acpi/nfit, libnvdimm: Add unlock of nvdimm support for Intel DIMMs

Add support to unlock the dimm via the kernel key management APIs. The
passphrase is expected to be pulled from userspace through keyutils.
The key management and sysfs attributes are libnvdimm generic.

Encrypted keys are used to protect the nvdimm passphrase at rest. The
master key can be a trusted-key sealed in a TPM, preferred, or an
encrypted-key, more flexible, but more exposure to a potential attacker.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Co-developed-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 148 insertions, 0 deletions

diff --git a/drivers/nvdimm/security.c b/drivers/nvdimm/security.c
new file mode 100644
index 000000000000..51d77a67a9fb
--- /dev/null
+++ b/drivers/nvdimm/security.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright(c) 2018 Intel Corporation. All rights reserved. */
+
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/ndctl.h>
+#include <linux/slab.h>
+#include <linux/io.h>
+#include <linux/mm.h>
+#include <linux/cred.h>
+#include <linux/key.h>
+#include <linux/key-type.h>
+#include <keys/user-type.h>
+#include <keys/encrypted-type.h>
+#include "nd-core.h"
+#include "nd.h"
+
+static bool key_revalidate = true;
+module_param(key_revalidate, bool, 0444);
+MODULE_PARM_DESC(key_revalidate, "Require key validation at init.");
+
+static void *key_data(struct key *key)
+{
+	struct encrypted_key_payload *epayload = dereference_key_locked(key);
+
+	lockdep_assert_held_read(&key->sem);
+
+	return epayload->decrypted_data;
+}
+
+static void nvdimm_put_key(struct key *key)
+{
+	up_read(&key->sem);
+	key_put(key);
+}
+
+/*
+ * Retrieve kernel key for DIMM and request from user space if
+ * necessary. Returns a key held for read and must be put by
+ * nvdimm_put_key() before the usage goes out of scope.
+ */
+static struct key *nvdimm_request_key(struct nvdimm *nvdimm)
+{
+	struct key *key = NULL;
+	static const char NVDIMM_PREFIX[] = "nvdimm:";
+	char desc[NVDIMM_KEY_DESC_LEN + sizeof(NVDIMM_PREFIX)];
+	struct device *dev = &nvdimm->dev;
+
+	sprintf(desc, "%s%s", NVDIMM_PREFIX, nvdimm->dimm_id);
+	key = request_key(&key_type_encrypted, desc, "");
+	if (IS_ERR(key)) {
+		if (PTR_ERR(key) == -ENOKEY)
+			dev_warn(dev, "request_key() found no key\n");
+		else
+			dev_warn(dev, "request_key() upcall failed\n");
+		key = NULL;
+	} else {
+		struct encrypted_key_payload *epayload;
+
+		down_read(&key->sem);
+		epayload = dereference_key_locked(key);
+		if (epayload->decrypted_datalen != NVDIMM_PASSPHRASE_LEN) {
+			up_read(&key->sem);
+			key_put(key);
+			key = NULL;
+		}
+	}
+
+	return key;
+}
+
+static struct key *nvdimm_key_revalidate(struct nvdimm *nvdimm)
+{
+	struct key *key;
+	int rc;
+
+	if (!nvdimm->sec.ops->change_key)
+		return NULL;
+
+	key = nvdimm_request_key(nvdimm);
+	if (!key)
+		return NULL;
+
+	/*
+	 * Send the same key to the hardware as new and old key to
+	 * verify that the key is good.
+	 */
+	rc = nvdimm->sec.ops->change_key(nvdimm, key_data(key), key_data(key));
+	if (rc < 0) {
+		nvdimm_put_key(key);
+		key = NULL;
+	}
+	return key;
+}
+
+static int __nvdimm_security_unlock(struct nvdimm *nvdimm)
+{
+	struct device *dev = &nvdimm->dev;
+	struct nvdimm_bus *nvdimm_bus = walk_to_nvdimm_bus(dev);
+	struct key *key = NULL;
+	int rc;
+
+	/* The bus lock should be held at the top level of the call stack */
+	lockdep_assert_held(&nvdimm_bus->reconfig_mutex);
+
+	if (!nvdimm->sec.ops || !nvdimm->sec.ops->unlock
+			|| nvdimm->sec.state < 0)
+		return -EIO;
+
+	/*
+	 * If the pre-OS has unlocked the DIMM, attempt to send the key
+	 * from request_key() to the hardware for verification.  Failure
+	 * to revalidate the key against the hardware results in a
+	 * freeze of the security configuration. I.e. if the OS does not
+	 * have the key, security is being managed pre-OS.
+	 */
+	if (nvdimm->sec.state == NVDIMM_SECURITY_UNLOCKED) {
+		if (!key_revalidate)
+			return 0;
+
+		key = nvdimm_key_revalidate(nvdimm);
+		if (!key)
+			return nvdimm_security_freeze(nvdimm);
+	} else
+		key = nvdimm_request_key(nvdimm);
+
+	if (!key)
+		return -ENOKEY;
+
+	rc = nvdimm->sec.ops->unlock(nvdimm, key_data(key));
+	dev_dbg(dev, "key: %d unlock: %s\n", key_serial(key),
+			rc == 0 ? "success" : "fail");
+
+	nvdimm_put_key(key);
+	nvdimm->sec.state = nvdimm_security_state(nvdimm);
+	return rc;
+}
+
+int nvdimm_security_unlock(struct device *dev)
+{
+	struct nvdimm *nvdimm = to_nvdimm(dev);
+	int rc;
+
+	nvdimm_bus_lock(dev);
+	rc = __nvdimm_security_unlock(nvdimm);
+	nvdimm_bus_unlock(dev);
+	return rc;
+}