August 2021 - Spectrum Development

This Week in Spectrum, 2021-W33
by Alyssa Ross 22 Aug '21

22 Aug '21

Hi! I've had a busy day today and am pretty tired, so I'm not sure how coherent my writing is at the moment. But I'd rather get this out on time, especially since tomorrow is also busy today. As I said last week[1], I took some time off this week as a preventative measure against burnout. [1]: https://spectrum-os.org/lists/archives/spectrum-devel/87lf51ybwk.fsf@alyssa… rust-vmm -------- One of my patches[2] was accepted, but another[3] is still waiting. As I said last week, I have more fixes for rust-vmm planned, but want to let them catch up with the changes I've already sent upstream first so I know what base I'm using for the next stuff. I expect the one that's still waiting to be accepted next week. [2]: https://github.com/rust-vmm/vmm-sys-util/pull/135 [3]: https://github.com/rust-vmm/vhost/pull/69 spectrum-live ------------- Last week, I'd just integrated dm-verity into the Spectrum live image I've been working on. When it came time to work on the actual root filesystem, instead of the initramfs, I hit a bit of a brick wall. I realised that trying to generate a whole operating system image using Nix was giving me real writers' block. There was too much inbetween me and how the files ended up on disk, and that meant there was too much overhead to keep in mind when I was thinking about how things should be designed and laid out. It might feel like making a Linux root filesystem should be a solved problem, but Spectrum has a bunch of special requirements. You might want to do something like start a VM for each hardware device of a specific type, and that's something that isn't really addressed by most standard stuff. All this stuff is definitely solveable, but it requires some experimentation to get right, and Nix was getting a bit in the way of that. So I created a new directory, and I wrote a Makefile that builds an ext4 image, and I just started putting files in an etc/ directory. This made reasoning about the system way easier, and I was immediately making progress. Nix is great for building known targets, and for making customisable systems (there's no way my Makefile-based system would allow the amount of customisation I'd easily be able to provide with Nix), but for experimentation, it's a lot nicer to be closer to the end product. So once I know how all this should look I'll make it Nix-aware. Currently, I have a root filesystem with a service manager that can respond to hardware appearing and disappearing. The next (more exciting) step will be to have it start some VMs, and assign hardware to them appropriately. I'm looking forward to getting to that next week. An interesting challenge I'll have to solve will be figuring out simple categories (e.g. "ethernet device") from the huge amount of very specific information the kernel provides. I think I might be able abuse the modules.alias file from the kernel, that defines the mappings from PCI etc. information to default drivers. Then all I'll have to do will be to write mappings from default drivers to whatever categories I come up with, or what VM I want to assign them to, or whatever. One neat thing I'm using for the first time here is tar2ext4[4], a utility program that's part of a larger Microsoft open source project I don't entirely understand the purpose of. It's really useful for me it builds ext4 images entirely in userspace, which will be great for using in Nix derivations where it's not possible to just mount an ext4 image and write directly to it. For previous Spectrum experiments, I'd always used SquashFS[5], entirely because I already knew of a tar2sqfs program[6] that made creating filesystem images really easy. I've added tar2ext4 to Nixpkgs[7], which will hopefully help other people who have similar problems discover it. [4]: https://github.com/microsoft/hcsshim/blob/master/cmd/tar2ext4/tar2ext4.go [5]: https://en.wikipedia.org/wiki/SquashFS [6]: https://github.com/AgentD/squashfs-tools-ng [7]: https://github.com/NixOS/nixpkgs/pull/134650 musl ---- While I was working on the root filesystem, I noticed that mount -a, which mounts all filesystems described in fstab(5), wasn't working. This turned out to be because of a bug in Musl's implementation of getmntent(3), a libc function for parsing fstab files. So I wrote some tests and a fix and sent them to Musl[8]. [8]: https://inbox.vuxu.org/musl/20210821085420.474615-1-hi@alyssa.is/ Hope that all made sense. Next week, I'll continue working on Spectrum live, and maybe fix the next rust-vmm issue I have on my todo list if my final outstanding PR is merged.

