linux-hardened VS opensnitch

Glossing over their hardening guide, we notice that the kernel-hardened package is mentioned. This is a fork of what once was the kernel of GrapheneOS. While this hardened kernel can be used on a variety of distros, unfortunately this doesn't apply to Fedora Silverblue. Furthermore, I haven't seen any mention of the hardened kernel being used on openSUSE Tumbleweed. Therefore I see no reason to believe that this is possible on openSUSE Aeon either. Though, I'd love to be corrected on this!

Here's the GitHub page for the linux-hardened package in the official Arch repos. You will find that lots of changes come from GrapheneOS. "Forked from GrapheneOS" is in tiny, tiny text near the top-left of the web page underneath the project name.

Here is the source code for the hardened Linux kernel.

so that we can use it liberally in CLI) > **Additionally, here's a 'building from the source section** - https://github.com/firecracker-microvm/firecracker/blob/main/docs/getting-started.md#building-from-source ### Running Firecracker > "*In production, Firecracker is designed to be run securely, inside an execution jail, carefully set up by the jailer binary. This is how our integration test suite does it. However, if you just want to see Firecracker booting up a guest Linux machine, you can do that as well.*" 1. We need to first obtain an "uncompressed Linux kernel binary, and an ext4 file system image (to use as rootfs)" ; great, these are two things that we need to seek out before we move forward in our 'adventure' (*this really feels like a "quest" of some sort, like the ones that they forced you to play on Runescape back in the days*) **How to Decompress Linux Kernel** (explicit instructions to be honest here) - https://0xax.gitbooks.io/linux-insides/content/Booting/linux-bootstrap-5.html **Linux-Hardened Kernel** - https://github.com/anthraxx/linux-hardened (this is something that they're all still actively working on at this very point in time) They also say that we need an 'ext4 file system image' (where do we obtain this from?) - found it **Full Guide on How to Create an EXT4 filesystem image here** -https://fabianlee.org/2020/01/13/linux-mounting-a-loopback-ext4-xfs-filesystem-to-isolate-or-enforce-storage-limits/ Assuming that the above has been handled, the directions insist that we create two separate shell prompts, (one to run Firecracker, and another one to control it [by writing to the API socket]; both shells have to run "in the same directory where the firecracker binary was placed") ^^ What? - This is a pain in the ass because this is something that they should've mentioned earlier (obv. everyone is going to move a binary where the rest of their binaries go ; and you're not going to just load up some random project to be used in that manner) - Not even sure what the end goal of opening up an API socket here would really be But fuck it, let's just assume that we play ball and we adhere to all of these (additional) steps that we're being put through (just for the setup up this virtualization tool!). ### Following Through on the Next Steps 1. Ensuring that Firecracker can create its own API ``` bash rm -f /tmp/firecracker.socket

Officially supported kernels Community support on forum and bug reporting is available for officially supported kernels. Stable — Vanilla Linux kernel and modules, with a few patches applied. https://www.kernel.org/ || linux Hardened — A security-focused Linux kernel applying a set of hardening patches to mitigate kernel and userspace exploits. It also enables more upstream kernel hardening features than linux. https://github.com/anthraxx/linux-hardened || linux-hardened Longterm — Long-term support (LTS) Linux kernel and modules. https://www.kernel.org/ || linux-lts Zen Kernel — Result of a collaborative effort of kernel hackers to provide the best Linux kernel possible for everyday systems. Some more details can be found on https://liquorix.net (which provides kernel binaries based on Zen for Debian). https://github.com/zen-kernel/zen-kernel || linux-zen

Overall those patches do protect you in a lot of cases. Per default upstream features are chose to honor security first. Furthermore patches do frequently protect against upstream failures and vulnerabilities. One of the latest examples is CVE-2022-1729 https://seclists.org/oss-sec/2022/q2/122 a local privilege vulnerability that linux-hardened simply protects since before day 0: https://github.com/anthraxx/linux-hardened/commit/4dd6bdf3b079ef73e597661ee961d225bfccbe2a On top the approach in several places of fail-early instead of potentially continuing with known corruption or certain use-after-free regularly uncovers problems that get fixed upstream and where the vanilla kernels just keep on running, which include exploitable problems. One example of a faulty very recent commit that has been bisected and fixed because of linux-hardened: https://git.kernel.org/pub/scm/linux/kernel/git/deller/linux-fbdev.git/commit/?h=for-next&id=acde4003efc16480375543638484d8f13f2e99a3

Those two don't protect the kernel itself from "misuse". To do that, there are ways like kernel hardening 3, using hardened kernel 4 5.

opensnitch has existed for a while now. I've never used it, so I can't comment on how well it works.

https://github.com/evilsocket/opensnitch

If you prefer a GUI try https://github.com/evilsocket/opensnitch

The whole BPF verifier and development process is so botched, it's ridiculous. It's like maintainers decided to make this as hard as possible out of pettiness and "they have to use C APIs instead" or something.

- Loading an eBPF module without the CAP_BPF (and in some cases without the CAP_NET_ADMIN which you need for XDP) capabilities will generate a "unknown/invalid memory access" error which is super useless as an error message.

- In my personal opinion a bytecode format for both little endian (bpfel) and big endian (bpfeb) machines is kinda unnecessary. I mean, it's a virtual bytecode format for a reason, right!?

- Compiling eBPF via clang to the bpf bytecode format without debug symbols will make every following error message down the line utterly useless. Took me a while to figure out what "unknown scalar" really means. If you forget that "-g" flag you're totally fucked.

