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

[Adel Abouchaev <adel.abushaev@gmail.com>]

Updated the commit message, will be visible in v3.

On 8/5/22 8:05 PM, Bagas Sanjaya wrote:
> 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.
>