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[PATCH www] todo.html: refresh
by Alyssa Ross 21 Aug '21

21 Aug '21

The old tasks listed here aren't really relevant any more. But I would love me a static veritysetup -- it would massively reduce initramfs size. --- todo.html | 25 +++++++------------------ 1 file changed, 7 insertions(+), 18 deletions(-) diff --git a/todo.html b/todo.html index 67cf072..dc768e3 100644 --- a/todo.html +++ b/todo.html @@ -1,5 +1,5 @@ <!doctype html> - +   <html lang="en"> @@ -44,23 +44,12 @@ might be able to help out. <ol> <li> - Implement - <a href="https://wayland.freedesktop.org/docs/html/apa.html#protocol-spec-wl_composi…">wl_compositor - v4</a> in - <a href="https://spectrum-os.org/doc/developer-manual.html#_sommelier">Sommelier</a>. - This will mean we no longer have to - <a href="https://spectrum-os.org/git/nixpkgs/tree/pkgs/development/libraries/wlroots…">patch</a> - wlroots to downgrade it to an older protocol. - - <li> - Implement a ceiling for host memory allocated by the - crosvm <a href="https://spectrum-os.org/doc/developer-manual.html#_the_memfd_server">memfd - server</a>. - - <li> - Create a minimal VM kernel configuration. This will make it much - easier to iterate on the VM kernel, by substantially reducing clean - build times. + <a href="https://github.com/NixOS/nixpkgs/issues/134948">nixpkgs + #134984</a>: cryptsetup cannot be built statically. This would let + us massively reduce the size of Spectrum's initramfs. For Spectrum, + we only need the <code>veritysetup</code> program from that package + at the moment, so it's okay for us if other features have to be + disabled to make static linking work. </ol> <p> -- 2.32.0

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[PATCH www] bibliography.html: link to cgit atom feed
by Alyssa Ross 16 Aug '21

16 Aug '21

This is a very Worse is Better approach to letting people subscribe to new links, but it also has zero setup cost, and my budget for this right now is by coincidence pretty much zero. :) --- bibliography.html | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/bibliography.html b/bibliography.html index e2445a0..1ac6bc1 100644 --- a/bibliography.html +++ b/bibliography.html @@ -22,6 +22,10 @@ <h1>Bibliography</h1> +<p>If you'd like to find out when new links are posted, subscribe to +the <a href="https://spectrum-os.org/git/www/atom/bibliography.html">cgit +atom feed for this page</a>. + <ul> <li><cite><a href="https://flatkill.org/">Flatpak — a security -- 2.32.0

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This (Last) Week in Spectrum, 2021-W32
by Alyssa Ross 16 Aug '21

16 Aug '21

It's a short update this week, because most of what I did was a continuation of stuff from last week. rust-vmm -------- Last week, I mentioned I'd identified some Rust safety issues in rust-vmm. Most of the patches for these are now up[1][2][3]. The first has been accepted already, and I expect another to be accepted later today. There's still a UB issue I'm aware of and haven't sent a fix for yet, because there are a number of ways to fix it and I wanted to get my other patches in first before I decided how to fix that one. I deliberately haven't made any progress on using cloud-hypervisor's vhost-user-net backend with crosvm, which is what got me looking at this code in the first place. I want to make sure I can work on rust-vmm-adjacent things at a pace where I don't get overwhelmed with having to keep track of loads of patches and whether I've got them upstream yet. So I'll be putting that work on hold until the current round of patches are upstreamed. [1]: https://github.com/rust-vmm/vhost/pull/68 [2]: https://github.com/rust-vmm/vmm-sys-util/pull/135 [3]: https://github.com/rust-vmm/vhost/pull/69 spectrum-live ------------- For the past little while, in the time when I wasn't writing regular updates, I've been working on a live system for testing Spectrum. This will be especially useful for testing things like GPU support, because I can just build a live image with everything I might need, plug it into all the computers I want to test, and have everything be automatic from there. It will also probably evolve directly into what becomes the Spectrum base system that we'll hopefully all be running as the host system on our machines at some point. I shifted my focus back to this this week because of wanting to not get ahead of myself with rust-vmm. (I have a funding milestone for GPU support, so getting that checked off soon would be good.) The main thing I did this week was integrate dm-verity[4], which I did mostly for fun and to satisfy my curiosity. dm-verity is a Linux mechanism to efficiently ensure that a read-only filesystem hasn't been tampered with, by constructing a Merkle tree out of filesystem block hashes, and providing the root hash to the kernel when the filesystem is mounted. dm-verity is a _great_ fit for Nix, because we can generate the hashes at the same time as creating the filesystem image, and then embed the hash into the initramfs we're also building. Getting this all working took less than a day. The idea is that (long) in the future, we'll also implement Secure Boot, which will make sure the kernel and initramfs haven't been tampered with, and dm-verity will extend that integrity guarantee to the host system's root filesystem. I recommend reading "Producing a trustworthy x86-based Linux appliance"[5] by Matthew Garrett for an overview of how this all comes together. dm-verity is something that's particularly exciting to me, because it's very useful to us, but it's something that's generally used to frustrate end user attempts to control computers they own. In Spectrum, it's instead a tool that protects the end user against malicious filesystem changes, while being almost completely transparent to the user if they do want to modify their own system. Protecting against root filesystem tampering (which would require a VM escape or physical device access) is hardly the biggest priority for Spectrum, but integrating dm-verity was fun, interesting, and provided good motivation for working on the live image, which is one of the highest priority bits of the system. (Because I'm tired of having to say "you can't" when people ask me how they can try out Spectrum.) [4]: https://lwn.net/Articles/459420/ [5]: https://mjg59.dreamwidth.org/57199.html This week, I'm going to take a bit of time off as an anti-burnout defense, but probably not the whole week. I'll still keep an eye on the rust-vmm patches throughout this time as well, to make sure they're not delayed in getting accepted upstream.

