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Re: [PATCH v5 0/6] Add vmnet.framework based network backend


From: Jason Wang
Subject: Re: [PATCH v5 0/6] Add vmnet.framework based network backend
Date: Tue, 16 Nov 2021 15:23:11 +0800

On Mon, Nov 15, 2021 at 6:45 PM Vladislav Yaroshchuk
<yaroshchuk2000@gmail.com> wrote:
>
>
>
> пн, 15 нояб. 2021 г. в 07:53, Jason Wang <jasowang@redhat.com>:
>>
>> On Fri, Nov 12, 2021 at 5:14 PM Vladislav Yaroshchuk
>> <yaroshchuk2000@gmail.com> wrote:
>> >
>> > macOS provides networking API for VMs called 'vmnet.framework':
>> > https://developer.apple.com/documentation/vmnet
>> >
>> > We can provide its support as the new QEMU network backends which
>> > represent three different vmnet.framework interface usage modes:
>> >
>> >   * `vmnet-shared`:
>> >     allows the guest to communicate with other guests in shared mode and
>> >     also with external network (Internet) via NAT. Has (macOS-provided)
>> >     DHCP server; subnet mask and IP range can be configured;
>> >
>> >   * `vmnet-host`:
>> >     allows the guest to communicate with other guests in host mode.
>> >     By default has enabled DHCP as `vmnet-shared`, but providing
>> >     network unique id (uuid) can make `vmnet-host` interfaces isolated
>> >     from each other and also disables DHCP.
>> >
>> >   * `vmnet-bridged`:
>> >     bridges the guest with a physical network interface.
>> >
>> > This backends cannot work on macOS Catalina 10.15 cause we use
>> > vmnet.framework API provided only with macOS 11 and newer. Seems
>> > that it is not a problem, because QEMU guarantees to work on two most
>> > recent versions of macOS which now are Big Sur (11) and Monterey (12).
>> >
>> > Also, we have one inconvenient restriction: vmnet.framework interfaces
>> > can create only privileged user:
>> > `$ sudo qemu-system-x86_64 -nic vmnet-shared`
>> >
>> > Attempt of `vmnet-*` netdev creation being unprivileged user fails with
>> > vmnet's 'general failure'.
>> >
>> > This happens because vmnet.framework requires `com.apple.vm.networking`
>> > entitlement which is: "restricted to developers of virtualization software.
>> > To request this entitlement, contact your Apple representative." as Apple
>> > documentation says:
>> > https://developer.apple.com/documentation/bundleresources/entitlements/com_apple_vm_networking
>>
>> Do you know how multipass work? Looks like it uses vmnet without privileges.
>>
>
> I've just checked this, and they still need root privileges. They have a
> `multipassd` daemon which is launched as root by launchd by default.
>
> ```
> bash-5.1$ ps axo ruser,ruid,comm | grep multipass
> root                 0 /Library/Application 
> Support/com.canonical.multipass/bin/multipassd
> root                 0 /Library/Application 
> Support/com.canonical.multipass/bin/hyperkit
> ```
>
> That's the reason why it's required to 'enter a password' while multipass 
> installation:
> it creates launchd plist (kinda launch rule) and places it to 
> /Library/LaunchDaemons/,
> which can be done only with root privileges.
>
> ```
> bash-5.1$ ll /Library/LaunchDaemons | grep multipass
> -rw-r--r--   1 root  wheel   1.1K 15 Nov 12:47 com.canonical.multipassd.plist
> ```
>
> And after this launchd launches this multipassd daemon as root every boot.
>
> So an unprivileged user can launch a multipass VM instance, but actually the
> `hyperkit` process which interacts with vmnet is gonna be launched by 
> multipassd
> running as root.

I wonder how it passes the vmnet object to qemu? Nothing obvious from
the qemu command line that multipass launched:

-nic vmnet-macos,mode=shared,model=virtio-net-pci,mac=52:54:00:52:e8:e4

(But I haven't had time to check their qemu codes).

>
> tl;dr sadly, we can't interact with vmnet.framework without having our binary 
> correctly
> signed and being an unprivileged user. Root privileges or special signature 
> with
> entitlement is required.

