[PATCH v3 4/5] host/rootfs: Sandbox Cloud Hypervisor

Demi Marie Obenour
2025-12-03T15:56:01Z

It only needs access to a small number of resources. Unfortunately, it
needs access to /dev/vfio right now. This should be fixed by using file
descriptor passing instead.

Furthermore, Cloud Hypervisor needs to be able to lock memory. Running
in a user namespace prevents it from having CAP_IPC_LOCK. Therefore, it
is necessary to increase RLIMIT_MLOCK before running Cloud Hypervisor.

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
---
.../image/etc/udev/rules.d/99-spectrum.rules | 3 ++
host/rootfs/image/usr/bin/run-vmm | 33 +++++++++++++++++++++-
2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/host/rootfs/image/etc/udev/rules.d/99-spectrum.rules b/host/rootfs/image/etc/udev/rules.d/99-spectrum.rules
index 337bbe47dbbc6f3828722d8244f2689a39f3090f..de0f682aa40f8481dc3c25a90c695e2326536316 100644
--- a/host/rootfs/image/etc/udev/rules.d/99-spectrum.rules
+++ b/host/rootfs/image/etc/udev/rules.d/99-spectrum.rules
@@ -3,3 +3,6 @@

# systemd-udevd unsets PATH, so fix that.
ACTION!="remove", ENV{PCI_CLASS}=="2????", RUN+="/usr/bin/env PATH=/usr/bin /usr/libexec/net-add"
+
+# make /dev/kvm world-accessible
+KERNEL=="kvm", MODE="0666"
diff --git a/host/rootfs/image/usr/bin/run-vmm b/host/rootfs/image/usr/bin/run-vmm
index ba8b59c2677408acdd01c2eda3cf2dd60992d881..24c3d607bfcf6fea6196b61d2941141486d33fd6 100755
--- a/host/rootfs/image/usr/bin/run-vmm
+++ b/host/rootfs/image/usr/bin/run-vmm
@@ -52,5 +52,36 @@ unexport !
fdmove -c 3 0
redirfd -r 0 /dev/null

+s6-softlimit -H -l 18446744073709551615
if { udevadm wait /dev/kvm }
-cloud-hypervisor --api-socket fd=3
+bwrap
+ --unshare-all
+ --unshare-user
+ --dev /dev
+ --dev-bind /dev/kvm /dev/kvm
+ --dev-bind /dev/vfio /dev/vfio
+ --tmpfs /dev/shm
+ --tmpfs /tmp
+ --tmpfs /var/tmp
+ --ro-bind /etc /etc
+ --ro-bind /lib /lib
+ --ro-bind /nix /nix
+ --ro-bind /usr /usr
+ --ro-bind /sys /sys
+ --bind /run /run
+ --proc /proc
+ --ro-bind /proc/sys /proc/sys
+ --tmpfs /proc/scsi
+ --remount-ro /proc/scsi
+ --tmpfs /proc/acpi
+ --remount-ro /proc/acpi
+ --tmpfs /proc/fs
+ --remount-ro /proc/fs
+ --tmpfs /proc/irq
+ --remount-ro /proc/irq
+ --ro-bind /dev/null /proc/timer_list
+ --ro-bind /dev/null /proc/kcore
+ --ro-bind /dev/null /proc/kallsyms
+ --ro-bind /dev/null /proc/sysrq-trigger
+ --
+ cloud-hypervisor --api-socket fd=3

--
2.52.0