipher.h>
+#include <linux/linkage.h>
+#include <linux/module.h>
+
+asmlinkage void chacha20_zvkb(const u32 key[8], const u8 *in, u8 *out,
+			      size_t len, const u32 iv[4]);
+
+static int riscv64_chacha20_crypt(struct skcipher_request *req)
+{
+	u32 iv[CHACHA_IV_SIZE / sizeof(u32)];
+	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;
+	int err;
+
+	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);
+		tail_bytes = walk.nbytes & (CHACHA_BLOCK_SIZE - 1);
+		kernel_vector_begin();
+		if (nbytes) {
+			chacha20_zvkb(ctx->key, walk.src.virt.addr,
+				      walk.dst.virt.addr, nbytes, 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_zvkb(ctx->key, block_buffer, block_buffer,
+				      CHACHA_BLOCK_SIZE, iv);
+			memcpy(walk.dst.virt.addr + nbytes, block_buffer,
+			       tail_bytes);
+			tail_bytes = 0;
+		}
+		kernel_vector_end();
+
+		err = skcipher_walk_done(&walk, tail_bytes);
+	}
+
+	return err;
+}
+
+static struct skcipher_alg riscv64_chacha_alg = {
+	.setkey = chacha20_setkey,
+	.encrypt = riscv64_chacha20_crypt,
+	.decrypt = riscv64_chacha20_crypt,
+	.min_keysize = CHACHA_KEY_SIZE,
+	.max_keysize = CHACHA_KEY_SIZE,
+	.ivsize = CHACHA_IV_SIZE,
+	.chunksize = CHACHA_BLOCK_SIZE,
+	.walksize = 4 * CHACHA_BLOCK_SIZE,
+	.base = {
+		.cra_blocksize = 1,
+		.cra_ctxsize = sizeof(struct chacha_ctx),
+		.cra_priority = 300,
+		.cra_name = "chacha20",
+		.cra_driver_name = "chacha20-riscv64-zvkb",
+		.cra_module = THIS_MODULE,
+	},
+};
+
+static int __init riscv64_chacha_mod_init(void)
+{
+	if (riscv_isa_extension_available(NULL, ZVKB) &&
+	    riscv_vector_vlen() >= 128)
+		return crypto_register_skcipher(&riscv64_chacha_alg);
+
+	return -ENODEV;
+}
+
+static void __exit riscv64_chacha_mod_exit(void)
+{
+	crypto_unregister_skcipher(&riscv64_chacha_alg);
+}
+
+module_init(riscv64_chacha_mod_init);
+module_exit(riscv64_chacha_mod_exit);
+
+MODULE_DESCRIPTION("ChaCha20 (RISC-V accelerated)");
+MODULE_AUTHOR("Jerry Shih <jerry.shih@sifive.com>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_CRYPTO("chacha20");