[crypto] Allow construction of shared public key to return an error

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/crypto/elliptic.c

@@ -42,8 +42,9 @@ FILE_SECBOOT ( PERMITTED );
  * @v exchange		Key exchange algorithm
  * @v private		Private key
  * @v public		Public key to fill in
+ * @ret rc		Return status code
  */
-void elliptic_share ( struct exchange_algorithm *exchange, const void *private,
+int elliptic_share ( struct exchange_algorithm *exchange, const void *private,
 		      void *public ) {
 	struct elliptic_curve *curve = exchange->priv;
 	size_t len = exchange->sharedsize;
@@ -57,10 +58,14 @@ void elliptic_share ( struct exchange_algorithm *exchange, const void *private,
 
 	/* Calculate public key */
 	result->format = ELLIPTIC_FORMAT_UNCOMPRESSED;
-	rc = elliptic_multiply ( curve, curve->base, private, &result->xy );
+	if ( ( rc = elliptic_multiply ( curve, curve->base, private,
+					&result->xy ) ) != 0 ) {
+		/* Can never fail when using the curve's own base point */
+		assert ( 0 );
+		return rc;
+	}
 
-	/* Can never fail when using the curve's own base point */
-	assert ( rc == 0 );
+	return rc;
 }
 
 /**

src/crypto/ffdhe.c

@@ -264,12 +264,13 @@ static int ffdhe ( struct ffdhe_group *group, const void *public,
  * @v exchange		Key exchange algorithm
  * @v private		Private key
  * @v public		Public key to fill in
+ * @ret rc		Return status code
  */
-void ffdhe_share ( struct exchange_algorithm *exchange, const void *private,
-		   void *public ) {
+int ffdhe_share ( struct exchange_algorithm *exchange, const void *private,
+		  void *public ) {
 	struct ffdhe_group *group = exchange->priv;
 
-	ffdhe ( group, NULL, private, public );
+	return ffdhe ( group, NULL, private, public );
 }
 
 /**

src/crypto/x25519.c

@@ -836,12 +836,15 @@ void x25519_key ( const struct x25519_value *base,
  * @v exchange		Key exchange algorithm
  * @v private		Private key
  * @v public		Public key to fill in
+ * @ret rc		Return status code
  */
-static void x25519_share ( struct exchange_algorithm *exchange __unused,
-			   const void *private, void *public ) {
+static int x25519_share ( struct exchange_algorithm *exchange __unused,
+			  const void *private, void *public ) {
 
 	/* Calculate public key */
 	x25519_key ( &x25519_generator, private, public );
+
+	return 0;
 }
 
 /**

src/include/ipxe/crypto.h

@@ -220,9 +220,10 @@ struct exchange_algorithm {
 	 * @v exchange		Key exchange algorithm
 	 * @v private		Private key
 	 * @v public		Public key to fill in
+	 * @ret rc		Return status code
 	 */
-	void ( * share ) ( struct exchange_algorithm *exchange,
-			   const void *private, void *public );
+	int ( * share ) ( struct exchange_algorithm *exchange,
+			  const void *private, void *public );
 	/**
 	 * Agree shared secret
 	 *
@@ -390,10 +391,10 @@ pubkey_match ( struct pubkey_algorithm *pubkey,
 	return pubkey->match ( pubkey, private_key, public_key );
 }
 
-static inline __attribute__ (( always_inline )) void
+static inline __attribute__ (( always_inline )) int
 exchange_share ( struct exchange_algorithm *exchange, const void *private,
 		 void *public ) {
-	exchange->share ( exchange, private, public );
+	return exchange->share ( exchange, private, public );
 }
 
 static inline __attribute__ (( always_inline )) int

src/include/ipxe/elliptic.h

@@ -29,8 +29,8 @@ FILE_SECBOOT ( PERMITTED );
 /** Format byte for uncompressed curve point representation */
 #define ELLIPTIC_FORMAT_UNCOMPRESSED 0x04
 
-extern void elliptic_share ( struct exchange_algorithm *exchange,
-			     const void *private, void *public );
+extern int elliptic_share ( struct exchange_algorithm *exchange,
+			    const void *private, void *public );
 extern int elliptic_agree ( struct exchange_algorithm *exchange,
 			    const void *private, const void *partner,
 			    void *shared );

src/include/ipxe/ffdhe.h

@@ -33,8 +33,8 @@ struct ffdhe_group {
 	uint32_t lsb32;
 };
 
-extern void ffdhe_share ( struct exchange_algorithm *exchange,
-			  const void *private, void *public );
+extern int ffdhe_share ( struct exchange_algorithm *exchange,
+			 const void *private, void *public );
 extern int ffdhe_agree ( struct exchange_algorithm *exchange,
 			 const void *private, const void *partner,
 			 void *shared );

src/net/tls.c

@@ -1820,7 +1820,10 @@ static int tls_send_client_key_exchange_ecdhe ( struct tls_connection *tls ) {
 			  htonl ( sizeof ( key_xchg ) -
 				  sizeof ( key_xchg.type_length ) ) );
 		key_xchg.public_len = sizeof ( key_xchg.public );
-		exchange_share ( exchange, private, key_xchg.public );
+		if ( ( rc = exchange_share ( exchange, private,
+					     key_xchg.public ) ) != 0 ) {
+			return rc;
+		}
 
 		/* Transmit Client Key Exchange record */
 		if ( ( rc = tls_send_handshake ( tls, &key_xchg,

src/tests/exchange_test.c

@@ -67,7 +67,8 @@ void exchange_okx ( struct exchange_test *test, const char *file,
 	/* Verify calculation of public key */
 	DBGC ( test, "KEX %s private key:\n", exchange->name );
 	DBGC_HDA ( test, 0, test->private, exchange->privsize );
-	exchange_share ( exchange, test->private, actual->public );
+	okx ( exchange_share ( exchange, test->private, actual->public ) == 0,
+	      file, line );
 	DBGC ( test, "KEX %s public key:\n", exchange->name );
 	DBGC_HDA ( test, 0, actual->public, exchange->pubsize );
 	okx ( memcmp ( actual->public, test->public, exchange->pubsize ) == 0,