svn commit: r361275 - in head/sys: conf dev/hyperv/hvsock dev/hyperv/include dev/hyperv/vmbus modules/hyperv modules/hyperv/hvsock sys

[Kyle Evans]

On Fri, May 29, 2020 at 12:08 PM Wei Hu <weh at microsoft.com> wrote:
> > -----Original Message-----
> > > > [... snip ...]
> > > > +void
> > > > +hvs_trans_init(void)
> > > > +{
> > > > +       /* Skip initialization of globals for non-default instances. */
> > > > +       if (!IS_DEFAULT_VNET(curvnet))
> > > > +               return;
> > > > +
> > > > +       if (vm_guest != VM_GUEST_HV)
> > > > +               return;
> > > > +
> > > > +       HVSOCK_DBG(HVSOCK_DBG_VERBOSE,
> > > > +           "%s: HyperV Socket hvs_trans_init called\n", __func__);
> > > > +
> > > > +       /* Initialize Globals */
> > > > +       previous_auto_bound_port = MAX_PORT;
> > > > +       sx_init(&hvs_trans_socks_sx, "hvs_trans_sock_sx");
> > > > +       mtx_init(&hvs_trans_socks_mtx,
> > > > +           "hvs_trans_socks_mtx", NULL, MTX_DEF);
> > > > +       LIST_INIT(&hvs_trans_bound_socks);
> > > > +       LIST_INIT(&hvs_trans_connected_socks);
> > > > +}
> > > > +
> > >
> > > I have a suspicion that all of these should really be per-vnet for
> > > correct semantics with VIMAGE, with the IS_DEFAULT_VNET check earlier
> > > dropped completely. I haven't read around the rest all that much, but
> > > this would at least seem to prevent port re-use by a different vnet,
> > > which is perhaps "good enough" but I think this is something that
> > > should be fixed in the mid-term.
> > >
> >
> > I have a follow-up concern about whether this is actually going to be
> > maintained... it's been a full week with not even an acknowledgement or
> > rebuttal of any of the concerns I've raised, with some of them being completely
> > trivial to address in the short-term. I don't think that we really want this in the
> > tree in its current state given this level of engagement.
> >
> Sorry for my late response, Kyle. I read your comments last week. To be honest I am
> not familiar to VNET and VIMAGE, so I don't quite understand. I got distracted
> into other work so my response to this was delayed.
>
> Do you mean to drop these two lines?
>        if (!IS_DEFAULT_VNET(curvnet))
>                return
> I copied these from other socket init code. If they are not necessary I can remove them.
>

Alright, let's rewind a little bit here. =-) Consider while reading
the below that I have no idea what the host-side of these sockets look
like beyond what I just very quickly skimmed from [0].

It's a little more involved than that; consider each vnet as its own
independent network stack that's largely isolated from other vnets.
The host starts out with a vnet, vnet0 (the default vnet), and root
may spawn additional vnets attached to jails to allow the jail to
operate its own network stack as well. Your pr_init will get called
once per vnet spawned, including the obvious default vnet, which is
why the check is there in the first place -- you may have some global
state that only needs to be initialized once, at which point you would
exclude non-default vnets from executing those bits.

The more I think about it, though, the more I wonder if hvsock makes
sense at all in non-default vnet contexts and whether hvs_trans_attach
should really be attaching to sockets outside of the default vnet. You
can bind in your FreeBSD HyperV guest to a port, and a host service's
option for connecting is specifying guest GUID + port; there's not
really any wiggle room for multiple entities within a guest to be
binding to a given port anyways. It may very well be the case that the
status quo is the optimal outcome.

Given that, does it make sense that the host connects via the guest
GUID and can potentially end up connected to some jail of unknown
trust operating its own network stack?

As a final scattered thought for the hour, does the Linux
implementation of this stuff do anything to give a guest admin
visibility into existing HyperV sockets on the system? AFAICT here,
there's no sockstat integration or anything else that might export
hvsock information to userland, so one's only option to tracking down
whether a HyperV socket even exists and to which process it belongs
would appear to be probing around in the kernel.

Thanks,

Kyle Evans

[0] https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/user-guide/make-integration-service