Re: [PATCH] host/rootfs: Sandbox Cloud Hypervisor

[Alyssa Ross <hi@alyssa.is>]

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Demi Marie Obenour <demiobenour@gmail.com> writes:

> 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.  Also, Cloud Hypervisor should not run as
> root.
>
> Cloud Hypervisor needs to be able to lock memory.  Running in a user
> namespace prevents it from using CAP_IPC_LOCK.  Therefore, it is
> necessary to increase RLIMIT_MLOCK before running Cloud Hypervisor.
>
> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
> ---
>  host/rootfs/image/usr/bin/run-vmm | 33 ++++++++++++++++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)

Looks good, but it seems to only work for VMs run as s6 services, not
those run through run-appimage or run-flatpak.  (I suppose the appimage
integration test is somehow not thorough enough to catch this, which
should be easier to fix once we understand the problem.)

bwrap: execvp cloud-hypervisor: No such file or directory

I suppose this is because etc/login sets PATH to /bin, and we don't
share /bin with the sandbox.  Changing that to /usr/bin would be a good
idea I suppose, but would it also be a good idea to share /bin with the
sandbox?  What do you think?

> 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
>
> ---
> base-commit: 92e219e7c08c479d216a46d2736ea9d229ff034d
> change-id: 20251206-b4-sandbox-9be7e5ed9926
>
> -- 
> Sincerely,
> Demi Marie Obenour (she/her/hers)

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