[tls] Report supported signature algorithms in ClientHello

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

src/include/ipxe/tls.h

 #define TLS_MAX_FRAGMENT_LENGTH_2048 3
 #define TLS_MAX_FRAGMENT_LENGTH_4096 4
 
+/* TLS signature algorithms extension */
+#define TLS_SIGNATURE_ALGORITHMS 13
+
 /** TLS RX state machine state */
 enum tls_rx_state {
 	TLS_RX_HEADER = 0,

src/net/tls.c

  * MD5+SHA1 is never explicitly specified.
  */
 struct tls_signature_hash_algorithm tls_signature_hash_algorithms[] = {
+	{
+		.code = {
+			.signature = TLS_RSA_ALGORITHM,
+			.hash = TLS_SHA1_ALGORITHM,
+		},
+		.pubkey = &rsa_algorithm,
+		.digest = &sha1_algorithm,
+	},
 	{
 		.code = {
 			.signature = TLS_RSA_ALGORITHM,
 			struct {
 				uint8_t max;
 			} __attribute__ (( packed )) max_fragment_length;
+			uint16_t signature_algorithms_type;
+			uint16_t signature_algorithms_len;
+			struct {
+				uint16_t len;
+				struct tls_signature_hash_id
+					code[TLS_NUM_SIG_HASH_ALGORITHMS];
+			} __attribute__ (( packed )) signature_algorithms;
 		} __attribute__ (( packed )) extensions;
 	} __attribute__ (( packed )) hello;
 	unsigned int i;
 		= htons ( sizeof ( hello.extensions.max_fragment_length ) );
 	hello.extensions.max_fragment_length.max
 		= TLS_MAX_FRAGMENT_LENGTH_4096;
+	hello.extensions.signature_algorithms_type
+		= htons ( TLS_SIGNATURE_ALGORITHMS );
+	hello.extensions.signature_algorithms_len
+		= htons ( sizeof ( hello.extensions.signature_algorithms ) );
+	hello.extensions.signature_algorithms.len
+		= htons ( sizeof ( hello.extensions.signature_algorithms.code));
+	for ( i = 0 ; i < TLS_NUM_SIG_HASH_ALGORITHMS ; i++ ) {
+		hello.extensions.signature_algorithms.code[i]
+			= tls_signature_hash_algorithms[i].code;
+	}
 
 	return tls_send_handshake ( tls, &hello, sizeof ( hello ) );
 }