[RFC PATCH v8 01/17] security: add ipe lsm & initial context creation

[Deven Bowers]

Integrity Policy Enforcement (IPE) is an LSM that provides an
complimentary approach to Mandatory Access Control than existing LSMs
today.

Existing LSMs have centered around the concept of access to a resource
should be controlled by the current user's credentials. IPE's approach,
is that access to a resource should be controlled by the system's trust
of a current resource.

The basis of this approach is that every process in the kernel is
associated with a context that determines the policy for what is
trusted by said process and its descendents, starting with 'init'.

Signed-off-by: Deven Bowers <deven.desai at linux.microsoft.com>
---
v2:
  + Split evaluation loop, access control hooks,
    and evaluation loop from policy parser and userspace
    interface to pass mailing list character limit

v3:
  + Move ipe_load_properties to patch 04.
  + Remove useless 0-initializations
  + Prefix extern variables with ipe_
  + Remove kernel module parameters, as these are
    exposed through sysctls.
  + Add more prose to the IPE base config option
    help text.
  + Use GFP_KERNEL for audit_log_start.
  + Remove unnecessary caching system.
  + Remove comments from headers
  + Use rcu_access_pointer for rcu-pointer null check
  + Remove usage of reqprot; use prot only.
  + Move policy load and activation audit event to 03/12

v4:
  + Remove sysctls in favor of securityfs nodes
  + Re-add kernel module parameters, as these are now
    exposed through securityfs.
  + Refactor property audit loop to a separate function.

v5:
  + fix minor grammatical errors
  + do not group rule by curly-brace in audit record,
    reconstruct the exact rule.

v6:
  + No changes

v7:
  + Further split lsm creation into a separate commit from the
    evaluation loop and audit system, for easier review.

  + Introduce the concept of an ipe_context, a scoped way to
    introduce execution policies, used initially for allowing for
    kunit tests in isolation.

v8:
  + Follow lsmname_hook_name convention for lsm hooks.
  + Move LSM blob accessors to ipe.c and mark LSM blobs as static.
---
 MAINTAINERS           |   6 ++
 security/Kconfig      |  11 ++--
 security/Makefile     |   1 +
 security/ipe/Kconfig  |  17 +++++
 security/ipe/Makefile |  11 ++++
 security/ipe/ctx.c    | 145 ++++++++++++++++++++++++++++++++++++++++++
 security/ipe/ctx.h    |  28 ++++++++
 security/ipe/hooks.c  |  54 ++++++++++++++++
 security/ipe/hooks.h  |  16 +++++
 security/ipe/ipe.c    |  73 +++++++++++++++++++++
 security/ipe/ipe.h    |  17 +++++
 11 files changed, 374 insertions(+), 5 deletions(-)
 create mode 100644 security/ipe/Kconfig
 create mode 100644 security/ipe/Makefile
 create mode 100644 security/ipe/ctx.c
 create mode 100644 security/ipe/ctx.h
 create mode 100644 security/ipe/hooks.c
 create mode 100644 security/ipe/hooks.h
 create mode 100644 security/ipe/ipe.c
 create mode 100644 security/ipe/ipe.h

diff --git a/MAINTAINERS b/MAINTAINERS
index a6d3bd9d2a8d..965fdac6d609 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9793,6 +9793,12 @@ T:	git git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git
 F:	security/integrity/ima/
 F:	security/integrity/
 
+INTEGRITY POLICY ENFORCEMENT (IPE)
+M:	Deven Bowers <deven.desai at linux.microsoft.com>
+M:	Fan Wu <wufan at linux.microsoft.com>
+S:	Supported
+F:	security/ipe/
+
 INTEL 810/815 FRAMEBUFFER DRIVER
 M:	Antonino Daplas <adaplas at gmail.com>
 L:	linux-fbdev at vger.kernel.org
diff --git a/security/Kconfig b/security/Kconfig
index f29e4c656983..7d4c641313ca 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -218,6 +218,7 @@ source "security/yama/Kconfig"
 source "security/safesetid/Kconfig"
 source "security/lockdown/Kconfig"
 source "security/landlock/Kconfig"
+source "security/ipe/Kconfig"
 
 source "security/integrity/Kconfig"
 
