[RFC PATCH v3 04/12] ipe: add property for trust of boot volume

deven.desai
2020-04-15T16:27:28Z

Add a property for IPE policy to express trust of the first superblock
where a file would be evaluated to determine trust.

Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
---
security/ipe/Kconfig | 2 +
security/ipe/Makefile | 4 ++
security/ipe/ipe-engine.c | 4 ++
security/ipe/ipe-hooks.c | 19 +++++
security/ipe/ipe-hooks.h | 2 +
security/ipe/ipe-pin.c | 93 +++++++++++++++++++++++++
security/ipe/ipe-pin.h | 56 +++++++++++++++
security/ipe/ipe.c | 24 +++++++
security/ipe/properties/Kconfig | 14 ++++
security/ipe/properties/Makefile | 11 +++
security/ipe/properties/boot-verified.c | 81 +++++++++++++++++++++
security/ipe/properties/prop-entry.h | 20 ++++++
security/ipe/utility.h | 22 ++++++
13 files changed, 352 insertions(+)
create mode 100644 security/ipe/ipe-pin.c
create mode 100644 security/ipe/ipe-pin.h
create mode 100644 security/ipe/properties/Kconfig
create mode 100644 security/ipe/properties/Makefile
create mode 100644 security/ipe/properties/boot-verified.c
create mode 100644 security/ipe/properties/prop-entry.h
create mode 100644 security/ipe/utility.h

diff --git a/security/ipe/Kconfig b/security/ipe/Kconfig
index 83fce5dce847..8f23176bef24 100644
--- a/security/ipe/Kconfig
+++ b/security/ipe/Kconfig
@@ -40,4 +40,6 @@ config SECURITY_IPE_PERMISSIVE_SWITCH

If unsure, answer Y.

+source "security/ipe/properties/Kconfig"
+
endif
diff --git a/security/ipe/Makefile b/security/ipe/Makefile
index 4dcfc5b26b58..741914ddc338 100644
--- a/security/ipe/Makefile
+++ b/security/ipe/Makefile
@@ -27,3 +27,7 @@ obj-$(CONFIG_SECURITY_IPE) += \
ipe-sysfs.o \

clean-files := ipe-bp.c
+
+obj-$(CONFIG_IPE_BOOT_PROP) += ipe-pin.o
+
+obj-$(CONFIG_SECURITY_IPE) += properties/
diff --git a/security/ipe/ipe-engine.c b/security/ipe/ipe-engine.c
index c79f422245c6..2eab680587ce 100644
--- a/security/ipe/ipe-engine.c
+++ b/security/ipe/ipe-engine.c
@@ -9,6 +9,8 @@
#include "ipe-policy.h"
#include "ipe-engine.h"
#include "ipe-audit.h"
+#include "ipe-pin.h"
+#include "utility.h"

#include <linux/types.h>
#include <linux/fs.h>
@@ -205,6 +207,8 @@ int ipe_process_event(const struct file *file, enum ipe_op op,
if (IS_ERR(ctx))
goto cleanup;

+ ipe_pin_superblock(ctx->file);
+
rc = evaluate(ctx);

cleanup:
diff --git a/security/ipe/ipe-hooks.c b/security/ipe/ipe-hooks.c
index 071c4af23a3d..45efe022be04 100644
--- a/security/ipe/ipe-hooks.c
+++ b/security/ipe/ipe-hooks.c
@@ -6,6 +6,7 @@
#include "ipe.h"
#include "ipe-hooks.h"
#include "ipe-engine.h"
+#include "ipe-pin.h"

