crypto: arm/chacha - expose ARM ChaCha routine as library function

Expose the accelerated NEON ChaCha routine directly as a symbol
export so that users of the ChaCha library API can use it directly.

Given that calls into the library API will always go through the
routines in this module if it is enabled, switch to static keys
to select the optimal implementation available (which may be none
at all, in which case we defer to the generic implementation for
all invocations).
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/arm/crypto/Kconfig

@@ -130,6 +130,7 @@ config CRYPTO_CRC32_ARM_CE
 config CRYPTO_CHACHA20_NEON
 	tristate "NEON and scalar accelerated ChaCha stream cipher algorithms"
 	select CRYPTO_SKCIPHER
+	select CRYPTO_ARCH_HAVE_LIB_CHACHA
 
 config CRYPTO_NHPOLY1305_NEON
 	tristate "NEON accelerated NHPoly1305 hash function (for Adiantum)"

arch/arm/crypto/chacha-glue.c

@@ -11,6 +11,7 @@
 #include <crypto/internal/chacha.h>
 #include <crypto/internal/simd.h>
 #include <crypto/internal/skcipher.h>
+#include <linux/jump_label.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 
@@ -29,9 +30,11 @@ asmlinkage void hchacha_block_neon(const u32 *state, u32 *out, int nrounds);
 asmlinkage void chacha_doarm(u8 *dst, const u8 *src, unsigned int bytes,
 			     const u32 *state, int nrounds);
 
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(use_neon);
+
 static inline bool neon_usable(void)
 {
-	return crypto_simd_usable();
+	return static_branch_likely(&use_neon) && crypto_simd_usable();
 }
 
 static void chacha_doneon(u32 *state, u8 *dst, const u8 *src,
@@ -60,6 +63,40 @@ static void chacha_doneon(u32 *state, u8 *dst, const u8 *src,
 	}
 }
 
+void hchacha_block_arch(const u32 *state, u32 *stream, int nrounds)
+{
+	if (!IS_ENABLED(CONFIG_KERNEL_MODE_NEON) || !neon_usable()) {
+		hchacha_block_arm(state, stream, nrounds);
+	} else {
+		kernel_neon_begin();
+		hchacha_block_neon(state, stream, nrounds);
+		kernel_neon_end();
+	}
+}
+EXPORT_SYMBOL(hchacha_block_arch);
+
+void chacha_init_arch(u32 *state, const u32 *key, const u8 *iv)
+{
+	chacha_init_generic(state, key, iv);
+}
+EXPORT_SYMBOL(chacha_init_arch);
+
+void chacha_crypt_arch(u32 *state, u8 *dst, const u8 *src, unsigned int bytes,
+		       int nrounds)
+{
+	if (!IS_ENABLED(CONFIG_KERNEL_MODE_NEON) || !neon_usable() ||
+	    bytes <= CHACHA_BLOCK_SIZE) {
+		chacha_doarm(dst, src, bytes, state, nrounds);
+		state[12] += DIV_ROUND_UP(bytes, CHACHA_BLOCK_SIZE);
+		return;
+	}
+
+	kernel_neon_begin();
+	chacha_doneon(state, dst, src, bytes, nrounds);
+	kernel_neon_end();
+}
+EXPORT_SYMBOL(chacha_crypt_arch);
+
 static int chacha_stream_xor(struct skcipher_request *req,
 			     const struct chacha_ctx *ctx, const u8 *iv,
 			     bool neon)
@@ -269,6 +306,8 @@ static int __init chacha_simd_mod_init(void)
 			for (i = 0; i < ARRAY_SIZE(neon_algs); i++)
 				neon_algs[i].base.cra_priority = 0;
 			break;
+		default:
+			static_branch_enable(&use_neon);
 		}
 
 		err = crypto_register_skciphers(neon_algs, ARRAY_SIZE(neon_algs));