Subject: Re: [RFC net-next v2 1/6] Documentation on QUIC kernel Tx crypto.

From: Bagas Sanjaya <[email-masked]>
Date: Sat, 6 Aug 2022 10:05:21 +0700

On Fri, Aug 05, 2022 at 05:11:48PM -0700, Adel Abouchaev wrote:
> Adding Documentation/networking/quic.rst file to describe kernel QUIC
> code.
> 

Better say "Add documentation for kernel QUIC code".

> diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
> index 03b215bddde8..656fa1dac26b 100644
> --- a/Documentation/networking/index.rst
> +++ b/Documentation/networking/index.rst
> @@ -90,6 +90,7 @@ Contents:
>     plip
>     ppp_generic
>     proc_net_tcp
> +   quic
>     radiotap-headers
>     rds
>     regulatory
> diff --git a/Documentation/networking/quic.rst b/Documentation/networking/quic.rst
> new file mode 100644
> index 000000000000..416099b80e60
> --- /dev/null
> +++ b/Documentation/networking/quic.rst
> @@ -0,0 +1,186 @@
> +.. _kernel_quic:
> +
> +===========
> +KERNEL QUIC
> +===========
> +
> +Overview
> +========
> +
> +QUIC is a secure general-purpose transport protocol that creates a stateful
> +interaction between a client and a server. QUIC provides end-to-end integrity
> +and confidentiality. Refer to RFC 9000 for more information on QUIC.
> +
> +The kernel Tx side offload covers the encryption of the application streams
> +in the kernel rather than in the application. These packets are 1RTT packets
> +in QUIC connection. Encryption of every other packets is still done by the
> +QUIC library in user space.
> +
> +
> +
> +User Interface
> +==============
> +
> +Creating a QUIC connection
> +--------------------------
> +
> +QUIC connection originates and terminates in the application, using one of many
> +available QUIC libraries. The code instantiates QUIC client and QUIC server in
> +some form and configures them to use certain addresses and ports for the
> +source and destination. The client and server negotiate the set of keys to
> +protect the communication during different phases of the connection, maintain
> +the connection and perform congestion control.
> +
> +Requesting to add QUIC Tx kernel encryption to the connection
> +-------------------------------------------------------------
> +
> +Each flow that should be encrypted by the kernel needs to be registered with
> +the kernel using socket API. A setsockopt() call on the socket creates an
> +association between the QUIC connection ID of the flow with the encryption
> +parameters for the crypto operations:
> +
> +.. code-block:: c
> +
> +	struct quic_connection_info conn_info;
> +	char conn_id[5] = {0x01, 0x02, 0x03, 0x04, 0x05};
> +	const size_t conn_id_len = sizeof(conn_id);
> +	char conn_key[16] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
> +			     0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f};
> +	char conn_iv[12] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
> +			    0x08, 0x09, 0x0a, 0x0b};
> +	char conn_hdr_key[16] = {0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
> +				 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
> +				};
> +
> +	conn_info.cipher_type = TLS_CIPHER_AES_GCM_128;
> +
> +	memset(&conn_info.key, 0, sizeof(struct quic_connection_info_key));
> +	conn_info.key.conn_id_length = 5;
> +	memcpy(&conn_info.key.conn_id[QUIC_MAX_CONNECTION_ID_SIZE
> +				      - conn_id_len],
> +	       &conn_id, conn_id_len);
> +
> +	memcpy(&conn_info.payload_key, conn_key, sizeof(conn_key));
> +	memcpy(&conn_info.payload_iv, conn_iv, sizeof(conn_iv));
> +	memcpy(&conn_info.header_key, conn_hdr_key, sizeof(conn_hdr_key));
> +
> +	setsockopt(fd, SOL_UDP, UDP_QUIC_ADD_TX_CONNECTION, &conn_info,
> +		   sizeof(conn_info));
> +
> +
> +Requesting to remove QUIC Tx kernel crypto offload control messages
> +-------------------------------------------------------------------
> +
> +All flows are removed when the socket is closed. To request an explicit remove
> +of the offload for the connection during the lifetime of the socket the process
> +is similar to adding the flow. Only the connection ID and its length are
> +necessary to supply to remove the connection from the offload:
> +