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[PATCH nixpkgs] chromiumOSPackages.libqmi: don't enable doc twice
by Alyssa Ross 16 Aug '21

16 Aug '21

This is already enabled in the original derivation, so overriding it to add it here just means we end up passing the option twice. --- pkgs/os-specific/linux/chromium-os/libqmi/default.nix | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/pkgs/os-specific/linux/chromium-os/libqmi/default.nix b/pkgs/os-specific/linux/chromium-os/libqmi/default.nix index b96b5224b57..7328642d0b4 100644 --- a/pkgs/os-specific/linux/chromium-os/libqmi/default.nix +++ b/pkgs/os-specific/linux/chromium-os/libqmi/default.nix @@ -15,7 +15,7 @@ libqmi.overrideAttrs ( # ModemManager tests fail with QRTR in Chromium OS 91. # Will hopefully be fixed in CrOS 92. - configureFlags = configureFlags ++ [ "--enable-gtk-doc" "--disable-qrtr" ]; + configureFlags = configureFlags ++ [ "--disable-qrtr" ]; passthru = passthru // { updateScript = ../update.py; -- 2.32.0

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[PATCH nixpkgs] spectrumPackages: update execline backtick uses
by Alyssa Ross 12 Aug '21

12 Aug '21

execline 2.8.0.0 changed how backtick's options work: * -i (exit with the program's error code on failure) and -n (chomp off a trailing newline from the captured output) are now the defaults. * -E has been introduced, which does importas automatically. -E is fantastic, because we followed every single use of backtick with importas. Even we didn't have -n before, it's okay that chomping will now be enabled from the default, because in all those cases, there won't be a trailing newline anyway. --- .../linux/spectrum/testhost/default.nix | 14 ++++---------- pkgs/os-specific/linux/spectrum/vm/app/default.nix | 3 +-- pkgs/os-specific/linux/spectrum/vm/net/default.nix | 6 ++---- 3 files changed, 7 insertions(+), 16 deletions(-) diff --git a/pkgs/os-specific/linux/spectrum/testhost/default.nix b/pkgs/os-specific/linux/spectrum/testhost/default.nix index de62f0add67..d81ff8b826e 100644 --- a/pkgs/os-specific/linux/spectrum/testhost/default.nix +++ b/pkgs/os-specific/linux/spectrum/testhost/default.nix @@ -52,18 +52,14 @@ let # routers from clients. Other bits are reserved. # 5-6 Last two octets of client's IP (in 100.64.0.0/16). # - backtick -i router_mac { + backtick -E router_mac { pipeline { printf %.4x ${toString sys-vms.app.vmID} } sed s/^\$..\$\$..\$$/0A:B3:EC:80:\\1:\\2/ } - backtick -i client_mac { + backtick -E client_mac { pipeline { printf %.4x ${toString sys-vms.app.vmID} } sed s/^\$..\$\$..