// SPDX-License-Identifier: GPL-2.0
/* Lock down the kernel
 *
 * Copyright (C) 2016 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/security.h>
#include <linux/export.h>
#include <linux/lsm_hooks.h>
#include <uapi/linux/lsm.h>

static enum lockdown_reason kernel_locked_down;

static const enum lockdown_reason lockdown_levels[] = {LOCKDOWN_NONE,
                                                 LOCKDOWN_INTEGRITY_MAX,
                                                 LOCKDOWN_CONFIDENTIALITY_MAX};

/*
 * Put the kernel into lock-down mode.
 */
static int lock_kernel_down(const char *where, enum lockdown_reason level)
{
        if (kernel_locked_down >= level)
                return -EPERM;

        kernel_locked_down = level;
        pr_notice("Kernel is locked down from %s; see man kernel_lockdown.7\n",
                  where);
        return 0;
}

static int __init lockdown_param(char *level)
{
        if (!level)
                return -EINVAL;

        if (strcmp(level, "integrity") == 0)
                lock_kernel_down("command line", LOCKDOWN_INTEGRITY_MAX);
        else if (strcmp(level, "confidentiality") == 0)
                lock_kernel_down("command line", LOCKDOWN_CONFIDENTIALITY_MAX);
        else
                return -EINVAL;

        return 0;
}

early_param("lockdown", lockdown_param);

/**
 * lockdown_is_locked_down - Find out if the kernel is locked down
 * @what: Tag to use in notice generated if lockdown is in effect
 */
static int lockdown_is_locked_down(enum lockdown_reason what)
{
        if (WARN(what >= LOCKDOWN_CONFIDENTIALITY_MAX,
                 "Invalid lockdown reason"))
                return -EPERM;

        if (kernel_locked_down >= what) {
                if (lockdown_reasons[what])
                        pr_notice_ratelimited("Lockdown: %s: %s is restricted; see man kernel_lockdown.7\n",
                                  current->comm, lockdown_reasons[what]);
                return -EPERM;
        }

        return 0;
}

static struct security_hook_list lockdown_hooks[] __ro_after_init = {
        LSM_HOOK_INIT(locked_down, lockdown_is_locked_down),
};

static const struct lsm_id lockdown_lsmid = {
        .name = "lockdown",
        .id = LSM_ID_LOCKDOWN,
};

static int __init lockdown_lsm_init(void)
{
#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
        lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
        lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
#endif
        security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
                           &lockdown_lsmid);
        return 0;
}

static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
                             loff_t *ppos)
{
        char temp[80] = "";
        int i, offset = 0;

        for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
                enum lockdown_reason level = lockdown_levels[i];

                if (lockdown_reasons[level]) {
                        const char *label = lockdown_reasons[level];

                        if (kernel_locked_down == level)
                                offset += sprintf(temp+offset, "[%s] ", label);
                        else
                                offset += sprintf(temp+offset, "%s ", label);
                }
        }

        /* Convert the last space to a newline if needed. */
        if (offset > 0)
                temp[offset-1] = '\n';

        return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
}

static ssize_t lockdown_write(struct file *file, const char __user *buf,
                              size_t n, loff_t *ppos)
{
        char *state;
        int i, len, err = -EINVAL;

        state = memdup_user_nul(buf, n);
        if (IS_ERR(state))
                return PTR_ERR(state);

        len = strlen(state);
        if (len && state[len-1] == '\n') {
                state[len-1] = '\0';
                len--;
        }

        for (i = 0; i < ARRAY_SIZE(lockdown_levels); i++) {
                enum lockdown_reason level = lockdown_levels[i];
                const char *label = lockdown_reasons[level];

                if (label && !strcmp(state, label))
                        err = lock_kernel_down("securityfs", level);
        }

        kfree(state);
        return err ? err : n;
}

static const struct file_operations lockdown_ops = {
        .read  = lockdown_read,
        .write = lockdown_write,
};

static int __init lockdown_secfs_init(void)
{
        struct dentry *dentry;

        dentry = securityfs_create_file("lockdown", 0644, NULL, NULL,
                                        &lockdown_ops);
        return PTR_ERR_OR_ZERO(dentry);
}

#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY
DEFINE_EARLY_LSM(lockdown) = {
#else
DEFINE_LSM(lockdown) = {
#endif
        .id = &lockdown_lsmid,
        .init = lockdown_lsm_init,
        .initcall_core = lockdown_secfs_init,
};