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}
127