IPv6 and dual (IPv4 and IPv6) stack support #1187
Since a long time, IPv6 code was around in our TCP/IP stack (thanks to @nojb
who developed it in 2014). Some months ago, @hannesm and @MagnusS got excited
to use it. After we managed to fix some bugs and add some test cases, and
writing more code to setup IPv6-only and dual stacks, we are eager to share
this support for MirageOS in a released version. We expect there to be bugs
lingering around, but duplicate address detection (neighbour solicitation and
advertisements) has been implemented, and (unless
"--accept-router-advertisement=false") router advertisements are decoded and
used to configure the IPv6 part of the stack. Configuring a static IPv6 address
is also possible (with "--ipv6=2001::42/64").
While at it, we unified the boot arguments between the different targets:
namely, on Unix (when using the socket stack), you can now pass
"--ipv4=127.0.0.1/24" to the same effect as the direct stack: only listen
on 127.0.0.1 (the subnet mask is ignored for the Unix socket stack).
A dual stack unikernel has "--ipv4-only=BOOL" and "--ipv6-only=BOOL" parameters,
so a unikernel binary could support both Internet Protocol versions, while the
operator can decide which protocol version to use.
Please also note that the default IPv4 network configuration no longer uses
10.0.0.1 as default gateway (since there was no way to unset the default
For unikernel developers, there are some API changes in the Mirage module
- New "v4v6" types for IP protocols and stacks
- The ipv6_config record was adjusted in the same fashion as the ipv4_config
type: it is now a record of a network (V6.Prefix.t) and gateway (V6.t option)
Some parts of the Mirage_key module were unified as well:
- Arp.ip_address is available (for a dual Ipaddr.t)
- Arg.ipv6_address replaces Arg.ipv6 (for an Ipaddr.V6.t)
- Arg.ipv6 replaces Arg.ipv6_prefix (for a Ipaddr.V6.Prefix.t)
- V6.network and V6.gateway are available, mirroring the V4 submodule
If you're ready to experiment with the dual stack, here's a diff for our basic
network example (from mirage-skeleton/device-usage/network) replacing IPv4
with a dual stack:
diff --git a/device-usage/network/config.ml b/device-usage/network/config.ml
The Xen backend is a minimal legacy-free re-write: Solo5 (since 0.6.6) provides
the low-level glue code, and ocaml-freestanding provides the OCaml runtime. The
PV-only Mini-OS implementation has been retired.
The only supported virtualization mode is now Xen PVH (version 2 or above),
supported since Xen version 4.10 or later (and Qubes OS 4.0).
The support for the ARM32 architecture on Xen has been removed.
Security posture improvements:
With the move to a Solo5 and ocaml-freestanding base MirageOS gains several
notable improvements to security posture for unikernels on Xen:
- Stack smashing protection is enabled unconditionally for all C code.
- W^X is enforced throughout, i.e.
read-only, non-executable and
.data, heap and stack are read-write and
- The memory allocator used by the OCaml runtime is now dlmalloc (provided by
ocaml-freestanding), which is a big improvement over the Mini-OS malloc, and
incorporates features such as heap canaries.
- With the rewrite of the Xen core platform stack, several Xen-specific APIs
have changed in incompatible ways; unikernels may need to be updated. Please
refer to the mirage-xen v6.0.0 change
log for a list of
interfaces that have changed along with their replacements.
- OCaml 4.08 is the minimum supported version.
- A dummy
dev-repofield is emitted for the generated opam file.
- .xe files are no longer generated.
- Previous versions of MirageOS would strip boot parameters on Xen, since Qubes
OS 3.x added arguments that could not be interpreted by our command line
parser. Since Qubes OS 4.0 this is no longer an issue, and MirageOS no longer
strips any boot parameters. You may need to execute
qvm-prefs qube-name kernelopts ''.
- Thanks to Roger Pau Monné, Andrew Cooper and other core Xen developers for
help with understanding the specifics of how PVHv2 works, and how to write an
implementation from scratch.
- Thanks to Marek Marczykowski-Górecki for help with the Qubes OS specifics, and
for forward-porting some missing parts of PVHv2 to Qubes OS version of Xen.
- Thanks to @palainp on Github for help with testing on Qubes OS.
- handle errors from Bos.OS.Cmd.run_out
- use PREFIX if defined (no need to call "opam config var prefix")
- adapt to conduit 2.2.0, tls 0.12, mirage-crypto 0.7.0 changes