1NDCTL-WAIT-OVERWRI(1) ndctl Manual NDCTL-WAIT-OVERWRI(1)
2
6 ndctl-wait-overwrite - wait for an overwrite operation to complete
7
9 ndctl wait-overwrite <nmem0> [<nmem1>..<nmemN>] [<options>]
10
12 The kernel provides a POLL(2) capable sysfs file (security) to indicate
13 the state of overwrite. This command waits for a change in the state of
14 this file across all specified dimms.
15
17 <dimm>
18 A nmemX device name, or a dimm id number. Restrict the operation to
19 the specified dimm(s). The keyword all can be specified to indicate
20 the lack of any restriction, however this is the same as not
21 supplying a --dimm option at all.
22 -b, --bus=
24 A bus id number, or a provider string (e.g. "ACPI.NFIT"). Restrict
25 the operation to the specified bus(es). The keyword all can be
26 specified to indicate the lack of any restriction, however this is
27 the same as not supplying a --bus option at all.
28 -v, --verbose
30 Emit debug messages.
31
33 The Intel Device Specific Methods (DSM) specification v1.7 and v1.8 [1]
34 introduced the following security management operations: enable
35 passhprase, update passphrase, unlock DIMM, disable security, freeze
36 security, secure (crypto) erase, overwrite, master passphrase enable,
37 master passphrase update, and master passphrase secure erase.
38 The security management for NVDIMMs is comprised of two parts. The
40 front end uses the Linux key management framework (trusted and
41 encrypted keys [2]) to store the encrypted passphrases in the
42 kernel-managed keyring. The interface for this is the keyutils utility
43 which uses the key management APIs in the Linux kernel. The back end
44 takes the decrypted payload (which is the DIMM passphrase) and passes
45 it to the DIMM.
46 Unlike other DSMs which are composed by libndctl and sent to the kernel
48 via an ioctl, the security DSMs are managed through the security sysfs
49 attribute under the dimm device. A key-ID is written to the security
50 attribute and the kernel pulls the associated key material from the
51 user keyring that is maintained by the kernel.
52 The security process begins with the generation of a master key that is
54 used to seal (encrypt) the passphrase for the DIMM. There can either be
55 one common master key that is used to encrypt every DIMM’s passphrase,
56 or a separate key can be generated for each DIMM. The master key is
57 also referred to as the key-encryption-key (kek). The kek can either be
58 generated by the TPM (Trusted Platform Module) on the system, or
59 alternatively, the System Master Key can also be used as the kek
60 For testing purposes a user key with randomized payload can also be
62 used as a kek. See [2] for details. To perform any security operations,
63 it is expected that the kek has been added to the kernel’s user keyring
64 as shown in example below:
65 .ft C
68 # 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 .ft
74 Before performing any of the security operations, all the regions
77 associated with the DIMM in question need to be disabled. For the
78 overwrite operation, in addition to the regions, the dimm also needs to
79 be disabled.
80 [1] http://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf [2]
82 https://www.kernel.org/doc/Documentation/security/keys/trusted-encrypted.rst
83 The following sub-sections describe specifics of each security feature.
85 UNLOCK
87 Unlock is performed by the kernel, however a preparation step must
88 happen before the unlock DSM can be issued by the kernel. It is
89 expected that from the initramfs, a setup command (ndctl load-keys) is
90 executed before the libnvdimm module is loaded by modprobe. This
91 command will inject the kek and the encrypted passphrases into the
92 kernel’s user keyring. During the probe of the libnvdimm driver, it
93 will:
94 1. Check the security state of the device and see if the DIMM is
96 locked
97 2. Request the associated encrypted passphrase from the kernel’s user
99 key ring
100 3. Use the kek to decrypt the passphrase
102 4. Create the unlock DSM, copy the decrypted payload into the DSM
104 5. Issue the DSM to unlock the DIMM
106 If the DIMM is already unlocked, the kernel will attempt to revalidate
108 the passphrase. If we fail to revalidate the passphrase, the kernel
109 will freeze the security and disallow any further security
110 configuration changes. A kernel module parameter is available to
111 override this behavior.
112 SETUP USER PASSPHRASE
114 To setup the passphrase for a DIMM, it is expected that the kek to be
115 used is present in the kernel’s user keyring. The kek encrypts the DIMM
116 passphrase using the enc32 key format. The plaintext passphrase is
117 never provided by or made visible to the user. It is instead randomly
118 generated by the kernel and userspace does not have access to it. Upon
119 encryption, a binary blob of the passphrase is written to the
120 passphrase blob storage directory (/etc/ndctl/keys). The user is
121 responsible for backing up the passphrase blobs to a secure location.
122 UPDATE USER PASSPHRASE
124 The update user passphrase operation uses the same DSM command as
125 enable user passphrase. Most of the work is done on the key management
126 side. The user has the option of providing a new kek for the new
127 passphrase, but continuing to use the existing kek is also acceptable.
128 The following operations are performed for update-passphrase:
129 1. Remove the encrypted passphrase from the kernel’s user keyring.
131 2. Rename the passphrase blob to old.
133 3. Load this old passphrase blob into the keyring with an "old" name.
135 4. Create the new passphrase and encrypt with the kek.
137 5. Send DSM with the old and new decrypted passphrases.
139 6. Remove old passphrase and the passphrase blob from the keyring.
141 REMOVE USER PASSPHRASE
143 The key-ID for the passphrase to be removed is written to sysfs. The
144 kernel then sends the DSM to disable security, and the passphrase is
145 then removed from the keyring, and the associated passphrase blob is
146 deleted.
147 CRYPTO (SECURE) ERASE
149 This operation is similar to remove-passphrase. The kernel issues a
150 WBINVD instruction before and after the operation to ensure no data
151 corruption from a stale CPU cache. Use ndctl’s sanitize-dimm command
152 with the --crypto-erase option to perform this operation.
153 OVERWRITE
155 This is invoked using --overwrite option for ndctl sanitize-dimm. The
156 overwrite operation wipes the entire NVDIMM. The operation can take a
157 significant amount of time. NOTE: When the command returns
158 successfully, it just means overwrite has been successfully started,
159 and not that the overwrite is complete. Subsequently, 'ndctl
160 wait-overwrite’can be used to wait for the NVDIMMs that are performing
161 overwrite. Upon successful completion of an overwrite, the WBINVD
162 instruction is issued by the kernel. If both --crypto-erase and
163 --overwrite options are supplied, then crypto-erase is performed before
164 overwrite.
165 SECURITY FREEZE
167 This operation does not require a passphrase. This will cause any
168 security command other than a status query to be locked out until the
169 next boot.
170 MASTER PASSPHRASE SETUP, UPDATE, and CRYPTO ERASE
172 These operations are similar to the user passphrase enable and update.
173 The only difference is that a different passphrase is used. The master
174 passphrase has no relation to the master key (kek) which is used for
175 encryption of either passphrase.
176
178 Copyright © 2016 - 2020, Intel Corporation. License GPLv2: GNU GPL
179 version 2 http://gnu.org/licenses/gpl.html. This is free software: you
180 are free to change and redistribute it. There is NO WARRANTY, to the
181 extent permitted by law.
182
184 ndctl-sanitize-dimm(1)
185ndctl 71.1 01/26/2021 NDCTL-WAIT-OVERWRI(1)