Documentation/driver-api/nvdimm/security.rst - linux - Git at Google

 ===============
 NVDIMM Security
 ===============

 1. Introduction
 ---------------

 With the introduction of Intel Device Specific Methods (DSM) v1.8
 specification [1], security DSMs are introduced. The spec added the following
 security DSMs: "get security state", "set passphrase", "disable passphrase",
 "unlock unit", "freeze lock", "secure erase", and "overwrite". A security_ops
 data structure has been added to struct dimm in order to support the security
 operations and generic APIs are exposed to allow vendor neutral operations.

 2. Sysfs Interface
 ------------------
 The "security" sysfs attribute is provided in the nvdimm sysfs directory. For
 example:
 /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/security

 The "show" attribute of that attribute will display the security state for
 that DIMM. The following states are available: disabled, unlocked, locked,
 frozen, and overwrite. If security is not supported, the sysfs attribute
 will not be visible.

 The "store" attribute takes several commands when it is being written to
 in order to support some of the security functionalities:
 update <old_keyid> <new_keyid> - enable or update passphrase.
 disable <keyid> - disable enabled security and remove key.
 freeze - freeze changing of security states.
 erase <keyid> - delete existing user encryption key.
 overwrite <keyid> - wipe the entire nvdimm.
 master_update <keyid> <new_keyid> - enable or update master passphrase.
 master_erase <keyid> - delete existing user encryption key.

 3. Key Management
 -----------------

 The key is associated to the payload by the DIMM id. For example:
 # cat /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/nfit/id
 8089-a2-1740-00000133
 The DIMM id would be provided along with the key payload (passphrase) to
 the kernel.

 The security keys are managed on the basis of a single key per DIMM. The
 key "passphrase" is expected to be 32bytes long. This is similar to the ATA
 security specification [2]. A key is initially acquired via the request_key()
 kernel API call during nvdimm unlock. It is up to the user to make sure that
 all the keys are in the kernel user keyring for unlock.

 A nvdimm encrypted-key of format enc32 has the description format of:
 nvdimm:<bus-provider-specific-unique-id>

 See file ``Documentation/security/keys/trusted-encrypted.rst`` for creating
 encrypted-keys of enc32 format. TPM usage with a master trusted key is
 preferred for sealing the encrypted-keys.

 4. Unlocking
 ------------
 When the DIMMs are being enumerated by the kernel, the kernel will attempt to
 retrieve the key from the kernel user keyring. This is the only time
 a locked DIMM can be unlocked. Once unlocked, the DIMM will remain unlocked
 until reboot. Typically an entity (i.e. shell script) will inject all the
 relevant encrypted-keys into the kernel user keyring during the initramfs phase.
 This provides the unlock function access to all the related keys that contain
 the passphrase for the respective nvdimms.  It is also recommended that the
 keys are injected before libnvdimm is loaded by modprobe.

 5. Update
 ---------
 When doing an update, it is expected that the existing key is removed from
 the kernel user keyring and reinjected as different (old) key. It's irrelevant
 what the key description is for the old key since we are only interested in the
 keyid when doing the update operation. It is also expected that the new key
 is injected with the description format described from earlier in this
 document.  The update command written to the sysfs attribute will be with
 the format:
 update <old keyid> <new keyid>

 If there is no old keyid due to a security enabling, then a 0 should be
 passed in.

 6. Freeze
 ---------
 The freeze operation does not require any keys. The security config can be
 frozen by a user with root privelege.

 7. Disable
 ----------
 The security disable command format is:
 disable <keyid>

 An key with the current passphrase payload that is tied to the nvdimm should be
 in the kernel user keyring.

 8. Secure Erase
 ---------------
 The command format for doing a secure erase is:
 erase <keyid>

 An key with the current passphrase payload that is tied to the nvdimm should be
 in the kernel user keyring.

 9. Overwrite
 ------------
 The command format for doing an overwrite is:
 overwrite <keyid>

 Overwrite can be done without a key if security is not enabled. A key serial
 of 0 can be passed in to indicate no key.

 The sysfs attribute "security" can be polled to wait on overwrite completion.
 Overwrite can last tens of minutes or more depending on nvdimm size.

 An encrypted-key with the current user passphrase that is tied to the nvdimm
 should be injected and its keyid should be passed in via sysfs.

 10. Master Update
 -----------------
 The command format for doing a master update is:
 update <old keyid> <new keyid>

 The operating mechanism for master update is identical to update except the
 master passphrase key is passed to the kernel. The master passphrase key
 is just another encrypted-key.

 This command is only available when security is disabled.

 11. Master Erase
 ----------------
 The command format for doing a master erase is:
 master_erase <current keyid>

 This command has the same operating mechanism as erase except the master
 passphrase key is passed to the kernel. The master passphrase key is just
 another encrypted-key.

 This command is only available when the master security is enabled, indicated
 by the extended security status.

