By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), March 17, 2021 10:30 am
Room: Moderated Discussions
Doug S (foo.delete@this.bar.bar) on March 17, 2021 9:30 am wrote:
> While everyone agrees that the performance hit of microkernels is real, for applications where
> security is paramount it is totally worth it.

Bah, you're just parroting the usual party line that had absolutely no basis in reality and when you look into the details, doesn't actually hold up.

It's all theory and handwaving and just repeating the same old FUD that was never actually really relevant.

If you actually want security - and this isn't some theory, this is how people actually do it - you implement physically separate systems, and you make the secure side much simpler, and you do code review like there is no tomorrow. Ie automotive, automation, things like that.

Yes, the secure side might have a very small kernel, because it might be some special automotive grade electronics that might not even have a real MMU on it. But that's not what people mean when they talk about microkernels in the sense of "compared to monolithic". That kernel is simply not even comparable from a capability standpoint.

So if there is some correlation between extremely secure systems and microkernels, it's exactly that: a correlation, not causation. You minimize the loads, you minimize the hardware, and you might end up with a microkernel as a result. But it's not more secure because of the microkernel, it's more secure because you did that minimalism.

So even the security argument is actually mostly just complete garbage. Even if you were to use a microkernel (I'm sure it happens - but often mainly because of hardware limitations), it's just not a real and comparable general purpose system.

The real security comes from limiting the load, not the use microkernels, in other words. Often together with simplifying the hardware too, because complex hardware is fundamentally more fragile (you mention spectre etc, which is kind of relevant to the whole bedtime story about how secure microkernels are, but it's bigger than that - in extreme cases it's about rad-hardening etc too).

In extreme cases you don't just separate the loads, you actually replicate the secure side and do multiple independent implementations and things like that. It's very very rare because it's so expensive and complex to do, but security and reliability go hand in hand in many ways.

And yes, simplifying the load very much also works with monolithic kernels. It's not even unusual. Sometimes you really want the advantage of a more unified system, so you partition the hardware (depending on how sensitive you are to security concerns, either physically separate or just by cores or possibly even by just virtualization) and you just make the secure side run much more limited and controlled loads.

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TopicPosted ByDate
x86 - why unite when you can fragment?anonymou52021/03/12 06:16 PM
  x86 - why unite when you can fragment?Linus Torvalds2021/03/13 01:18 PM
    x86 - why unite when you can fragment?Jon Masters2021/03/13 07:25 PM
      x86 - why unite when you can fragment?Jon Masters2021/03/13 07:44 PM
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        x86 - why unite when you can fragment?anonymou52021/03/14 05:31 PM
          x86 - why unite when you can fragment?anon22021/03/14 08:07 PM
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                    Microkernel?Anon2021/03/15 09:05 AM
                      Microkernel?iz2021/03/16 01:25 AM
                        Microkernel?Andrey2021/03/16 02:54 AM
                          Microkernel?iz2021/03/16 08:36 AM
                            Microkernel?Andrey2021/03/16 10:06 AM
                              Microkernel?anonymou52021/03/16 11:44 AM
                              Microkernel?iz2021/03/21 02:58 AM
                                Microkernel?Andrey2021/03/21 09:34 AM
                  Microkernel?anon22021/03/15 08:31 AM
                    Microkernel?Simon Farnsworth2021/03/16 04:42 AM
            Microkernel?Gabriele Svelto2021/03/15 03:21 AM
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                    Microkernel?Gabriele Svelto2021/03/16 07:23 AM
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                        Microkernel?anon22021/03/16 05:16 PM
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                            Microkernel?Linus Torvalds2021/03/17 10:30 AM
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                              Microkernel?Jose2021/03/18 09:35 AM
                            Microkernel?zArchJon2021/03/18 05:42 PM
                          TransputerRichardC2021/03/17 09:47 AM
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                          Microkernel?NvaxPlus2021/03/17 11:48 AM
                            Microkernel?Michael S2021/03/18 03:32 AM
                              Microkernel?Adrian2021/03/18 04:12 AM
                                Microkernel?dmcq2021/03/18 06:30 AM
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                                  Microkernel?Adrian2021/03/18 08:35 AM
                                    Microkernel?---2021/03/18 09:49 AM
                                    Microkernel?dmcq2021/03/18 10:59 AM
                                      Microkernel?dmcq2021/03/18 04:09 PM
                              Microkernel?---2021/03/18 09:27 AM
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                Microkernel?dmcq2021/03/15 11:51 AM
                  Microkernel?anon22021/03/15 08:31 PM
                    Microkernel?dmcq2021/03/16 09:17 AM
                      Microkernel?Jukka Larja2021/03/16 11:22 AM
                        Microkernel?dmcq2021/03/16 04:06 PM
                          Microkernel?Jukka Larja2021/03/17 03:42 AM
                            Microkernel?dmcq2021/03/17 07:00 AM
                      Microkernel?anon22021/03/16 05:26 PM
                    Microkernel?---2021/03/16 10:07 AM
            Microkernel?-.-2021/03/15 08:15 PM
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                  Read the thread (NT)anon22021/03/16 05:27 PM
                    Already did (NT)Foo_2021/03/17 02:55 AM
                      Already didanon22021/03/17 03:46 AM
                        Already didEtienne Lorrain2021/03/18 02:31 AM
                Microkernel?-.-2021/03/17 05:04 AM
                  Microkernel?Gabriele Svelto2021/03/17 08:53 AM
                    Microkernel?-.-2021/03/17 02:43 PM
              Microkernel?dmcq2021/03/16 08:40 AM
        x86 - why unite when you can fragment?Konrad Schwarz2021/03/17 10:19 AM
    x86 - why unite when you can fragment?anonon2021/03/15 07:37 AM
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