From 5fb6a3ba3af6aff7cdc53d319fc4cc6f79555ca1 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Tue, 11 Jan 2022 14:37:41 +0100
Subject: lib/crypto: blake2s: move hmac construction into wireguard

commit d8d83d8ab0a453e17e68b3a3bed1f940c34b8646 upstream.

Basically nobody should use blake2s in an HMAC construction; it already
has a keyed variant. But unfortunately for historical reasons, Noise,
used by WireGuard, uses HKDF quite strictly, which means we have to use
this. Because this really shouldn't be used by others, this commit moves
it into wireguard's noise.c locally, so that kernels that aren't using
WireGuard don't get this superfluous code baked in. On m68k systems,
this shaves off ~314 bytes.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/wireguard/noise.c | 45 ++++++++++++++++++++++++++++++-----
 include/crypto/blake2s.h      |  3 ---
 lib/crypto/blake2s-selftest.c | 31 ------------------------
 lib/crypto/blake2s.c          | 37 ----------------------------
 4 files changed, 39 insertions(+), 77 deletions(-)

--- a/drivers/net/wireguard/noise.c
+++ b/drivers/net/wireguard/noise.c
@@ -302,6 +302,41 @@ void wg_noise_set_static_identity_privat
 		static_identity->static_public, private_key);
 }
 
+static void hmac(u8 *out, const u8 *in, const u8 *key, const size_t inlen, const size_t keylen)
+{
+	struct blake2s_state state;
+	u8 x_key[BLAKE2S_BLOCK_SIZE] __aligned(__alignof__(u32)) = { 0 };
+	u8 i_hash[BLAKE2S_HASH_SIZE] __aligned(__alignof__(u32));
+	int i;
+
+	if (keylen > BLAKE2S_BLOCK_SIZE) {
+		blake2s_init(&state, BLAKE2S_HASH_SIZE);
+		blake2s_update(&state, key, keylen);
+		blake2s_final(&state, x_key);
+	} else
+		memcpy(x_key, key, keylen);
+
+	for (i = 0; i < BLAKE2S_BLOCK_SIZE; ++i)
+		x_key[i] ^= 0x36;
+
+	blake2s_init(&state, BLAKE2S_HASH_SIZE);
+	blake2s_update(&state, x_key, BLAKE2S_BLOCK_SIZE);
+	blake2s_update(&state, in, inlen);
+	blake2s_final(&state, i_hash);
+
+	for (i = 0; i < BLAKE2S_BLOCK_SIZE; ++i)
+		x_key[i] ^= 0x5c ^ 0x36;
+
+	blake2s_init(&state, BLAKE2S_HASH_SIZE);
+	blake2s_update(&state, x_key, BLAKE2S_BLOCK_SIZE);
+	blake2s_update(&state, i_hash, BLAKE2S_HASH_SIZE);
+	blake2s_final(&state, i_hash);
+
+	memcpy(out, i_hash, BLAKE2S_HASH_SIZE);
+	memzero_explicit(x_key, BLAKE2S_BLOCK_SIZE);
+	memzero_explicit(i_hash, BLAKE2S_HASH_SIZE);
+}
+
 /* This is Hugo Krawczyk's HKDF:
  *  - https://eprint.iacr.org/2010/264.pdf
  *  - https://tools.ietf.org/html/rfc5869
@@ -322,14 +357,14 @@ static void kdf(u8 *first_dst, u8 *secon
 		 ((third_len || third_dst) && (!second_len || !second_dst))));
 
 	/* Extract entropy from data into secret */
-	blake2s256_hmac(secret, data, chaining_key, data_len, NOISE_HASH_LEN);
+	hmac(secret, data, chaining_key, data_len, NOISE_HASH_LEN);
 
 	if (!first_dst || !first_len)
 		goto out;
 
 	/* Expand first key: key = secret, data = 0x1 */
 	output[0] = 1;
-	blake2s256_hmac(output, output, secret, 1, BLAKE2S_HASH_SIZE);
+	hmac(output, output, secret, 1, BLAKE2S_HASH_SIZE);
 	memcpy(first_dst, output, first_len);
 
 	if (!second_dst || !second_len)
@@ -337,8 +372,7 @@ static void kdf(u8 *first_dst, u8 *secon
 
 	/* Expand second key: key = secret, data = first-key || 0x2 */
 	output[BLAKE2S_HASH_SIZE] = 2;
-	blake2s256_hmac(output, output, secret, BLAKE2S_HASH_SIZE + 1,
-			BLAKE2S_HASH_SIZE);
+	hmac(output, output, secret, BLAKE2S_HASH_SIZE + 1, BLAKE2S_HASH_SIZE);
 	memcpy(second_dst, output, second_len);
 
 	if (!third_dst || !third_len)
@@ -346,8 +380,7 @@ static void kdf(u8 *first_dst, u8 *secon
 
 	/* Expand third key: key = secret, data = second-key || 0x3 */
 	output[BLAKE2S_HASH_SIZE] = 3;
-	blake2s256_hmac(output, output, secret, BLAKE2S_HASH_SIZE + 1,
-			BLAKE2S_HASH_SIZE);
+	hmac(output, output, secret, BLAKE2S_HASH_SIZE + 1, BLAKE2S_HASH_SIZE);
 	memcpy(third_dst, output, third_len);
 
 out: