1NDCTL-REMOVE-PASSP(1) NDCTL-REMOVE-PASSP(1)
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6 ndctl-remove-passphrase - Stop a DIMM from locking at power-loss and
7 requiring a passphrase to access media
8
10 ndctl remove-passphrase <nmem0> [<nmem1>..<nmemN>] [<options>]
11
13 Search the user keyring for an encrypted passphrase for the NVDIMM in
14 question. If not found, attempt to load the passphrase blob. After
15 disabling the passphrase, remove the key-ID from the keyring as well as
16 the passphrase blob from the file system.
17
19 <dimm>
20 A nmemX device name, or a dimm id number. Restrict the operation to
21 the specified dimm(s). The keyword all can be specified to indicate
22 the lack of any restriction, however this is the same as not
23 supplying a --dimm option at all.
24 -b, --bus=
26 A bus id number, or a provider string (e.g. "ACPI.NFIT"). Restrict
27 the operation to the specified bus(es). The keyword all can be
28 specified to indicate the lack of any restriction, however this is
29 the same as not supplying a --bus option at all.
30 -v, --verbose
32 Emit debug messages.
33 -m, --master-passphrase
35 Indicates that we are managing the master passphrase instead of the
36 user passphrase.
37
39 The Intel Device Specific Methods (DSM) specification v1.7 and v1.8 [1]
40 introduced the following security management operations: enable
41 passphrase, update passphrase, unlock DIMM, disable security, freeze
42 security, secure (crypto) erase, overwrite, master passphrase enable,
43 master passphrase update, and master passphrase secure erase.
44 The security management for NVDIMMs is comprised of two parts. The
46 front end uses the Linux key management framework (trusted and
47 encrypted keys [2]) to store the encrypted passphrases in the
48 kernel-managed keyring. The interface for this is the keyutils utility
49 which uses the key management APIs in the Linux kernel. The back end
50 takes the decrypted payload (which is the DIMM passphrase) and passes
51 it to the DIMM.
52 Unlike other DSMs which are composed by libndctl and sent to the kernel
54 via an ioctl, the security DSMs are managed through the security sysfs
55 attribute under the dimm device. A key-ID is written to the security
56 attribute and the kernel pulls the associated key material from the
57 user keyring that is maintained by the kernel.
58 The security process begins with the generation of a master key that is
60 used to seal (encrypt) the passphrase for the DIMM. There can either be
61 one common master key that is used to encrypt every DIMM’s passphrase,
62 or a separate key can be generated for each DIMM. The master key is
63 also referred to as the key-encryption-key (kek). The kek can either be
64 generated by the TPM (Trusted Platform Module) on the system, or
65 alternatively, the System Master Key can also be used as the kek
66 For testing purposes a user key with randomized payload can also be
68 used as a kek. See [2] for details. To perform any security operations,
69 it is expected that the kek has been added to the kernel’s user keyring
70 as shown in example below:
71 # keyctl show
73 Session Keyring
74 736023423 --alswrv 0 0 keyring: _ses
75 675104189 --alswrv 0 65534 \_ keyring: _uid.0
76 680187394 --alswrv 0 0 \_ trusted: nvdimm-master
77 Before performing any of the security operations, all the regions
79 associated with the DIMM in question need to be disabled. For the
80 overwrite operation, in addition to the regions, the dimm also needs to
81 be disabled.
