Re: [PATCH v1 2/3] dm-inlinecrypt: add target for inline block device encryption

[Eric Biggers <ebiggers@kernel.org>]

On Wed, Mar 04, 2026 at 04:17:27AM -0800, Linlin Zhang wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> Add a new device-mapper target "dm-inlinecrypt" that is similar to
> dm-crypt but uses the blk-crypto API instead of the regular crypto API.
> This allows it to take advantage of inline encryption hardware such as
> that commonly built into UFS host controllers.
> 
> The table syntax matches dm-crypt's, but for now only a stripped-down
> set of parameters is supported.  For example, for now AES-256-XTS is the
> only supported cipher.
> 
> dm-inlinecrypt is based on Android's dm-default-key with the
> controversial passthrough support removed.  Note that due to the removal
> of passthrough support, use of dm-inlinecrypt in combination with
> fscrypt causes double encryption of file contents (similar to dm-crypt +
> fscrypt), with the fscrypt layer not being able to use the inline
> encryption hardware.  This makes dm-inlinecrypt unusable on systems such
> as Android that use fscrypt and where a more optimized approach is
> needed.  It is however suitable as a replacement for dm-crypt.
> 
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> Signed-off-by: Linlin Zhang <linlin.zhang@oss.qualcomm.com>

I don't think it's plausible that this new patch was actually tested.
The version I sent in 2024 was tested at the time
(https://lore.kernel.org/r/20241016232748.134211-3-ebiggers@kernel.org/),
but I see at least two things that would make this new patch not work.

First, the call to blk_crypto_init_key() will always fail, since it's
being passed BLK_CRYPTO_KEY_TYPE_HW_WRAPPED but using a 64-byte raw key.

It needs to be BLK_CRYPTO_KEY_TYPE_RAW.  (BLK_CRYPTO_KEY_TYPE_HW_WRAPPED
support would make sense to add as an extra feature, once the basic raw
key support is working.  Note that when I sent the first version of this
patch, support for wrapped keys was not yet upstream at all.)

Second, since v7.0-rc1, submitters of bios don't automatically get
blk-crypto-fallback support; they need to request it explicitly.  So,
this patch will not work with blk-crypto-fallback anymore.

If you'd like to continue work on this patch, it might be helpful to
check the latest version of dm-default-key.c in "android-mainline"
(https://android.googlesource.com/kernel/common/+/android-mainline/drivers/md/dm-default-key.c)
and resynchronize this patch with it.  It already has the code to
correctly support both key types and blk-crypto-fallback, for example.

Either way, this patch also needs to be re-tested with the latest
upstream kernel, which doesn't seem to have happened unfortunately.

- Eric