ndctl-update-passphrase − update the security passphrase for an NVDIMM
ndctl update−passphrase <nmem0> [<nmem1>..<nmemN>] [<options>]
Update the security passphrase for one or more NVDIMMs. Prerequisites for command to succeed:
1. The kek has been loaded into the kernel’s user keyring.
2. setup−passphrase has successfully been executed on the NVDIMM.
• Alternatively, the NVDIMM is unlocked.
The updated key blobs will be created in the /etc/ndctl/keys directory with a file name format of "nvdimm_<dimm−unique−id>_<hostname>.blob".
<dimm>
A nmemX device name, or a dimm id number. Restrict the operation to the specified dimm(s). The keyword all can be specified to indicate the lack of any restriction, however this is the same as not supplying a −−dimm option at all.
−b, −−bus=
A bus id number, or a provider string (e.g. "ACPI.NFIT"). Restrict the operation to the specified bus(es). The keyword all can be specified to indicate the lack of any restriction, however this is the same as not supplying a −−bus option at all.
−k, −−key_handle=
Handle for the master
kek (key−encryption−key) that will be
used for sealing the passphrase(s) for the given DIMM(s).
The format is: <key type>:<key description> e.g.
trusted:nvdimm−master
NOTE: The kek is expected to have been loaded into
the user keyring.
−m, −−master−passphrase
Indicates that we are managing the master passphrase instead of the user passphrase.
−v, −−verbose
Emit debug messages.
The Intel Device Specific Methods (DSM) specification v1.7 and v1.8 [1] introduced the following security management operations: enable passhprase, update passphrase, unlock DIMM, disable security, freeze security, secure (crypto) erase, overwrite, master passphrase enable, master passphrase update, and master passphrase secure erase.
The security management for NVDIMMs is comprised of two parts. The front end uses the Linux key management framework (trusted and encrypted keys [2]) to store the encrypted passphrases in the kernel−managed keyring. The interface for this is the keyutils utility which uses the key management APIs in the Linux kernel. The back end takes the decrypted payload (which is the DIMM passphrase) and passes it to the DIMM.
Unlike other DSMs which are composed by libndctl and sent to the kernel via an ioctl, the security DSMs are managed through the security sysfs attribute under the dimm device. A key−ID is written to the security attribute and the kernel pulls the associated key material from the user keyring that is maintained by the kernel.
The security process begins with the generation of a master key that is used to seal (encrypt) the passphrase for the DIMM. There can either be one common master key that is used to encrypt every DIMM’s passphrase, or a separate key can be generated for each DIMM. The master key is also referred to as the key−encryption−key (kek). The kek can either be generated by the TPM (Trusted Platform Module) on the system, or alternatively, the System Master Key can also be used as the kek
For testing purposes a user key with randomized payload can also be used as a kek. See [2] for details. To perform any security operations, it is expected that the kek has been added to the kernel’s user keyring as shown in example below:
# keyctl show
Session Keyring
736023423 −−alswrv 0 0 keyring: _ses
675104189 −−alswrv 0 65534 \_ keyring: _uid.0
680187394 −−alswrv 0 0 \_ trusted:
nvdimm−master
Before performing any of the security operations, all the regions associated with the DIMM in question need to be disabled. For the overwrite operation, in addition to the regions, the dimm also needs to be disabled.
[1]
<http://pmem.io/documents/NVDIMM_DSM_Interface−V1.8.pdf>
[2]
<https://www.kernel.org/doc/Documentation/security/keys/trusted−encrypted.rst>
The following sub−sections describe specifics of each security feature.
UNLOCK
Unlock is performed by the kernel, however a preparation
step must happen before the unlock DSM can be issued by the
kernel. It is expected that from the initramfs, a setup
command (ndctl load−keys) is executed before
the libnvdimm module is loaded by modprobe. This command
will inject the kek and the encrypted passphrases
into the kernel’s user keyring. During the
probe of the libnvdimm driver, it will:
1. Check the security state of the device and see if the DIMM is locked
2. Request the associated encrypted passphrase from the kernel’s user key ring
3. Use the kek to decrypt the passphrase
4. Create the unlock DSM, copy the decrypted payload into the DSM
5. Issue the DSM to unlock the DIMM
If the DIMM is already unlocked, the kernel will attempt to revalidate the passphrase. If we fail to revalidate the passphrase, the kernel will freeze the security and disallow any further security configuration changes. A kernel module parameter is available to override this behavior.
SETUP USER
PASSPHRASE
To setup the passphrase for a DIMM, it is expected that the
kek to be used is present in the kernel’s user
keyring. The kek encrypts the DIMM passphrase using
the enc32 key format. The plaintext passphrase is
never provided by or made visible to the user. It is instead
randomly generated by the kernel and userspace does not have
access to it. Upon encryption, a binary blob of the
passphrase is written to the passphrase blob storage
directory (/etc/ndctl/keys). The user is responsible for
backing up the passphrase blobs to a secure location.
UPDATE USER
PASSPHRASE
The update user passphrase operation uses the same DSM
command as enable user passphrase. Most of the work is done
on the key management side. The user has the option of
providing a new kek for the new passphrase, but
continuing to use the existing kek is also
acceptable. The following operations are performed for
update−passphrase:
1. Remove the encrypted passphrase from the kernel’s user keyring.
2. Rename the passphrase blob to old.
3. Load this old passphrase blob into the keyring with an "old" name.
4. Create the new passphrase and encrypt with the kek.
5. Send DSM with the old and new decrypted passphrases.
6. Remove old passphrase and the passphrase blob from the keyring.
REMOVE USER
PASSPHRASE
The key−ID for the passphrase to be removed is
written to sysfs. The kernel then sends the DSM to disable
security, and the passphrase is then removed from the
keyring, and the associated passphrase blob is deleted.
CRYPTO
(SECURE) ERASE
This operation is similar to remove−passphrase. The
kernel issues a WBINVD instruction before and after the
operation to ensure no data corruption from a stale CPU
cache. Use ndctl’s sanitize−dimm command with
the −−crypto−erase option to perform this
operation.
OVERWRITE
This is invoked using −−overwrite option for
ndctl sanitize−dimm. The overwrite operation
wipes the entire NVDIMM. The operation can take a
significant amount of time. NOTE: When the command returns
successfully, it just means overwrite has been successfully
started, and not that the overwrite is complete.
Subsequently, 'ndctl wait−overwrite’can be used
to wait for the NVDIMMs that are performing overwrite. Upon
successful completion of an overwrite, the WBINVD
instruction is issued by the kernel. If both
−−crypto−erase and −−overwrite
options are supplied, then crypto−erase is performed
before overwrite.
SECURITY
FREEZE
This operation does not require a passphrase. This will
cause any security command other than a status query to be
locked out until the next boot.
MASTER
PASSPHRASE SETUP, UPDATE, and CRYPTO ERASE
These operations are similar to the user passphrase enable
and update. The only difference is that a different
passphrase is used. The master passphrase has no relation to
the master key (kek) which is used for encryption of
either passphrase.
Copyright © 2016 − 2022, Intel Corporation. License GPLv2: GNU GPL version 2 <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.
ndctl−setup−passphrase(1), ndctl−remove−passphrase(1)