> +.. code-block:: c
> +
> +	memset(&conn_info.key, 0, sizeof(struct quic_connection_info_key));
> +	conn_info.key.conn_id_length = 5;
> +	memcpy(&conn_info.key.conn_id[QUIC_MAX_CONNECTION_ID_SIZE
> +				      - conn_id_len],
> +	       &conn_id, conn_id_len);
> +	setsockopt(fd, SOL_UDP, UDP_QUIC_DEL_TX_CONNECTION, &conn_info,
> +		   sizeof(conn_info));
> +
> +Sending QUIC application data
> +-----------------------------
> +
> +For QUIC Tx encryption offload, the application should use sendmsg() socket
> +call and provide ancillary data with information on connection ID length and
> +offload flags for the kernel to perform the encryption and GSO support if
> +requested.
> +
> +.. code-block:: c
> +
> +	size_t cmsg_tx_len = sizeof(struct quic_tx_ancillary_data);
> +	uint8_t cmsg_buf[CMSG_SPACE(cmsg_tx_len)];
> +	struct quic_tx_ancillary_data * anc_data;
> +	size_t quic_data_len = 4500;
> +	struct cmsghdr * cmsg_hdr;
> +	char quic_data[9000];
> +	struct iovec iov[2];
> +	int send_len = 9000;
> +	struct msghdr msg;
> +	int err;
> +
> +	iov[0].iov_base = quic_data;
> +	iov[0].iov_len = quic_data_len;
> +	iov[1].iov_base = quic_data + 4500;
> +	iov[1].iov_len = quic_data_len;
> +
> +	if (client.addr.sin_family == AF_INET) {
> +		msg.msg_name = &client.addr;
> +		msg.msg_namelen = sizeof(client.addr);
> +	} else {
> +		msg.msg_name = &client.addr6;
> +		msg.msg_namelen = sizeof(client.addr6);
> +	}
> +
> +	msg.msg_iov = iov;
> +	msg.msg_iovlen = 2;
> +	msg.msg_control = cmsg_buf;
> +	msg.msg_controllen = sizeof(cmsg_buf);
> +	cmsg_hdr = CMSG_FIRSTHDR(&msg);
> +	cmsg_hdr->cmsg_level = IPPROTO_UDP;
> +	cmsg_hdr->cmsg_type = UDP_QUIC_ENCRYPT;
> +	cmsg_hdr->cmsg_len = CMSG_LEN(cmsg_tx_len);
> +	anc_data = CMSG_DATA(cmsg_hdr);
> +	anc_data->flags = 0;
> +	anc_data->next_pkt_num = 0x0d65c9;
> +	anc_data->conn_id_length = conn_id_len;
> +	err = sendmsg(self->sfd, &msg, 0);
> +
> +QUIC Tx offload in kernel will read the data from userspace, encrypt and
> +copy it to the ciphertext within the same operation.
> +
> +
> +Sending QUIC application data with GSO
> +--------------------------------------
> +When GSO is in use, the kernel will use the GSO fragment size as the target
> +for ciphertext. The packets from the user space should align on the boundary
> +of GSO fragment size minus the size of the tag for the chosen cipher. For the
> +GSO fragment 1200, the plain packets should follow each other at every 1184
> +bytes, given the tag size of 16. After the encryption, the rest of the UDP
> +and IP stacks will follow the defined value of GSO fragment which will include
> +the trailing tag bytes.
> +
> +To set up GSO fragmentation:
> +
> +.. code-block:: c
> +
> +	setsockopt(self->sfd, SOL_UDP, UDP_SEGMENT, &frag_size,
> +		   sizeof(frag_size));
> +
> +If the GSO fragment size is provided in ancillary data within the sendmsg()
> +call, the value in ancillary data will take precedence over the segment size
> +provided in setsockopt to split the payload into packets. This is consistent
> +with the UDP stack behavior.
> +
> +Integrating to userspace QUIC libraries
> +---------------------------------------
> +
> +Userspace QUIC libraries integration would depend on the implementation of the
> +QUIC protocol. For MVFST library, the control plane is integrated into the
> +handshake callbacks to properly configure the flows into the socket; and the
> +data plane is integrated into the methods that perform encryption and send
> +the packets to the batch scheduler for transmissions to the socket.
> +
> +MVFST library can be found at https://github.com/facebookincubator/mvfst.
> +
> +Statistics
> +==========
> +
> +QUIC Tx offload to the kernel has counters
> +(``/proc/net/quic_stat``):
> +
> +- ``QuicCurrTxSw`` -
> +  number of currently active kernel offloaded QUIC connections
> +- ``QuicTxSw`` -
> +  accumulative total number of offloaded QUIC connections
> +- ``QuicTxSwError`` -
> +  accumulative total number of errors during QUIC Tx offload to kernel
> +

The documentation looks OK (no new warnings).

Thanks.

-- 
An old man doll... just what I always wanted! - Clara