The network stack

The stack is EDOS’s own, from the Ethernet frame up. It talks to the real internet through QEMU’s user networking, and to a real LAN on Intel e1000e hardware.

Layers

Layer	What exists
Ethernet	frame RX and TX against the e1000e driver
ARP	resolution and a cache
IPv4	routing to a default gateway, plus fragment reassembly
ICMP	echo request and reply, which is what ping uses
UDP	datagram sockets
TCP	a state machine with retransmission, delayed ACK and TIME-WAIT, driven by a dedicated tcp-retransmit kernel thread
DHCP	client; configures the interface at boot
DNS	resolver

DHCP runs as soon as the NIC is up. On a guest boot that is roughly a millisecond after the driver reports ready:

[0.808125] <cpu-2:e1000e:k:6> e1000e: initialized, MAC 52:54:00:12:34:56
[0.808210] <cpu-2:e1000e:k:6> net: dhcp: sending DISCOVER
[0.808449] <cpu-2:e1000e:k:6> net: dhcp: received OFFER 10.0.2.15
[0.808546] <cpu-2:e1000e:k:6> net: dhcp: received ACK, IP 10.0.2.15

From the shell

/ $ ping 10.0.2.2
PING 10.0.2.2
Reply from 10.0.2.2: seq=0 time=0.12ms
--- ping statistics ---
4 packets sent, 4 received
rtt min/avg/max = 0.08/0.09/0.12 ms

/ $ dns example.com
example.com -> 172.66.147.243

/ $ wget http://example.com
wget: saved to 'index.html' (559 bytes)

ping, dns, dnsprobe, http, wget and tcptest all ship in /bin.

Logging in over SSH

sshd is an SSH-2 server: curve25519-sha256 key exchange, an ssh-ed25519 host key generated on first run, aes128-ctr with hmac-sha2-256, password authentication, and a session channel carrying a pty and a shell. A stock OpenSSH client connects with no options.

$ ssh edgar@edos
edgar@edos's password:
EDOS 0.8.0 shell
Type 'help' for commands.
/ $ uname -a
EDOS 0.8.0 x86_64

edos-init starts it, but only on a system that has an /etc/sshd.conf to configure it; the shipped image has none, so a machine whose owner never asked for SSH does not listen. There is no bignum arithmetic anywhere in the system, which is why the host key is ed25519 and there is no RSA option.

The crypto is the ordinary crates from crates.io, unmodified: sha2, hmac, aes, ctr, x25519-dalek, ed25519-dalek. They compile for x86_64-unknown-edos as they are, and the kernel’s own randomness reaches them through getrandom.

The driver

e1000e, verified on real Intel I219, I218 and I217 parts as well as in QEMU. RX and TX are interrupt-driven; the e1000e kernel thread owns the rings, and tcp-retransmit owns the timers.

Capturing traffic

make run-capture      # writes /tmp/edos.pcap

Open the result in Wireshark. This is the fastest way to tell a stack bug from a driver bug.

Locking

The stack’s locks are ranked between 240 and 270: the stack itself, then the port table, then a socket, then a connection. They are always taken in that order. See lock order.