path: root/Documentation/nvdimm
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authorDave Jiang <>2018-12-10 13:36:14 -0700
committerDan Williams <>2018-12-21 12:44:41 -0800
commit1f4883f300da4f4d9d31eaa80f7debf6ce74843b (patch)
treef93ab39ad10f1d83f374e60fe69232c1c7a2b8ae /Documentation/nvdimm
parentecaa4a97b3908be0bf3ad12181ae8c44d1816d40 (diff)
libnvdimm/security: Add documentation for nvdimm security support
Add theory of operation for the security support that's going into libnvdimm. Signed-off-by: Dave Jiang <> Reviewed-by: Jing Lin <> Signed-off-by: Dan Williams <>
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+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
+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
+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:
+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.