#include <linux/types.h>
#include <linux/fs.h>
@@ -147,3 +148,21 @@ int ipe_on_kernel_load_data(enum kernel_load_data_id id)
ipe_hook_kernel_load);
}
}
+
+/**
+ * ipe_sb_free_security: LSM hook called on sb_free_security.
+ * @mnt_sb: Super block that is being freed.
+ *
+ * IPE does not currently utilize the super block security hook,
+ * it utilizes this hook to invalidate the saved super block for
+ * the boot_verified property.
+ *
+ * For more information, see the LSM hook, sb_free_security.
+ *
+ * Return:
+ * 0 - OK
+ */
+void ipe_sb_free_security(struct super_block *mnt_sb)
+{
+ ipe_invalidate_pinned_sb(mnt_sb);
+}
diff --git a/security/ipe/ipe-hooks.h b/security/ipe/ipe-hooks.h
index 806659b7cdbe..5e46726f2562 100644
--- a/security/ipe/ipe-hooks.h
+++ b/security/ipe/ipe-hooks.h
@@ -58,4 +58,6 @@ int ipe_on_kernel_read(struct file *file, enum kernel_read_file_id id);

int ipe_on_kernel_load_data(enum kernel_load_data_id id);

+void ipe_sb_free_security(struct super_block *mnt_sb);
+
#endif /* IPE_HOOK_H */
diff --git a/security/ipe/ipe-pin.c b/security/ipe/ipe-pin.c
new file mode 100644
index 000000000000..a963be8e5321
--- /dev/null
+++ b/security/ipe/ipe-pin.c
@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This file has been heavily adapted from the source code of the
+ * loadpin LSM. The source code for loadpin is co-located in the linux
+ * tree under security/loadpin/loadpin.c.
+ *
+ * Please see loadpin.c for up-to-date information about
+ * loadpin.
+ */
+
+#include "ipe.h"
+
+#include <linux/types.h>
+#include <linux/spinlock_types.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/magic.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+
+static DEFINE_SPINLOCK(pinned_sb_spinlock);
+
+static struct super_block *pinned_sb;
+
+/**
+ * ipe_is_from_pinned_sb: Determine if @file originates from the initial
+ * super block that a file was executed from.
+ * @file: File to check if it originates from the super block.
+ *
+ * Return:
+ * true - File originates from the initial super block
+ * false - File does not originate from the initial super block
+ */
+bool ipe_is_from_pinned_sb(const struct file *file)
+{
+ bool rv = false;
+
+ spin_lock(&pinned_sb_spinlock);
+
+ /*
+ * Check if pinned_sb is set:
+ * NULL == not set -> exit
+ * ERR == was once set (and has been unmounted) -> exit
+ * AND check that the pinned sb is the same as the file's.
+ */
+ if (!IS_ERR_OR_NULL(pinned_sb) &&
+ file->f_path.mnt->mnt_sb == pinned_sb) {
+ rv = true;
+ goto cleanup;
+ }
+
+cleanup:
+ spin_unlock(&pinned_sb_spinlock);
+ return rv;
+}
+
+/**
+ * ipe_pin_superblock: Attempt to save a file's super block address to later
+ * determine if a file originates from a super block.
