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It might be useful that some code in a single process have access while other parts do not. How would you propose an OS handle those cases?

by jayd16 5y ago

vsareto 5y ago
I don't think that's particularly useful though. A program with requirements like that seems more likely to be split up into two independent pieces.
- Jweb_Guru 5y ago
  But that's not at all the case in practice. Logging is intertwined with other program functionality.
  - samus 5y ago
    Most logging libraries are facades over a concrete implementation. And there exist adapters for those that aren't. One could easily provide one that pipes the log stream to a child process that drops privileges and is restricted down by the OS. This will probably entail a performance penalty, but it could be worth it. It would be nice to have such a capability in-process though.
alerighi 5y ago
And how do you do that, without operating system support? I mean, you can't of course limit that based on the code, in the JVM there is only a single address space, thus every method or class can be instantiated from anywhere in the code (despite public/private/etc. that are only for programmer convenience, they are easily circumvented with reflection, they don't provide any security at all). You can imagine doing something like adding some bytecode instructions that if encountered by the JVM block the network access to every other request done in the call stack after that instruction. Something that reduces efficiency drastically and still can easily be circumvented if you don't implement different address spaces for different parts of the code (something that only the OS can do).
- jayd16 5y ago
  If you're asking how th jvm might do it, I can assure you I do not know. If the question is "can this be a language feature" then I say, surely it can be. A language that supports static analysis and can disallow dynamic dispatch would do the trick, no?
  - alerighi 5y ago
    There are ways to call a function that cannot be caught by static analysis: basically you just need a way to jump to an arbitrary address of memory where a particular function is stored. If we exclude languages that by design sandbox the code (for example JavaScript, and most of the time it isn't enough because engines are bugged and thus browsers also use facilities of the operating system to sandbox the entire engine itself) no other programming language can do that.
- naasking 5y ago
  > I mean, you can't of course limit that based on the code, in the JVM there is only a single address space You can in principle, just look at the Joe-E language. The article is likely talking about revisions to existing VM designs though, because capabilities are a fundamental, architectural decision that underlie the runtime.

It might be useful that some code in a single process have access while other parts do not. How would you propose an OS handle those cases?

by jayd16 5y ago

It might be useful that some code in a single process have access while other parts do not. How would you propose an OS handle those cases?

vsareto 5y ago

I don't think that's particularly useful though. A program with requirements like that seems more likely to be split up into two independent pieces.

Jweb_Guru 5y ago
But that's not at all the case in practice. Logging is intertwined with other program functionality.
- samus 5y ago
  Most logging libraries are facades over a concrete implementation. And there exist adapters for those that aren't. One could easily provide one that pipes the log stream to a child process that drops privileges and is restricted down by the OS. This will probably entail a performance penalty, but it could be worth it. It would be nice to have such a capability in-process though.

alerighi 5y ago

And how do you do that, without operating system support? I mean, you can't of course limit that based on the code, in the JVM there is only a single address space, thus every method or class can be instantiated from anywhere in the code (despite public/private/etc. that are only for programmer convenience, they are easily circumvented with reflection, they don't provide any security at all). You can imagine doing something like adding some bytecode instructions that if encountered by the JVM block the network access to every other request done in the call stack after that instruction. Something that reduces efficiency drastically and still can easily be circumvented if you don't implement different address spaces for different parts of the code (something that only the OS can do).

jayd16 5y ago
If you're asking how th jvm might do it, I can assure you I do not know. If the question is "can this be a language feature" then I say, surely it can be. A language that supports static analysis and can disallow dynamic dispatch would do the trick, no?
- alerighi 5y ago
  There are ways to call a function that cannot be caught by static analysis: basically you just need a way to jump to an arbitrary address of memory where a particular function is stored. If we exclude languages that by design sandbox the code (for example JavaScript, and most of the time it isn't enough because engines are bugged and thus browsers also use facilities of the operating system to sandbox the entire engine itself) no other programming language can do that.
naasking 5y ago
> I mean, you can't of course limit that based on the code, in the JVM there is only a single address space You can in principle, just look at the Joe-E language. The article is likely talking about revisions to existing VM designs though, because capabilities are a fundamental, architectural decision that underlie the runtime.