[RFC PATCH v7 01/16] security: add ipe lsm & initial context creation

deven.desai
2021-10-13T19:06:45Z

From: Deven Bowers <deven.desai@linux.microsoft.com>

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@linux.microsoft.com>
---

Relevant changes since v6:
* Split up patch 02/11 into three parts:
1. context creation (new) [this patch]
2. parser (refactored)
3. evaluation loop
* Refactor series to:
1. Support a context structure, enabling easier testing

---
MAINTAINERS | 6 ++
security/Kconfig | 11 +--
security/Makefile | 1 +
security/ipe/Kconfig | 19 +++++
security/ipe/Makefile | 11 +++
security/ipe/ctx.c | 161 ++++++++++++++++++++++++++++++++++++++++++
security/ipe/ctx.h | 28 ++++++++
security/ipe/hooks.c | 58 +++++++++++++++
security/ipe/hooks.h | 16 +++++
security/ipe/ipe.c | 57 +++++++++++++++
security/ipe/ipe.h | 19 +++++
11 files changed, 382 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 e0bca0de0df7..f1e76f791d47 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9279,6 +9279,12 @@ S: Supported
T: git git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git
F: security/integrity/ima/

+INTEGRITY POLICY ENFORCEMENT (IPE)
+M: Deven Bowers <deven.desai@linux.microsoft.com>
+M: Fan Wu <wufan@linux.microsoft.com>
+S: Supported
+F: security/ipe/
+
INTEL 810/815 FRAMEBUFFER DRIVER
M: Antonino Daplas <adaplas@gmail.com>
L: linux-fbdev@vger.kernel.org
diff --git a/security/Kconfig b/security/Kconfig
index 0ced7fd33e4d..6ed9b3b5a75c 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -239,6 +239,7 @@ source "security/yama/Kconfig"
source "security/safesetid/Kconfig"
source "security/lockdown/Kconfig"
source "security/landlock/Kconfig"
+source "security/ipe/Kconfig"

source "security/integrity/Kconfig"

@@ -278,11 +279,11 @@ 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-$(CONFIG_INTEGRITY) += integrity/
diff --git a/security/ipe/Kconfig b/security/ipe/Kconfig
new file mode 100644
index 000000000000..c4503083e92d
--- /dev/null
+++ b/security/ipe/Kconfig
@@ -0,0 +1,19 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Integrity Policy Enforcement (IPE) configuration
+#
+
+menuconfig SECURITY_IPE
+ bool "Integrity Policy Enforcement (IPE)"
+ depends on SECURITY && SECURITYFS
+ select PKCS7_MESSAGE_PARSER
+ select SYSTEM_DATA_VERIFICATION
+ help
+ This option enables the Integrity Policy Enforcement subsystem
+ allowing systems to enforce integrity having no dependencies
+ on filesystem metadata, making its decisions based off of kernel-
+ resident features and data structures. A key feature of IPE is a
+ customizable policy to allow admins to reconfigure integrity
+ requirements on the fly.
+
+ If unsure, answer N.
diff --git a/security/ipe/Makefile b/security/ipe/Makefile
new file mode 100644
index 000000000000..ba3df729e252
--- /dev/null
+++ b/security/ipe/Makefile
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) Microsoft Corporation. All rights reserved.
+#
+# Makefile for building the IPE module as part of the kernel tree.
+#
+
+obj-$(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..c24f5d1d41bd
--- /dev/null
+++ b/security/ipe/ctx.c
@@ -0,0 +1,161 @@
+// 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_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_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_ns: Decrement the reference of an ipe_context structure,
+ * scheduling a free as necessary.s
+ * @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..ed0c886eaa5a
--- /dev/null
+++ b/security/ipe/hooks.c
@@ -0,0 +1,58 @@
+// 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;
+
+ /*
+ * This reference was the initial creation, no need to increment
+ * refcount
+ */
+ 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..d600346702e5
--- /dev/null
+++ b/security/ipe/ipe.c
@@ -0,0 +1,57 @@
+// 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>
+
+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_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..09c492b8fd03
--- /dev/null
+++ b/security/ipe/ipe.h
@@ -0,0 +1,19 @@
+/* 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>
+
+extern struct lsm_blob_sizes ipe_blobs;
+
+#endif /* IPE_H */
--
2.33.0