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SubjectRe: Virtual Machines, JVM in kernel, hot-swapped kernel
On Fri, Aug 28, 1998 at 06:20:35PM -0300, Brandon S. Allbery KF8NH wrote:
> In message <m0zCNTx-000aPKC@the-village.bc.nu>, Alan Cox writes:
> |
> | The BPF filters in 2.1.x and in BSD are very much byte code. BPF isnt turing
> | complete and doesnt do a lot, but it is also quite possible to convert it to
> | native code. Right now we dont do that but the hooks exist in the kernel
> +--->8
>
> Not sure I want native code; I prefer that it be sandboxed, even at the
> price of speed. (Just what we need, a virus vector in the kernel...
> although I suppose that modules already give us one such.)
>

You are still sand-boxed even if you convert to native code. A naive
conversion to native code such as done by the TYA Java JIT-compiler
achieves significant speed improvements over interpretation.

An alternative if you want even better performance is to look into
Proof-Carrying-Code which means that instead of having a JIT in the
kernel, you have a proof-verifier. Instead of byte code you use
native code with an accompanying proof. The proof shows that the code
has no side-effects beyond the defined ones. This has been used to
implement packets-filters in (research) kernels.

> What I was thinking of is something like the packet filtering used by
> CheckPoint FireWall-1 (not available for Linux AFAIK); this involves a
> kernel module which implements arbitrarily complex (limited by memory
> assigned for bytecode and table storage) stateful packet filters. It runs
> bytecode. (For those who've seen FW-1, the things you can do with their GUI
> filter editor are a subset of its full capability; you have to write
> low-level INSPECT code to use its full power. INSPECT is *not* a simple
> language to work with, though, which is why I was thinking of more normal
> languages such as Java or Icon.)
>
> BPF doesn't appear to be capable of supporting all of the capabilities of
> this kind of filter, even ignoring the "stateful" part.
>

US citizens might want to look into their "byte-code-in-the-kernel"-patent.

astor

--
Alexander Kjeldaas, Guardian Networks AS, Trondheim, Norway
http://www.guardian.no/

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