82 [1] http://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf [2]
84 https://www.kernel.org/doc/Documentation/security/keys/trusted-encrypted.rst
85 The following sub-sections describe specifics of each security feature.
87 UNLOCK
89 Unlock is performed by the kernel, however a preparation step must
90 happen before the unlock DSM can be issued by the kernel. It is
91 expected that from the initramfs, a setup command (ndctl load-keys) is
92 executed before the libnvdimm module is loaded by modprobe. This
93 command will inject the kek and the encrypted passphrases into the
94 kernel’s user keyring. During the probe of the libnvdimm driver, it
95 will:
96 1. Check the security state of the device and see if the DIMM is
98 locked
99 2. Request the associated encrypted passphrase from the kernel’s user
101 key ring
102 3. Use the kek to decrypt the passphrase
104 4. Create the unlock DSM, copy the decrypted payload into the DSM
106 5. Issue the DSM to unlock the DIMM
108 If the DIMM is already unlocked, the kernel will attempt to revalidate
110 the passphrase. If we fail to revalidate the passphrase, the kernel
111 will freeze the security and disallow any further security
112 configuration changes. A kernel module parameter is available to
113 override this behavior.
114 SETUP USER PASSPHRASE
116 To setup the passphrase for a DIMM, it is expected that the kek to be
117 used is present in the kernel’s user keyring. The kek encrypts the DIMM
118 passphrase using the enc32 key format. The plaintext passphrase is
119 never provided by or made visible to the user. It is instead randomly
120 generated by the kernel and userspace does not have access to it. Upon
121 encryption, a binary blob of the passphrase is written to the
122 passphrase blob storage directory (/etc/ndctl/keys). The user is
123 responsible for backing up the passphrase blobs to a secure location.
124 UPDATE USER PASSPHRASE
126 The update user passphrase operation uses the same DSM command as
127 enable user passphrase. Most of the work is done on the key management
128 side. The user has the option of providing a new kek for the new
129 passphrase, but continuing to use the existing kek is also acceptable.
130 The following operations are performed for update-passphrase:
131 1. Remove the encrypted passphrase from the kernel’s user keyring.
133 2. Rename the passphrase blob to old.
135 3. Load this old passphrase blob into the keyring with an "old" name.
137 4. Create the new passphrase and encrypt with the kek.
139 5. Send DSM with the old and new decrypted passphrases.
141 6. Remove old passphrase and the passphrase blob from the keyring.
143 REMOVE USER PASSPHRASE
145 The key-ID for the passphrase to be removed is written to sysfs. The
146 kernel then sends the DSM to disable security, and the passphrase is
147 then removed from the keyring, and the associated passphrase blob is
148 deleted.
149 CRYPTO (SECURE) ERASE
151 This operation is similar to remove-passphrase. The kernel issues a
152 WBINVD instruction before and after the operation to ensure no data
153 corruption from a stale CPU cache. Use ndctl’s sanitize-dimm command
154 with the --crypto-erase option to perform this operation.
155 OVERWRITE
157 This is invoked using --overwrite option for ndctl sanitize-dimm. The
158 overwrite operation wipes the entire NVDIMM. The operation can take a
159 significant amount of time. NOTE: When the command returns
160 successfully, it just means overwrite has been successfully started,
161 and not that the overwrite is complete. Subsequently, ndctl
162 wait-overwrite can be used to wait for the NVDIMMs that are performing
163 overwrite. Upon successful completion of an overwrite, the WBINVD
164 instruction is issued by the kernel. If both --crypto-erase and
165 --overwrite options are supplied, then crypto-erase is performed before
166 overwrite.
167 SECURITY FREEZE
169 This operation does not require a passphrase. This will cause any
170 security command other than a status query to be locked out until the
171 next boot.
172 MASTER PASSPHRASE SETUP, UPDATE, and CRYPTO ERASE
174 These operations are similar to the user passphrase enable and update.
175 The only difference is that a different passphrase is used. The master
176 passphrase has no relation to the master key (kek) which is used for
177 encryption of either passphrase.
178
180 Copyright © 2016 - 2022, Intel Corporation. License GPLv2: GNU GPL
181 version 2 http://gnu.org/licenses/gpl.html. This is free software: you
182 are free to change and redistribute it. There is NO WARRANTY, to the
183 extent permitted by law.
184
186 linkndctl:ndctl-setup-passphrase[1],
187 linkndctl:ndctl-update-passphrase[1]
188 08/03/2023 NDCTL-REMOVE-PASSP(1)