On Thu, Jun 20, 2019 at 06:19:14PM -0700, Matthew Garrett wrote: > 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 <mjg59@xxxxxxxxxx> > Cc: David Howells <dhowells@xxxxxxxxxx> > --- > .../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.c > > diff --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 the > diff --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. > 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? > 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..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? > + 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.o > diff --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@xxxxxxxxxx) > + * > + * 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) = { > +#endif Ah, 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