1NDCTL-WAIT-OVERWRI(1)                                    NDCTL-WAIT-OVERWRI(1)
2
3
4

NAME

6       ndctl-wait-overwrite - wait for an overwrite operation to complete
7

SYNOPSIS

9       ndctl wait-overwrite <nmem0> [<nmem1>..<nmemN>] [<options>]
10

DESCRIPTION

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

OPTIONS

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
23       -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
29       -v, --verbose
30           Emit debug messages.
31

THEORY OF OPERATION

33       The Intel Device Specific Methods (DSM) specification v1.7 and v1.8 [1]
34       introduced the following security management operations: enable
35       passphrase, 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
39       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
47       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
53       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
61       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
66           # keyctl show
67           Session Keyring
68            736023423 --alswrv      0     0  keyring: _ses
69            675104189 --alswrv      0 65534   \_ keyring: _uid.0
70            680187394 --alswrv      0     0       \_ trusted: nvdimm-master
71
72       Before performing any of the security operations, all the regions
73       associated with the DIMM in question need to be disabled. For the
74       overwrite operation, in addition to the regions, the dimm also needs to
75       be disabled.
76
77       [1] http://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf [2]
78       https://www.kernel.org/doc/Documentation/security/keys/trusted-encrypted.rst
79
80       The following sub-sections describe specifics of each security feature.
81
82   UNLOCK
83       Unlock is performed by the kernel, however a preparation step must
84       happen before the unlock DSM can be issued by the kernel. It is
85       expected that from the initramfs, a setup command (ndctl load-keys) is
86       executed before the libnvdimm module is loaded by modprobe. This
87       command will inject the kek and the encrypted passphrases into the
88       kernel’s user keyring. During the probe of the libnvdimm driver, it
89       will:
90
91        1. Check the security state of the device and see if the DIMM is
92           locked
93
94        2. Request the associated encrypted passphrase from the kernel’s user
95           key ring
96
97        3. Use the kek to decrypt the passphrase
98
99        4. Create the unlock DSM, copy the decrypted payload into the DSM
100
101        5. Issue the DSM to unlock the DIMM
102
103       If the DIMM is already unlocked, the kernel will attempt to revalidate
104       the passphrase. If we fail to revalidate the passphrase, the kernel
105       will freeze the security and disallow any further security
106       configuration changes. A kernel module parameter is available to
107       override this behavior.
108
109   SETUP USER PASSPHRASE
110       To setup the passphrase for a DIMM, it is expected that the kek to be
111       used is present in the kernel’s user keyring. The kek encrypts the DIMM
112       passphrase using the enc32 key format. The plaintext passphrase is
113       never provided by or made visible to the user. It is instead randomly
114       generated by the kernel and userspace does not have access to it. Upon
115       encryption, a binary blob of the passphrase is written to the
116       passphrase blob storage directory (/etc/ndctl/keys). The user is
117       responsible for backing up the passphrase blobs to a secure location.
118
119   UPDATE USER PASSPHRASE
120       The update user passphrase operation uses the same DSM command as
121       enable user passphrase. Most of the work is done on the key management
122       side. The user has the option of providing a new kek for the new
123       passphrase, but continuing to use the existing kek is also acceptable.
124       The following operations are performed for update-passphrase:
125
126        1. Remove the encrypted passphrase from the kernel’s user keyring.
127
128        2. Rename the passphrase blob to old.
129
130        3. Load this old passphrase blob into the keyring with an "old" name.
131
132        4. Create the new passphrase and encrypt with the kek.
133
134        5. Send DSM with the old and new decrypted passphrases.
135
136        6. Remove old passphrase and the passphrase blob from the keyring.
137
138   REMOVE USER PASSPHRASE
139       The key-ID for the passphrase to be removed is written to sysfs. The
140       kernel then sends the DSM to disable security, and the passphrase is
141       then removed from the keyring, and the associated passphrase blob is
142       deleted.
143
144   CRYPTO (SECURE) ERASE
145       This operation is similar to remove-passphrase. The kernel issues a
146       WBINVD instruction before and after the operation to ensure no data
147       corruption from a stale CPU cache. Use ndctl’s sanitize-dimm command
148       with the --crypto-erase option to perform this operation.
149
150   OVERWRITE
151       This is invoked using --overwrite option for ndctl sanitize-dimm. The
152       overwrite operation wipes the entire NVDIMM. The operation can take a
153       significant amount of time. NOTE: When the command returns
154       successfully, it just means overwrite has been successfully started,
155       and not that the overwrite is complete. Subsequently, ndctl
156       wait-overwrite can be used to wait for the NVDIMMs that are performing
157       overwrite. Upon successful completion of an overwrite, the WBINVD
158       instruction is issued by the kernel. If both --crypto-erase and
159       --overwrite options are supplied, then crypto-erase is performed before
160       overwrite.
161
162   SECURITY FREEZE
163       This operation does not require a passphrase. This will cause any
164       security command other than a status query to be locked out until the
165       next boot.
166
167   MASTER PASSPHRASE SETUP, UPDATE, and CRYPTO ERASE
168       These operations are similar to the user passphrase enable and update.
169       The only difference is that a different passphrase is used. The master
170       passphrase has no relation to the master key (kek) which is used for
171       encryption of either passphrase.
172
174       Copyright © 2016 - 2022, Intel Corporation. License GPLv2: GNU GPL
175       version 2 http://gnu.org/licenses/gpl.html. This is free software: you
176       are free to change and redistribute it. There is NO WARRANTY, to the
177       extent permitted by law.
178

SEE ALSO

180       linkndctl:ndctl-sanitize-dimm[1]
181
182
183
184                                  08/03/2023             NDCTL-WAIT-OVERWRI(1)
Impressum