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}