tree 35ccce8f0415ae932faa158fdace9e342789b15a
parent e13617100d40079b79863ed504c79e7ef22b084e
author Satya Tangirala <satyat@google.com> 1614580327 -0800
committer Satya Tangirala <satyat@google.com> 1617840961 +0000

Make vold use keystore2 instead of keymaster

Make vold use keystore2 for all its operations instead of directly using
keymaster. This way, we won't have any clients that bypass keystore2,
and we'll no longer need to reserve a keymaster operation for vold.

Note that we now hardcode "SecurityLevel::TRUSTED_ENVIRONMENT" (TEE)
when talking to Keystore2 since Keystore2 only allows TEE and STRONGBOX.
Keystore2 presents any SOFTWARE implementation as a TEE to callers when
no "real" TEE is present. As far as storage encryption is concerned,
there's no advantage to using a STRONGBOX when a "real" TEE is present,
and a STRONGBOX can't be present if a "real" TEE isn't, so asking
Keystore2 for a TEE is the best we can do in any situation.

The difference in behaviour only really affects the full disk encryption
code in cryptfs.cpp, which used to explicitly check that the keymaster
device is a "real" TEE (as opposed to a SOFTWARE implementation) before
using it (it can no longer do so since Keystore2 doesn't provide a way
to do this).

A little code history digging (7c49ab0a0b in particular) shows that
cryptfs.cpp cared about two things when using a keymaster.
 - 1) that the keys generated by the keymaster were "standalone" keys -
      i.e. that the keymaster could operate on those keys without
      requiring /data or any other service to be available.
 - 2) that the keymaster was a non-SOFTWARE implementation so that things
      would still work in case a "real" TEE keymaster was ever somehow
      added to the device after first boot.

Today, all "real" TEE keymasters always generate "standalone" keys, and
a TEE has been required in Android devices since at least Android N. The
only two exceptions are Goldfish and ARC++, which have SOFTWARE
keymasters, but both those keymasters also generate "standalone" keys.

We're also no longer worried about possibly adding a "real" TEE KM to
either of those devices after first boot. So there's no longer a reason
cryptfs.cpp can't use the SOFTWARE keymaster on those devices.

There's also already an upgrade path in place (see
test_mount_encrypted_fs() in cryptfs.cpp) to upgrade the kdf that's
being used once a TEE keymaster is added to the device. So it's safe for
cryptfs.cpp to ask for a TEE keymaster from Keystore2 and use it
blindly, without checking whether or not it's a "real" TEE, which is why
Keymaster::isSecure() just returns true now. A future patch will remove
that function and simplify its callers.

Bug: 181910578
Test: cuttlefish and bramble boot. Adding, switching between, stopping
      and removing users work.
Change-Id: Iaebfef082eca0da8a305043fafb6d85e5de14cf8