Hello everyone, I could imagine that this question has been discussed before already, and if this should be the case, then I'm very sorry for posting this (I'd be thankful for an according link if so though).
I think that I've gained quite much knowledge about possible attack surfaces provided on hardware and software level during the last 15 years, trying to keep up-to-date and often doing research on new approaches in this field. First of all, I'd like to stress that the 'objection' (which I don't mean as such) I may raise by this post does not have any intention of criticizing the great work and effort done by the QubesOS developers and the community (it's not meant as an unhelpful 'critique' at all). Much rather I have a huge respect for the commitment shown by everyone involved in the development of QubesOS. Having compared various approaches in this field (e. g. OpenBSD, Linux using a hardened security kernel, GNU Hurd), I'd basically come to the conclusion that QubesOS is the most promising approach, especially if VT-d isolation is available. However, the main points I'd like to address are: 1) XEN is developed by people working for a company based in the U.S. (I know the difference between open-source and proprietary software, but still they belong to the same team/company). If even developers of TrueCrypt received one of those 'blue letters' - What is the reason to assume that the XEN developers didn't receive one of those as well? Seen from the perspective of the NSA it looks totally odd and irrational to me if they would not to so, since they can do so, and it's their task to thwart any efforts which might hinder them from collecting data. I don't regard those people as being 'evil' or anything like that (nor do I regard this as being positive, which should go without saying), I just look at things in a rational way: If QubesOS is a great approach to ensure security, then one must be naive to assume that this won't automatically lead to classifiying this as a 'high priority target' - With all the consequences. 1.2) Since this looks so obvious to me: Why isn't it a top priority for QubesOS developers to make use of a supervisor (or develop an independent one, which would surely need endless efforts, but wouldn't it be worth it?), which is not subjected to the objections I tried to express? 2) QubesOS totally relies on 2.1) trusting XEN developers to completely understand the more than just complex x64 architecture being used today and 2.2) on trusting Intel's VT technology. Regarding 2.2): Just assuming Intel would have received some kind of 'advice' (they may even find motivation without getting such - I certainly don't think that Intel is an 'NSA subcontractor', but they are simply a big and profit-orientated company, not an idealistic open-source community like the QubesOS developers etc.) - Then how realistic is it that an absolutely professionally designed and implemented backdoor etc. as the result of sheer endless human, technological and financial ressources gets discovered by people like the QubesOS community, no matter how enthusiastic, intelligent, cautious and sceptical those are? Referring once again to 2.1) I'd like to point to and quote from a highly interesting Qubes Security Bulletin (https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-018-2015.txt): "2) We are not entirely convinced if the way Xen Security Team decided to address this vulnerability is really optimal, security wise. It seems like a more defensive approach would be to get rid of this dangerous construct of reusing the same memory for both an internal pointer and VM-provided data. Apparently Xen developers believe that they can fully understand the code, with all its execution paths, for decoding x86 operands. This optimistic attitude seems surprising, given the very bug we're discussing today." [One should read the whole bulletin to know the context, but I didn't want this to become too long.] One might also like to take a look at this bulletin, which gives me, among other XEN-related informations and facts, the strong impression that seeking an alternative hyperadvisor should have higest priority for the QubesOS development (believe me, I'd more than like to contribute to doing so by myself, too, and if I shold be able to aquire the necessary skills, I'll definitely try to do so): https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-024-2016.txt "A more radical reader might be of the opinion that we should completely replace Xen with some other hypervisor. Such an opinion is surely not unfounded, as we have previously expressed our disappointment in the Xen security process [5]. Sadly, not much has improved over the past several months. Moreover, even though Qubes is now based on a hypervisor-abstracting architecture ("Odyssey"), which should make switching to a different VMM a relatively easy task, the primary problem that remains is the lack of a good alternative hypervisor to which we could move [6]." Hopefully my post won't get misunderstood or even discourage people (if so, I'd really regret having written this) - I'm just worried regarding those points, and I believe that nothing is more dangerous than thinking one would have ensured security and therefore feeling even more motivated to rely on this (imaginary) security with all the consequences (to express this using quite harsh words: In the worst case users of QubesOS might be enticed to step into a huge honeypot, and I'd be pretty sure that - if this should be true - won't become known for many years, allowing the NSA etc. to collect petabytes of data in the meantime). Finally, I don't think (this might sound even more provocative to many people) that organisations like the NSA etc. are 'useless' or 'to be abolished by all means' - This is similar to a simple but fundamental problem like "Well, complete disarment would surely be a great thing, but we'll run into big trouble if other nations won't think so", and of course I don't feel sorry at all for any terrorist etc. who gets prevented from killing other people because of getting caught before he can do that (or for criminals being caught). But nonetheless everyone knows where mass surveilance can lead to, and I think governments should generally respect people's privacy unless they have good reasons to watch them (and this should not be determined by computer algorithms) - But that's not what I wanted to address here, and I think it also doesn't belong here at all. I'd be very curious to hear other people's opinions regarding the issues I addressed above. 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