+ * @file: File to source the super block from.
+ */
+void ipe_pin_superblock(const struct file *file)
+{
+ spin_lock(&pinned_sb_spinlock);
+
+ /* if set, return */
+ if (pinned_sb || !file)
+ goto cleanup;
+
+ pinned_sb = file->f_path.mnt->mnt_sb;
+cleanup:
+ spin_unlock(&pinned_sb_spinlock);
+}
+
+/**
+ * ipe_invalidate_pinned_sb: Invalidate the saved super block.
+ * @mnt_sb: Super block to compare against the saved super block.
+ *
+ * This avoids authorizing a file when the super block does not exist anymore.
+ */
+void ipe_invalidate_pinned_sb(const struct super_block *mnt_sb)
+{
+ spin_lock(&pinned_sb_spinlock);
+
+ /*
+ * On pinned sb unload - invalidate the pinned address
+ * by setting the pinned_sb to ERR_PTR(-EIO)
+ */
+ if (!IS_ERR_OR_NULL(pinned_sb) && mnt_sb == pinned_sb)
+ pinned_sb = ERR_PTR(-EIO);
+
+ spin_unlock(&pinned_sb_spinlock);
+}
diff --git a/security/ipe/ipe-pin.h b/security/ipe/ipe-pin.h
new file mode 100644
index 000000000000..7c3773d8387d
--- /dev/null
+++ b/security/ipe/ipe-pin.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+#ifndef IPE_PIN_H
+#define IPE_PIN_H
+
+#include <linux/types.h>
+#include <linux/fs.h>
+
+#ifdef CONFIG_IPE_BOOT_PROP
+
+/**
+ * ipe_is_from_pinned_sb: Determine if @file originates from the initial
+ * super block that a file was executed from.
+ * @file: File to check if it originates from the super block.
+ *
+ * Return:
+ * true - File originates from the initial super block
+ * false - File does not originate from the initial super block
+ */
+bool ipe_is_from_pinned_sb(const struct file *file);
+
+/**
+ * ipe_pin_superblock: Attempt to save a file's super block address to later
+ * determine if a file originates from a super block.
+ * @file: File to source the super block from.
+ */
+void ipe_pin_superblock(const struct file *file);
+
+/**
+ * ipe_invalidate_pinned_sb: Invalidate the saved super block.
+ * @mnt_sb: Super block to compare against the saved super block.
+ *
+ * This avoids authorizing a file when the super block does not exist anymore.
+ */
+void ipe_invalidate_pinned_sb(const struct super_block *mnt_sb);
+
+#else /* CONFIG_IPE_BOOT_PROP */
+
+static inline bool ipe_is_from_pinned_sb(const struct file *file)
+{
+ return false;
+}
+
+static inline void ipe_pin_superblock(const struct file *file)
+{
+}
+
+static inline void ipe_invalidate_pinned_sb(const struct super_block *mnt_sb)
+{
+}
+
+#endif /* !CONFIG_IPE_BOOT_PROP */
+
+#endif /* IPE_PIN_H */
diff --git a/security/ipe/ipe.c b/security/ipe/ipe.c
index 07f855ffb79a..c23d90126cc6 100644
--- a/security/ipe/ipe.c
+++ b/security/ipe/ipe.c
@@ -8,6 +8,7 @@
#include "ipe-hooks.h"
#include "ipe-secfs.h"
#include "ipe-sysfs.h"
+#include "properties/prop-entry.h"