\$$/0A:B3:EC:00:\\1:\\2/ } - multisubstitute { - importas -iu router_mac router_mac - importas -iu client_mac client_mac - } # Create the net VM end, and attach it to the net VM. # @@ -143,12 +139,11 @@ let # is allowed to fail because it might already know that, in # which case it'll return EEXIST. if { modprobe vfio-pci } - backtick -in device_id { + backtick -E device_id { if { dd bs=2 skip=1 count=2 status=none if=''${PCI_PATH}/vendor } if { printf " " } dd bs=2 skip=1 count=2 status=none if=''${PCI_PATH}/device } - importas -iu device_id device_id foreground { redirfd -w 1 /sys/bus/pci/drivers/vfio-pci/new_id printf "%s" $device_id @@ -205,8 +200,7 @@ writeScriptBin "spectrum-testhost" '' if { redirfd -w 1 /proc/sys/net/ipv4/ip_forward echo 1 } importas -iu runtime_dir XDG_RUNTIME_DIR - backtick -in TOP { mktemp -dp $runtime_dir spectrum.XXXXXXXXXX } - importas -iu top TOP + backtick -E top { mktemp -dp $runtime_dir spectrum.XXXXXXXXXX } if { echo $top } if { rsync -r --chmod=Du+w ${servicesDir}/ ''${top}/service } background { diff --git a/pkgs/os-specific/linux/spectrum/vm/app/default.nix b/pkgs/os-specific/linux/spectrum/vm/app/default.nix index f8ff480932c..9ffed7e5b13 100644 --- a/pkgs/os-specific/linux/spectrum/vm/app/default.nix +++ b/pkgs/os-specific/linux/spectrum/vm/app/default.nix @@ -26,12 +26,11 @@ runCommand "vm-app" rec { oneshot ''; up = writeText "net-up" '' - backtick -i LOCAL_IP { + backtick -E LOCAL_IP { pipeline { ip -j link show eth0 } pipeline { jq -r ".[0].address | split(\":\") | .[4:6] | \"0x\" + .[]" } xargs printf "100.64.%d.%d" } - importas -iu LOCAL_IP LOCAL_IP if { ip address add ''${LOCAL_IP}/32 dev eth0 } if { ip link set eth0 up } diff --git a/pkgs/os-specific/linux/spectrum/vm/net/default.nix b/pkgs/os-specific/linux/spectrum/vm/net/default.nix index 5921b62fcf7..75c86b8f92c 100644 --- a/pkgs/os-specific/linux/spectrum/vm/net/default.nix +++ b/pkgs/os-specific/linux/spectrum/vm/net/default.nix @@ -54,12 +54,11 @@ runCommand "vm-net" rec { # Our IP is encoded in the NIC-specific portion of the # interface's MAC address. - backtick -i CLIENT_IP { + backtick -E CLIENT_IP { pipeline { ip -j link show $INTERFACE } pipeline { jq -r ".[0].address | split(\":\") | .[4:6] | \"0x\" + .[]" } xargs printf "100.64.%d.%d" } - importas -iu CLIENT_IP CLIENT_IP if { ip address add 169.254.0.1/32 dev $INTERFACE } if { ip link set $INTERFACE up } @@ -121,7 +120,7 @@ runCommand "vm-net" rec { ''; run = writeScript "connman-run" '' #! ${execline}/bin/execlineb -S0 - backtick -in HARDWARE_INTERFACES { + backtick -E HARDWARE_INTERFACES { pipeline { find -L /sys/class/net -mindepth 2 -maxdepth 2 -name address -print0 } @@ -132,7 +131,6 @@ runCommand "vm-net" rec { # Extract the interface names from the address file paths. awk -F/ "{if (NR > 1) printf \",\"; printf \"%s\", $5}" } - importas -iu HARDWARE_INTERFACES HARDWARE_INTERFACES ${connman}/bin/connmand -ni $HARDWARE_INTERFACES ''; base-commit: d2e147bedf251976ed99b94b6c905d6761f7a892 -- 2.32.0

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This Week in Spectrum, 2021-W31
by Alyssa Ross 08 Aug '21