@@ -257,11 +258,11 @@ endchoice
 
 config LSM
 	string "Ordered list of enabled LSMs"
-	default "landlock,lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
-	default "landlock,lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
-	default "landlock,lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
-	default "landlock,lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC
-	default "landlock,lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf"
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf,ipe" if DEFAULT_SECURITY_SMACK
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf,ipe" if DEFAULT_SECURITY_APPARMOR
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf,ipe" if DEFAULT_SECURITY_TOMOYO
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,bpf,ipe" if DEFAULT_SECURITY_DAC
+	default "landlock,lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf,ipe"
 	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 18121f8f85cd..527b1864d96c 100644
--- a/security/Makefile
+++ b/security/Makefile
@@ -24,6 +24,7 @@ obj-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown/
 obj-$(CONFIG_CGROUPS)			+= device_cgroup.o
 obj-$(CONFIG_BPF_LSM)			+= bpf/
 obj-$(CONFIG_SECURITY_LANDLOCK)		+= landlock/
+obj-$(CONFIG_SECURITY_IPE)		+= ipe/
 
 # Object integrity file lists
 obj-$(CONFIG_INTEGRITY)			+= integrity/
diff --git a/security/ipe/Kconfig b/security/ipe/Kconfig
new file mode 100644
index 000000000000..e4875fb04883
--- /dev/null
+++ b/security/ipe/Kconfig
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Integrity Policy Enforcement (IPE) configuration
+#
+
+menuconfig SECURITY_IPE
+	bool "Integrity Policy Enforcement (IPE)"
+	depends on SECURITY && SECURITYFS
+	select PKCS7_MESSAGE_PARSER
+	select SYSTEM_DATA_VERIFICATION
+	help
+	  This option enables the Integrity Policy Enforcement LSM
+	  allowing users to define a policy to enforce a trust-based access
+	  control. A key feature of IPE is a customizable policy to allow
+	  admins to reconfigure trust requirements on the fly.
+
+	  If unsure, answer N.
diff --git a/security/ipe/Makefile b/security/ipe/Makefile
new file mode 100644
index 000000000000..ba3df729e252
--- /dev/null
+++ b/security/ipe/Makefile
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) Microsoft Corporation. All rights reserved.
+#
+# Makefile for building the IPE module as part of the kernel tree.
+#
+
+obj-$(CONFIG_SECURITY_IPE) += \
+	ctx.o \
+	hooks.o \
+	ipe.o \
diff --git a/security/ipe/ctx.c b/security/ipe/ctx.c
new file mode 100644
index 000000000000..d51fe2e13ad9
--- /dev/null
+++ b/security/ipe/ctx.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include "ipe.h"
+#include "ctx.h"
+
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/parser.h>
+#include <linux/refcount.h>
+#include <linux/spinlock.h>
+
+/**
+ * ipe_current_ctx: Helper to retrieve the ipe_context for the current task.
+ *
+ * Return:
+ *	See ipe_get_ctx_rcu
+ */
+struct ipe_context *ipe_current_ctx(void)
+{
+	return ipe_get_ctx_rcu(*ipe_tsk_ctx(current));
+}
+
+/**
+ * ipe_get_ctx_rcu: Retrieve the underlying ipe_context in an rcu protected
+ *		    address space.
+ * @ctx: Context to dereference.
+ *
+ * This function will increment the reference count of the dereferenced
+ * ctx, ensuring that it is valid outside of the rcu_read_lock.
+ *
+ * However, if a context has a reference count of 0 (and thus being)
+ * freed, this API will return NULL.
+ *
+ * Return:
+ *	!NULL - Valid context
+ *	NULL - the dereferenced context will not exist outside after the
+ *	       next grace period.
