Ubuntu Manpage: ndctl-remove-passphrase - Stop a DIMM from locking at power-loss and requiring a

NAME

       ndctl-remove-passphrase - Stop a DIMM from locking at power-loss and requiring a
       passphrase to access media

SYNOPSIS

       ndctl remove-passphrase <nmem0> [<nmem1>..<nmemN>] [<options>]

DESCRIPTION

       Search the user keyring for an encrypted passphrase for the NVDIMM in question. If not
       found, attempt to load the passphrase blob. After disabling the passphrase, remove the
       key-ID from the keyring as well as the passphrase blob from the file system.

OPTIONS

       <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.

       -v, --verbose
           Emit debug messages.

       -m, --master-passphrase
           Indicates that we are managing the master passphrase instead of the user passphrase.

THEORY OF OPERATION

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

       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.