From 8f0009a225171cc1b76a6b443de5137b26e1374b Mon Sep 17 00:00:00 2001
From: Milan Broz <gmazyland@gmail.com>
Date: Thu, 16 Mar 2017 15:39:44 +0100
Subject: dm crypt: optionally support larger encryption sector size

Add  optional "sector_size"  parameter that specifies encryption sector
size (atomic unit of block device encryption).

Parameter can be in range 512 - 4096 bytes and must be power of two.
For compatibility reasons, the maximal IO must fit into the page limit,
so the limit is set to the minimal page size possible (4096 bytes).

NOTE: this device cannot yet be handled by cryptsetup if this parameter
is set.

IV for the sector is calculated from the 512 bytes sector offset unless
the iv_large_sectors option is used.

Test script using dmsetup:

  DEV="/dev/sdb"
  DEV_SIZE=$(blockdev --getsz $DEV)
  KEY="9c1185a5c5e9fc54612808977ee8f548b2258d31ddadef707ba62c166051b9e3cd0294c27515f2bccee924e8823ca6e124b8fc3167ed478bca702babe4e130ac"
  BLOCK_SIZE=4096

  # dmsetup create test_crypt --table "0 $DEV_SIZE crypt aes-xts-plain64 $KEY 0 $DEV 0 1 sector_size:$BLOCK_SIZE"
  # dmsetup table --showkeys test_crypt

Signed-off-by: Milan Broz <gmazyland@gmail.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 Documentation/device-mapper/dm-crypt.txt | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'Documentation/device-mapper')

diff --git a/Documentation/device-mapper/dm-crypt.txt b/Documentation/device-mapper/dm-crypt.txt
index 8140b71f3c54..3b3e1de21c9c 100644
--- a/Documentation/device-mapper/dm-crypt.txt
+++ b/Documentation/device-mapper/dm-crypt.txt
@@ -122,6 +122,20 @@ integrity:<bytes>:<type>
     integrity for the encrypted device. The additional space is then
     used for storing authentication tag (and persistent IV if needed).
 
+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
+   IV generators will use sector number counted in <sector_size> units
+   instead of default 512 bytes sectors.
+
+   For example, if <sector_size> is 4096 bytes, plain64 IV for the second
+   sector will be 8 (without flag) and 1 if iv_large_sectors is present.
+   The <iv_offset> must be multiple of <sector_size> (in 512 bytes units)
+   if this flag is specified.
+
 Example scripts
 ===============
 LUKS (Linux Unified Key Setup) is now the preferred way to set up disk
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