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SubjectRe: Virtual Machines, JVM in kernel, hot-swapped kernel
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In message <19980829151440.62950@lucifer.guardian.no>, Alexander Kjeldaas 
write
s:
+-----
| On Fri, Aug 28, 1998 at 06:20:35PM -0300, Brandon S. Allbery KF8NH wrote:
| > 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...
| 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.
+--->8

Code produced by a designated compiler might be safe, but if you're loading
native code (i.e. the compiler isn't in the kernel) then it would be
possible to load arbitrary code. This would not be possible if the kernel
used a bytecode interpreter with restricted operations (file ops would not
be wanted or needed for this, for instance, nor would arbitrary pointer ops).

JIT wouldn't suffer from this (modulo bugs), but it *would* have a
significantly larger footprint. I don't think that is a very good idea,
either, especially since it wouldn't be pageable code.

| 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
+--->8

A certain Knuth quote springs to mind. And if the proof verifier were
np-complete (wouldn't it have to be?), it would present still another way to
hang a system inadvertently. (I ignore deliberate attacks because anyone
able to do so could just as easily insmod a killer module, not to mention
any number of other nasties possible to someone with root access.)

| US citizens might want to look into their "byte-code-in-the-kernel"-patent.
+--->8

!!! Wouldn't the BPF constitute prior art?

--
brandon s. allbery [os/2][linux][solaris][japh] allbery@kf8nh.apk.net
system administrator [WAY too many hats] allbery@ece.cmu.edu
electrical and computer engineering KF8NH
carnegie mellon university



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