In a Java Policy file it's possible to do Property Expansion in grants such as:

java.io.FilePermission "${java.home}${/}-", "read"

Reference https://docs.oracle.com/javase/8/docs/technotes/guides/security/PolicyFiles.html

However the current implementation of permissions in JBoss Modules does not allow it. We should add this feature to make permissions more usable where the deployment environment is unknown.