From patchwork Wed Jul 31 22:15:51 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Matthew Garrett X-Patchwork-Id: 11069639 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 73C0114DB for ; Wed, 31 Jul 2019 22:16:39 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6230527F17 for ; Wed, 31 Jul 2019 22:16:39 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 5683127F94; Wed, 31 Jul 2019 22:16:39 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.5 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,RCVD_IN_DNSWL_HI,USER_IN_DEF_DKIM_WL autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6E23F27F17 for ; Wed, 31 Jul 2019 22:16:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731167AbfGaWQf (ORCPT ); Wed, 31 Jul 2019 18:16:35 -0400 Received: from mail-pf1-f201.google.com ([209.85.210.201]:56774 "EHLO mail-pf1-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731161AbfGaWQf (ORCPT ); Wed, 31 Jul 2019 18:16:35 -0400 Received: by mail-pf1-f201.google.com with SMTP id x10so44196088pfa.23 for ; Wed, 31 Jul 2019 15:16:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=8bsfxMGI0ih4pMPPTAd5DGb7PjaX6MOPHshFINx/tPw=; b=T8uBhn8F/ebCXCZz2jG/dmMBma/ouENxi0HKWAV964xKK73heHQ5Ra/HzG/HvRQwlg B4JKuzhKDXFW75XvHPJix48g3361z/2MwfwidKZ2ktXR1eq+O0ilRgQgCssdwO8U+RKc 3n2dswQwFvDauZmmoe7gX+lo8nh34Acf1SdsBk4sHFr3HzEdoCX7pVfuVIGGOzwgzEQm dvNawHjayohqrMVboebjhR1NcnR9g2i/V3Ll66Pe4ot+DdTUNqc6/zJ9Em3eSKos+tmV 127ExBYZ4BuOvK1e0Bb1ANPHPPcEb1W2XphOYtxNIQBTyPme9OwpRSxqv9t0T3WrNXpo 1hsQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=8bsfxMGI0ih4pMPPTAd5DGb7PjaX6MOPHshFINx/tPw=; b=EdIL1nK/8Bf9IYtdvepdqPjZxy+PbvoNdec3ODBBrEmgKVjCdmgA6CdoNAb6KbPoDN skTxikiTeVPjSDLCk3xwiCtQ8qx20BO70RJkB3sw+KdMLYoAgY9M6iVZHwhNhQuxb5gg WzMQxbvFFf1QGJvbu4HpMdFnsZWbIe+DX+Y4zXvBb7KyI9tXxDi1EdoyO2rwVS59VTjL tA8DRbFoy+rQ0JQw+FNRXYMwTkN0/e+YpTepTbbNjbizqxRcyGaYYfLEPXTOQthLK/93 aaTVQD2CRgX7fq/M448gPuNAJXOEaGUkFRBlINdV1CAEnK6ejv4xgOvwEBYjBxmOKn88 jvkg== X-Gm-Message-State: APjAAAXZDugcecu4P6OkcFK0JrnCU8+v84UhT1cgwGGR7eB20XCOStQs XrpioAVz16Ww/eG5LmyFhGs7rjAl9/FQAbAVTMZuyA== X-Google-Smtp-Source: APXvYqyDtr49MmYBTKFlbKYjg7EQeCqIVdXTvKdl9KZF4JUS8Zi+2yH0uSkl3nFdWiWd4/qUFgElR5qHaJCW1NxybxnT2Q== X-Received: by 2002:a63:204b:: with SMTP id r11mr75966516pgm.121.1564611393620; Wed, 31 Jul 2019 15:16:33 -0700 (PDT) Date: Wed, 31 Jul 2019 15:15:51 -0700 In-Reply-To: <20190731221617.234725-1-matthewgarrett@google.com> Message-Id: <20190731221617.234725-4-matthewgarrett@google.com> Mime-Version: 1.0 References: <20190731221617.234725-1-matthewgarrett@google.com> X-Mailer: git-send-email 2.22.0.770.g0f2c4a37fd-goog Subject: [PATCH V37 03/29] security: Add a static lockdown policy LSM From: Matthew Garrett To: jmorris@namei.org Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Matthew Garrett , Matthew Garrett , Kees Cook , David Howells Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP While existing LSMs can be extended to handle lockdown policy, distributions generally want to be able to apply a straightforward static policy. This patch adds a simple LSM that can be configured to reject either integrity or all lockdown queries, and can be configured at runtime (through securityfs), boot time (via a kernel parameter) or build time (via a kconfig option). Based on initial code by David Howells. Signed-off-by: Matthew Garrett Reviewed-by: Kees Cook Cc: David Howells --- .../admin-guide/kernel-parameters.txt | 9 + include/linux/security.h | 3 + security/Kconfig | 11 +- security/Makefile | 2 + security/lockdown/Kconfig | 47 +++++ security/lockdown/Makefile | 1 + security/lockdown/lockdown.c | 172 ++++++++++++++++++ 7 files changed, 240 insertions(+), 5 deletions(-) create mode 100644 security/lockdown/Kconfig create mode 100644 security/lockdown/Makefile create mode 100644 security/lockdown/lockdown.c diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index ef52d01524af..0b962844ac2a 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2267,6 +2267,15 @@ lockd.nlm_udpport=M [NFS] Assign UDP port. Format: + lockdown= [SECURITY] + { integrity | confidentiality } + Enable the kernel lockdown feature. If set to + integrity, kernel features that allow userland to + modify the running kernel are disabled. If set to + confidentiality, kernel features that allow userland + to extract confidential information from the kernel + are also disabled. + locktorture.nreaders_stress= [KNL] Set the number of locking read-acquisition kthreads. Defaults to being automatically set based on the diff --git a/include/linux/security.h b/include/linux/security.h index c2b1204e8e26..54a0532ec12f 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -97,6 +97,9 @@ enum lsm_event { * potentially a moving target. It is easy to misuse this information * in a way that could break userspace. Please be careful not to do * so. + * + * If you add to this, remember to extend lockdown_reasons in + * security/lockdown/lockdown.c. */ enum lockdown_reason { LOCKDOWN_NONE, diff --git a/security/Kconfig b/security/Kconfig index 0d65594b5196..2a1a2d396228 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -237,6 +237,7 @@ source "security/apparmor/Kconfig" source "security/loadpin/Kconfig" source "security/yama/Kconfig" source "security/safesetid/Kconfig" +source "security/lockdown/Kconfig" source "security/integrity/Kconfig" @@ -276,11 +277,11 @@ endchoice config LSM string "Ordered list of enabled LSMs" - default "yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK - default "yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR - default "yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO - default "yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC - default "yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor" + default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK + default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR + default "lockdown,yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO + default "lockdown,yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC + default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor" help A comma-separated list of LSMs, in initialization order. Any LSMs left off this list will be ignored. This can be diff --git a/security/Makefile b/security/Makefile index c598b904938f..be1dd9d2cb2f 100644 --- a/security/Makefile +++ b/security/Makefile @@ -11,6 +11,7 @@ subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor subdir-$(CONFIG_SECURITY_YAMA) += yama subdir-$(CONFIG_SECURITY_LOADPIN) += loadpin subdir-$(CONFIG_SECURITY_SAFESETID) += safesetid +subdir-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown # always enable default capabilities obj-y += commoncap.o @@ -27,6 +28,7 @@ obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/ obj-$(CONFIG_SECURITY_YAMA) += yama/ obj-$(CONFIG_SECURITY_LOADPIN) += loadpin/ obj-$(CONFIG_SECURITY_SAFESETID) += safesetid/ +obj-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown/ obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o # Object integrity file lists diff --git a/security/lockdown/Kconfig b/security/lockdown/Kconfig new file mode 100644 index 000000000000..7374ba76d8eb --- /dev/null +++ b/security/lockdown/Kconfig @@ -0,0 +1,47 @@ +config SECURITY_LOCKDOWN_LSM + bool "Basic module for enforcing kernel lockdown" + depends on SECURITY + help + Build support for an LSM that enforces a coarse kernel lockdown + behaviour. + +config SECURITY_LOCKDOWN_LSM_EARLY + bool "Enable lockdown LSM early in init" + depends on SECURITY_LOCKDOWN_LSM + help + Enable the lockdown LSM early in boot. This is necessary in order + to ensure that lockdown enforcement can be carried out on kernel + boot parameters that are otherwise parsed before the security + subsystem is fully initialised. If enabled, lockdown will + unconditionally be called before any other LSMs. + +choice + prompt "Kernel default lockdown mode" + default LOCK_DOWN_KERNEL_FORCE_NONE + depends on SECURITY_LOCKDOWN_LSM + help + The kernel can be configured to default to differing levels of + lockdown. + +config LOCK_DOWN_KERNEL_FORCE_NONE + bool "None" + help + No lockdown functionality is enabled by default. Lockdown may be + enabled via the kernel commandline or /sys/kernel/security/lockdown. + +config LOCK_DOWN_KERNEL_FORCE_INTEGRITY + bool "Integrity" + help + The kernel runs in integrity mode by default. Features that allow + the kernel to be modified at runtime are disabled. + +config LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY + bool "Confidentiality" + help + The kernel runs in confidentiality mode by default. Features that + allow the kernel to be modified at runtime or that permit userland + code to read confidential material held inside the kernel are + disabled. + +endchoice + diff --git a/security/lockdown/Makefile b/security/lockdown/Makefile new file mode 100644 index 000000000000..e3634b9017e7 --- /dev/null +++ b/security/lockdown/Makefile @@ -0,0 +1 @@ +obj-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown.o diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c new file mode 100644 index 000000000000..d30c4d254b5f --- /dev/null +++ b/security/lockdown/lockdown.c @@ -0,0 +1,172 @@ +// 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 +#include +#include + +static enum lockdown_reason kernel_locked_down; + +static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { + [LOCKDOWN_NONE] = "none", + [LOCKDOWN_INTEGRITY_MAX] = "integrity", + [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", +}; + +static 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 (kernel_locked_down >= what) { + if (lockdown_reasons[what]) + pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n", + lockdown_reasons[what]); + return -EPERM; + } + + return 0; +} + +static struct security_hook_list lockdown_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(locked_down, lockdown_is_locked_down), +}; + +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"); + 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", 0600, NULL, NULL, + &lockdown_ops); + if (IS_ERR(dentry)) + return PTR_ERR(dentry); + + return 0; +} + +core_initcall(lockdown_secfs_init); + +#ifdef CONFIG_SECURITY_LOCKDOWN_LSM_EARLY +DEFINE_EARLY_LSM(lockdown) = { +#else +DEFINE_LSM(lockdown) = { +#endif + .name = "lockdown", + .init = lockdown_lsm_init, +};