+ */
+struct ipe_context *ipe_get_ctx_rcu(struct ipe_context __rcu *ctx)
+{
+	struct ipe_context *rv = NULL;
+
+	rcu_read_lock();
+
+	rv = rcu_dereference(ctx);
+	if (!rv || !refcount_inc_not_zero(&rv->refcount))
+		rv = NULL;
+
+	rcu_read_unlock();
+
+	return rv;
+}
+
+/**
+ * free_ctx_work: Worker function to deallocate a context structure.
+ * @work: work_struct passed to schedule_work
+ */
+static void free_ctx_work(struct work_struct *const work)
+{
+	struct ipe_context *ctx = NULL;
+
+	ctx = container_of(work, struct ipe_context, free_work);
+
+	kfree(ctx);
+}
+
+/**
+ * create_ctx: Allocate a context structure.
+ *
+ * The reference count at this point will be set to 1.
+ *
+ * Return:
+ * !IS_ERR - OK
+ * ERR_PTR(-ENOMEM) - Lack of memory.
+ */
+static struct ipe_context *create_ctx(void)
+{
+	int rc = 0;
+	struct ipe_context *ctx = NULL;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	if (!ctx) {
+		rc = -ENOMEM;
+		goto err;
+	}
+
+	INIT_WORK(&ctx->free_work, free_ctx_work);
+	refcount_set(&ctx->refcount, 1);
+	spin_lock_init(&ctx->lock);
+
+	return ctx;
+
+err:
+	ipe_put_ctx(ctx);
+	return ERR_PTR(rc);
+}
+
+/**
+ * ipe_put_ctx: Decrement the reference of an ipe_context structure,
+ *	       scheduling a free as necessary.
+ * @ctx: Structure to free
+ *
+ * This function no-ops on error and null values for @ctx, and the
+ * deallocation will only occur if the refcount is 0.
+ */
+void ipe_put_ctx(struct ipe_context *ctx)
+{
+	if (IS_ERR_OR_NULL(ctx) || !refcount_dec_and_test(&ctx->refcount))
+		return;
+
+	schedule_work(&ctx->free_work);
+}
+
+/**
+ * ipe_init_ctx: Initialize the init context.
+ *
+ * This is called at LSM init, and marks the kernel init process
+ * with a context. All processes descendent from kernel
+ * init will inherit this context.
+ *
+ * Return:
+ * 0 - OK
+ * -ENOMEM: Not enough memory to allocate the init context.
+ */
+int __init ipe_init_ctx(void)
+{
+	int rc = 0;
+	struct ipe_context *lns = NULL;
+
+	lns = create_ctx();
+	if (IS_ERR(lns)) {
+		rc = PTR_ERR(lns);
+		goto err;
+	}
+
+	rcu_assign_pointer(*ipe_tsk_ctx(current), lns);
+
+	return 0;
+err:
+	ipe_put_ctx(lns);
+	return rc;
+}
diff --git a/security/ipe/ctx.h b/security/ipe/ctx.h
new file mode 100644
index 000000000000..69a2c92c0a8c
--- /dev/null
+++ b/security/ipe/ctx.h
@@ -0,0 +1,28 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+#ifndef IPE_CONTEXT_H
+#define IPE_CONTEXT_H
+
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/refcount.h>
+#include <linux/spinlock.h>
+#include <linux/workqueue.h>
+
+struct ipe_context {
+	refcount_t refcount;
+	/* Protects concurrent writers */
+	spinlock_t lock;
+
+	struct work_struct free_work;
+};
+
+int __init ipe_init_ctx(void);
+struct ipe_context __rcu **ipe_tsk_ctx(struct task_struct *tsk);
+struct ipe_context *ipe_current_ctx(void);
+struct ipe_context *ipe_get_ctx_rcu(struct ipe_context __rcu *ctx);
+void ipe_put_ctx(struct ipe_context *ctx);
+
+#endif /* IPE_CONTEXT_H */
diff --git a/security/ipe/hooks.c b/security/ipe/hooks.c
new file mode 100644
index 000000000000..dd9606962fa5
--- /dev/null
+++ b/security/ipe/hooks.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include "ipe.h"
+#include "ctx.h"
+#include "hooks.h"
+
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/refcount.h>
+#include <linux/rcupdate.h>
+
+/**
+ * ipe_task_alloc: Assign a new context for an associated task structure.
+ * @task: Supplies the task structure to assign a context to.
+ * @clone_flags: unused.
+ *
+ * The context assigned is always the context of the current task.
