dm: add documentation for dm-inlinecrypt target

This adds the admin-guide documentation for dm-inlinecrypt.

dm-inlinecrypt.rst is the guide to using dm-inlinecrypt.

Signed-off-by: Linlin Zhang <[email protected]>

Author: Linlin Zhang

Documentation/admin-guide/device-mapper/dm-inlinecrypt.rst

@@ -0,0 +1,123 @@
+========
+dm-inlinecrypt
+========
+
+Device-Mapper's "inlinecrypt" target provides transparent encryption of block devices
+using the inline encryption hardware.
+
+For a more detailed description of inline encryption, see:
+https://docs.kernel.org/block/inline-encryption.html
+
+Parameters::
+
+	      <cipher> <key> <iv_offset> <device path> \
+	      <offset> [<#opt_params> <opt_params>]
+
+<cipher>
+    Encryption cipher type.
+
+    The cipher specifications format is::
+
+       cipher
+
+    Examples::
+
+       aes-xts-plain64
+
+    The cipher type corresponds to the encryption modes supported by
+    inline crypto in the block layer. Currently, only
+    BLK_ENCRYPTION_MODE_AES_256_XTS (i.e. aes-xts-plain64) is supported.
+
+<key>
+    Key used for encryption. It is encoded either as a hexadecimal number
+    or it can be passed as <key_string> prefixed with single colon
+    character (':') for keys residing in kernel keyring service.
+    You can only use key sizes that are valid for the selected cipher.
+    Note that the size in bytes of a valid key must be in bellow range.
+
+        [BLK_CRYPTO_KEY_TYPE_RAW, BLK_CRYPTO_KEY_TYPE_HW_WRAPPED]
+
+<key_string>
+    The kernel keyring key is identified by string in following format:
+    <key_size>:<key_type>:<key_description>.
+
+<key_size>
+    The encryption key size in bytes. The kernel key payload size must match
+    the value passed in <key_size>.
+
+<key_type>
+    Either 'logon', or 'trusted' kernel key type.
+
+<key_description>
+    The kernel keyring key description inlinecrypt target should look for
+    when loading key of <key_type>.
+
+<iv_offset>
+    The IV offset is a sector count that is added to the sector number
+    before creating the IV.
+
+<device path>
+    This is the device that is going to be used as backend and contains the
+    encrypted data.  You can specify it as a path like /dev/xxx or a device
+    number <major>:<minor>.
+
+<offset>
+    Starting sector within the device where the encrypted data begins.
+
+<#opt_params>
+    Number of optional parameters. If there are no optional parameters,
+    the optional parameters section can be skipped or #opt_params can be zero.
+    Otherwise #opt_params is the number of following arguments.
+
+    Example of optional parameters section:
+        allow_discards sector_size:4096 iv_large_sectors
+
+allow_discards
+    Block discard requests (a.k.a. TRIM) are passed through the inlinecrypt
+    device. The default is to ignore discard requests.
+
+    WARNING: Assess the specific security risks carefully before enabling this
+    option.  For example, allowing discards on encrypted devices may lead to
+    the leak of information about the ciphertext device (filesystem type,
+    used space etc.) if the discarded blocks can be located easily on the
+    device later.
+
+sector_size:<bytes>
+    Use <bytes> as the encryption unit instead of 512 bytes sectors.
+    This option can be in range 512 - 4096 bytes and must be power of two.
+    Virtual device will announce this size as a minimal IO and logical sector.
+
+iv_large_sectors
+    Use <sector_size>-based sector numbers for IV generation instead of
+    512-byte sectors.
+
+    For dm-inlinecrypt, this flag must be specified when <sector_size>
+    is larger than 512 bytes. The legacy 512-byte-based IV behavior is
+    not supported.
+
+    When specified, if <sector_size> is 4096 bytes, plain64 IV for the
+    second sector will be 1, and <iv_offset> must be a multiple of
+    <sector_size> (in 512-byte units).
+
+Example scripts
+===============
+Currently, dm-inlinecrypt devices must be set up directly using dmsetup.
+There is no userspace support yet to integrate dm-inlinecrypt with LUKS
+or cryptsetup. In particular, cryptsetup currently only supports
+dm-crypt, and cannot be used to create dm-inlinecrypt mappings.
+
+The following examples demonstrate how to create dm-inlinecrypt devices
+using dmsetup
+
+::
+
+	#!/bin/sh
+	# Create a inlinecrypt device using dmsetup
+	dmsetup create inlinecrypt1 --table "0 `blockdev --getsz $1` inlinecrypt aes-xts-plain64 babebabebabebabebabebabebabebabebabebabebabebabebabebabebabebabe 0 $1 0"
+
+::
+
+	#!/bin/sh
+	# Create a inlinecrypt device using dmsetup when encryption key is stored in keyring service
+	dmsetup create inlinecrypt2 --table "0 `blockdev --getsz $1` inlinecrypt aes-xts-plain64 :64:logon:fde:dminlinecrypt_test_key 0 $1 0"
+