8 ms·

> If there was only one of pipes, sockets, system calls, and the filesystem, that would be fine. Instead there are all of those and more. So you choose ONE for

by zvrba 9y ago

> If there was only one of pipes, sockets, system calls, and the filesystem, that would be fine. Instead there are all of those and more. So you choose ONE for the message-passing mechanism. If the process does not incorporate code that opens a pipe and reads from it, you cannot force it to do so. Alternatively, there are all of these and you want to add VMCALL to that soup as well. > There's no fundamental reason shared memory should be less safe than sockets (say); ultimately it's just bytes. We're talking about a unikernel writing to the hypervisor's address space. A bug in the hypervisor's validation (or another exploit) will allow it to overwrite arbitrary memory in the hypervisor. Sockets will not.

lmm 9y ago
> So you choose ONE for the message-passing mechanism. If the process does not incorporate code that opens a pipe and reads from it, you cannot force it to do so. But then you find that somewhere in the lower layers of the framework/interpreter you were using there's something that relies on it. You disable all the sysctls you thought you weren't using and then your image library turns out to need them. Once the functionality has ever existed in the ecosystem, it's very hard to get away from. > Alternatively, there are all of these and you want to add VMCALL to that soup as well. I want to deprecate all the others at the same time, otherwise there would indeed be no point. > We're talking about a unikernel writing to the hypervisor's address space. A bug in the hypervisor's validation (or another exploit) will allow it to overwrite arbitrary memory in the hypervisor. Sockets will not. What's the difference between a unikernel sending data to the hypervisor and a process sending data to the kernel? The data always has to cross the boundary one way or another. Why would one approach be any more or less safe than the other?
- zvrba 9y ago
  > But then you find that somewhere in the lower layers of the framework/interpreter you were using there's something that relies on it. So you refrain from using the framework in question because the very same framework wouldn't work at all in the hypothetical VM because files do not exist there. You have to write everything from scratch using only your IPC mechanism of choice, just like with VMCALL. > What's the difference between a unikernel sending data to the hypervisor and a process sending data to the kernel? Ultimately, trust. 1. The developers. I have more confidence in the implementors of, say, Linux kernel, than in developers of, say, Chrome or Firefox or Safari. 2. Testing. Kernels routinely handle successfully vastly more corner-cases than web-browsers. [Yes, I see upon all of current Linux, Windows, etc. installations as continuous, live, in-production testing.] If kernels were as shabby as today's browsers, nobody would use them for anything but toys. On the other hand, try to find a person who gets genuinely surprised when a web browser crashes.
  - lmm 9y ago
    > So you refrain from using the framework in question because the very same framework wouldn't work at all in the hypothetical VM because files do not exist there. You have to write everything from scratch using only your IPC mechanism of choice, just like with VMCALL. It's always going to take a new standard and a new community/ecosystem that fits things into that new standard or rewrites the things that can't be fitted. The only way such an effort can ever hope to succeed is a) an extremely clear standard with a rigorous conformance test b) a way to run legacy programs that don't comply with the standard c) but in such a way that there are still incentives for programs to move onto the new way. In theory we could create a stripped-down linux that only offered one limited form of IPC and then start porting libraries and processes to run on that stripped-down linux. But it would be difficult to get a consensus on exactly what system calls etc. are allowed, and what would you do for running legacy processes? You have to add the alternative IPC systems etc. back in and add an opt-out mechanism, and then a) every component, even well-behaved ones, loses the advantages of the new system (fast booting, low overhead and so on) b) there's very little incentive for a component to ever be ported to the new system. > 1. The developers. I have more confidence in the implementors of, say, Linux kernel, than in developers of, say, Chrome or Firefox or Safari. I'm not sure where web browsers comes into it. I have a lot more confidence in the unikernel folks than the container folks from what I've seen of their tool choices and code quality. > Kernels routinely handle successfully vastly more corner-cases than web-browsers. Kernels get very little direct exposure to actively hostile userspace programs, and local privilege escalation vulnerabilities are relatively common - indeed I'd say more common than browser vulnerabilities.
    - zvrba 9y ago
      > The only way such an effort can ever hope to succeed is a) an extremely clear standard with a rigorous conformance test VMCALL is too flexible for being able to call it a "standard". What does the original article suggest? Yeah, define a struct and pass a pointer to it. As "standard" as defining protobuf messages. Heck, even the "big" (Xen, HyperV, VMWare, VirtualBox) hypervisors don't agree on their hypercalls. The problem of having multiple incompatible OS-interfaces is repeating itself, just one level below, on the hypervisor level. Madness. Ironically, these problems would not exist had the world gone the way of IDL and microkernels. > b) a way to run legacy programs that don't comply with the standard No-go unless the VM implements all of the stuff that you want to get rid of. Plus, whatever you decide to run in a VM may want to talk to a service in another VM. How do they talk to each other? [continue the exercise until you reimplement one or more of existing IPC mechanisms].

