RFR: 6983726: remove Proxy from MethodHandleProxies.asInterfaceInstance SAM conversion [v6]

[Jorn Vernee]

On Thu, 6 Apr 2023 17:04:02 GMT, Johannes Kuhn <jkuhn at openjdk.org> wrote:

>> I don't think that's good enough. If an instance implements an interface that just happens to also have an entry in the INTERFACE_INFOS cache, then e.g. `MethodHandleProxies::wrapperInstanceTarget` could be used to retrieve the class data of a class that wasn't generated using MethodHandleProxies.
>> 
>> I think some explicit marker is needed for class generated by MethodHandleProxies.
>> 
>> Switching back to the `WrapperInstance` interface, and then defining the class using `IMPL_LOOKUP`, as opposed to defining the class in a dynamic module, could be an option (since we determined that the wrapper instance can not be used to escalate privilege. I'm just not sure if that will work for target interfaces in non-exported packages. Proxy seems to be able to do that too though.
>
> An other possibility to to add some key into the ClassData that can't be imitated - such as the `InterfaceInfo` itself.  
> An `instanceof` check on the ClassData at a fixed position could then determine if is a MHP.

It looks like Proxy forcibly adds reads and exports edges from the module of the target interface to the module that defines the proxy: https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/reflect/Proxy.java#L855-L868 I think we can do the same here

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PR Review Comment: https://git.openjdk.org/jdk/pull/13197#discussion_r1160074618