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(struct selinux_state *state)
43{
44	struct selinux_kernel_status   *status;
45	struct page		       *result = NULL;
46
47	mutex_lock(&state->status_lock);
48	if (!state->status_page) {
49		state->status_page = alloc_page(GFP_KERNEL|__GFP_ZERO);
50
51		if (state->status_page) {
52			status = page_address(state->status_page);
53
54			status->version = SELINUX_KERNEL_STATUS_VERSION;
55			status->sequence = 0;
56			status->enforcing = enforcing_enabled(state);
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(state);
66		}
67	}
68	result = state->status_page;
69	mutex_unlock(&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(struct selinux_state *state,
80				      int enforcing)
81{
82	struct selinux_kernel_status   *status;
83
84	mutex_lock(&state->status_lock);
85	if (state->status_page) {
86		status = page_address(state->status_page);
87
88		status->sequence++;
89		smp_wmb();
90
91		status->enforcing = enforcing;
92
93		smp_wmb();
94		status->sequence++;
95	}
96	mutex_unlock(&state->status_lock);
97}
98
99/*
100 * selinux_status_update_policyload
101 *
102 * It updates status of the times of policy reloaded, and current
103 * setting of deny_unknown.
104 */
105void selinux_status_update_policyload(struct selinux_state *state,
106				      int seqno)
107{
108	struct selinux_kernel_status   *status;
109
110	mutex_lock(&state->status_lock);
111	if (state->status_page) {
112		status = page_address(state->status_page);
113
114		status->sequence++;
115		smp_wmb();
116
117		status->policyload = seqno;
118		status->deny_unknown = !security_get_allow_unknown(state);
119
120		smp_wmb();
121		status->sequence++;
122	}
123	mutex_unlock(&state->status_lock);
124}
125