by zvrba 9y ago

lmm 9y ago

> So you choose ONE for the message-passing mechanism. If the process does not incorporate code that opens a pipe and reads from it, you cannot force it to do so. But then you find that somewhere in the lower layers of the framework/interpreter you were using there's something that relies on it. You disable all the sysctls you thought you weren't using and then your image library turns out to need them. Once the functionality has ever existed in the ecosystem, it's very hard to get away from. > Alternatively, there are all of these and you want to add VMCALL to that soup as well. I want to deprecate all the others at the same time, otherwise there would indeed be no point. > We're talking about a unikernel writing to the hypervisor's address space. A bug in the hypervisor's validation (or another exploit) will allow it to overwrite arbitrary memory in the hypervisor. Sockets will not. What's the difference between a unikernel sending data to the hypervisor and a process sending data to the kernel? The data always has to cross the boundary one way or another. Why would one approach be any more or less safe than the other?

zvrba 9y ago
> But then you find that somewhere in the lower layers of the framework/interpreter you were using there's something that relies on it. So you refrain from using the framework in question because the very same framework wouldn't work at all in the hypothetical VM because files do not exist there. You have to write everything from scratch using only your IPC mechanism of choice, just like with VMCALL. > What's the difference between a unikernel sending data to the hypervisor and a process sending data to the kernel? Ultimately, trust. 1. The developers. I have more confidence in the implementors of, say, Linux kernel, than in developers of, say, Chrome or Firefox or Safari. 2. Testing. Kernels routinely handle successfully vastly more corner-cases than web-browsers. [Yes, I see upon all of current Linux, Windows, etc. installations as continuous, live, in-production testing.] If kernels were as shabby as today's browsers, nobody would use them for anything but toys. On the other hand, try to find a person who gets genuinely surprised when a web browser crashes.
- lmm 9y ago
  > So you refrain from using the framework in question because the very same framework wouldn't work at all in the hypothetical VM because files do not exist there. You have to write everything from scratch using only your IPC mechanism of choice, just like with VMCALL. It's always going to take a new standard and a new community/ecosystem that fits things into that new standard or rewrites the things that can't be fitted. The only way such an effort can ever hope to succeed is a) an extremely clear standard with a rigorous conformance test b) a way to run legacy programs that don't comply with the standard c) but in such a way that there are still incentives for programs to move onto the new way. In theory we could create a stripped-down linux that only offered one limited form of IPC and then start porting libraries and processes to run on that stripped-down linux. But it would be difficult to get a consensus on exactly what system calls etc. are allowed, and what would you do for running legacy processes? You have to add the alternative IPC systems etc. back in and add an opt-out mechanism, and then a) every component, even well-behaved ones, loses the advantages of the new system (fast booting, low overhead and so on) b) there's very little incentive for a component to ever be ported to the new system. > 1. The developers. I have more confidence in the implementors of, say, Linux kernel, than in developers of, say, Chrome or Firefox or Safari. I'm not sure where web browsers comes into it. I have a lot more confidence in the unikernel folks than the container folks from what I've seen of their tool choices and code quality. > Kernels routinely handle successfully vastly more corner-cases than web-browsers. Kernels get very little direct exposure to actively hostile userspace programs, and local privilege escalation vulnerabilities are relatively common - indeed I'd say more common than browser vulnerabilities.
  - zvrba 9y ago
    > The only way such an effort can ever hope to succeed is a) an extremely clear standard with a rigorous conformance test VMCALL is too flexible for being able to call it a "standard". What does the original article suggest? Yeah, define a struct and pass a pointer to it. As "standard" as defining protobuf messages. Heck, even the "big" (Xen, HyperV, VMWare, VirtualBox) hypervisors don't agree on their hypercalls. The problem of having multiple incompatible OS-interfaces is repeating itself, just one level below, on the hypervisor level. Madness. Ironically, these problems would not exist had the world gone the way of IDL and microkernels. > b) a way to run legacy programs that don't comply with the standard No-go unless the VM implements all of the stuff that you want to get rid of. Plus, whatever you decide to run in a VM may want to talk to a service in another VM. How do they talk to each other? [continue the exercise until you reimplement one or more of existing IPC mechanisms].