https://en.wikipedia.org/wiki/MINIX_3#Reliability_policies
With a monolithic kernel such as Linux, the reliability benefits of running some drivers in userspace are negligible, as the TCB is still millions of LoCs with no proofs.
Fuchsia, Genode and HelenOS are relatively active, promising open source operating systems with a microkernel, multi-server architecture and drivers running as unprivileged processes.
Try seeing it the other way around. It minimizes what needs proving (it isn't cheap) by having the microkernel (small and proven) enforce separation.
Capabilities (not to be confused with POSIX capabilities, which are something else) do help massively here. Refer to the Genode Book[0] introduction chapter for an introduction to capabilities.
In the driver example, running the driver unprivileged means the damage a faulty driver can be contained. In combination with a iommu, it can be made so that the hardware can only talk to the driver, to complete the protection. This is only possible if the kernel itself can be trusted, which would mean the kernel has to be proven, and that's unrealistic unless it's a microkernel, as it is a very costly process that doesn't even scale linearly with LoC.
The alternative is to make all drivers part of the TCB, which isn't realistic for the same reason. Unfortunately, on top of this, driver code quality is known to be particularly bad.
The goal we are trying to achieve in this project here is to show that drivers can (and should) be written in better languages to improve security and safety. Note that one of the drivers in the thesis is written in Rust.
And regarding XDP being safer than Rust: Yes of course. But it's also very limiting; you can't write a driver in eBPF. (It currently just prohibits jumps with negative offsets but there's some ongoing work to allow for at least some bounded loops). We are interesting in making drivers themselves safer, not applications building on top of them.
(As advisor of the thesis I however agree that XDP should have been mentioned; I'm not super happy with the length of the thesis but quite happy with the implementations)
The most interesting / surprising thing about this paper is how damning it is for the Intel IOMMU.
We can also confirm their result about the IOMMU TLB size of only 64 on the CPUs we have here. (Yes, the TLB size is completely undocumented and there are no performance counters...)
I see no mention of Dune [0] in the bibliography. Given the narrow focus of this research I think it is required.
Once processors are tuned for cloud workloads, they will have the affordances that will make full blown operating systems optional.