 [1]: https://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf

 [2]: http://www.t13.org/documents/UploadedDocuments/docs2006/e05179r4-ACS-SecurityClarifications.pdf
	===============
	NVDIMM Security
	===============

	1. Introduction
	---------------

	With the introduction of Intel Device Specific Methods (DSM) v1.8
	specification [1], security DSMs are introduced. The spec added the following
	security DSMs: "get security state", "set passphrase", "disable passphrase",
	"unlock unit", "freeze lock", "secure erase", and "overwrite". A security_ops
	data structure has been added to struct dimm in order to support the security
	operations and generic APIs are exposed to allow vendor neutral operations.

	2. Sysfs Interface
	------------------
	The "security" sysfs attribute is provided in the nvdimm sysfs directory. For
	example:
	/sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/security

	The "show" attribute of that attribute will display the security state for
	that DIMM. The following states are available: disabled, unlocked, locked,
	frozen, and overwrite. If security is not supported, the sysfs attribute
	will not be visible.

	The "store" attribute takes several commands when it is being written to
	in order to support some of the security functionalities:
	update <old_keyid> <new_keyid> - enable or update passphrase.
	disable <keyid> - disable enabled security and remove key.
	freeze - freeze changing of security states.
	erase <keyid> - delete existing user encryption key.
	overwrite <keyid> - wipe the entire nvdimm.
	master_update <keyid> <new_keyid> - enable or update master passphrase.
	master_erase <keyid> - delete existing user encryption key.

	3. Key Management
	-----------------

	The key is associated to the payload by the DIMM id. For example:
	# cat /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/nfit/id
	8089-a2-1740-00000133
	The DIMM id would be provided along with the key payload (passphrase) to
	the kernel.

	The security keys are managed on the basis of a single key per DIMM. The
	key "passphrase" is expected to be 32bytes long. This is similar to the ATA
	security specification [2]. A key is initially acquired via the request_key()
	kernel API call during nvdimm unlock. It is up to the user to make sure that
	all the keys are in the kernel user keyring for unlock.

	A nvdimm encrypted-key of format enc32 has the description format of:
	nvdimm:<bus-provider-specific-unique-id>

	See file ``Documentation/security/keys/trusted-encrypted.rst`` for creating
	encrypted-keys of enc32 format. TPM usage with a master trusted key is
	preferred for sealing the encrypted-keys.

	4. Unlocking
	------------
	When the DIMMs are being enumerated by the kernel, the kernel will attempt to
	retrieve the key from the kernel user keyring. This is the only time
	a locked DIMM can be unlocked. Once unlocked, the DIMM will remain unlocked
	until reboot. Typically an entity (i.e. shell script) will inject all the
	relevant encrypted-keys into the kernel user keyring during the initramfs phase.
	This provides the unlock function access to all the related keys that contain
	the passphrase for the respective nvdimms. It is also recommended that the
	keys are injected before libnvdimm is loaded by modprobe.

	5. Update
	---------
	When doing an update, it is expected that the existing key is removed from
	the kernel user keyring and reinjected as different (old) key. It's irrelevant
	what the key description is for the old key since we are only interested in the
	keyid when doing the update operation. It is also expected that the new key
	is injected with the description format described from earlier in this
	document. The update command written to the sysfs attribute will be with
	the format:
	update <old keyid> <new keyid>

	If there is no old keyid due to a security enabling, then a 0 should be
	passed in.

	6. Freeze
	---------
	The freeze operation does not require any keys. The security config can be
	frozen by a user with root privelege.

	7. Disable
	----------
	The security disable command format is:
	disable <keyid>

	An key with the current passphrase payload that is tied to the nvdimm should be
	in the kernel user keyring.

	8. Secure Erase
	---------------
	The command format for doing a secure erase is:
	erase <keyid>

	An key with the current passphrase payload that is tied to the nvdimm should be
	in the kernel user keyring.

	9. Overwrite
	------------
	The command format for doing an overwrite is:
	overwrite <keyid>

	Overwrite can be done without a key if security is not enabled. A key serial
	of 0 can be passed in to indicate no key.

	The sysfs attribute "security" can be polled to wait on overwrite completion.
	Overwrite can last tens of minutes or more depending on nvdimm size.

	An encrypted-key with the current user passphrase that is tied to the nvdimm
	should be injected and its keyid should be passed in via sysfs.

	10. Master Update
	-----------------
	The command format for doing a master update is:
	update <old keyid> <new keyid>

	The operating mechanism for master update is identical to update except the
	master passphrase key is passed to the kernel. The master passphrase key
	is just another encrypted-key.

	This command is only available when security is disabled.

	11. Master Erase
	----------------
	The command format for doing a master erase is:
	master_erase <current keyid>

	This command has the same operating mechanism as erase except the master
	passphrase key is passed to the kernel. The master passphrase key is just
	another encrypted-key.

	This command is only available when the master security is enabled, indicated
	by the extended security status.

	[1]: https://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf

	[2]: http://www.t13.org/documents/UploadedDocuments/docs2006/e05179r4-ACS-SecurityClarifications.pdf