Disallowing the dynamic loading of agents by default (revised)

Remi Forax forax at univ-mlv.fr
Thu Apr 6 08:18:54 UTC 2017

----- Mail original -----
> De: "mark reinhold" <mark.reinhold at oracle.com>
> À: jigsaw-dev at openjdk.java.net
> Envoyé: Mercredi 5 Avril 2017 18:15:20
> Objet: Disallowing the dynamic loading of agents by default (revised)

> Thanks to everyone for the quick feedback on this topic, and especially
> to Andrew for the constructive dialogue.
> Here's a revised proposal:
>  - Define a new VM option, `-XX:+EnableDynamicAgentLoading`, that's
>    on by default in JDK 9 but off by default in JDK 10.
>    This will allow launch scripts that use this option on JDK 10 to
>    work on JDK 9 without change, and will allow early testing of the
>    JDK 10 behavior on JDK 9.


>  - Revise the `com.sun.tools.attach` API to forbid attachment to the
>    current process or to an ancestor of the current process, and
>    define a read-only system property that allows such attachment to
>    be enabled via the command line.
>    This will discourage the inadvertent use of libraries that, for
>    better or for worse, intentionally violate strong encapsulation.

don't get this one, as David said, if you span a new VM with an exec, you have more right ??

>  - Enhance the `-jar` launcher option so that if the JAR file being
>    launched contains a `Premain-Class` attribute then it's launched
>    as both an application and as an agent for that application.
>    This will allow `java -jar foo.jar` to be used in place of the
>    more verbose `java -javaagent:foo.jar -jar foo.jar` [1].

Can be very useful indeed.
(with another name that "Premain-Class" for backward compatibility).

> Taken together, these changes are intended to enable the continued use
> of legitimate dynamically-loaded agents without change on JDK 9 and with
> a small change on JDK 10.  That later change will align the treatment of
> such agents with the other means of breaking encapsulation (`--add-opens`,
> etc.) in order to ensure integrity by default for all code.
> This proposal does not attempt to lock down platform classes as distinct
> from user classes.  Many agents have legitimate reasons to transform
> platform classes, so an additional mechanism to protect those classes
> does not appear to be worthwhile.
> Comments?
> - Mark
> [1] http://mail.openjdk.java.net/pipermail/jigsaw-dev/2017-April/012000.html


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