Add documentation for the tcp ULP tls interface.
Signed-off-by: Boris Pismenny <borisp@xxxxxxxxxxxx>
Signed-off-by: Dave Watson <davejwatson@xxxxxx>
---
Documentation/networking/tls.txt | 120 +++++++++++++++++++++++++++++++++++++++
1 file changed, 120 insertions(+)
create mode 100644 Documentation/networking/tls.txt
diff --git a/Documentation/networking/tls.txt b/Documentation/networking/tls.txt
new file mode 100644
index 0000000..7bfb256
--- /dev/null
+++ b/Documentation/networking/tls.txt
@@ -0,0 +1,120 @@
+Overview
+========
+
+Transport Layer Security (TLS) is a Upper Layer Protocol (ULP) that runs over
+TCP. TLS provides end-to-end data integrity and confidentiality.
+
+User interface
+==============
+
+Creating a TLS connection
+-------------------------
+
+First create a new TCP socket and set the TLS ULP.
+
+ sock = socket(AF_INET, SOCK_STREAM, 0);
+ setsockopt(sock, SOL_TCP, TCP_ULP, "tls", sizeof("tls"));
+
+Setting the TLS ULP allows us to set/get TLS socket options. Currently
+only the symmetric encryption is handled in the kernel. After the TLS
+handshake is complete, we have all the parameters required to move the
+data-path to the kernel. There is a separate socket option for moving
+the transmit and the receive into the kernel.
+
+ /* From linux/tls.h */
+ struct tls_crypto_info {
+ unsigned short version;
+ unsigned short cipher_type;
+ };
+
+ struct tls12_crypto_info_aes_gcm_128 {
+ struct tls_crypto_info info;
+ unsigned char iv[TLS_CIPHER_AES_GCM_128_IV_SIZE];
+ unsigned char key[TLS_CIPHER_AES_GCM_128_KEY_SIZE];
+ unsigned char salt[TLS_CIPHER_AES_GCM_128_SALT_SIZE];
+ unsigned char rec_seq[TLS_CIPHER_AES_GCM_128_REC_SEQ_SIZE];
+ };
+
+
+ struct tls12_crypto_info_aes_gcm_128 crypto_info;
+
+ crypto_info.info.version = TLS_1_2_VERSION;
+ crypto_info.info.cipher_type = TLS_CIPHER_AES_GCM_128;
+ memcpy(crypto_info.iv, iv_write, TLS_CIPHER_AES_GCM_128_IV_SIZE);
+ memcpy(crypto_info.rec_seq, seq_number_write,
+ TLS_CIPHER_AES_GCM_128_REC_SEQ_SIZE);
+ memcpy(crypto_info.key, cipher_key_write, TLS_CIPHER_AES_GCM_128_KEY_SIZE);
+ memcpy(crypto_info.salt, implicit_iv_write, TLS_CIPHER_AES_GCM_128_SALT_SIZE);
+
+ setsockopt(sock, SOL_TLS, TLS_TX, &crypto_info, sizeof(crypto_info));
+
+Sending TLS application data
+----------------------------
+
+After setting the TLS_TX socket option all application data sent over this
+socket is encrypted using TLS and the parameters provided in the socket option.
+For example, we can send an encrypted hello world record as follows:
+
+ const char *msg = "hello world\n";
+ send(sock, msg, strlen(msg));
+
+send() data is directly encrypted from the userspace buffer provided
+to the encrypted kernel send buffer if possible.
+
+The sendfile system call will send the file's data over TLS records of maximum
+length (2^14).
+
+ file = open(filename, O_RDONLY);
+ fstat(file, &stat);
+ sendfile(sock, file, &offset, stat.st_size);
+
+TLS records are created and sent after each send() call, unless
+MSG_MORE is passed. MSG_MORE will delay creation of a record until
+MSG_MORE is not passed, or the maximum record size is reached.
+
+The kernel will need to allocate a buffer for the encrypted data.
+This buffer is allocated at the time send() is called, such that
+either the entire send() call will return -ENOMEM (or block waiting
+for memory), or the encryption will always succeed. If send() returns
+-ENOMEM and some data was left on the socket buffer from a previous
+call using MSG_MORE, the MSG_MORE data is left on the socket buffer.
+
+Send TLS control messages
+-------------------------
+
+Other than application data, TLS has control messages such as alert
+messages (record type 21) and handshake messages (record type 22), etc.
+These messages can be sent over the socket by providing the TLS record type
+via a CMSG. For example the following function sends @data of @length bytes
+using a record of type @record_type.
+
+/* send TLS control message using record_type */
+ static int klts_send_ctrl_message(int sock, unsigned char record_type,
+ void *data, size_t length)
+ {
+ struct msghdr msg = {0};
+ int cmsg_len = sizeof(record_type);
+ struct cmsghdr *cmsg;
+ char buf[CMSG_SPACE(cmsg_len)];
+ struct iovec msg_iov; /* Vector of data to send/receive into. */
+
+ msg.msg_control = buf;
+ msg.msg_controllen = sizeof(buf);
+ cmsg = CMSG_FIRSTHDR(&msg);
+ cmsg->cmsg_level = SOL_TLS;
+ cmsg->cmsg_type = TLS_SET_RECORD_TYPE;
+ cmsg->cmsg_len = CMSG_LEN(cmsg_len);
+ *CMSG_DATA(cmsg) = record_type;
+ msg.msg_controllen = cmsg->cmsg_len;
+
+ msg_iov.iov_base = data;
+ msg_iov.iov_len = length;
+ msg.msg_iov = &msg_iov;
+ msg.msg_iovlen = 1;
+
+ return sendmsg(sock, &msg, 0);
+ }
+
+Control message data should be provided unencrypted, and will be
+encrypted by the kernel. At a high level, the kernel TLS ULP is a
+replacement for the record layer of a userspace TLS library.
--
2.9.3
