[PATCH 1/4] IMA: Define an IMA hook to measure keys

[Lakshmi Ramasubramanian <nramas@linux.microsoft.com>]

Measure asymmetric keys used for verifying file signatures,
certificates, etc.

This patch defines a new IMA hook namely ima_post_key_create_or_update()
to measure the payload used to create a new asymmetric key or
update an existing asymmetric key.

Added a new config CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS that is
enabled when CONFIG_IMA and CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE
are defined. Asymmetric key structure is defined only when
CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE is defined. Since the IMA hook
measures asymmetric keys, the IMA hook is defined in a new file namely
ima_asymmetric_keys.c which is built only if
CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS is defined.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Reported-by: kbuild test robot <lkp@intel.com> # ima_asymmetric_keys.c
is built as a kernel module when it is actually not.
Fixes: 88e70da170e8 ("IMA: Define an IMA hook to measure keys")
---
 security/integrity/ima/Kconfig               |  9 ++++
 security/integrity/ima/Makefile              |  1 +
 security/integrity/ima/ima_asymmetric_keys.c | 52 ++++++++++++++++++++
 3 files changed, 62 insertions(+)
 create mode 100644 security/integrity/ima/ima_asymmetric_keys.c

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 838476d780e5..73a3974712d8 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -310,3 +310,12 @@ config IMA_APPRAISE_SIGNED_INIT
 	default n
 	help
 	   This option requires user-space init to be signed.
+
+config IMA_MEASURE_ASYMMETRIC_KEYS
+	bool "Enable measuring asymmetric keys on key create or update"
+	depends on IMA=y
+	depends on ASYMMETRIC_PUBLIC_KEY_SUBTYPE=y
+	default y
+	help
+	   This option enables measuring asymmetric keys when
+	   the key is created or updated.
diff --git a/security/integrity/ima/Makefile b/security/integrity/ima/Makefile
index 31d57cdf2421..3e9d0ad68c7b 100644
--- a/security/integrity/ima/Makefile
+++ b/security/integrity/ima/Makefile
@@ -12,3 +12,4 @@ ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
 ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o
 ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
 obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
+obj-$(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) += ima_asymmetric_keys.o
diff --git a/security/integrity/ima/ima_asymmetric_keys.c b/security/integrity/ima/ima_asymmetric_keys.c
new file mode 100644
index 000000000000..994d89d58af9
--- /dev/null
+++ b/security/integrity/ima/ima_asymmetric_keys.c
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 Microsoft Corporation
+ *
+ * Author: Lakshmi Ramasubramanian (nramas@linux.microsoft.com)
+ *
+ * File: ima_asymmetric_keys.c
+ *       Defines an IMA hook to measure asymmetric keys on key
+ *       create or update.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <keys/asymmetric-type.h>
+#include "ima.h"
+
+/**
+ * ima_post_key_create_or_update - measure asymmetric keys
+ * @keyring: keyring to which the key is linked to
+ * @key: created or updated key
+ * @payload: The data used to instantiate or update the key.
+ * @payload_len: The length of @payload.
+ * @flags: key flags
+ * @create: flag indicating whether the key was created or updated
+ *
+ * Keys can only be measured, not appraised.
+ * The payload data used to instantiate or update the key is measured.
+ */
+void ima_post_key_create_or_update(struct key *keyring, struct key *key,
+				   const void *payload, size_t payload_len,
+				   unsigned long flags, bool create)
+{
+	/* Only asymmetric keys are handled by this hook. */
+	if (key->type != &key_type_asymmetric)
+		return;
+
+	if (!payload || (payload_len == 0))
+		return;
+
+	/*
+	 * keyring->description points to the name of the keyring
+	 * (such as ".builtin_trusted_keys", ".ima", etc.) to
+	 * which the given key is linked to.
+	 *
+	 * The name of the keyring is passed in the "eventname"
+	 * parameter to process_buffer_measurement() and is set
+	 * in the "eventname" field in ima_event_data for
+	 * the key measurement IMA event.
+	 */
+	process_buffer_measurement(payload, payload_len,
+				   keyring->description, KEY_CHECK, 0);
+}
-- 
2.17.1