VUOS is a Virtual Operating System implemented at user space. Currently it implements about 150 Linux-compatible system calls providing support for a wide range of applications. Each process or even each thread in VUOS can see a different execution environment: file system contents, networking, devices, user ids etc. The main idea behind VUOS is that it is possible to give processes their own "view" using partial virtual machines.
VUOS is a different perspective on namespaces, anykernels and related concepts.
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.
Processes
v
+------------------+
| PSV hypervisor | --> virtualizing modules
+------------------+
v
(linux) kernel
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 stack, change the structure of the file system tree, create virtual devices.
The hypervisor is just a user process so while it gives new perspective for processes, it does not widen the attack surface of the kernel.
... just to show something VUOS is capable of. NB: VUOS is much much more than this, and it is under active developmemnt.
This example uses umvu: a user-mode implementation of the VUOS concepts based on ptrace. In the future VUOS could be re-implemented on other tracing/virtualizing supports.
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 fuse
nothing is currently mounted on /mnt
$$ ls /mnt
run the FUSE handler program (it uses the virtual /dev/fuse) $$ fuse-ext2 -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).
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
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 $$ to show the difference
$ PS1='\$\$ '
let us load vudev and fuse: vudev to virtualize devices and fuse as in the previous example
$$ vu_insmod vudev fuse
Note: it is possible to use vufuse instead of fuse. the command is 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
$$ /sbin/mkfs.ext4 /dev/hda1
mke2fs 1.45.1 (12-May-2019)
warning: Unable to get device geometry for /dev/hda1
Creating filesystem with 204800 1k blocks and 51200 inodes
Filesystem UUID: c96c6499-40cd-43df-addf-52e06d7e6842
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
now the file system on /dev/hda1 can be mounted on /mnt
$$ fuse-ext2 -o rw+ /dev/hda1 /mnt
Note: the mount command for vufuse instead of fuse is 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
$$ exit
$
It is possible to provide network partial virtualization using the vunet module
start the hypervisor, and run a bash inside the partial virtual machine
$ umvu bash
This is the prompt of the partial virtualized shell, let us change it to $$ to show the difference
$ PS1='\$\$ '
let us load vunet
$$ vu_insmod vunet
the following command mounts a vde network on /dev/net/myvde using libioth. (see https://github.com/rd235/vdeplug4) (any ioth supported stack can be used. The mount source argument is the stack implementation to use, vdestack in this example).
$$ vumount -t vunetioth -o vxvde:// vdestack /dev/net/myvde
Alternatively: the following command uses a vunet specific implementation of vdestack:
$$ vumount -t vunetvdestack vxvde:// /dev/net/myvde
vustack is the command to select the stack to use.
$$ 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
$N$
umvu has a three layer architecture:
- core
umvuhypervisor - modules (e.g.
vufuse, vunet, vufs, vudev) - submodules (e.g. vufuseext2, vudevpartx, vudevnull, vunetvdestack
umvu traces all the system call requests generated by the processes and by the modules and decides if the request is real or virtual and in this latter case which is the module to reroute the request.
Absolute pathnames, file descriptors, family of protocols, ioctl tags, syscall number can be used to select the right module.
Modules register their boundary of responsibility to the core hypervisor: i.e. which path prefixes, file descriptors,
etc. they are responsible for.
The API of modules consists of a subset of the system call API. When a process uses a read system call on a virtualized
file (e.g. a file in a vumounted partition), the corresponding module receives a read request having the same signature
of the standard system call. As an example the test module test_modules/unreal.c, provides a view of the entire file
system in /unreal and in /unreal/unreal simply using the system calls as module methods. (e.g. the function to implement
lstat in the module is lstat, and so on. The only two function that had to be defined were: getdents64 as gliibc does not provide an interface to it and access as it lacks a flags argument).
The API between modules and submodules is tailored to the specific requirements. The API for filesystems has been chose to provide source level compatibility with FUSE modules.
In order to test umvu several libraries and helper tools are required. The tests here above have been run on debian sid.
For the sake of compleness (and hopefully clarity), it is possible to install all the code by hand, step by step as briefly explained in the following.
First of all install the following packets:
git python3 build-essential cmake make autogen autoconf libtool libcap-dev libattr1-dev libfuse-dev libexecs-dev
libssl1.0-dev libmhash-dev libpam0g-dev libfuse-dev e2fsprogs comerr-dev e2fslibs-dev libpam-dev libmhash-dev
Then install libraries and tools from the following list of git repositories:
https://github.com/rd235/strcase.git
https://github.com/virtualsquare/vde-2.git
https://github.com/rd235/vdeplug4.git
https://github.com/virtualsquare/purelibc.git
https://github.com/rd235/libvolatilestream.git
https://github.com/rd235/libstropt.git
https://github.com/rd235/libfduserdata.git
https://github.com/rd235/libvpoll-eventfd.git
https://github.com/rd235/libvdestack.git
https://github.com/rd235/vdeplug_vlan.git
https://github.com/rd235/cado.git
https://github.com/alperakcan/fuse-ext2.git
https://github.com/rd235/vdeplug_agno.git
https://github.com/rd235/vdens.git
https://github.com/virtualsquare/libioth.git
https://github.com/virtualsquare/vuos.git
A symbolic link is required to make vufuseext2 reachable in the right dir
ln -s /usr/local/lib/umview/modules/umfuseext2.so /usr/local/lib/vu/modules/vufuseext2.so