UMVU(1)

NAME
umvu – user-mode implementation of VUOS

SYNOPSIS
umvu [options ...] command [args]

DESCRIPTION
VUOS: view based operating system. VUOS gives processes their own view of the system resources. VUOS is a different perspective on namespaces, anykernels and related concepts. The main idea behind VUOS is that it is possible to give processes their own view using partial virtual machines.

A partial virtual machine intercepts the system call requests and operates like a filter: system call can be forwarded to the kernel of the hosting system or processed by the partial virtual machine hypervisor.

In this way processes can see a mix of resources provided by the kernel (on which they have the same view of the other processes) and virtual resource. It is possible to mount filesystems, load networking stacks, change the structure of the file system tree, create virtual devices, etc.

umvu is a user mode implementation of VUOS concepts It is a modular partial virtual machine. Before loading any module, umvu is completely transparent, a process behaves inside umvu as it would have behaved outside. vu_insmod(1) is the tool to load modules, e.g. vufuse for file system virtualization, vunet for networking, vudev for virtual devices, etc. These are just some examples of modules provided by the VirtualSquare team: modules are dynamic library based plugins so can be designed and implemented independently and loaded/unloaded at run time.

umvu (VUOS hypervisor) is just a user process so, while it gives new perspective for processes, it does not widen the attack surface of the kernel.

OPTIONS

-h, --help
    Print a short help message and exit.

-x, --nonesting
    umvu provides nested virtualization. It means that the system call requests of the modules can refer to virtual resource. (for example it is possible to mount a file system stored on a virtual device). The -x or --nonesting option disables this feature.

-S, --noseccomp
    umvu uses a seccomp filter to speed-up the virtualization. The -S or --noseccomp option disables this feature.

-f file, --rc file
    Execute commands from file instead of the system wide initialization file /etc/vurc and the standard personal initialization file ~/.vurc

-N, --norc
    Do not run the system wide initialization file /etc/vurc and the standard personal initialization file ~/.vurc

-V name, --vu_name name
    set the name of the view. This name can be read and set using vuname(1)

-d debugtags, --debugtags debugtags
    set the debug tags enabled from the beginning. e.g. -d s enables log messages of system call requests. (see vudebug(1) for a detailed description)

-D colorspec, --debugcols colorspec
    set color and font effects for log messages. e.g. -D p:r -D c:g# means that path resolution messages will be displayed in red while module choice log will be in reverse green. Color definition can refer to enable and disabled categories (the option defines the colors for a successive activation). (see vudebug(1) for a detailed description)

-l level, --loglevel level
    set the debug level. Only messages having level less or equal of the parameter of this option will be displayed. (0 = emergency, 1 = alert, 2 = critical, 3 = error, 4 = warning, 5 = notice, 6 = info, 7 = debug). The default level is 4.

-s level, --syslog level
    use syslog(2) for logging and log messages having level less or equal of the parameter of this option. (0 = emergency, 1 = alert, 2 = critical, 3 = error, 4 = warning, 5 = notice, 6 = info, 7 = debug). This option is disabled by default.

EXAMPLES

  mount a file system image
The following example mounts /tmp/linux.img on /mnt.

start the hypervisor, and run a bash inside the partial virtual machine

        $ umvu bash

This is the prompt of the partial virtualized shell, let us change it to $$ to show the difference

        $ PS1='\$\$ '`

let us load vufuse: a user-mode implementation of FUSE (source compatible with FUSE modules)

        $$ vu_insmod vufuse

nothing is currently mounted on /mnt

        $$ ls /mnt

the following command mounts the filesystem image /tmp/linux.img

        $$ vumount -t vufuseext2 -o ro /tmp/linux.img /mnt

now the image has been mounted:

        $$ ls /mnt
        bin  boot  dev  etc  lib  lost+found  mnt  proc  sbin  tmp  usr
        $$ vuumount /mnt
        $$ ls /mnt
        $$ exit

We have left the partial virtual machine

Comments: user can mount any filesystem they like, on any directory. The linux kernel is not involved for all the system calls related to files in the mounted filesystem. The effects of this mount is just perceived by the processes running in the partial virtual machine. vumount is just a wrapper to the mount(1) system call (the command mount(8) does much much more, it is setuid root and requires real uid to be root to permit filesystem mounting (mount(8) works in umvu adding a module of uid/gid virtualization).

  create a disk image, partition it, create a filesystem and mount it
In this example an 1GiB empty file is seen as a virtual disk, this disk gets partitioned (GPT), an ext4 file system is created on its first partition and finally this file system is mounted on /mnt

start the hypervisor, and run a bash inside the partial virtual machine

        $ umvu bash

This is the prompt of the partial virtualized shell, let us change it to $$ to show the difference

        $ PS1='\$\$ '

let us load vudev and vufuse: vudev to virtualize devices and vufuse as in the previous example

        $$ vu_insmod vudev vufuse

create a 1 GiB large empty file

        $$ truncate -s 1G /tmp/disk
        $$ ls -l /tmp/disk
        -rw-r--r-- 1 renzo renzo 1073741824 Jun  3 11:55 /tmp/disk

let us mount the empty file as a partitioned virtual disk:

        $$ vumount -t vudevpartx /tmp/disk /dev/hda
        Bad MBR signature 0 0

clearly if not a partitioned disk, yet. Let us add a partitioning scheme:

