1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * mmap based event notifications for SELinux
4 *
5 * Author: KaiGai Kohei <kaigai@ak.jp.nec.com>
6 *
7 * Copyright (C) 2010 NEC corporation
8 */
9#include <linux/kernel.h>
10#include <linux/gfp.h>
11#include <linux/mm.h>
12#include <linux/mutex.h>
13#include "avc.h"
14#include "security.h"
15
16/*
17 * The selinux_status_page shall be exposed to userspace applications
18 * using mmap interface on /selinux/status.
19 * It enables to notify applications a few events that will cause reset
20 * of userspace access vector without context switching.
21 *
22 * The selinux_kernel_status structure on the head of status page is
23 * protected from concurrent accesses using seqlock logic, so userspace
24 * application should reference the status page according to the seqlock
25 * logic.
26 *
27 * Typically, application checks status->sequence at the head of access
28 * control routine. If it is odd-number, kernel is updating the status,
29 * so please wait for a moment. If it is changed from the last sequence
30 * number, it means something happen, so application will reset userspace
31 * avc, if needed.
32 * In most cases, application shall confirm the kernel status is not
33 * changed without any system call invocations.
34 */
35
36/*
37 * selinux_kernel_status_page
38 *
39 * It returns a reference to selinux_status_page. If the status page is
40 * not allocated yet, it also tries to allocate it at the first time.
41 */
42struct page *selinux_kernel_status_page(void)
43{
44	struct selinux_kernel_status   *status;
45	struct page		       *result = NULL;
46
47	mutex_lock(&selinux_state.status_lock);
48	if (!selinux_state.status_page) {
49		selinux_state.status_page = alloc_page(GFP_KERNEL|__GFP_ZERO);
50
51		if (selinux_state.status_page) {
52			status = page_address(selinux_state.status_page);
53
54			status->version = SELINUX_KERNEL_STATUS_VERSION;
55			status->sequence = 0;
56			status->enforcing = enforcing_enabled();
57			/*
58			 * NOTE: the next policyload event shall set
59			 * a positive value on the status->policyload,
60			 * although it may not be 1, but never zero.
61			 * So, application can know it was updated.
62			 */
63			status->policyload = 0;
64			status->deny_unknown =
65				!security_get_allow_unknown();
66		}
67	}
68	result = selinux_state.status_page;
69	mutex_unlock(&selinux_state.status_lock);
70
71	return result;
72}
73
74/*
75 * selinux_status_update_setenforce
76 *
77 * It updates status of the current enforcing/permissive mode.
78 */
79void selinux_status_update_setenforce(bool enforcing)
80{
81	struct selinux_kernel_status   *status;
82
83	mutex_lock(&selinux_state.status_lock);
84	if (selinux_state.status_page) {
85		status = page_address(selinux_state.status_page);
86
87		status->sequence++;
88		smp_wmb();
89
90		status->enforcing = enforcing ? 1 : 0;
91
92		smp_wmb();
93		status->sequence++;
94	}
95	mutex_unlock(&selinux_state.status_lock);
96}
97
98/*
99 * selinux_status_update_policyload
100 *
101 * It updates status of the times of policy reloaded, and current
102 * setting of deny_unknown.
103 */
104void selinux_status_update_policyload(u32 seqno)
105{
106	struct selinux_kernel_status   *status;
107
108	mutex_lock(&selinux_state.status_lock);
109	if (selinux_state.status_page) {
110		status = page_address(selinux_state.status_page);
111
112		status->sequence++;
113		smp_wmb();
114
115		status->policyload = seqno;
116		status->deny_unknown = !security_get_allow_unknown();
117
118		smp_wmb();
119		status->sequence++;
120	}
121	mutex_unlock(&selinux_state.status_lock);
122}
123