Re: [RFC PATCH v2 0/5] Support for hardware-wrapped inline encryption keys

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Sep 16, 2021 at 10:49:23AM -0700, Eric Biggers wrote:
> [ NOTE: this patchset is an RFC that isn't ready for merging yet because
>   it doesn't yet include the vendor-specific UFS or eMMC driver changes
>   needed to actually use the feature.  I.e., this patchset isn't
>   sufficient to actually use hardware-wrapped keys with upstream yet.
> 
>   For context, hardware-wrapped key support has been out-of-tree in the
>   Android kernels since early last year; upstreaming has been blocked on
>   hardware availability and support.  However, an SoC that supports this
>   feature (SM8350, a.k.a. Qualcomm Snapdragon 888) finally has been
>   publicly released and had basic SoC support upstreamed.  Also, some
>   other hardware will support the same feature soon.  So, things should
>   be progressing soon.  So while the driver changes are gotten into an
>   upstream-ready form, I wanted to get things started and give people a
>   chance to give early feedback on the plan for how the kernel will
>   support this type of hardware.]
> 
> This patchset adds framework-level support (i.e., block and fscrypt
> support) for hardware-wrapped keys when the inline encryption hardware
> supports them.  Hardware-wrapped keys are inline encryption keys that
> are wrapped (encrypted) by a key internal to the hardware.  Except at
> initial unlocking time, the wrapping key is an ephemeral, per-boot key.
> Hardware-wrapped keys can only be unwrapped (decrypted) by the hardware,
> e.g. when a key is programmed into a keyslot.  They are never visible to
> software in raw form, except optionally during key generation (the
> hardware supports importing keys as well as generating keys itself).
> 
> This feature protects the encryption keys from read-only compromises of
> kernel memory, such as that which can occur during a cold boot attack.
> It does this without limiting the number of keys that can be used, as
> would be the case with solutions that didn't use key wrapping.
> 
> The kernel changes to support this feature basically consist of changes
> to blk-crypto to allow a blk_crypto_key to be hardware-wrapped and to
> allow storage drivers to support hardware-wrapped keys, new block device
> ioctls for creating and preparing hardware-wrapped keys, and changes to
> fscrypt to allow the fscrypt master keys to be hardware-wrapped.
> 
> For full details, see the individual patches, especially the detailed
> documentation they add to Documentation/block/inline-encryption.rst and
> Documentation/filesystems/fscrypt.rst.
> 
> This patchset is organized as follows:
> 
> - Patch 1 adds the block support and documentation, excluding the ioctls
>   needed to get a key ready to be used in the first place.
> 
> - Patch 2 adds new block device ioctls for creating and preparing
>   hardware-wrapped keys.
> 
> - Patches 3-4 clean up the fscrypt documentation and key validation
>   logic.  These aren't specific to hardware-wrapped keys per se, so
>   these don't need to wait for the rest of the patches.
> 
> - Patch 5 adds the fscrypt support and documentation.
> 
> This patchset applies to v5.15-rc1 plus my other patchset
> "[PATCH v2 0/4] blk-crypto cleanups".  It can also be retrieved from tag
> "wrapped-keys-v2" of
> https://git.kernel.org/pub/scm/fs/fscrypt/fscrypt.git.

I'd greatly appreciate any feedback on this patch series; I don't know whether
silence means everyone likes this, or everyone hates this, or no one cares :-)
(Or maybe no one is interested until driver changes are included?)

- Eric