Mike, Zone append BIOs (REQ_OP_ZONE_APPEND) always specify the start sector of the zone to be written instead of the actual location sector to write. The write location is determined by the device and returned to the host upon completion of the operation. This interface, while simple and efficient for writing into sequential zones of a zoned block device, is incompatible with the use of sector values to calculate a cypher block IV. All data written in a zone is encrypted using an IV calculated from the first sectors of the zone, but read operation will specify any sector within the zone, resulting in an IV mismatch between encryption and decryption. Reads fail in that case. Using a single sector value (e.g. the zone start sector) for all read and writes into a zone can solve this problem, but at the cost of weakening the cypher chosen by the user. Emulating zone append using regular writes would be another potential solution, but it is complex and would add a lot of overhead. Instead, to solve this problem, explicitly disable support for zone append operations in dm-crypt if the target was setup using a cypher IV mode using sector values. The null and random IV modes can still be used with zone append operations. This lack of support for zone append is exposed to the user by setting the dm-crypt target queue limit max_zone_append_sectors to 0. This change is done in patches 1 and 2. Patch 3 fixes zonefs to fall back to using regular write when max_zone_append_sectors is 0 (Note: I can take this patch through the zonefs tree. But since I have nothing else for an eventual rc8 and next cycle, you can take it too. No chance of conflict). Overall, these changes do not break user space: 1) There is no interface allowing a user to use zone append write without a file system. So applications using directly a raw dm-crypt device will continue working using regular write operations. 2) btrfs zoned support was added in 5.12. Anybody trying btrfs-zoned on top of dm-crypt would have faced the read failures already. So there are no existing deployments to preserve. Same for zonefs. For file systems, using zone append with encryption will need to be supported within the file system (e.g. fscrypt). In this case, cypher IV calculation can rely for instance on file block offsets as these are known before a zone append operation write these blocks to disk at unknown locations. Reviews and comments are very much welcome. Changes from v1: * Addressed Johannes comments by renaming the CRYPT_IV_NO_SECTORS flag to CRYPT_IV_ZONE_APPEND to avoid a double negation with !test_bit(). This also clarifies that the flag is used solely to check zone append support. * Removed btrfs patch (former patch 3) as David is taking that patch through the btrfs tree misc-next branch. * Added reviewed-by, Fixes and Cc tags. Damien Le Moal (3): dm: Introduce zone append support control dm crypt: Fix zoned block device support zonefs: fix synchronous write to sequential zone files drivers/md/dm-crypt.c | 49 ++++++++++++++++++++++++++++------- drivers/md/dm-table.c | 41 +++++++++++++++++++++++++++++ fs/zonefs/super.c | 16 +++++++++--- fs/zonefs/zonefs.h | 2 ++ include/linux/device-mapper.h | 6 +++++ 5 files changed, 101 insertions(+), 13 deletions(-) -- 2.30.2
