@@ -13066,6 +13066,12 @@ F: drivers/slimbus/
F: Documentation/devicetree/bindings/slimbus/
F: include/linux/slimbus.h
+SIDECHANNEL SECURITY MODULE
+M: Casey Schaufler <casey.schaufler@intel.com>
+L: linux-security-module@vger.kernel.org
+S: Maintained
+F: security/sidechannel/
+
SMACK SECURITY MODULE
M: Casey Schaufler <casey@schaufler-ca.com>
L: linux-security-module@vger.kernel.org
@@ -2088,5 +2088,10 @@ void __init loadpin_add_hooks(void);
#else
static inline void loadpin_add_hooks(void) { };
#endif
+#ifdef CONFIG_SECURITY_SIDECHANNEL
+void __init sidechannel_add_hooks(void);
+#else
+static inline void sidechannel_add_hooks(void) { };
+#endif
#endif /* ! __LINUX_LSM_HOOKS_H */
@@ -237,6 +237,7 @@ source security/tomoyo/Kconfig
source security/apparmor/Kconfig
source security/loadpin/Kconfig
source security/yama/Kconfig
+source security/sidechannel/Kconfig
source security/integrity/Kconfig
@@ -10,6 +10,7 @@ subdir-$(CONFIG_SECURITY_TOMOYO) += tomoyo
subdir-$(CONFIG_SECURITY_APPARMOR) += apparmor
subdir-$(CONFIG_SECURITY_YAMA) += yama
subdir-$(CONFIG_SECURITY_LOADPIN) += loadpin
+subdir-$(CONFIG_SECURITY_SIDECHANNEL) += sidechannel
# always enable default capabilities
obj-y += commoncap.o
@@ -25,6 +26,7 @@ obj-$(CONFIG_SECURITY_TOMOYO) += tomoyo/
obj-$(CONFIG_SECURITY_APPARMOR) += apparmor/
obj-$(CONFIG_SECURITY_YAMA) += yama/
obj-$(CONFIG_SECURITY_LOADPIN) += loadpin/
+obj-$(CONFIG_SECURITY_SIDECHANNEL) += sidechannel/
obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o
# Object integrity file lists
@@ -80,6 +80,7 @@ int __init security_init(void)
capability_add_hooks();
yama_add_hooks();
loadpin_add_hooks();
+ sidechannel_add_hooks();
/*
* Load all the remaining security modules.
new file mode 100644
@@ -0,0 +1,65 @@
+config SECURITY_SIDECHANNEL
+ bool "Sidechannel attack safety extra checks"
+ depends on SECURITY
+ default n
+ help
+ Look for a variety of cases where a side-channel attack
+ could potentially be exploited. Instruct the switching
+ code to use the indirect_branch_prediction_barrier in
+ cases where the passed task and the current task may be
+ at risk.
+
+ If you are unsure how to answer this question, answer N.
+
+config SECURITY_SIDECHANNEL_ALWAYS
+ bool "Sidechannel assumed to always be possible"
+ depends on SECURITY_SIDECHANNEL
+ default n
+ help
+ Assume that all tasks may be subject to side-channel attacks.
+ Always instruct the system to use countermeasures regardless
+ of the potential impact.
+
+ If you are unsure how to answer this question, answer N.
+
+config SECURITY_SIDECHANNEL_UIDS
+ bool "Sidechannel check on UID"
+ depends on SECURITY_SIDECHANNEL
+ depends on !SECURITY_SIDECHANNEL_ALWAYS
+ default n
+ help
+ Assume that tasks with different effective UIDs may be
+ subject to side-channel attacks. As most task switching
+ occurs between tasks with different effective UIDs this
+ can have a significant performance impact.
+
+ If you are unsure how to answer this question, answer N.
