1/*
  2 * mmap based event notifications for SELinux
  3 *
  4 * Author: KaiGai Kohei <kaigai@ak.jp.nec.com>
  5 *
  6 * Copyright (C) 2010 NEC corporation
  7 *
  8 * This program is free software; you can redistribute it and/or modify
  9 * it under the terms of the GNU General Public License version 2,
 10 * as published by the Free Software Foundation.
 11 */
 12#include <linux/kernel.h>
 13#include <linux/gfp.h>
 14#include <linux/mm.h>
 15#include <linux/mutex.h>
 16#include "avc.h"
 17#include "services.h"
 18
 19/*
 20 * The selinux_status_page shall be exposed to userspace applications
 21 * using mmap interface on /selinux/status.
 22 * It enables to notify applications a few events that will cause reset
 23 * of userspace access vector without context switching.
 24 *
 25 * The selinux_kernel_status structure on the head of status page is
 26 * protected from concurrent accesses using seqlock logic, so userspace
 27 * application should reference the status page according to the seqlock
 28 * logic.
 29 *
 30 * Typically, application checks status->sequence at the head of access
 31 * control routine. If it is odd-number, kernel is updating the status,
 32 * so please wait for a moment. If it is changed from the last sequence
 33 * number, it means something happen, so application will reset userspace
 34 * avc, if needed.
 35 * In most cases, application shall confirm the kernel status is not
 36 * changed without any system call invocations.
 37 */
 38static struct page *selinux_status_page;
 39static DEFINE_MUTEX(selinux_status_lock);
 40
 41/*
 42 * selinux_kernel_status_page
 43 *
 44 * It returns a reference to selinux_status_page. If the status page is
 45 * not allocated yet, it also tries to allocate it at the first time.
 46 */
 47struct page *selinux_kernel_status_page(void)
 48{
 49	struct selinux_kernel_status   *status;
 50	struct page		       *result = NULL;
 51
 52	mutex_lock(&selinux_status_lock);
 53	if (!selinux_status_page) {
 54		selinux_status_page = alloc_page(GFP_KERNEL|__GFP_ZERO);
 55
 56		if (selinux_status_page) {
 57			status = page_address(selinux_status_page);
 58
 59			status->version = SELINUX_KERNEL_STATUS_VERSION;
 60			status->sequence = 0;
 61			status->enforcing = selinux_enforcing;
 62			/*
 63			 * NOTE: the next policyload event shall set
 64			 * a positive value on the status->policyload,
 65			 * although it may not be 1, but never zero.
 66			 * So, application can know it was updated.
 67			 */
 68			status->policyload = 0;
 69			status->deny_unknown = !security_get_allow_unknown();
 70		}
 71	}
 72	result = selinux_status_page;
 73	mutex_unlock(&selinux_status_lock);
 74
 75	return result;
 76}
 77
 78/*
 79 * selinux_status_update_setenforce
 80 *
 81 * It updates status of the current enforcing/permissive mode.
 82 */
 83void selinux_status_update_setenforce(int enforcing)
 84{
 85	struct selinux_kernel_status   *status;
 86
 87	mutex_lock(&selinux_status_lock);
 88	if (selinux_status_page) {
 89		status = page_address(selinux_status_page);
 90
 91		status->sequence++;
 92		smp_wmb();
 93
 94		status->enforcing = enforcing;
 95
 96		smp_wmb();
 97		status->sequence++;
 98	}
 99	mutex_unlock(&selinux_status_lock);
100}
101
102/*
103 * selinux_status_update_policyload
104 *
105 * It updates status of the times of policy reloaded, and current
106 * setting of deny_unknown.
107 */
108void selinux_status_update_policyload(int seqno)
109{
110	struct selinux_kernel_status   *status;
111
112	mutex_lock(&selinux_status_lock);
113	if (selinux_status_page) {
114		status = page_address(selinux_status_page);
115
116		status->sequence++;
117		smp_wmb();
118
119		status->policyload = seqno;
120		status->deny_unknown = !security_get_allow_unknown();
121
122		smp_wmb();
123		status->sequence++;
124	}
125	mutex_unlock(&selinux_status_lock);
126}