On Sat, 2021-01-30 at 19:53 +0200, Jarkko Sakkinen wrote:

On Thu, 2021-01-28 at 18:31 +0100, Ahmad Fatoum wrote:

quoted

Hello,

I've been looking into how a migration to using trusted/encrypted
keys would look like (particularly with dm-crypt).

Currently, it seems the the only way is to re-encrypt the
partitions because trusted/encrypted keys always generate their
payloads from RNG.

If instead there was a key command to initialize a new
trusted/encrypted key with a user provided value, users could use
whatever mechanism they used beforehand to get a plaintext key and
use that to initialize a new trusted/encrypted key. From there on,
the key will be like any other trusted/encrypted key and not be
disclosed again to userspace.

What are your thoughts on this? Would an API like

  keyctl add trusted dmcrypt-key 'set <content>' # user-supplied
content

be acceptable?

Maybe it's the lack of knowledge with dm-crypt, but why this would be
useful? Just want to understand the bottleneck, that's all.

There was a recent patch to dm-crypt to add encrypted key support:
27f5411a718c ("dm crypt: support using encrypted keys").  The
implementation requires the actual disk encryption master key to be in
the payload.  Most people don't want to change that key because it
involves re-encrypting the whole disk (usually what people mean when
they say "key" for dm-crypt is a passphrase that decrypts this master
key from a keyslot in the metadata, which is why you can change your
passphrase without changing the underlying encryption).

However, once we get the trusted key rework upstream, we do have a
solution:  The key format becomes interoperable with the
openssl_tpm2_engine and we can now do seal_tpm2_data on any payload and
the kernel will accept it.

James