[PATCH v5 5/5] sidechannel: Linux Security Module for sidechannel
From: Casey Schaufler
Date: Wed Sep 26 2018 - 16:34:56 EST
From: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
This is a new Linux Security Module (LSM) that checks for
potential sidechannel issues that are not covered in the
ptrace PTRACE_MODE_SCHED option. Namespace differences are
checked in this intitial version. Additional checks should
be added when they are determined to be useful.
Signed-off-by: Casey Schaufler <casey.schaufler@xxxxxxxxx>
---
include/linux/lsm_hooks.h | 5 ++
security/Kconfig | 1 +
security/Makefile | 2 +
security/security.c | 1 +
security/sidechannel/Kconfig | 13 +++++
security/sidechannel/Makefile | 1 +
security/sidechannel/sidechannel.c | 88 ++++++++++++++++++++++++++++++
7 files changed, 111 insertions(+)
create mode 100644 security/sidechannel/Kconfig
create mode 100644 security/sidechannel/Makefile
create mode 100644 security/sidechannel/sidechannel.c
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 97a020c616ad..3cb6516dba3c 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2081,5 +2081,10 @@ 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 */
diff --git a/security/Kconfig b/security/Kconfig
index d9aa521b5206..6b814a3f93ea 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -236,6 +236,7 @@ source security/tomoyo/Kconfig
source security/apparmor/Kconfig
source security/loadpin/Kconfig
source security/yama/Kconfig
+source security/sidechannel/Kconfig
source security/integrity/Kconfig
diff --git a/security/Makefile b/security/Makefile
index 4d2d3782ddef..d0c9e1b227f9 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -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-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o
# Object integrity file lists
diff --git a/security/security.c b/security/security.c
index 736e78da1ab9..2129b0e31d7b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -83,6 +83,7 @@ int __init security_init(void)
capability_add_hooks();
yama_add_hooks();
loadpin_add_hooks();
+ sidechannel_add_hooks();
/*
* Load all the remaining security modules.
diff --git a/security/sidechannel/Kconfig b/security/sidechannel/Kconfig
new file mode 100644
index 000000000000..653033027415
--- /dev/null
+++ b/security/sidechannel/Kconfig
@@ -0,0 +1,13 @@
+config SECURITY_SIDECHANNEL
+ bool "Sidechannel attack safety extra checks"
+ depends on SECURITY
+ default n
+ help
+ Look for a variety of cases where a side-channel attack
+ could potentially be exploited. Instruct the switching
+ code to use the indirect_branch_prediction_barrier in
+ cases where the passed task and the current task may be
+ at risk.
+
+ If you are unsure how to answer this question, answer N.
+
diff --git a/security/sidechannel/Makefile b/security/sidechannel/Makefile
new file mode 100644
index 000000000000..f61d83f28035
--- /dev/null
+++ b/security/sidechannel/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SECURITY_SIDECHANNEL) += sidechannel.o
diff --git a/security/sidechannel/sidechannel.c b/security/sidechannel/sidechannel.c
new file mode 100644
index 000000000000..18a67d19c020
--- /dev/null
+++ b/security/sidechannel/sidechannel.c
@@ -0,0 +1,88 @@
+/* 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>
+#include <linux/ptrace.h>
+
+#ifdef CONFIG_NAMESPACES
+/**
+ * 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;
+
+ /*
+ * 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;
+ if (current->cred->user_ns != p->cred->user_ns)
+ return -EACCES;
+ if (task_active_pid_ns(current) != task_active_pid_ns(p))
+ return -EACCES;
+ return 0;
+}
+#else
+static int safe_by_namespace(struct task_struct *p)
+{
+ return 0;
+}
+#endif
+
+/**
+ * sidechannel_ptrace_access_check - Are task and current sidechannel safe?
+ * @p: task to check on
+ * @mode: ptrace access mode
+ *
+ * Returns 0 if the tasks are sidechannel safe, -EACCES otherwise.
+ */
+static int sidechannel_ptrace_access_check(struct task_struct *p,
+ unsigned int mode)
+{
+ int rc;
+
+ if ((mode & PTRACE_MODE_SCHED) == 0)
+ return 0;
+
+ rc = safe_by_namespace(p);
+ if (rc)
+ return rc;
+ return 0;
+}
+
+static struct security_hook_list sidechannel_hooks[] __lsm_ro_after_init = {
+ LSM_HOOK_INIT(ptrace_access_check, sidechannel_ptrace_access_check),
+};
+
+void __init sidechannel_add_hooks(void)
+{
+ pr_info("Extra sidechannel checks enabled\n");
+ security_add_hooks(sidechannel_hooks, ARRAY_SIZE(sidechannel_hooks),
+ "sidechannel");
+}
--
2.17.1