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Comment by dlevi | Hacker News Reader

Thanks for that - it pretty much answers my question. In this case it seems that Qubes exposes less attack surface.

I'm from Subgraph and I disagree.

On Qubes OS the networking VM runs a standard Linux kernel with no special security hardening at all apart from the simple fact that it runs in a separate Xen VM. If an attacker is able to compromise NetVM, they may not have direct access to user data, but they have dangerous access to perform further attacks:

  - Attacks against hypervisor to break isolation
  - Side channel attacks against other Qubes VMs to steal cryptographic keys
  - Interception and tampering with networking traffic
  - Attacks against any internal network this Qubes OS computer connects to.

So if you assume that remote attacks against the Linux kernel networking stack are an important threat, the consequences of a successful attack even against Qubes are pretty bad.

Subgraph OS hardens the Linux kernel with grsecurity, which includes many defenses against exploitation which have historically prevented local exploitation of most security vulnerabilities against the kernel. Exploiting kernel vulnerabilities locally is so much easier, probably never less than an order of magnitude easier. It's so rare to reliably exploit kernel vulnerabilities remotely even against an unhardened kernel that teams present papers at top security conferences about a single exploit:

https://www.blackhat.com/presentations/bh-usa-07/Ortega/Whit...

I know it's contentious to say so, but I don't believe that anybody will ever remotely exploit a kernel vulnerability against a grsecurity hardened Linux kernel, especially since RAP was introduced:

https://grsecurity.net/rap_announce.php

The threat of remotely attacking the Linux kernel through the networking or USB stack was always low in my opinion, but as the threat approaches zero it raises some questions about how justifiable the system VMs are in Qubes OS considering the system complexity and usability impairment they introduce.

I agree with your comments about grsecurity making the kernel much more secure. However your comments about remote exploits and Qubes are somewhat contradictory. You claim that a remote kernel exploit is very rare/difficult, therefore the Qubes NetVM must be very difficult to attack because it runs no applications or services. It functions as a router and does essentially nothing else. By your own argument it would be very difficult to attack the NetVM. It is only the AppVMs or any others which run applications that are vulnerable, and if these are attacked, Qubes's design will likely prevent a permanent backdoor from being installed in that VM and make it difficult for the attacker to gain access to any of the other AppVMs.

I still think Subgraph looks promising and I look forward to your future work.

I'm answering a comment chain about how Subgraph OS does not 'isolate' the network or USB stacks which is frequently brought up as an important deficiency in comparison to Qubes OS. My point is that this isn't a significant advantage of Qubes because such attacks are rare and difficult, and because they're even harder to perform against Subgraph OS.

I wasn't talking about AppVMs at all, but you can of course persistently backdoor Qubes AppVMs in numerous ways by writing to the user home directory. In Subgraph OS we design our application sandboxes to prevent exactly this.

Thank you for your answer, I'll definitely look further into SubgraphOS and grsecurity. I nevertheless believe that the kind of attacks you describe, specially the one against hypervisor in NetVM to break isolation, are quite unlikely in Qubes.

Could you also answer my question about SubgraphOS main use case and threat model?

Is it mainly for anonymous and pseudonymous usage?

If it is designed mainly for everyday use (including non-anonymous use cases like banking, social media, personal/work email, etc.) as it seems to me I don't quite understand the design choice to enforce all traffic via Tor by default. That seems unnecessary as anonymity is not needed and even dangerous.

Yeah, we agree, actually. Tor probably won't even be the default. We are adding flexibility to network support right now. Soon you'll be able to have just cleartext SGOS, or be able to send sandboxed apps through different paths: one app might exit through a VPN, another through Tor only, another through i2p maybe, etc, enforced by the sandbox.

That sounds great!

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