wireguard: global: add __nonstring annotations for unterminated strings

When a character array without a terminating NUL character has a static
initializer, GCC 15's -Wunterminated-string-initialization will only
warn if the array lacks the "nonstring" attribute[1]. Mark the arrays
with __nonstring to correctly identify the char array as "not a C string"
and thereby eliminate the warning:

../drivers/net/wireguard/cookie.c:29:56: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (9 chars into 8 available) [-Wunterminated-string-initialization]
   29 | static const u8 mac1_key_label[COOKIE_KEY_LABEL_LEN] = "mac1----";
      |                                                        ^~~~~~~~~~
../drivers/net/wireguard/cookie.c:30:58: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (9 chars into 8 available) [-Wunterminated-string-initialization]
   30 | static const u8 cookie_key_label[COOKIE_KEY_LABEL_LEN] = "cookie--";
      |                                                          ^~~~~~~~~~
../drivers/net/wireguard/noise.c:28:38: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (38 chars into 37 available) [-Wunterminated-string-initialization]
   28 | static const u8 handshake_name[37] = "Noise_IKpsk2_25519_ChaChaPoly_BLAKE2s";
      |                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/net/wireguard/noise.c:29:39: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (35 chars into 34 available) [-Wunterminated-string-initialization]
   29 | static const u8 identifier_name[34] = "WireGuard v1 zx2c4 Jason@zx2c4.com";
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The arrays are always used with their fixed size, so use __nonstring.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20250521212707.1767879-3-Jason@zx2c4.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: kees

drivers/net/wireguard/cookie.c

@@ -26,8 +26,8 @@ void wg_cookie_checker_init(struct cookie_checker *checker,
 }
 
 enum { COOKIE_KEY_LABEL_LEN = 8 };
-static const u8 mac1_key_label[COOKIE_KEY_LABEL_LEN] = "mac1----";
-static const u8 cookie_key_label[COOKIE_KEY_LABEL_LEN] = "cookie--";
+static const u8 mac1_key_label[COOKIE_KEY_LABEL_LEN] __nonstring = "mac1----";
+static const u8 cookie_key_label[COOKIE_KEY_LABEL_LEN] __nonstring = "cookie--";
 
 static void precompute_key(u8 key[NOISE_SYMMETRIC_KEY_LEN],
 			   const u8 pubkey[NOISE_PUBLIC_KEY_LEN],

drivers/net/wireguard/noise.c

@@ -25,8 +25,8 @@
  * <- e, ee, se, psk, {}
  */
 
-static const u8 handshake_name[37] = "Noise_IKpsk2_25519_ChaChaPoly_BLAKE2s";
-static const u8 identifier_name[34] = "WireGuard v1 zx2c4 Jason@zx2c4.com";
+static const u8 handshake_name[37] __nonstring = "Noise_IKpsk2_25519_ChaChaPoly_BLAKE2s";
+static const u8 identifier_name[34] __nonstring = "WireGuard v1 zx2c4 Jason@zx2c4.com";
 static u8 handshake_init_hash[NOISE_HASH_LEN] __ro_after_init;
 static u8 handshake_init_chaining_key[NOISE_HASH_LEN] __ro_after_init;
 static atomic64_t keypair_counter = ATOMIC64_INIT(0);