+
+
+config SECURITY_SIDECHANNEL_CAPABILITIES
+ bool "Sidechannel check on capability sets"
+ depends on SECURITY_SIDECHANNEL
+ depends on !SECURITY_SIDECHANNEL_ALWAYS
+ default n
+ select SECURITY_SIDECHANNEL_NAMESPACES if USER_NS
+ help
+ Assume that tasks with different sets of privilege may be
+ subject to side-channel attacks. Potential interactions
+ where the attacker lacks capabilities the attacked has
+ are blocked. Selecting this when user namespaces (USER_NS)
+ are enabled will enable SECURITY_SIDECHANNEL_NAMESPACES.
+
+ If you are unsure how to answer this question, answer N.
+
+config SECURITY_SIDECHANNEL_NAMESPACES
+ bool "Sidechannel check on namespaces"
+ depends on SECURITY_SIDECHANNEL
+ depends on !SECURITY_SIDECHANNEL_ALWAYS
+ depends on NAMESPACES
+ default n
+ help
+ Assume that tasks in different namespaces may be
+ subject to side-channel attacks. User, PID and cgroup
+ namespaces are checked.
+
+ If you are unsure how to answer this question, answer N.
new file mode 100644
@@ -0,0 +1 @@
+obj-$(CONFIG_SECURITY_SIDECHANNEL) += sidechannel.o
new file mode 100644
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Side Channel Safety Security Module
+ *
+ * Copyright (C) 2018 Intel Corporation.
+ *
+ */
+
+#define pr_fmt(fmt) "SideChannel: " fmt
+
+#include <linux/types.h>
+#include <linux/lsm_hooks.h>
+#include <linux/capability.h>
+#include <linux/cred.h>
+#include <linux/sched.h>
+#include <linux/string_helpers.h>
+#include <linux/nsproxy.h>
+#include <linux/pid_namespace.h>
+
+#ifdef CONFIG_SECURITY_SIDECHANNEL_ALWAYS
+static int sidechannel_task_safe_sidechannel(struct task_struct *p)
+{
+ return -EACCES;
+}
+#else
+/*
+ * safe_by_uid - Are task and current sidechannel safe?
+ * @p: task to check on
+ *
+ * Returns 0 if the tasks are sidechannel safe, -EACCES otherwise.
+ */
+#ifdef CONFIG_SECURITY_SIDECHANNEL_UIDS
+static int safe_by_uid(struct task_struct *p)
+{
+ const struct cred *ccred = current_real_cred();
+ const struct cred *pcred = rcu_dereference_protected(p->real_cred, 1);
+
+ /*
+ * Credential checks. Considered safe if:
+ * UIDs are the same
+ */
+ if (ccred != pcred && ccred->euid.val != pcred->euid.val)
+ return -EACCES;
+ return 0;
+}
+#else
+static inline int safe_by_uid(struct task_struct *p)
+{
+ return 0;
+}
+#endif
+
+/*
+ * safe_by_capability - Are task and current sidechannel safe?
+ * @p: task to check on
+ *
+ * Returns 0 if the tasks are sidechannel safe, -EACCES otherwise.
+ */
+#ifdef CONFIG_SECURITY_SIDECHANNEL_CAPABILITIES
+static int safe_by_capability(struct task_struct *p)
+{
+ const struct cred *ccred = current_real_cred();
+ const struct cred *pcred = rcu_dereference_protected(p->real_cred, 1);
+
+ /*
+ * Capabilities checks. Considered safe if:
+ * current has all the capabilities p does
+ */
+ if (ccred != pcred &&
+ !cap_issubset(pcred->cap_effective, ccred->cap_effective))
+ return -EACCES;
+ return 0;
+}
+#else
+static inline int safe_by_capability(struct task_struct *p)
+{
+ return 0;
+}
+#endif
+
+#ifdef CONFIG_SECURITY_SIDECHANNEL_NAMESPACES
+
+/**
+ * safe_by_user_namespace - Are task and current sidechannel safe?
+ * @p: task to check on
+ *
+ * Returns 0 if the tasks are sidechannel safe, -EACCES otherwise.