+ * Reference counts are dropped by ipe_task_free
+ *
+ * Return:
+ * 0 - OK
+ * -ENOMEM - Out of Memory
+ */
+int ipe_task_alloc(struct task_struct *task, unsigned long clone_flags)
+{
+	struct ipe_context __rcu **ctx = NULL;
+	struct ipe_context *current_ctx = NULL;
+
+	current_ctx = ipe_current_ctx();
+	ctx = ipe_tsk_ctx(task);
+	rcu_assign_pointer(*ctx, current_ctx);
+	refcount_inc(&current_ctx->refcount);
+
+	ipe_put_ctx(current_ctx);
+	return 0;
+}
+
+/**
+ * ipe_task_free: Drop a reference to an ipe_context associated with @task.
+ *		  If there are no tasks remaining, the context is freed.
+ * @task: Supplies the task to drop an ipe_context reference to.
+ */
+void ipe_task_free(struct task_struct *task)
+{
+	struct ipe_context *ctx;
+
+	rcu_read_lock();
+	ctx = rcu_dereference(*ipe_tsk_ctx(task));
+	ipe_put_ctx(ctx);
+	rcu_read_unlock();
+}
diff --git a/security/ipe/hooks.h b/security/ipe/hooks.h
new file mode 100644
index 000000000000..e0ae3c7dfb5b
--- /dev/null
+++ b/security/ipe/hooks.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+#ifndef IPE_HOOKS_H
+#define IPE_HOOKS_H
+
+#include <linux/types.h>
+#include <linux/sched.h>
+
+int ipe_task_alloc(struct task_struct *task,
+		   unsigned long clone_flags);
+
+void ipe_task_free(struct task_struct *task);
+
+#endif /* IPE_HOOKS_H */
diff --git a/security/ipe/ipe.c b/security/ipe/ipe.c
new file mode 100644
index 000000000000..8a1e0b1c7240
--- /dev/null
+++ b/security/ipe/ipe.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include "ipe.h"
+#include "ctx.h"
+#include "hooks.h"
+
+#include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/security.h>
+#include <linux/rcupdate.h>
+#include <linux/lsm_hooks.h>
+
+static struct lsm_blob_sizes ipe_blobs __lsm_ro_after_init = {
+	.lbs_task = sizeof(struct ipe_context __rcu *),
+};
+
+static struct security_hook_list ipe_hooks[] __lsm_ro_after_init = {
+	LSM_HOOK_INIT(task_alloc, ipe_task_alloc),
+	LSM_HOOK_INIT(task_free, ipe_task_free),
+};
+
+/**
+ * ipe_tsk_ctx: Retrieve the RCU-protected address of the task
+ *		that contains the ipe_context.
+ * @tsk: Task to retrieve the address from.
+ *
+ * Callers need to use the rcu* family functions to interact with
+ * the ipe_context, or ipe_get_ctx_rcu.
+ *
+ * Return:
+ *	Valid Address to a location containing an RCU-protected ipe_context.
+ */
+struct ipe_context __rcu **ipe_tsk_ctx(struct task_struct *tsk)
+{
+	return tsk->security + ipe_blobs.lbs_task;
+}
+
+/**
+ * ipe_init: Entry point of IPE.
+ *
+ * This is called at LSM init, which happens occurs early during kernel
+ * start up. During this phase, IPE loads the properties compiled into
+ * the kernel, and register's IPE's hooks. The boot policy is loaded
+ * later, during securityfs init, at which point IPE will start
+ * enforcing its policy.
+ *
+ * Return:
+ * 0 - OK
+ * -ENOMEM - Context creation failed.
+ */
+static int __init ipe_init(void)
+{
+	int rc = 0;
+
+	rc = ipe_init_ctx();
+	if (rc)
+		return rc;
+
+	security_add_hooks(ipe_hooks, ARRAY_SIZE(ipe_hooks), "ipe");
+
+	return rc;
+}
+
+DEFINE_LSM(ipe) = {
+	.name = "ipe",
+	.init = ipe_init,
+	.blobs = &ipe_blobs,
+};
diff --git a/security/ipe/ipe.h b/security/ipe/ipe.h
new file mode 100644
index 000000000000..152ae28f3cdd
--- /dev/null
+++ b/security/ipe/ipe.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#ifndef IPE_H
+#define IPE_H
+
+#define pr_fmt(fmt) "IPE " fmt "\n"
+
+#include "ctx.h"
+
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/lsm_hooks.h>
+
+#endif /* IPE_H */
-- 
2.25.1