1NDCTL-REMOVE-PASSPHRASE(1) ndctl Manual NDCTL-REMOVE-PASSPHRASE(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>]
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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
35 The Intel Device Specific Methods (DSM) specification v1.7 and v1.8 [1]
36 introduced the following security management operations: enable
37 passhprase, update passphrase, unlock DIMM, disable security, freeze
38 security, secure (crypto) erase, overwrite, master passphrase enable,
39 master passphrase update, and master passphrase secure erase.
40 The security management for NVDIMMs is comprised of two parts. The
42 front end uses the Linux key management framework (trusted and
43 encrypted keys [2]) to store the encrypted passphrases in the
44 kernel-managed keyring. The interface for this is the keyutils utility
45 which uses the key management APIs in the Linux kernel. The back end
46 takes the decrypted payload (which is the DIMM passphrase) and passes
47 it to the DIMM.
48 Unlike other DSMs which are composed by libndctl and sent to the kernel
50 via an ioctl, the security DSMs are managed through the security sysfs
51 attribute under the dimm device. A key-ID is written to the security
52 attribute and the kernel pulls the associated key material from the
53 user keyring that is maintained by the kernel.
54 The security process begins with the generation of a master key that is
56 used to seal (encrypt) the passphrase for the DIMM. There can either be
57 one common master key that is used to encrypt every DIMM’s passphrase,
58 or a separate key can be generated for each DIMM. The master key is
59 also referred to as the key-encryption-key (kek). The kek can either be
60 generated by the TPM (Trusted Platform Module) on the system, or
61 alternatively, the System Master Key can also be used as the kek
62 For testing purposes a user key with randomized payload can also be
64 used as a kek. See [2] for details. To perform any security operations,
65 it is expected that the kek has been added to the kernel’s user keyring
66 as shown in example below:
67 # keyctl show
69 Session Keyring
70 736023423 --alswrv 0 0 keyring: _ses
71 675104189 --alswrv 0 65534 \_ keyring: _uid.0
72 680187394 --alswrv 0 0 \_ trusted: nvdimm-master
73 Before performing any of the security operations, all the regions
75 associated with the DIMM in question need to be disabled. For the
76 overwrite operation, in addition to the regions, the dimm also needs to
77 be disabled.
78 [1] http://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf
80 [2]
81 https://www.kernel.org/doc/Documentation/security/keys/trusted-encrypted.rst
82 The following sub-sections describe specifics of each security feature.
84 UNLOCK
86 Unlock is performed by the kernel, however a preparation step must
87 happen before the unlock DSM can be issued by the kernel. It is
88 expected that from the initramfs, a setup command (ndctl load-keys) is
89 executed before the libnvdimm module is loaded by modprobe. This
90 command will inject the kek and the encrypted passphrases into the
91 kernel’s user keyring. During the probe of the libnvdimm driver, it
92 will:
93 1. Check the security state of the device and see if the DIMM is
95 locked
96 2. Request the associated encrypted passphrase from the kernel’s user
98 key ring
99 3. Use the kek to decrypt the passphrase
101 4. Create the unlock DSM, copy the decrypted payload into the DSM
103 5. Issue the DSM to unlock the DIMM
105 If the DIMM is already unlocked, the kernel will attempt to revalidate
107 the passphrase. If we fail to revalidate the passphrase, the kernel
108 will freeze the security and disallow any further security
109 configuration changes. A kernel module parameter is available to
110 override this behavior.
111 SETUP USER PASSPHRASE
113 To setup the passphrase for a DIMM, it is expected that the kek to be
114 used is present in the kernel’s user keyring. The kek encrypts the DIMM
115 passphrase using the enc32 key format. The plaintext passphrase is
116 never provided by or made visible to the user. It is instead randomly
117 generated by the kernel and userspace does not have access to it. Upon
118 encryption, a binary blob of the passphrase is written to the
119 passphrase blob storage directory (/etc/ndctl/keys). The user is
120 responsible for backing up the passphrase blobs to a secure location.
121 UPDATE USER PASSPHRASE
123 The update user passphrase operation uses the same DSM command as
124 enable user passphrase. Most of the work is done on the key management
125 side. The user has the option of providing a new kek for the new
126 passphrase, but continuing to use the existing kek is also acceptable.
127 The following operations are performed for update-passphrase:
128 1. Remove the encrypted passphrase from the kernel’s user keyring.
130 2. Rename the passphrase blob to old.
132 3. Load this old passphrase blob into the keyring with an "old" name.
134 4. Create the new passphrase and encrypt with the kek.
136 5. Send DSM with the old and new decrypted passphrases.
138 6. Remove old passphrase and the passphrase blob from the keyring.
140 REMOVE USER PASSPHRASE
142 The key-ID for the passphrase to be removed is written to sysfs. The
143 kernel then sends the DSM to disable security, and the passphrase is
144 then removed from the keyring, and the associated passphrase blob is
145 deleted.
146 CRYPTO (SECURE) ERASE
148 This operation is similar to remove-passphrase. The kernel issues a
149 WBINVD instruction before and after the operation to ensure no data
150 corruption from a stale CPU cache. Use ndctl’s sanitize-dimm command
151 with the --crypto-erase option to perform this operation.
152 OVERWRITE
154 This is invoked using --overwrite option for ndctl sanitize-dimm. The
155 overwrite operation wipes the entire NVDIMM. The operation can take a
156 significant amount of time. NOTE: When the command returns
157 successfully, it just means overwrite has been successfully started,
158 and not that the overwrite is complete. Subsequently, 'ndctl
159 wait-overwrite’can be used to wait for the NVDIMMs that are performing
160 overwrite. Upon successful completion of an overwrite, the WBINVD
161 instruction is issued by the kernel. If both --crypto-erase and
162 --overwrite options are supplied, then crypto-erase is performed before
163 overwrite.
164 SECURITY FREEZE
166 This operation does not require a passphrase. This will cause any
167 security command other than a status query to be locked out until the
168 next boot.
169 MASTER PASSPHRASE SETUP, UPDATE, and CRYPTO ERASE
171 These operations are similar to the user passphrase enable and update.
172 The only difference is that a different passphrase is used. The master
173 passphrase has no relation to the master key (kek) which is used for
174 encryption of either passphrase.
175
177 Copyright (c) 2016 - 2019, Intel Corporation. License GPLv2: GNU GPL
178 version 2 http://gnu.org/licenses/gpl.html. This is free software: you
179 are free to change and redistribute it. There is NO WARRANTY, to the
180 extent permitted by law.
181
183 ndctl-setup-passphrase(1), ndctl-update-passphrase(1)
184ndctl 2020-03-24 NDCTL-REMOVE-PASSPHRASE(1)