Ubuntu Manpage: ndctl-update-passphrase - update the security passphrase for an NVDIMM

NAME

       ndctl-update-passphrase - update the security passphrase for an NVDIMM

SYNOPSIS

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

DESCRIPTION

       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".

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.

       -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.

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 (c) 2016 - 2019, 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.