Comment by teiferer
2 hours ago
The thing I don't get: We'll now run those N unikernel things in VMs with a hypervisor underneath. How is that different from running static binaries in a locked-down OS, i.e., with a traditional kernel? You can surely break out of a unikernel by "popping the kvm" as the article mentions. How is that more secure? In principle we are running the same things, just call them differently (app becomes unikernel+app, kernel becomes hypervisor).
It is not any different. Actually, it is worse because a VM is a much worse environment to run a application since you need that unikernel stub as well as the application.
The only advantage is that cloud services provide VM tenants so you are already stuck with a VM substrate and you want to minimize layers from that point on.
However, as a practical matter, the design of the Linux kernel is grossly insecure and basically impossible to make even remotely safe as evidenced by the unending sprawl of LPEs. Hypervisors are generally designed and configured in a way that is only reasonably insecure.
However, there is nothing stopping you from designing a kernel in a similar way and providing shared tenant processes with similar guarantees. You just need to port your applications to the new operating system, but you would need to port them to a unikernel anyways if you wanted to go that route.
The only free action is lumping your applications with the full OS and dumping it onto a hyoervisor. Anything else has porting work.
Both have weaknesses, but with an OS, you have certain bottlenecks - like your app memory is paged and has its own memory space, data structures are often duplicated in user and kernel memory, syscalls have cost, which is why io_uring is a thing in Linux.
This is all unnecessary overhead and complexity, as the OS doesn't really mediate hardware access in this case.
But you're right on some points, it's not really more secure, but there's a hell of a lot less complexity where things can go wrong.
It's conceptually equivalent but the details differ. The program has access to more abilities and in terms of common conventions the security boundary is much more robust. If nothing else I'd argue it's a superior abstraction with which to make the delineation.