> Your knowledge is out of date: Windows has supported capabilities from the start of NT and does run a lot drivers in isolated processes, along with most OS services.
Thanks! I quickly googled this point before posting earlier to make sure I was still right. Gemini helpfully told me that yes indeed, drivers in windows run in the kernel's main process. Thanks, AI.
> This article I wrote is more about language/runtime level capabilities but OS capabilities are not much better.
I think I responded to this article at the time. I still find this article somewhat confusing and unconvincing. For example, you conflate Java's SecurityManager with capability systems, even though it seems more like an permission based access control system. Then you point out many of its weaknesses. To what end? What conclusion about capability systems am I supposed to draw from a criticism of this quite different security model?
A capability is not a permission flag. Unlike your example, a good capability system would generally pass all HTTP requests to a given endpoint through a single capability object. You wouldn't need different caps for each HTTP method like SecurityManager apparently requires. It's like file handles. You don't create several different file handles to interact with the same file, one for reading, one for writing and so on. We just open the file once, with whatever options are needed. Then the file descriptor can be passed into any function which needs to access that file. And whatever code receives the file descriptor doesn't know if they're talking to an actual file, or some in-memory object or something else. Just like a virtual object.
You also say this:
> File descriptors are a kind of capability provided by the kernel, but a rather odd and inflexible kind. They aren’t a great example of object capabilities.
Huh? File descriptors are often treated as the canonical example of object capabilities. This comment makes me wonder if we're even talking about the same thing. At the risk of being indelicate, are you sure you know what capabilities are? Can you give a definition of object capabilities which doesn't describe file descriptors?
The point about god objects lands. I also agree that trying to retrofit a language like java to make modules unable to share memory is difficult. But many aspects of language design work like this. Consider garbage collectors. Before GC languages existed, I could write the same article talking about the difficulties of hacking a GC into C. But that wouldn't teach me anything about how well a GC would work in a language like Java or Ruby.
Anyway, the main advantage of capabilities is the ability to split programs out into sub-modules such that a compromise or bug in one part of the system doesn't lead to the entire system failing. We can argue about whether bringing this into the language runtime is a good idea. But I feel pretty confident that this sort of separation is a good idea at the systems level, helping with security and reliability. We can look at Chrome, SeL4, Erlang and - apparently - windows for examples. Even if they don't all think of this as a capability based problem.
