crypto: arm/chacha - add XChaCha12 support

Now that the 32-bit ARM NEON implementation of ChaCha20 and XChaCha20
has been refactored to support varying the number of rounds, add support
for XChaCha12.  This is identical to XChaCha20 except for the number of
rounds, which is 12 instead of 20.

XChaCha12 is faster than XChaCha20 but has a lower security margin,
though still greater than AES-256's since the best known attacks make it
through only 7 rounds.  See the patch "crypto: chacha - add XChaCha12
support" for more details about why we need XChaCha12 support.
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/arm/crypto/Kconfig

@@ -126,7 +126,7 @@ config CRYPTO_CRC32_ARM_CE
 	select CRYPTO_HASH
 
 config CRYPTO_CHACHA20_NEON
-	tristate "NEON accelerated ChaCha20 stream cipher algorithms"
+	tristate "NEON accelerated ChaCha stream cipher algorithms"
 	depends on KERNEL_MODE_NEON
 	select CRYPTO_BLKCIPHER
 	select CRYPTO_CHACHA20

arch/arm/crypto/chacha-neon-glue.c

 /*
- * ChaCha20 (RFC7539) and XChaCha20 stream ciphers, NEON accelerated
+ * ARM NEON accelerated ChaCha and XChaCha stream ciphers,
+ * including ChaCha20 (RFC7539)
  *
  * Copyright (C) 2016 Linaro, Ltd. <ard.biesheuvel@linaro.org>
  *
@@ -154,6 +155,22 @@ static struct skcipher_alg algs[] = {
 		.setkey			= crypto_chacha20_setkey,
 		.encrypt		= xchacha_neon,
 		.decrypt		= xchacha_neon,
+	}, {
+		.base.cra_name		= "xchacha12",
+		.base.cra_driver_name	= "xchacha12-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_chacha12_setkey,
+		.encrypt		= xchacha_neon,
+		.decrypt		= xchacha_neon,
 	}
 };
 
@@ -180,3 +197,5 @@ MODULE_ALIAS_CRYPTO("chacha20");
 MODULE_ALIAS_CRYPTO("chacha20-neon");
 MODULE_ALIAS_CRYPTO("xchacha20");
 MODULE_ALIAS_CRYPTO("xchacha20-neon");
+MODULE_ALIAS_CRYPTO("xchacha12");
+MODULE_ALIAS_CRYPTO("xchacha12-neon");