08 Aug '21

What a week. Progress has felt a bit slow, but the work has been consistently interesting, and there have been some exciting developments in the ecosystem. Nixpkgs ------- Last week I'd posted the patches required to get all of Spectrum working with a more up-to-date Nixpkgs. After last week's email, Cole reviewed the patch set, so I applied it, and merged the nixpkgs-update branch into master, so now Spectrum is using a reasonably up-to-date Nixpkgs for the first time in a long time. I also said > Once that's done, it's time for another chromiumOSPackages upgrade, but > that should be pretty easy this time because we're only one version behind. Alas, it's never that simple. Firstly, the chromiumOSPackages update script broke, because the information about the currently released Chromium OS build seems to have gone missing. Google is apparently[1] serving build number 13982, but their published build metadata[2] includes builds 13981 and 13983, but not 13982. This means it's not possible for me to know what Git revisions are used in the currently released Chromium OS. Assuming this is just a one time thing, I hacked the update script to just look at the previous build, but we should keep an eye on this. If it ever happens again we should probably implement some sort of mitigation in the update script. Once I had new versions of the Chromium OS packages it was time to get them to build, which was straightforward enough for everything except crosvm. For Spectrum, we have a patch[3] for crosvm to make it support VIRTIO_NET_F_MAC[4], which is a mechanism by which the host system can indicate to the guest kernel what it should set as the MAC address of a virtual network device. After the update, this patch no longer applied, because all of a sudden crosvm has two different virtual network device implementations. This turns out to be because crosvm has implemented vhost-user[5], a protocol to allow virtual devices to be implemented outside the VMM program! This is great news, but it's also surprising. virtiofs[6] was designed to be implemented with vhost-user, but when crosvm implemented it a while ago, they became the only implementer to do so in-VMM. It's great to see them moving in the vhost-user direction, because it makes it much easier to mix and match virtual device implementation and VMMs. Most excitingly, I saw a reference to vhost-user-wl, meaning a standalone implementation of Virtio Wayland. This would allow us to use Virtio Wayland with other, non-crosvm VMMs, which is great because I think cloud-hypervisor[7] is probably going to end up being a better fit for Spectrum, but Virtio Wayland was crosvm's killer app. I'd even thought about trying to port crosvm's virtio wayland implementation to vhost-user myself, so it's great to know that when the time comes, that'll already have been done for me. While I could have fixed my crosvm patch for all this new virtual network device code, the introduction of vhost-user support means we should be able to drop the patch altogether. cloud-hypervisor provides a vhost-user-net implementation[8] that already supports VIRTIO_NET_F_MAC, so if we can just get crosvm to talk to cloud-hypervisor's vhost-user-net implementation we shouldn't have to carry any patch for this any more. [1]: https://cros-updates-serving.appspot.com/ [2]: https://chromium.googlesource.com/chromiumos/manifest-versions [3]: https://spectrum-os.org/git/nixpkgs/tree/pkgs/os-specific/linux/chromium-os… [4]: https://docs.oasis-open.org/virtio/virtio/v1.1/virtio-v1.1.html [5]: https://qemu.readthedocs.io/en/latest/interop/vhost-user.html [6]: https://virtio-fs.gitlab.io/index.html#overview [7]: https://github.com/cloud-hypervisor/cloud-hypervisor [8]: https://github.com/cloud-hypervisor/cloud-hypervisor/tree/db2159b5638eb4ccf… cloud-hypervisor / rust-vmm --------------------------- So I started looking at cloud-hypervisor to try to hook this all up, but it looks like cloud-hypervisor still has some issues where it doesn't quite follow the vhost-user specification. As I was trying to debug this, I noticed some UB in rust-vmm[9] (the shared utility code project for crosvm and its derivatives like cloud-hypervisor and Firecracker[10]). Being a good citizen, I started working on a fix for this, and then I encountered some more issues with functions that should have been marked as unsafe but weren't. So that's going to need to be fixed too. But the rust-vmm code is otherwise very high quality and easy to work with, and they're very responsive, so it shouldn't take long to get these issues fixed. The affected code is fortunately all to do with communication between vhost-user backends and the VMM, so it's very very unlikely that it's anything that could be exploited by a guest. These sorts of problems are exactly the sort of thing that Rust is supposed to prevent, so it was disappointing to discover these issues. But on the other hand, Rust made them stand out like sore thumbs to me, so even though these issues managed to sneak in, there's definitely still a huge benefit to using Rust for these sorts of programs. [9]: https://github.com/rust-vmm [10]: https://firecracker-microvm.github.io/ In the next week, I'm hoping to get all the rust-vmm issues I've discovered fixed, and maybe get cloud-hypervisor's backends to speak proper vhost-user. I'm getting my second vaccination next week as well though, so we'll see. I might just end up being sick.

