User permissions for functions

User permissions for functions

The users can access the database only via rules. Some of the rules do call
functions.
I found in PG notes that: "An SQL or plpgsql function invoked by a rule
would be executed with the current user's permissions, not the rule
owner's." What exactly does this mean? What do I need to do with respect to
user rights regarding these functions?
Do I need to enhance user rights with respect to these functions? How?

Thank you all.