- Anything pointer related that eBPF verifier itself doesn't support will lead to "unknown scalar" errors which are actually out of bounds errors most of the time (e.g. have to use if pointer < size(packet) around it), which only happen in the verification process and can only be shown using the bpftool. If you miss them, good luck getting a better error message out of the kernel while loading the module.

- The bpftool maintainer is kind of unfriendly, he's telling you to read a book about the bytecode format if your code doesn't compile and you're asking about examples on how to use pointers inside a BPF codebase because it seems to enforce specific rules in terms of what kind of method (__always_static) are allowed to modify or allocate memory. There's a lot of limitations that are documented _nowhere_ on the internet, and seemingly all developers are supposed to know them by reading the bpftool codebase itself!? Who's the audience for using the bpftool then? Developers of the bpftool itself?

- The BCC tools (bpf compiler collection) are still using examples that can't compile on an up-to-date kernel. [1] If you don't have the old headers, you'll find a lot of issues that show you the specific git hash where the "bpf-helpers.h" file was still inside the kernel codebase.

- The libbpf repo contain also examples that won't compile. Especially the xdp related ones [2]

- There's also an ongoing migration of all projects (?) to xdp-tools, which seems to be redundant in terms of bpf related topics, but also has only a couple examples that somehow work [3]

- Literally the only userspace eBPF generation framework that worked outside a super outdated enterprise linux environment is the cilium ebpf project [4], but only because they're using the old "bpf-helpers.h" file that are meanwhile removed from the kernel itself. [5] They're also incomplete for things like the new "__u128" and "__bpf_helper_methods" syntax which are sometimes missing.

- The only working examples that can also be used for reference on "what's available" in terms of eBPF and kernel userspace APIs is a forked repo of the bootlin project [6] which literally taught me how to use eBPF in practice.

- All other (official?) examples show you how to make a bpf_printk call, but _none_ of them show you how to even interact with bpf maps (whose syntax changed like 5 times over the course of the last years, and 4 of them don't run through the verifier, obviously). They're also somewhat documented in the wiki of the libbpf project, without further explanation on why or what [7]. Without that bootlin repo I still would have no idea other than how to make a print inside a "kretprobe". Anything more advanced is totally undocumented.

- OpenSnitch even has a workflow that copies their own codebase inside the kernel codebase, just to make it compile - because all other ways are too redundant or too broken. Not kidding you. [8]

Note that none of any BPF related projects uses any kind of reliable version scheme, and none of those project uses anything "modern" like conan (or whatever) as a package manager. Because that would have been too easy to use, and too easy on documenting on what breaks when. /s

Overall I have to say, BPF was the worst development experience I ever had. Writing a kernel module is _easier_ than writing a BPF module, because then you have at least reliable tooling. In the BPF world, anything will and can break at any unpredictable moment. If you compare that to the experience of other development environments like say, JVM or even the JS world, where debuggers that interact with JIT compilers are the norm, well ... then you've successfully been transferred back to the PTSD moments of the 90s.

Honestly I don't know how people can use BPF and say "yeah this has been a great experience and I love it" and not realize how broken the tooling is on every damn level.

I totally recommend reading the book [9] and watching the YouTube videos of Liz Rice [10]. They're awesome, and they show you how to tackle some of the problems I mentioned. I think that without her work, BPF would have had zero chance of success.

What's missing in the BPF world is definitely better tooling, better error messages (e.g. "did you forget to do this?" or even "unexpected statement" would be sooooo much better than the current state), and an easier way to debug an eBPF program. Documentation on what's available and what is not is also necessary, because it's impossible to find out right now. If I am not allowed to use pointers or whatever, then say so in the beginning.

[1] https://github.com/iovisor/bcc

[2] https://github.com/libbpf/libbpf

[3] https://github.com/xdp-project/xdp-tools

[4] https://github.com/cilium/ebpf/

[5] https://github.com/cilium/ebpf/tree/master/examples/headers

[6] https://elixir.bootlin.com/linux/latest/source/tools/testing...

[7] https://github.com/libbpf/libbpf/wiki/Libbpf-1.0-migration-g...

[8] https://github.com/evilsocket/opensnitch/blob/master/ebpf_pr...

[9] https://isovalent.com/learning-ebpf/

[10] (e.g.) https://www.youtube.com/watch?v=L3_AOFSNKK8

Close to zero most probably. If you want something different, to block/monitor what applications access the internet, block ads, etc, try https://github.com/evilsocket/opensnitch

The last thing I built from source was a suckless utility which was nothing but a treat to play with and hack on, so I felt confident I could manage this even though the project's wiki page on compilation warned that it might fail on distro's other then debain and ubuntu. First order of business was translating the apt-get command for the dependencies into an emerge command that would install the same packages. Once that was done, I went on to the go dependencies which all seemed to install without a hitch except for the first one which gave this "build constraints eliminates all Go files" message but didn't tell me that the installation had failed otherwise. I spent a good amount of time trying to decipher this message which eventually turned into just familiarizing myself with go since I hadn't really touched it before before deciding it was fine. Then I tried to build it. It didn't work.

OpenSnitch is a clone of the popular 'LittleSnitch' firewall for Mac. The main feature is that it will tell you about every single connection your computer is doing. A bit annoying for the first few days, but not too bad once you've already allowed the apps you use regularly. I think this would have been the perfect tool for the job.

take a look at opensnitch or picosnitch