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[COMMIT] nixpkgs-update merged into master
by Alyssa Ross 04 Aug '21

04 Aug '21

Everything seems to be working. I'm going to start another merge immediately, so we're fully up to date. But the Nixpkgs I merged in was only from last week, so it shouldn't be too hard.

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[PATCH nixpkgs 0/6] Fix build failures after Nixpkgs update
by Alyssa Ross 03 Aug '21

03 Aug '21

Alyssa Ross (6): chromiumOSPackages.vm_protos: set full go_package chromiumOSPackages.modemmanager: disable patches chromiumOSPackages.modemmanager-next: add gtk-doc chromiumOSPackages.libqmi: disable QRTR linux_cros: fix build wlroots: update Spectrum patches ...ayland-downgrade-to-wl_compositor-v3.patch | 64 ++++++----- ...til-support-virtio_wl-shm-allocation.patch | 11 +- ...-mk-don-t-leak-source-absolute-paths.patch | 4 +- ...ommon-mk-.gn-don-t-hardcode-env-path.patch | 4 +- .../os-specific/linux/chromium-os/default.nix | 3 +- .../linux/chromium-os/libqmi/default.nix | 4 +- .../chromium-os/modem-manager/default.nix | 2 + .../linux/chromium-os/modem-manager/next.nix | 6 +- ...er-don-t-leak-source-absolute-paths.patch} | 6 +- ...tools-sommelier-Switch-to-the-stabl.patch} | 6 +- .../linux/chromium-os/sommelier/default.nix | 4 +- ...-goproto_library-source_relative-opt.patch | 48 +++++++++ ...tools-proto-set-go_package-correctly.patch | 102 ++++++++++++++++++ .../linux/chromium-os/vm_protos/default.nix | 5 + 14 files changed, 222 insertions(+), 47 deletions(-) rename pkgs/os-specific/linux/chromium-os/sommelier/{0003-sommelier-don-t-leak-source-absolute-paths.patch => 0005-sommelier-don-t-leak-source-absolute-paths.patch} (82%) rename pkgs/os-specific/linux/chromium-os/sommelier/{0004-Revert-Revert-vm_tools-sommelier-Switch-to-the-stabl.patch => 0006-Revert-Revert-vm_tools-sommelier-Switch-to-the-stabl.patch} (99%) create mode 100644 pkgs/os-specific/linux/chromium-os/vm_protos/0003-common-mk-add-goproto_library-source_relative-opt.patch create mode 100644 pkgs/os-specific/linux/chromium-os/vm_protos/0004-vm_tools-proto-set-go_package-correctly.patch base-commit: cab13e087c80c4e7476bb7df432e2b7deb56563d -- 2.32.0

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This (Last) Week in Spectrum, 2021-W30
by Alyssa Ross 02 Aug '21

