Re: [PATCH V33 03/30] security: Add a static lockdown policy LSM
From: Kees Cook <hidden>
Date: 2019-06-21 03:44:41
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On Thu, Jun 20, 2019 at 06:19:14PM -0700, Matthew Garrett wrote:
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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 <redacted> Cc: David Howells <dhowells@redhat.com> --- .../admin-guide/kernel-parameters.txt | 9 + include/linux/security.h | 4 + security/Kconfig | 3 +- security/Makefile | 2 + security/lockdown/Kconfig | 46 +++++ security/lockdown/Makefile | 1 + security/lockdown/lockdown.c | 168 ++++++++++++++++++ 7 files changed, 232 insertions(+), 1 deletion(-) create mode 100644 security/lockdown/Kconfig create mode 100644 security/lockdown/Makefile create mode 100644 security/lockdown/lockdown.cdiff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2b8ee90bb644..fa336f6cd5bc 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt@@ -2239,6 +2239,15 @@ lockd.nlm_udpport=M [NFS] Assign UDP port. Format: <integer> + 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 thediff --git a/include/linux/security.h b/include/linux/security.h index b75941c811e6..a86a7739ca24 100644 --- a/include/linux/security.h +++ b/include/linux/security.h@@ -76,6 +76,10 @@ enum lsm_event { LSM_POLICY_CHANGE, }; +/* + * If you add to this, remember to extend lockdown_reasons in + * security/lockdown/lockdown.c. + */
Best to add something like: BUILD_BUG_ON(ARRAY_SIZE(lockdown_reasons), LOCKDOWN_CONFIDENTIALLY_MAX); to actually enforce this.
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enum lockdown_reason { LOCKDOWN_NONE, LOCKDOWN_INTEGRITY_MAX,diff --git a/security/Kconfig b/security/Kconfig index 1d6463fb1450..c35aa72103df 100644 --- a/security/Kconfig +++ b/security/Kconfig@@ -236,12 +236,13 @@ source "security/apparmor/Kconfig" source "security/loadpin/Kconfig" source "security/yama/Kconfig" source "security/safesetid/Kconfig" +source "security/lockdown/Kconfig" source "security/integrity/Kconfig" config LSM string "Ordered list of enabled LSMs" - default "yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor" + default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor"
Is this needed? It seems like the early LSMs are totally ignored for ordering?
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help A comma-separated list of LSMs, in initialization order. Any LSMs left off this list will be ignored. This can bediff --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-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o # Object integrity file listsdiff --git a/security/lockdown/Kconfig b/security/lockdown/Kconfig new file mode 100644 index 000000000000..431cd2b9a14e --- /dev/null +++ b/security/lockdown/Kconfig@@ -0,0 +1,46 @@ +config SECURITY_LOCKDOWN_LSM + bool "Basic module for enforcing kernel lockdown" + depends on SECURITY + help + Build support for an LSM that enforces a coarse kernel lockdown + behaviour. + +config SECURITY_LOCKDOWN_LSM_EARLY + bool "Enable lockdown LSM early in init"
whitespace glitches?
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+ depends on SECURITY_LOCKDOWN_LSM + help + Enable the lockdown LSM early in boot. This is necessary in order + to ensure that lockdown enforcement can be carried out on kernel + boot parameters that are otherwise parsed before the security + subsystem is fully initialised. + +choice + prompt "Kernel default lockdown mode" + default LOCK_DOWN_KERNEL_FORCE_NONE + depends on SECURITY_LOCKDOWN_LSM + help + The kernel can be configured to default to differing levels of + lockdown. + +config LOCK_DOWN_KERNEL_FORCE_NONE + bool "None" + help + No lockdown functionality is enabled by default. Lockdown may be + enabled via the kernel commandline or /sys/kernel/security/lockdown. + +config LOCK_DOWN_KERNEL_FORCE_INTEGRITY + bool "Integrity" + help + The kernel runs in integrity mode by default. Features that allow + the kernel to be modified at runtime are disabled. + +config LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY + bool "Confidentiality" + help + The kernel runs in confidentiality mode by default. Features that + allow the kernel to be modified at runtime or that permit userland + code to read confidential material held inside the kernel are + disabled. + +endchoice +diff --git a/security/lockdown/Makefile b/security/lockdown/Makefile new file mode 100644 index 000000000000..e3634b9017e7 --- /dev/null +++ b/security/lockdown/Makefile@@ -0,0 +1 @@ +obj-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown.odiff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c new file mode 100644 index 000000000000..1ecb2eecb245 --- /dev/null +++ b/security/lockdown/lockdown.c@@ -0,0 +1,168 @@ +// 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> + +static enum lockdown_reason kernel_locked_down;
What's the use-case for runtime changing this value? (If you didn't, you could make it __ro_after_init.)
+
+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) && lockdown_reasons[what])
+ pr_notice("Lockdown: %s is restricted; see man kernel_lockdown.7\n",
+ lockdown_reasons[what]);
+ return (kernel_locked_down >= what);
+}
+
+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);
+ }
+ }I thought there were helpers for this kind of thing?
+
+ /* 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) = {
+#endifAh, I see now: it *might* be an early LSM. What states are missed if not early? Only parameters? I think the behavior differences need to be spelled out in Kconfig (or somewhere...)
+ .name = "lockdown", + .init = lockdown_lsm_init, +}; -- 2.22.0.410.gd8fdbe21b5-goog
-- Kees Cook