#include <linux/module.h>
#include <linux/lsm_hooks.h>
@@ -23,8 +24,27 @@ static struct security_hook_list ipe_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(kernel_read_file, ipe_on_kernel_read),
LSM_HOOK_INIT(kernel_load_data, ipe_on_kernel_load_data),
LSM_HOOK_INIT(file_mprotect, ipe_on_mprotect),
+ LSM_HOOK_INIT(sb_free_security, ipe_sb_free_security),
};

+/**
+ * ipe_load_properties: Call the property entry points for all the IPE modules
+ * that were selected at kernel build-time.
+ *
+ * Return:
+ * 0 - OK
+ */
+static int __init ipe_load_properties(void)
+{
+ int rc = 0;
+
+ rc = ipe_init_bootv();
+ if (rc != 0)
+ return rc;
+
+ return rc;
+}
+
/**
* ipe_init: Entry point of IPE.
*
@@ -42,6 +62,10 @@ static int __init ipe_init(void)
{
int rc;

+ rc = ipe_load_properties();
+ if (rc != 0)
+ panic("IPE: properties failed to load");
+
rc = ipe_sysctl_init();
if (rc != 0)
pr_err("failed to configure sysctl: %d", -rc);
diff --git a/security/ipe/properties/Kconfig b/security/ipe/properties/Kconfig
new file mode 100644
index 000000000000..9dc0db8817b2
--- /dev/null
+++ b/security/ipe/properties/Kconfig
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Integrity Policy Enforcement (IPE) configuration
+#
+
+config IPE_BOOT_PROP
+ bool "Enable trust for boot volume"
+ help
+ This option enables the property "boot_verified" in IPE policy.
+ This property 'pins' the initial superblock when something is
+ evaluated. This property will evaluate to true when the file
+ being evaluated originates from the initial superblock.
+
+ if unsure, answer N.
diff --git a/security/ipe/properties/Makefile b/security/ipe/properties/Makefile
new file mode 100644
index 000000000000..e3e7fe17cf58
--- /dev/null
+++ b/security/ipe/properties/Makefile
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) Microsoft Corporation. All rights reserved.
+#
+# Makefile for building the properties that IPE uses
+# as part of the kernel tree.
+#
+
+obj-$(CONFIG_SECURITY_IPE) += properties.o
+
+properties-$(CONFIG_IPE_BOOT_PROP) += boot-verified.o
diff --git a/security/ipe/properties/boot-verified.c b/security/ipe/properties/boot-verified.c
new file mode 100644
index 000000000000..1cdeddf0bf21
--- /dev/null
+++ b/security/ipe/properties/boot-verified.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include "../ipe.h"
+#include "../ipe-pin.h"
+#include "../ipe-property.h"
+#include "../utility.h"
+
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/audit.h>
+
+#define PROPERTY_NAME "boot_verified"
+
+static void audit(struct audit_buffer *ab, bool value)
+{
+ audit_log_format(ab, "%s", (value) ? "TRUE" : "FALSE");
+}
+
+static inline void audit_rule_value(struct audit_buffer *ab,
+ const void *value)
+{
+ audit(ab, (bool)value);
+}
+
+static inline void audit_ctx(struct audit_buffer *ab,
+ const struct ipe_engine_ctx *ctx)
+{
+ bool b = has_sb(ctx->file) && ipe_is_from_pinned_sb(ctx->file);
+
+ audit(ab, b);
+}
+
+static bool evaluate(const struct ipe_engine_ctx *ctx,
+ const void *value)
+{
+ bool expect = (bool)value;
+
+ if (!ctx->file || !has_sb(ctx->file))
+ return false;
+
+ return ipe_is_from_pinned_sb(ctx->file) == expect;
+}
+
+static int parse(const char *val_str, void **value)
+{
+ if (strcmp("TRUE", val_str) == 0)
+ *value = (void *)true;
+ else if (strcmp("FALSE", val_str) == 0)
+ *value = (void *)false;
+ else
+ return -EBADMSG;
+
+ return 0;
+}
+
+static inline int duplicate(const void *src, void **dest)
+{
+ *dest = (void *)(bool)src;
+
+ return 0;
+}
+
+static const struct ipe_property boot_verified = {
+ .property_name = PROPERTY_NAME,
+ .eval = evaluate,
+ .rule_audit = audit_rule_value,
+ .ctx_audit = audit_ctx,
+ .parse = parse,
+ .dup = duplicate,
+ .free_val = NULL,
+};
+
+int ipe_init_bootv(void)
+{
+ return ipe_register_property(&boot_verified);
+}
diff --git a/security/ipe/properties/prop-entry.h b/security/ipe/properties/prop-entry.h
new file mode 100644
index 000000000000..f598dd9608b9
--- /dev/null
+++ b/security/ipe/properties/prop-entry.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#include <linux/types.h>
+
+#ifndef IPE_PROP_ENTRY_H
+#define IPE_PROP_ENTRY_H
+
+#ifndef CONFIG_IPE_BOOT_PROP
+static inline int __init ipe_init_bootv(void)
+{
+ return 0;
+}
+#else
+int __init ipe_init_bootv(void);
+#endif /* CONFIG_IPE_BOOT_PROP */
+
+#endif /* IPE_PROP_ENTRY_H */
diff --git a/security/ipe/utility.h b/security/ipe/utility.h
new file mode 100644
index 000000000000..a13089bb0d8f
--- /dev/null
+++ b/security/ipe/utility.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) Microsoft Corporation. All rights reserved.
+ */
+
+#ifndef IPE_UTILITY_H
+#define IPE_UTILITY_H
+
+#include <linux/types.h>
+#include <linux/fs.h>
+
+static inline bool has_mount(const struct file *file)
+{
+ return file && file->f_path.mnt;
+}
+
+static inline bool has_sb(const struct file *file)
+{
+ return has_mount(file) && file->f_path.mnt->mnt_sb;
+}
+
+#endif /* IPE_UTILITY_H */
--
2.26.0