Initial Commit

vm/host/owuivm.service

@@ -0,0 +1,169 @@
+# =====================================================================
+# The VM sandbox. One unit, deliberately NOT a template.
+#
+# "Only one VM at a time" is a requirement, and systemd enforces it for
+# free here: a second `systemctl start owuivm.service` on an already
+# running unit is a no-op. Making this a template (owuivm@.service) would
+# move that guarantee into vmd's bookkeeping, where a crash between
+# "check" and "start" breaks it.
+#
+# THIS FILE IS THE PRIMARY ISOLATION CONTROL, NOT THE FIREWALL.
+#
+# IPAddressDeny= attaches a BPF filter to this unit's cgroup. It applies
+# to every socket the process opens, it covers loopback, and - the point -
+# `nft flush ruleset`, a ufw reload and an nftables package upgrade all
+# leave it completely untouched. 60-owuivm.nft says the same thing again
+# independently, and the negative suite is run twice: once with the nft
+# table deleted, once with these lines stripped from a scratch unit.
+# Neither layer is allowed to be the reason the suite passes.
+#
+# The guest reaches the internet and nothing else. Note that the deny on
+# 10.0.0.0/8 does not affect the guest's own 10.0.2.15 - those addresses
+# live inside libslirp and never become host packets - while the deny on
+# 127.0.0.0/8 is what closes SLIRP's host aliases 10.0.2.2 (this host's
+# loopback) and 10.0.2.3 (this host's DNS forwarder).
+# =====================================================================
+[Unit]
+Description=owuitools VM sandbox (one session at a time)
+After=network-online.target owuivm-nft-guard.service
+Wants=owuivm-nft-guard.service
+ConditionPathExists=/run/owuivm/session.env
+ConditionPathExists=/dev/kvm
+
+[Service]
+Type=simple
+EnvironmentFile=/run/owuivm/session.env
+ExecStart=/usr/local/libexec/owuivm-launch
+
+# Best-effort teardown that survives SIGKILL of the main process, because
+# systemd runs it whatever killed qemu. vmd reaps too, on its own start;
+# neither is trusted to be the only one that ran.
+#
+# A SESSION MACHINE IS KILLED, NOT ASKED TO LEAVE.
+#
+# The maintenance unit presses the power button and waits, because the
+# disk it is holding is the base image and pulling the plug on it is how
+# a qcow2 gets corrupted. A session has neither reason: its disk is a
+# throwaway overlay that is deleted moments later, and the project share
+# has already been committed and pushed by the time anything here runs -
+# `close` publishes BEFORE it destroys.
+#
+# So the only thing an ACPI power-down would buy is a tidier-looking
+# guest shutdown, at a cost of up to ninety seconds of CPU per session
+# spent watching a machine stop caring about itself. The operator's
+# call, and the right one.
+KillSignal=SIGKILL
+ExecStopPost=/usr/local/libexec/owuivm-teardown
+
+User=owuivm
+Group=owuivm
+SupplementaryGroups=kvm
+# 0007 so the sockets qemu creates in the session directory are group
+# writable and vmd - a member of group owuivm - can connect to them.
+UMask=0007
+
+# --- the network boundary -------------------------------------------
+# DENY-ONLY, AND THERE MUST NEVER BE AN IPAddressAllow= LINE HERE.
+#
+# systemd.resource-control(5) applies the two lists in this order:
+#   1. granted if the address matches IPAddressAllow=
+#   2. otherwise denied if it matches IPAddressDeny=
+#   3. otherwise granted
+# There is no longest-prefix arbitration between them. An
+# `IPAddressAllow=0.0.0.0/0` intended to mean "the internet is fine" is
+# therefore matched by rule 1 for EVERY address and makes this entire
+# deny list dead. That was the first thing written here, and it was
+# measured doing nothing: with the nft table deleted, a process in this
+# cgroup reached 192.168.1.10:7200, 172.17.0.1:11434 and 127.0.0.1:3000.
+# Rule 3 is what grants the internet; it needs no help.
+IPAddressDeny=127.0.0.0/8 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 169.254.0.0/16 100.64.0.0/10 192.0.0.0/24 224.0.0.0/4 240.0.0.0/4
+# No AF_INET6 at all. Cheaper and more durable than listing v6 ranges
+# that do not exist on this host yet; a range nobody added is a rule that
+# silently stops matching.