        $$  /sbin/gdisk /dev/hda
        GPT fdisk (gdisk) version 1.0.3
        Partition table scan:
        MBR: not present
        BSD: not present
        APM: not present
        GPT: not present
        Creating new GPT entries.
        Command (? for help):  n
        Partition number (1-128, default 1):
        First sector (34-2097118, default = 2048) or {+-}size{KMGTP}:
        Last sector (2048-2097118, default = 2097118) or {+-}size{KMGTP}: +200M
        Current type is 'Linux filesystem'
        Hex code or GUID (L to show codes, Enter = 8300):
        Changed type of partition to 'Linux filesystem'
        Command (? for help): n
        Partition number (2-128, default 2):
        First sector (34-2097118, default = 411648) or {+-}size{KMGTP}:
        Last sector (411648-2097118, default = 2097118) or {+-}size{KMGTP}:
        Current type is 'Linux filesystem'
        Hex code or GUID (L to show codes, Enter = 8300):
        Changed type of partition to 'Linux filesystem'
        Command (? for help): p
        Disk /dev/hda: 2097152 sectors, 1024.0 MiB
        Sector size (logical): 512 bytes
        Disk identifier (GUID): F2A76123-73ED-4052-BAFE-6B37473E6187
        Partition table holds up to 128 entries
        Main partition table begins at sector 2 and ends at sector 33
        First usable sector is 34, last usable sector is 2097118
        Partitions will be aligned on 2048-sector boundaries
        Total free space is 2014 sectors (1007.0 KiB)
        Number  Start (sector)    End (sector)  Size       Code  Name
        1            2048          411647   200.0 MiB   8300  Linux filesystem
        2          411648         2097118   823.0 MiB   8300  Linux filesystem
        Command (? for help): w
        Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
        PARTITIONS!!
        Do you want to proceed? (Y/N): Y
        OK; writing new GUID partition table (GPT) to /dev/hda.
        The operation has completed successfully.
        The disk has been partitioned:
        $$  ls -l /dev/hda1
        brw------- 0 renzo renzo 0, 1 Jan  1  1970 /dev/hda1
        $$ ls -l /dev/hda2
        brw------- 0 renzo renzo 0, 2 Jan  1  1970 /dev/hda2

Now it is possible to create an ext4 partition on /dev/hda1

        $$ /sbin/mkfs.ext4 /dev/hda1
        mke2fs 1.45.1 (12-May-2019)
        warning: Unable to get device geometry for /dev/hda1
        Creating filesystem with 204800 1k blocks and 51200 inodes
        Filesystem UUID: c96c6499-40cd-43df-addf-52e06d7e6842
        Superblock backups stored on blocks:
                8193, 24577, 40961, 57345, 73729
        Allocating group tables: done
        Writing inode tables: done
        Creating journal (4096 blocks): done
          Writing superblocks and filesystem accounting information: done

now the file system on /dev/hda1 can be mounted on /mnt

        $$ vumount -t vufuseext2 -o rw+ /dev/hda1 /mnt

add a significative file on /mnt

        $$ echo ciao * /mnt/hello
        $$ ls -l /mnt
        total 13
        -rw-r--r-- 1 renzo renzo     5 Jun  3 12:09 hello
        drwx------ 2 root  root  12288 Jun  3 12:06 lost+found
        $$ vuumount /mnt
        $$ vuumount /dev/hda
        $$ exit
        $

  mount a user-level networking stack
It is possible to provide network partial virtualization using the vunet module

start the hypervisor, and run a bash inside the partial virtual machine

        $ umvu bash

This is the prompt of the partial virtualized shell, let us change it to $$ to show the difference

        $ PS1='\$\$ '

let us load vunet

        $$ vu_insmod vunet

the following command #mounts# a vde network on /dev/net/myvde. (see https://github.com/rd235/vdeplug4)

        $$ vumount -t vunetvdestack vxvde:// /dev/net/myvde

vustack is the command to select the stack to use.

        $$ vustack /dev/net/myvde ip link
        1: lo: *LOOPBACK* mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000
            link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        2: vde0: *BROADCAST,MULTICAST* mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
            link/ether 7e:76:c0:d7:3b:37 brd ff:ff:ff:ff:ff:ff

without vustack I can still access the stack provided by the linux kernel

        $$ ip link
        1: lo: *LOOPBACK,UP,LOWER_UP* mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
            link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        2: eth0: *BROADCAST,MULTICAST,UP,LOWER_UP* mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
            link/ether 80:aa:bb:cc:dd:ee brd ff:ff:ff:ff:ff:ff

let us start a bash using /dev/net/myvde as itsdfault net

        $$ vustack /dev/net/myvde bash
        $ PS1='\$N\$ '

let us configure the net

        $N$ ip addr add 192.168.250.250/24 dev vde0
        $N$ ip link set vde0 up
        $N$ ip route add default via 192.168.250.1
        $N$ ip addr
        1: lo: *LOOPBACK* mtu 65536 qdisc noop state DOWN group default qlen 1000
            link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
        2: vde0: *BROADCAST,MULTICAST,UP,LOWER_UP* mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
            link/ether 7e:76:c0:d7:3b:37 brd ff:ff:ff:ff:ff:ff
            inet 192.168.250.250/24 scope global vde0
               valid_lft forever preferred_lft forever
            inet6 fe80::7c76:c0ff:fed7:3b37/64 scope link
               valid_lft forever preferred_lft forever
        $N$ ip route
        default via 192.168.250.1 dev vde0
        192.168.250.0/24 dev vde0 proto kernel scope link src 192.168.250.250
        $N$ ping 80.80.80.80
        PING 80.80.80.80 (80.80.80.80) 56(84) bytes of data.
        64 bytes from 80.80.80.80: icmp_seq=1 ttl=52 time=56.9 ms
        64 bytes from 80.80.80.80: icmp_seq=2 ttl=52 time=57.9 ms
        ^C
        $N$

SEE ALSO
vu_insmod(1), vu_lsmod(1), vu_rmmod(1), vumount(1), vuumount(1), vudebug(1)

AUTHOR
VirtualSquare. Project leader: Renzo Davoli