This is something similar to what happens in other OS. E.g for the tap
backend, it can't be created without privileges. So qemu allows to:

1) the TAP to be created by privileged program like libvirt, and its
fd could be passed to qemu via SCM_RIGHTS
2) run a set-uid helper to create and config TAP

This is something we need to consider now or in the future probably.

Thanks

>
>
>> Thanks
>>
>
> Thank you for your review, I will check it this week and reply as soon as 
> possible.
>
>>
>> >
>> > One more note: we still have quite useful but not supported
>> > 'vmnet.framework' features as creating port forwarding rules, IPv6
>> > NAT prefix specifying and so on.
>> >
>> > Nevertheless, new backends work fine and tested within `qemu-system-x86-64`
>> > on macOS Bir Sur 11.5.2 host with such nic models:
>> >   * e1000-82545em
>> >   * virtio-net-pci
>> >   * vmxnet3
>> >
>> > The guests were:
>> >   * macOS 10.15.7
>> >   * Ubuntu Bionic (server cloudimg)
>> >
>> >
>> > This series partially reuses patches by Phillip Tennen:
>> > https://patchew.org/QEMU/20210218134947.1860-1-phillip.ennen@gmail.com/
>> > So I included his signed-off line into one of the commit messages and
>> > also here.
>> >
>> > v1 -> v2:
>> >  Since v1 minor typos were fixed, patches rebased onto latest master,
>> >  redundant changes removed (small commits squashed)
>> >
>> > v2 -> v3:
>> >  - QAPI style fixes
>> >  - Typos fixes in comments
>> >  - `#include`'s updated to be in sync with recent master
>> > v3 -> v4:
>> >  - Support vmnet interfaces isolation feature
>> >  - Support vmnet-host network uuid setting feature
>> >  - Refactored sources a bit
>> > v4 -> v5:
>> >  - Missed 6.2 boat, now 7.0 candidate
>> >  - Fix qapi netdev descriptions and styles
>> >    (@subnetmask -> @subnet-mask)
>> >  - Support vmnet-shared IPv6 prefix setting feature
>> >
>> > Signed-off-by: Phillip Tennen <phillip@axleos.com>
>> > Signed-off-by: Vladislav Yaroshchuk <yaroshchuk2000@gmail.com>
>> >
>> > Vladislav Yaroshchuk (6):
>> >   net/vmnet: add vmnet dependency and customizable option
>> >   net/vmnet: add vmnet backends to qapi/net
>> >   net/vmnet: implement shared mode (vmnet-shared)
>> >   net/vmnet: implement host mode (vmnet-host)
>> >   net/vmnet: implement bridged mode (vmnet-bridged)
>> >   net/vmnet: update qemu-options.hx
>> >
>> >  meson.build                   |   4 +
>> >  meson_options.txt             |   2 +
>> >  net/clients.h                 |  11 ++
>> >  net/meson.build               |   7 +
>> >  net/net.c                     |  10 ++
>> >  net/vmnet-bridged.m           | 111 ++++++++++++
>> >  net/vmnet-common.m            | 325 ++++++++++++++++++++++++++++++++++
>> >  net/vmnet-host.c              | 111 ++++++++++++
>> >  net/vmnet-shared.c            |  92 ++++++++++
>> >  net/vmnet_int.h               |  48 +++++
>> >  qapi/net.json                 | 127 ++++++++++++-
>> >  qemu-options.hx               |  25 +++
>> >  scripts/meson-buildoptions.sh |   3 +
>> >  13 files changed, 874 insertions(+), 2 deletions(-)
>> >  create mode 100644 net/vmnet-bridged.m
>> >  create mode 100644 net/vmnet-common.m
>> >  create mode 100644 net/vmnet-host.c
>> >  create mode 100644 net/vmnet-shared.c
>> >  create mode 100644 net/vmnet_int.h
>> >
>> > --
>> > 2.23.0
>> >
>>
>
>
> --
> Best Regards,
>
> Vladislav Yaroshchuk




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