django permission

Good afternoon, I'm wanting in the template to make a loop to disable a button according to custom permission. The model code is:

# -*- coding: utf8 -*-
from __future__ import unicode_literals
from django.db import models
from django.contrib.auth.models import User

class PermUser(models.Model):
    user = models.OneToOneField(User,on_delete=models.CASCADE)
    tecnico = models.ForeignKey('imuno.Tecnico')

    def __str__(self):
        return ''

    class Meta:
        permissions = (
                       ("SIR", "Somente Imprimir Relatorio"),
                      )

In the template I do:

{% if show_save %}
       {% if perm.permissao.SIR %}
            <button type="submit" title="{% trans 'Save' %}" class="list-group-item disabled" name="_save">
              <span class="glyphicon glyphicon-floppy-disk"></span>
              <span class="text">{% trans 'Save' %}</span>
            </button>
       {% else %}
            <button type="submit" title="{% trans 'Save' %}" class="list-group-item active" name="_save">
              <span class="glyphicon glyphicon-floppy-disk"></span>
              <span class="text">{% trans 'Save' %}</span>
            </button>
       {% endif %}
 {% endif %}

With or without permission, it shows the button if I put "not" with or without permission is disabled. Would anyone know what the mistake was? in the django documentation shows this way of applying the perm call to the template.