linux-kernel - [PATCH 2/6] lib/crypto: curve25519: Add at_least decoration to fixed-size array params

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Message-ID: <20251122194206.31822-3-ebiggers@kernel.org>
Date: Sat, 22 Nov 2025 11:42:02 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: linux-crypto@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Ard Biesheuvel <ardb@...nel.org>,
	"Jason A . Donenfeld" <Jason@...c4.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-hardening@...r.kernel.org,
	Kees Cook <kees@...nel.org>,
	Eric Biggers <ebiggers@...nel.org>
Subject: [PATCH 2/6] lib/crypto: curve25519: Add at_least decoration to fixed-size array params

Add the at_least (i.e. 'static') decoration to the fixed-size array
parameters of the curve25519 library functions.  This causes clang to
warn when a too-small array of known size is passed.

Signed-off-by: Eric Biggers <ebiggers@...nel.org>
---
 include/crypto/curve25519.h | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/include/crypto/curve25519.h b/include/crypto/curve25519.h
index db63a5577c00..2362b48f8741 100644
--- a/include/crypto/curve25519.h
+++ b/include/crypto/curve25519.h
@@ -11,28 +11,32 @@
 
 enum curve25519_lengths {
 	CURVE25519_KEY_SIZE = 32
 };
 
-void curve25519_generic(u8 out[CURVE25519_KEY_SIZE],
-			const u8 scalar[CURVE25519_KEY_SIZE],
-			const u8 point[CURVE25519_KEY_SIZE]);
+void curve25519_generic(u8 out[at_least CURVE25519_KEY_SIZE],
+			const u8 scalar[at_least CURVE25519_KEY_SIZE],
+			const u8 point[at_least CURVE25519_KEY_SIZE]);
 
-bool __must_check curve25519(u8 mypublic[CURVE25519_KEY_SIZE],
-			     const u8 secret[CURVE25519_KEY_SIZE],
-			     const u8 basepoint[CURVE25519_KEY_SIZE]);
+bool __must_check
+curve25519(u8 mypublic[at_least CURVE25519_KEY_SIZE],
+	   const u8 secret[at_least CURVE25519_KEY_SIZE],
+	   const u8 basepoint[at_least CURVE25519_KEY_SIZE]);
 
-bool __must_check curve25519_generate_public(u8 pub[CURVE25519_KEY_SIZE],
-					     const u8 secret[CURVE25519_KEY_SIZE]);
+bool __must_check
+curve25519_generate_public(u8 pub[at_least CURVE25519_KEY_SIZE],
+			   const u8 secret[at_least CURVE25519_KEY_SIZE]);
 
-static inline void curve25519_clamp_secret(u8 secret[CURVE25519_KEY_SIZE])
+static inline void
+curve25519_clamp_secret(u8 secret[at_least CURVE25519_KEY_SIZE])
 {
 	secret[0] &= 248;
 	secret[31] = (secret[31] & 127) | 64;
 }
 
-static inline void curve25519_generate_secret(u8 secret[CURVE25519_KEY_SIZE])
+static inline void
+curve25519_generate_secret(u8 secret[at_least CURVE25519_KEY_SIZE])
 {
 	get_random_bytes_wait(secret, CURVE25519_KEY_SIZE);
 	curve25519_clamp_secret(secret);
 }
 
-- 
2.51.2