1 =============== 2 NVDIMM Security 3 =============== 4 5 1. Introduction 6 --------------- 7 8 With the introduction of Intel Device Specific Methods (DSM) v1.8 9 specification [1], security DSMs are introduced. The spec added the following 10 security DSMs: "get security state", "set passphrase", "disable passphrase", 11 "unlock unit", "freeze lock", "secure erase", and "overwrite". A security_ops 12 data structure has been added to struct dimm in order to support the security 13 operations and generic APIs are exposed to allow vendor neutral operations. 14 15 2. Sysfs Interface 16 ------------------ 17 The "security" sysfs attribute is provided in the nvdimm sysfs directory. For 18 example: 19 /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/security 20 21 The "show" attribute of that attribute will display the security state for 22 that DIMM. The following states are available: disabled, unlocked, locked, 23 frozen, and overwrite. If security is not supported, the sysfs attribute 24 will not be visible. 25 26 The "store" attribute takes several commands when it is being written to 27 in order to support some of the security functionalities: 28 update <old_keyid> <new_keyid> - enable or update passphrase. 29 disable <keyid> - disable enabled security and remove key. 30 freeze - freeze changing of security states. 31 erase <keyid> - delete existing user encryption key. 32 overwrite <keyid> - wipe the entire nvdimm. 33 master_update <keyid> <new_keyid> - enable or update master passphrase. 34 master_erase <keyid> - delete existing user encryption key. 35 36 3. Key Management 37 ----------------- 38 39 The key is associated to the payload by the DIMM id. For example: 40 # cat /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/nfit/id 41 8089-a2-1740-00000133 42 The DIMM id would be provided along with the key payload (passphrase) to 43 the kernel. 44 45 The security keys are managed on the basis of a single key per DIMM. The 46 key "passphrase" is expected to be 32bytes long. This is similar to the ATA 47 security specification [2]. A key is initially acquired via the request_key() 48 kernel API call during nvdimm unlock. It is up to the user to make sure that 49 all the keys are in the kernel user keyring for unlock. 50 51 A nvdimm encrypted-key of format enc32 has the description format of: 52 nvdimm:<bus-provider-specific-unique-id> 53 54 See file ``Documentation/security/keys/trusted-encrypted.rst`` for creating 55 encrypted-keys of enc32 format. TPM usage with a master trusted key is 56 preferred for sealing the encrypted-keys. 57 58 4. Unlocking 59 ------------ 60 When the DIMMs are being enumerated by the kernel, the kernel will attempt to 61 retrieve the key from the kernel user keyring. This is the only time 62 a locked DIMM can be unlocked. Once unlocked, the DIMM will remain unlocked 63 until reboot. Typically an entity (i.e. shell script) will inject all the 64 relevant encrypted-keys into the kernel user keyring during the initramfs phase. 65 This provides the unlock function access to all the related keys that contain 66 the passphrase for the respective nvdimms. It is also recommended that the 67 keys are injected before libnvdimm is loaded by modprobe. 68 69 5. Update 70 --------- 71 When doing an update, it is expected that the existing key is removed from 72 the kernel user keyring and reinjected as different (old) key. It's irrelevant 73 what the key description is for the old key since we are only interested in the 74 keyid when doing the update operation. It is also expected that the new key 75 is injected with the description format described from earlier in this 76 document. The update command written to the sysfs attribute will be with 77 the format: 78 update <old keyid> <new keyid> 79 80 If there is no old keyid due to a security enabling, then a 0 should be 81 passed in. 82 83 6. Freeze 84 --------- 85 The freeze operation does not require any keys. The security config can be 86 frozen by a user with root privilege. 87 88 7. Disable 89 ---------- 90 The security disable command format is: 91 disable <keyid> 92 93 An key with the current passphrase payload that is tied to the nvdimm should be 94 in the kernel user keyring. 95 96 8. Secure Erase 97 --------------- 98 The command format for doing a secure erase is: 99 erase <keyid> 100 101 An key with the current passphrase payload that is tied to the nvdimm should be 102 in the kernel user keyring. 103 104 9. Overwrite 105 ------------ 106 The command format for doing an overwrite is: 107 overwrite <keyid> 108 109 Overwrite can be done without a key if security is not enabled. A key serial 110 of 0 can be passed in to indicate no key. 111 112 The sysfs attribute "security" can be polled to wait on overwrite completion. 113 Overwrite can last tens of minutes or more depending on nvdimm size. 114 115 An encrypted-key with the current user passphrase that is tied to the nvdimm 116 should be injected and its keyid should be passed in via sysfs. 117 118 10. Master Update 119 ----------------- 120 The command format for doing a master update is: 121 update <old keyid> <new keyid> 122 123 The operating mechanism for master update is identical to update except the 124 master passphrase key is passed to the kernel. The master passphrase key 125 is just another encrypted-key. 126 127 This command is only available when security is disabled. 128 129 11. Master Erase 130 ---------------- 131 The command format for doing a master erase is: 132 master_erase <current keyid> 133 134 This command has the same operating mechanism as erase except the master 135 passphrase key is passed to the kernel. The master passphrase key is just 136 another encrypted-key. 137 138 This command is only available when the master security is enabled, indicated 139 by the extended security status. 140 141 [1]: https://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf 142 143 [2]: http://www.t13.org/documents/UploadedDocuments/docs2006/e05179r4-ACS-SecurityClarifications.pdf
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