+RestrictAddressFamilies=AF_UNIX AF_INET
+# qemu opens no listening socket of its own here - no hostfwd, no VNC on
+# TCP - and this asserts it rather than trusting the argv.
+SocketBindDeny=any
+
+# --- devices ---------------------------------------------------------
+# PrivateDevices=yes would hide /dev/kvm, so the allowlist is explicit
+# instead. DevicePolicy=closed still permits null/zero/full/random/
+# urandom/tty, which is everything else qemu needs.
+DevicePolicy=closed
+DeviceAllow=/dev/kvm rw
+
+# --- filesystem ------------------------------------------------------
+# THE SANDBOX GETS ITS OWN RESOLVER, AND THIS IS NOT COSMETIC.
+#
+# SLIRP hands every guest 10.0.2.3 as its nameserver over DHCP. That is a
+# forwarder inside the qemu process, and it relays to whatever the HOST's
+# /etc/resolv.conf says - here 127.0.0.53, systemd-resolved, which
+# forwards to the LAN's own DNS and knows every internal name in the
+# house. This unit denies 127.0.0.0/8, correctly, so that relay is dead.
+#
+# The result is a guest with working TCP to the internet and no name
+# resolution whatsoever, which presents as "no internet" and sends
+# whoever is looking at it to entirely the wrong place. It did exactly
+# that to a hand-installed image.
+#
+# Bind-mounting a resolv.conf of our own fixes it for every guest without
+# the guest being configured at all, and without the host's resolver ever
+# becoming reachable from the sandbox.
+BindReadOnlyPaths=/etc/owuivm/resolv.conf:/etc/resolv.conf
+
+ProtectSystem=strict
+ProtectHome=yes
+PrivateTmp=yes
+ReadWritePaths=/run/owuivm @POOL_ROOT@/vmrun
+ProtectKernelTunables=yes
+ProtectKernelLogs=yes
+ProtectControlGroups=yes
+ProtectClock=yes
+ProtectHostname=yes
+ProtectProc=invisible
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+LockPersonality=yes
+MemoryDenyWriteExecute=no
+NoNewPrivileges=yes
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallErrorNumber=EPERM
+
+# --- resources -------------------------------------------------------
+# 8 GB of guest RAM plus qemu's own overhead. CPUQuota is 700% and not
+# 800% on purpose: Ollama needs cores for sampling while a session runs,
+# and this host has one GPU shared with the model the agent is using.
+# MEASURED: 10G made the machine crawl, and it was not obvious why.
+#
+# The guest's RAM is a memfd with share=on (virtiofs requires it), so the
+# kernel accounts all 8 GiB of it as *shmem* in this cgroup - and with no
+# swap on this host, shmem cannot be reclaimed at all. That left about
+# 1.5 GiB for every page of ISO and disk I/O the VM does, so the cgroup
+# hit its hard limit 6,782 times in one boot (memory.events max), evicting
+# and re-reading the same installer media over and over.
+#
+# The first fix was to raise this to 14G so the page cache had room.
+# That worked - reclaim went to zero - and it was the wrong fix: it gave
+# one VM twelve gigabytes of a 58 GB host that is also running Ollama,
+# and the host started running short instead. Raising a limit to make
+# room for something that should not have been in there.
+#
+# The right fix is one line in owuivm-launch: cache=none on every drive,
+# so this VM's I/O never enters the page cache at all. What is left in
+# the cgroup is the guest's RAM and qemu itself, which is what this limit
+# was always meant to bound. 11G is 8 GiB of guest, about 1 GiB of qemu,
+# and slack.
+MemoryMax=@VM_MEMORY_MAX@
+CPUQuota=@VM_CPU_QUOTA@
+AllowedCPUs=@VM_ALLOWED_CPUS@
+TasksMax=512
+
+# A guest that will not die is a guest that wedges the next caller.
+# Short, because nothing here waits for the guest any more: SIGKILL goes
+# to qemu the moment the unit is stopped and this is only the backstop
+# for a process that ignores even that.
+TimeoutStopSec=10
+KillMode=mixed
+Restart=no