02 Aug '21

Hi, it's been a long time since I've done one of these, but so much interesting stuff happened this week, and there's been a bit of renewed interest in the project, that it _really_ needed an update. So here it is. As always when I'm not keeping up with TWiS, this update is limited to only things that happened in the last week, because otherwise it would just be far too long. Wayland ------- A problem I've been thinking about for a long time is Wayland access control. The Linux desktop ecosystem is moving towards access controls for most functionality through xdg-desktop-portal[1] (which sadly doesn't seem to have a website). But it doesn't cover stuff that's part of the core Wayland protocol, like access to the clipboard. And some compositors (wlroots-based ones) provide extra Wayland protocols for things like screenshots. And up to now, Wayland compositors haven't really done any authorization for these potentially dangerous APIs. (All of this is only really meaningful for sandboxed applications -- running in Flatpak or a Spectrum VM or something. Linux isn't really set up to do separation between processes running as the same user without namespaces.) So earlier this week, I posted[2] to the Wayland mailing list with an idea I'd been thinking about for a while[3], which was to place a proxy program in front of the Wayland compositor, that would intercept client->compositor requests and handle access control. I was quickly convinced that a proxy wasn't a good idea, but there was a lot of discussion, and it was really helpful to me figuring out what the right way to do it might be. There are really two problems to be solved here, one of which I hadn't even thought much about. The first is securely identifying a Wayland client. A compositor needs to be able to form the question "Should client X be able to do this?", and to do that it needs to be able to identify a client as client X, and know if it tries to interact with client X later, that it'll be talking to the same client. In a non-virtualized system, the obvious way to do this would be getting the pid of the client from the connection socket and then looking it up in proc(5) to find out executable path, but this approach is fundamentally insecure[4]. The way forward here (and one that would work for Spectrum) appears to be the proposed Security Contexts protocol[5], which would allow a sandbox implementation to provide a security context identifier for a client before handing off the Wayland connection to the client. Once the security context had been set up, it wouldn't be allowed to be modified, so once the sandboxed client was given the connection, it wouldn't be able to change the security context identifier. In Spectrum, the security context identifier here would likely be a unique, user-provided name for the VM, and the security context setup would be done by the virtio wayland implementation in the VMM. The second part of this puzzle is how the compositor should decide whether a client should be allowed to perform a particular operation, like a paste or going fullscreen (which is risky because it might spoof a desktop). There was actually a previous attempt at this a long time ago. libwsm[7] (short for Wayland Security Module) was a library that compositors would have integrated to make authorization decisions. But it wasn't adopted by compositors, and it some things we now know[8] to be bad ideas, like setting policy based on the executable path. It also made compositors responsible for any sort of authorization UI. In my opinion, it's better to have that done by the external piece, so that compositors have as little work to do as possible and therefore authorization is implemented as widely as possible. The compositor could implement an authorization system entirely on its own, but this would be a lot of code for each compositor to write, and it would limit the user to whatever permissions system the compositor came up with, which might not be able to accommodate their needs. (An example of this would be a Spectrum user that wanted to allow pasting between two applications, but not allow pasting between either of those and any other application.) It could also be implemented by having the compositors integrate with something like polkit[6], but compositor authors are reluctant to integrate directly with a single system like that, and even polkit might not support everything that would be desirable in an authorization system. (For example, it might be nice to implement libwsm's concept of a soft allow, where an action is permitted, but a notification is shown so the user is aware it's happened.) So a third solution, suggested by ifreund, a Wayland compositor author, in the Spectrum IRC channel, would be to have a privileged Wayland client that the compositor could ask authorization questions to, with a new protocol. The compositor would know that this particular client should be privileged because it either wouldn't be in a security context, or would be given a special security context identifier known to the compositor ahead of time. Then, implementations of this protocol could do authorization however they wanted, with the only limitation being the questions the compositor was programmed to ask them. I think this is a good way forward, but it'd be important to discuss with more compositor authors before getting to excited about it. Next steps from here with Wayland are: * Figure out what needs to happen to move the security contexts proposal forward. If it needs an experimental implementation, maybe we could help with that? * Inquire about the authorization protocol idea, and see how other compositor offers would feel about it. If there's a generally positive reaction, figure out how to move forward with it. [1]: https://github.com/flatpak/xdg-desktop-portal/ [2]: https://lists.freedesktop.org/archives/wayland-devel/2021-July/041896.html [3]: https://spectrum-os.org/lists/archives/spectrum-discuss/8735ueudel.fsf@alys… [4]: https://gitlab.freedesktop.org/wayland/weston/-/issues/206#note_176699 [5]: https://gitlab.freedesktop.org/wayland/wayland-protocols/-/merge_requests/68 [6]: https://www.freedesktop.org/software/polkit/docs/latest/polkit.8.html [7]: https://github.com/mupuf/libwsm [8]: https://lore.kernel.org/lkml/87r1xplsku.fsf@x220.int.ebiederm.org/ Nixpkgs ------- I created a branch in Spectrum's nixpkgs repository[9] for the long-overdue merge with upstream, did the merge, and posted some patches[10] to spectrum-devel that fix all the builds that broke as a result. I've been letting them sit for a few days hoping for a review. Once that's done, it's time for another chromiumOSPackages upgrade, but that should be pretty easy this time because we're only one version behind. [9]: https://spectrum-os.org/git/nixpkgs [10]: https://spectrum-os.org/lists/archives/spectrum-devel/20210729100928.196534… Thanks for keeping up with Spectrum. :)

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