Re: New user getting started questions

Thomas Leonard
2021-01-06T15:56:56Z

On Wed, 6 Jan 2021 at 07:01, Alyssa Ross <hi@alyssa.is> wrote:
>
> Hi! Thanks for getting in touch. :)
>
> To be honest, I'm surprised you got as far as you did -- like Michael
> says, I'm currently working towards a proof of concept, so none of what
> you've tried out so far is really meant for use outside of that proof of
> concept.
[...]
> > nix-build . -A spectrumPackages && ./result-3/bin/spectrum-vm
> >
> > (I'm fairly new to Nix, so not sure if this is the right way to do things)
>
> Pretty close -- spectrumPackages is an attribute set containing lots of
> derivations, which is why you end up with lots of numbered result-*
> symlinks. If you do -A spectrumPackages.spectrum-vm it'll just give you
> a single result symlink pointing to that, and you won't need to go
> hunting for the right one. :)

That's better, thanks!

[...]
> > - I tried adding `--shared-dir /tmp/ff:ff:type=9p` to share a host
> > directory. Then `mount -t 9p -o trans=virtio,version=9p2000.L ff /tmp`
> > in the VM seemed to work, but `ls /tmp` crashed the VM.
>
> Yeah, this is a known issue. I have a patch[1] for it but didn't add it
> to the package since I mostly have been working with my own source
> builds of crosvm.
>
> [1]: https://spectrum-os.org/git/crosvm/commit/?id=1e318da5b57c12f67bed3b528100dbe4ec287ac5

Ah, I didn't realise it was using seccomp too. I'm not sure how to
compile specific versions of crosvm. I tried with:

srcs = lib.genAttrs [
"src/third_party/adhd"
"src/aosp/external/minijail"
] getSrc // { "src/platform/crosvm" = /home/.../crosvm; };

and blanked out the hash as it requested, but then:

error: failed to sync Caused by: failed to load pkg lockfile Caused
by: failed to resolve patches for
`https://github.com/rust-lang/crates.io-index` Caused by: failed to
load source for dependency `libvda` Caused by: Unable to update
/build/src/platform2/arc/vm/libvda/rust Caused by: failed to read
`/build/src/platform2/arc/vm/libvda/rust/Cargo.toml`

Looks like this happens since 57df6a0ab23c3b2ba233b9aa5886ecf47ba3f91f
(added a dependency?). Commit 460406d10bbfaa890d56d616b4610813da63a312
just before that gets further, but:

error: the lock file /build/src/platform/crosvm/Cargo.lock needs to be
updated but --frozen was passed to prevent this

How do you build it?

(sorry for these basic Nix/Rust questions)

However, I could get 9p to work by running the previous version with
--seccomp-log-failures. With that, I can read and write files from the
console, but I can't chown things and so can't write from the terminal
window, which is running as a user. I guess it needs uidmap set, but
I'm not sure how to make that work.

> > - I tried using `-d /dev/mapper/disk` to share an LVM partition, but
> > `mount -t ext4 /dev/vdb /tmp` refused to mount it.
>
> Never tried that, so I don't know anything about it I'm afraid.

OK, I'll keep trying stuff. I have discovered that if I add the
squashfs file as another device (--root "$rootfs" -d "$rootfs") then
it shows an error but mounts it anyway!

# ls /tmp
# mount /dev/vdb /tmp
[ 15.288873] /dev/vdb: Can't open blockdev
# ls /tmp
bin dev etc nix proc run sbin sys tmp

Sadly, this didn't work with my ext4 partition.

> > - I tried enabling networking with `--host_ip 10.0.0.1`, etc, but it
> > said it couldn't create a tap device. I guess it needs more
> > privileges.
>
> Yeah, crosvm needs to be CAP_NET_ADMIN for that (which is difficult to
> do with Nix). You can make a TAP device yourself iproute2 and use
> --tap-fd to tell crosvm to use it, or you can use the mktuntap program I
> wrote (with a privelege drop after running mktuntap), like this:
>
> sudo mktuntap -pvB 3 \
> sudo -u $USER -C 4 result/bin/spectrum-vm -- --tap-fd 3

OK, I tried like this:

exec sudo "$mktuntap" -pvB 3 \
sudo -u "$USER" -C 4 \
"$crosvm" run \
-p init=/sbin/init \
-p "spectrumcmd=$(printf %s "$command" | base64 -w0)" \
--tap-fd 3 \
--seccomp-log-failures \
--root "$rootfs" \
--host_ip 10.0.0.1 \
--netmask 255.0.0.0 \
--mac c0:ff:ee:c0:ff:ee \
-m 4096 \
"$@" \
"$kernel"

I got "sudo: you are not permitted to use the -C option", which I
fixed by editing the sudoers file. Then it fails with:

[ERROR:src/main.rs:1351] The architecture failed to build the vm:
error creating devices: failed to set up virtio networking: failed to
open tap device: failed to create tap interface: Operation not
permitted (os error 1)

Strace shows:

openat(AT_FDCWD, "/dev/net/tun", O_RDWR|O_NONBLOCK|O_CLOEXEC) = 31
ioctl(31, TUNSETIFF, 0x7ffee7ede238) = -1 EPERM (Operation not permitted)

Maybe it's just because my crosvm is too old?

> > Ideally, I'd like to run a VM with each of my old Qubes filesystems,
> > to get back to where I was with my Qubes setup, before investigating
> > new spectrum stuff (e.g. one app per VM). Do you have any advice on
> > this? I see these lists are a bit quiet - I hope someone is still
> > working on this because it sounds great :-)
>
> Like Michael said, there's a lot I need to do before it's really ready
> to use like this, but I am working on it (or at least I will be again
> once my anti-burnout break ends).

Great! I'm on a break myself at the moment, which is why I have some
time to try all this out.

> Once I am, I hope to be more active
> on the lists again. I used to post weekly status updates, and would
> like to get into doing that again once I'm back because they were a
> great way to keep people up to date with the project and for me to have
> a record of what I'd been doing. Reading some of the old status updates
> should give you a bit of a feel for where things are, although things
> are a bit further along than they were when I wrote the last one because
> I put the status updates on hold to try to chase a funding milestone.

I've read some of them - they're very helpful!

> Hope that's all clear -- please ask more questions if you have them,
> although if it's anything particularly in the weeds I might wait until
> I'm back from my break to answer. :)

I have many questions :-) But don't feel pressured to answer them; I
need to figure out how to make this all work myself anyway, and it's
just a bonus if you've already done the work for me...

--
talex5 (GitHub/Twitter) http://roscidus.com/blog/
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