| Message ID | 20190622000358.19895-4-matthewgarrett@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Lockdown as an LSM | expand |
On Fri, Jun 21, 2019 at 05:03:32PM -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@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> -Kees > 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 | 47 +++++ > security/lockdown/Makefile | 1 + > security/lockdown/lockdown.c | 172 ++++++++++++++++++ > 7 files changed, 237 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 9eaf02e70707..c808d344ec75 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. > + */ > 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" > 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..8e39b36b8f33 > --- /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 <linux/security.h> > +#include <linux/export.h> > +#include <linux/lsm_hooks.h> > + > +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, > +}; > -- > 2.22.0.410.gd8fdbe21b5-goog >
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 9eaf02e70707..c808d344ec75 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. + */ 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" 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..8e39b36b8f33 --- /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 <linux/security.h> +#include <linux/export.h> +#include <linux/lsm_hooks.h> + +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, +};
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@google.com> 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 | 47 +++++ security/lockdown/Makefile | 1 + security/lockdown/lockdown.c | 172 ++++++++++++++++++ 7 files changed, 237 insertions(+), 1 deletion(-) create mode 100644 security/lockdown/Kconfig create mode 100644 security/lockdown/Makefile create mode 100644 security/lockdown/lockdown.c