[v13,17/17] libnvdimm/security: Add documentation for nvdimm security support
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Message ID 154456001766.26509.5196378229920284095.stgit@djiang5-desk3.ch.intel.com
State Superseded
Headers show
Series
  • Adding security support for nvdimm
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Commit Message

Dave Jiang Dec. 11, 2018, 8:26 p.m. UTC
Add theory of operation for the security support that's going into
libnvdimm.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 Documentation/nvdimm/security.txt |  143 +++++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)
 create mode 100644 Documentation/nvdimm/security.txt

Patch
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diff --git a/Documentation/nvdimm/security.txt b/Documentation/nvdimm/security.txt
new file mode 100644
index 000000000000..027160f9c3b8
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+++ b/Documentation/nvdimm/security.txt
@@ -0,0 +1,143 @@ 
+NVDIMM SECURITY
+===============
+
+1. Introduction
+---------------
+
+With the introduction of Intel DSM v1.8 specification [1], security DSMs are
+introduced. The spec added the following security DSMs: "get security state",
+"set passphrase", "disable passphrase", "unlock unit", "freeze lock",
+"secure erase", and "overwrite". A security_ops data structure has been
+added to struct dimm in order to support the security operations and generic
+APIs are exposed to allow vendor neutral operations.
+
+2. Sysfs Interface
+------------------
+The "security" sysfs attribute is provided in the nvdimm sysfs directory. For
+example:
+/sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/security
+
+The "show" function of that attribute will display the security state for
+that DIMM. The following states are available: disabled, unlocked, locked,
+frozen, and overwrite. If security is not supported, the sysfs attribute
+will not be visible.
+
+The "store" function takes several commands when the attribute is written to
+in order to support some of the security functionalities:
+update <old_keyid> <new_keyid> - enable or update passphrase.
+disable <keyid> - disable enabled security and remove key.
+freeze - freeze changing of security states.
+erase <keyid> - generate new ecryption key for DIMM and crypto-scrambles
+	all existing user data using the user passphrase.
+overwrite <keyid> - wipe the entire nvdimm.
+master_update <keyid> <new_keyid> - enable or update master passphrase.
+master_erase <keyid> - generate new ecryption key for DIMM and crypto-scrambles
+	all existing user data using the master passphrase.
+master
+
+3. Key Management
+-----------------
+
+The key is associted to the payload by the DIMM id. For example:
+# cat /sys/devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0012:00/ndbus0/nmem0/nfit/id
+8089-a2-1740-00000133
+The DIMM id would be provided along with the key payload (passphrase) to
+the kernel.
+
+The security keys are managed on the basis of a single key per DIMM. The
+key "passphrase" is expected to be 32bytes long. This is similar to the ATA
+security specification [2]. A key is initially acquired via the request_key()
+kernel API call during nvdimm unlock. It is up to the user to make sure that
+all the keys are in the kernel user keyring for unlock.
+
+A nvdimm encrypted-key of format enc32 has the description format of:
+nvdimm:<bus-provider-specific-unique-id>
+
+See file ``Documentation/security/keys/trusted-encrypted.rst`` for creating
+encrypted-keys of enc32 format. TPM usage with a master trusted key is
+preferred for sealing the encrypted-keys.
+
+4. Unlocking
+------------
+When the DIMMs are being enumerated by the kernel, the kernel will attempt to
+retrieve the key from the kernel user keyring. This is the only time
+a locked DIMM can be unlocked. Once unlocked, the DIMM will remain unlocked
+until reboot. Typically, an entity (i.e. shell script) will inject all the
+relevant encrypted-keys into the kernel user keyring during initramfs phase.
+It is also recommended that the keys are injected before libnvdimm is loaded
+by modprobe.
+
+5. Update
+---------
+When doing an update, it is expected that the existing key is removed from
+tkey key user keyring and injected as the old key. It's irrelevant what
+the key description is for the old key since we are only interested in the
+key id when doing the update operation. It is also expected that the new key
+is injected with the description format described from earlier in this
+document.  The update command written to the sysfs attribute will be with
+the format:
+update <old keyid> <new keyid>
+
+If there is no old keyid due to a security enabling, then a 0 should be
+passed in.
+
+6. Freeze
+---------
+The freeze operation does not require any keys. The security config can be
+frozen by a user with root privelege.
+
+7. Disable
+----------
+The security disable command format is:
+disable <keyid>
+
+An key with the current passphrase payload that is tied to the nvdimm should be
+in the kernel user keyring.
+
+8. Secure Erase
+---------------
+The command format for doing a secure erase is:
+erase <keyid>
+
+An key with the current passphrase payload that is tied to the nvdimm should be
+in the kernel user keyring.
+
+9. Overwrite
+------------
+The command format for doing an overwrite is:
+overwrite <keyid>
+
+Overwrite can be done without a key if security is not enabled. A key serial
+of 0 can be passed in to indicate no key.
+
+The sysfs attribute "security" can be polled to wait on overwrite completion.
+Overwrite can last tens of minutes or more depending on nvdimm size.
+
+An encrypted-key with the current user passphrase that is tied to the nvdimm
+should be injected and its keyid should be passed in via sysfs.
+
+10. Master Update
+-----------------
+The command format for doing a master update is:
+update <old keyid> <new keyid>
+
+The operating mechansim for master update is identical to update except the
+master passphrase key is passed to the kernel. The master passphrase key
+is just another encrypted-key.
+
+This command is only available when security is disabled.
+
+11. Master Erase
+----------------
+The command format for doing a master erase is:
+master_erase <current keyid>
+
+This command has the same operating mechanism as erase except the master
+passphrase key is passed to the kernel. The master passphrase key is just
+another encrypted-key.
+
+This command is only available when the master security is enabled, indicated
+by the extended security status.
+
+[1]: http://pmem.io/documents/NVDIMM_DSM_Interface-V1.8.pdf
+[2]: http://www.t13.org/documents/UploadedDocuments/docs2006/e05179r4-ACS-SecurityClarifications.pdf