When you say "(no) hace falta" you are not using a passive form actually.
The "se" you are talking about is an impersonal pronoun.
Please , have a look on this to see the usage of "el se impersonal"
Examples:
"Se necesita tiempo"
"No se necesitan mas de dos carros"
"Se planea construir un edificio"
There is another usage of "se" along with a verb. In this case "se" is a personal pronoun than becomes "me", "te", "nos", "os", "se") when the associated verb is conjugated. (Either in reflexive or reciprocal forms). E.g:
"Ella se lava". (Verb: "lavarse" used as reflexive)
"Nosotros nos necesitamos". (Verb: "necesitarse" conjugated using the 1st person in plural, as reciprocal)
"Se faltaron el respeto". (Verb: "faltarse" conjugated using 3rd person in plural, as reciprocal)
In the case of "faltar", it is a verb used as impersonal in "hace falta" but simply it does not require "se".
I hope this may help. Adiosss!