[RFC PATCH 20/20] crypto: arm/ghash - provide a synchronous version

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

GHASH is used by the GCM mode, which is often used in contexts where
only synchronous ciphers are permitted. So provide a synchronous version
of GHASH based on the existing code. This requires a non-SIMD fallback
to deal with invocations occurring from a context where SIMD instructions
may not be used.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/arm/crypto/ghash-ce-glue.c | 78 +++++++++++++-------
 1 file changed, 52 insertions(+), 26 deletions(-)

diff --git a/arch/arm/crypto/ghash-ce-glue.c b/arch/arm/crypto/ghash-ce-glue.c
index 39d1ccec1aab..ebb237ca874b 100644
--- a/arch/arm/crypto/ghash-ce-glue.c
+++ b/arch/arm/crypto/ghash-ce-glue.c
@@ -12,6 +12,7 @@
 #include <asm/neon.h>
 #include <asm/simd.h>
 #include <asm/unaligned.h>
+#include <crypto/b128ops.h>
 #include <crypto/cryptd.h>
 #include <crypto/internal/hash.h>
 #include <crypto/internal/simd.h>
@@ -33,6 +34,8 @@ struct ghash_key {
 	u64	h2[2];
 	u64	h3[2];
 	u64	h4[2];
+
+	be128	k;
 };
 
 struct ghash_desc_ctx {
@@ -65,6 +68,36 @@ static int ghash_init(struct shash_desc *desc)
 	return 0;
 }
 
+static void ghash_do_update(int blocks, u64 dg[], const char *src,
+			    struct ghash_key *key, const char *head)
+{
+	if (likely(crypto_simd_usable())) {
+		kernel_neon_begin();
+		pmull_ghash_update(blocks, dg, src, key, head);
+		kernel_neon_end();
+	} else {
+		be128 dst = { cpu_to_be64(dg[1]), cpu_to_be64(dg[0]) };
+
+		do {
+			const u8 *in = src;
+
+			if (head) {
+				in = head;
+				blocks++;
+				head = NULL;
+			} else {
+				src += GHASH_BLOCK_SIZE;
+			}
+
+			crypto_xor((u8 *)&dst, in, GHASH_BLOCK_SIZE);
+			gf128mul_lle(&dst, &key->k);
+		} while (--blocks);
+
+		dg[0] = be64_to_cpu(dst.b);
+		dg[1] = be64_to_cpu(dst.a);
+	}
+}
+
 static int ghash_update(struct shash_desc *desc, const u8 *src,
 			unsigned int len)
 {
@@ -88,10 +121,8 @@ static int ghash_update(struct shash_desc *desc, const u8 *src,
 		blocks = len / GHASH_BLOCK_SIZE;
 		len %= GHASH_BLOCK_SIZE;
 
-		kernel_neon_begin();
-		pmull_ghash_update(blocks, ctx->digest, src, key,
-				   partial ? ctx->buf : NULL);
-		kernel_neon_end();
+		ghash_do_update(blocks, ctx->digest, src, key,
+				partial ? ctx->buf : NULL);
 		src += blocks * GHASH_BLOCK_SIZE;
 		partial = 0;
 	}
@@ -109,9 +140,7 @@ static int ghash_final(struct shash_desc *desc, u8 *dst)
 		struct ghash_key *key = crypto_shash_ctx(desc->tfm);
 
 		memset(ctx->buf + partial, 0, GHASH_BLOCK_SIZE - partial);
-		kernel_neon_begin();
-		pmull_ghash_update(1, ctx->digest, ctx->buf, key, NULL);
-		kernel_neon_end();
+		ghash_do_update(1, ctx->digest, ctx->buf, key, NULL);
 	}
 	put_unaligned_be64(ctx->digest[1], dst);
 	put_unaligned_be64(ctx->digest[0], dst + 8);
@@ -135,24 +164,25 @@ static int ghash_setkey(struct crypto_shash *tfm,
 			const u8 *inkey, unsigned int keylen)
 {
 	struct ghash_key *key = crypto_shash_ctx(tfm);
-	be128 h, k;
+	be128 h;
 
 	if (keylen != GHASH_BLOCK_SIZE) {
 		crypto_shash_set_flags(tfm, CRYPTO_TFM_RES_BAD_KEY_LEN);
 		return -EINVAL;
 	}
 
-	memcpy(&k, inkey, GHASH_BLOCK_SIZE);
-	ghash_reflect(key->h, &k);
+	/* needed for the fallback */
+	memcpy(&key->k, inkey, GHASH_BLOCK_SIZE);
+	ghash_reflect(key->h, &key->k);
 
-	h = k;
-	gf128mul_lle(&h, &k);
+	h = key->k;
+	gf128mul_lle(&h, &key->k);
 	ghash_reflect(key->h2, &h);
 
-	gf128mul_lle(&h, &k);
+	gf128mul_lle(&h, &key->k);
 	ghash_reflect(key->h3, &h);
 
-	gf128mul_lle(&h, &k);
+	gf128mul_lle(&h, &key->k);
 	ghash_reflect(key->h4, &h);
 
 	return 0;
@@ -165,15 +195,13 @@ static struct shash_alg ghash_alg = {
 	.final			= ghash_final,
 	.setkey			= ghash_setkey,
 	.descsize		= sizeof(struct ghash_desc_ctx),
-	.base			= {
-		.cra_name	= "__ghash",
-		.cra_driver_name = "__driver-ghash-ce",
-		.cra_priority	= 0,
-		.cra_flags	= CRYPTO_ALG_INTERNAL,
-		.cra_blocksize	= GHASH_BLOCK_SIZE,
-		.cra_ctxsize	= sizeof(struct ghash_key),
-		.cra_module	= THIS_MODULE,
-	},
+
+	.base.cra_name		= "ghash",
+	.base.cra_driver_name	= "ghash-ce-sync",
+	.base.cra_priority	= 300 - 1,
+	.base.cra_blocksize	= GHASH_BLOCK_SIZE,
+	.base.cra_ctxsize	= sizeof(struct ghash_key),
+	.base.cra_module	= THIS_MODULE,
 };
 
 static int ghash_async_init(struct ahash_request *req)
@@ -288,9 +316,7 @@ static int ghash_async_init_tfm(struct crypto_tfm *tfm)
 	struct cryptd_ahash *cryptd_tfm;
 	struct ghash_async_ctx *ctx = crypto_tfm_ctx(tfm);
 
-	cryptd_tfm = cryptd_alloc_ahash("__driver-ghash-ce",
-					CRYPTO_ALG_INTERNAL,
-					CRYPTO_ALG_INTERNAL);
+	cryptd_tfm = cryptd_alloc_ahash("ghash-ce-sync", 0, 0);
 	if (IS_ERR(cryptd_tfm))
 		return PTR_ERR(cryptd_tfm);
 	ctx->cryptd_tfm = cryptd_tfm;
-- 
2.20.1