Accessing module internals from bytecode rewriting agent

Andrew Dinn adinn at
Tue Apr 25 08:19:39 UTC 2017

On 25/04/17 07:22, Alan Bateman wrote:
> On 25/04/2017 04:26, Martin Buchholz wrote:
>> :
>> java.lang.IllegalArgumentException: illegal lookupClass: class
>> java.util.PriorityQueue
>> Bytecode rewriting agents have the power to inject code into classes;
>> they
>> should somehow also be able to reflectively inspect those same classes!
>> But how?  We ran into similar problems trying to port java agents at
>> Google
>> to jdk9.
> <snip>
> On Byteman, Andrew Dinn has been working with us on jigsaw-dev on the
> agent support. From the stack trace then I suspect the issue you are
> running into is that Byteman has also changed to use the new reflection
> API (java.lang.invoke) and is running into a long standing check to
> prevent full power lookups to full privileged classes from leaking.
> Andrew brought this up on jigsaw-dev [1] a few days ago and we could
> probably move that thread to core-libs-dev.

This discussion really ought to be happening on the Byteman forum but
anyway ...

Yes, Alan is right that this is exactly what is going on. Byteman on
jdk9 (the 4.0.0-BETA release series) now uses method handles in place of
reflection. Unfortunately, it is limited by a slightly arbitrary
restriction on the use of method handles in java.* and sun.* packages (a
blunt instrument to provide some security guarantees).

This is being addressed on two fronts. I am in the process of adding
unit tests to complete a workaround which remedies this problem by
falling back to reflection in the specific cases where the restriction
applies (yes, that means there is probably going to be another
4.0.0-BETA release before jdk9 goes live %-/ ).

Meanwhile, Mandy Chung has kindly offered to look into the security
considerations that are at play and come up with a less restrictive
policy which enforces the security needs more accurately. At that point
I will probably remove the fallback -- in part because I hope that by
then both reflection and method handles will employ a common blacklist
of inaccessible methods. I think it would make sense for them both to
offer equivalent access and for that access to take security seriously.


Andrew Dinn
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in England and Wales under Company Registration No. 03798903
Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander

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