+ */
+#ifdef CONFIG_USER_NS
+static int safe_by_user_namespace(struct task_struct *p)
+{
+ const struct cred *ccred = current_real_cred();
+ const struct cred *pcred = rcu_dereference_protected(p->real_cred, 1);
+
+ if (ccred->user_ns != pcred->user_ns)
+ return -EACCES;
+ return 0;
+}
+#else
+static inline int safe_by_user_namespace(struct task_struct *p)
+{
+ return 0;
+}
+#endif
+
+/**
+ * safe_by_namespace - Are task and current sidechannel safe?
+ * @p: task to check on
+ *
+ * Returns 0 if the tasks are sidechannel safe, -EACCES otherwise.
+ */
+static int safe_by_namespace(struct task_struct *p)
+{
+ struct cgroup_namespace *ccgn = NULL;
+ struct cgroup_namespace *pcgn = NULL;
+ int rc;
+
+ /*
+ * Namespace checks. Considered safe if:
+ * cgroup namespace is the same
+ * User namespace is the same
+ * PID namespace is the same
+ */
+ if (current->nsproxy)
+ ccgn = current->nsproxy->cgroup_ns;
+ if (p->nsproxy)
+ pcgn = p->nsproxy->cgroup_ns;
+ if (ccgn != pcgn)
+ return -EACCES;
+
+ rc = safe_by_user_namespace(p);
+ if (rc)
+ return rc;
+
+ if (task_active_pid_ns(current) != task_active_pid_ns(p))
+ return -EACCES;
+ return 0;
+}
+#else
+static inline int safe_by_namespace(struct task_struct *p)
+{
+ return 0;
+}
+#endif
+
+/**
+ * sidechannel_task_safe_sidechannel - Are task and current sidechannel safe?
+ * @p: task to check on
+ *
+ * Returns 0 if the tasks are sidechannel safe, -EACCES otherwise.
+ */
+static int sidechannel_task_safe_sidechannel(struct task_struct *p)
+{
+ int rc;
+
+ /*
+ * Easy optimizations
+ */
+ if (p == current || p->pid == current->pid)
+ return 0;
+
+ rc = safe_by_uid(p);
+ if (rc)
+ return rc;
+ rc = safe_by_capability(p);
+ if (rc)
+ return rc;
+ rc = safe_by_namespace(p);
+ if (rc)
+ return rc;
+ return 0;
+}
+#endif /* CONFIG_SECURITY_SIDECHANNEL_ALWAYS */
+
+static struct security_hook_list sidechannel_hooks[] __lsm_ro_after_init = {
+ LSM_HOOK_INIT(task_safe_sidechannel, sidechannel_task_safe_sidechannel),
+};
+
+void __init sidechannel_add_hooks(void)
+{
+ pr_info("Extra sidechannel checks enabled\n");
+ security_add_hooks(sidechannel_hooks, ARRAY_SIZE(sidechannel_hooks),
+ "sidechannel");
+}
The sidechannel LSM checks for cases where a side-channel attack may be dangerous based on security attributes of tasks. This includes: Effective UID of the tasks is different Capablity sets are different Tasks are in different namespaces An option is also provided to assert that task are never to be considered safe. This is high paranoia, and expensive as well. Signed-off-by: Casey Schaufler <casey.schaufler@intel.com> --- MAINTAINERS | 6 + include/linux/lsm_hooks.h | 5 + security/Kconfig | 1 + security/Makefile | 2 + security/security.c | 1 + security/sidechannel/Kconfig | 65 ++++++++++ security/sidechannel/Makefile | 1 + security/sidechannel/sidechannel.c | 184 +++++++++++++++++++++++++++++ 8 files changed, 265 insertions(+) create mode 100644 security/sidechannel/Kconfig create mode 100644 security/sidechannel/Makefile create mode 100644 security/sidechannel/sidechannel.c