Re: [PATCH v7 00/17] Enroll kernel keys thru MOK

Jarkko Sakkinen
2021-11-16T16:00:41Z

On Mon, 2021-11-15 at 19:15 -0500, Eric Snowberg wrote:
> Back in 2013 Linus requested a feature to allow end-users to have the
> ability "to add their own keys and sign modules they trust". This was
> his *second* order outlined here [1]. There have been many attempts
> over the years to solve this problem, all have been rejected.  Many
> of the failed attempts loaded all preboot firmware keys into the kernel,
> including the Secure Boot keys. Many distributions carry one of these
> rejected attempts [2], [3], [4]. This series tries to solve this problem
> with a solution that takes into account all the problems brought up in
> the previous attempts.
>
> On UEFI based systems, this series introduces a new Linux kernel keyring
> containing the Machine Owner Keys (MOK) called machine. It also defines
> a new MOK variable in shim. This variable allows the end-user to decide
> if they want to load MOK keys into the machine keyring. Mimi has suggested
> that only CA keys contained within the MOK be loaded into the machine
> keyring. All other certs will load into the platform keyring instead.
>
> By default, nothing changes; MOK keys are not loaded into the machine
> keyring.  They are only loaded after the end-user makes the decision
> themselves.  The end-user would set this through mokutil using a new
> --trust-mok option [5]. This would work similar to how the kernel uses
> MOK variables to enable/disable signature validation as well as use/ignore
> the db. Any kernel operation that uses either the builtin or secondary
> trusted keys as a trust source shall also reference the new machine
> keyring as a trust source.
>
> Secure Boot keys will never be loaded into the machine keyring.  They
> will always be loaded into the platform keyring.  If an end-user wanted
> to load one, they would need to enroll it into the MOK.
>
> Steps required by the end user:
>
> Sign kernel module with user created key:
> $ /usr/src/kernels/$(uname -r)/scripts/sign-file sha512 \
>    machine_signing_key.priv machine_signing_key.x509 my_module.ko
>
> Import the key into the MOK
> $ mokutil --import machine_signing_key.x509
>
> Setup the kernel to load MOK keys into the .machine keyring
> $ mokutil --trust-mok
>
> Then reboot, the MokManager will load and ask if you want to trust the
> MOK key and enroll the MOK into the MOKList.  Afterwards the signed kernel
> module will load.
>
> I have included  a link to the mokutil [5] changes I have made to support
> this new functionality.  The shim changes have now been accepted
> upstream [6].
>
> [1] https://marc.info/?l=linux-kernel&m=136185386310140&w=2
> [2] https://lore.kernel.org/lkml/1479737095.2487.34.camel@linux.vnet.ibm.com/
> [3] https://lore.kernel.org/lkml/1556221605.24945.3.camel@HansenPartnership.com/
> [4] https://lore.kernel.org/linux-integrity/1e41f22b1f11784f1e943f32bf62034d4e054cdb.camel@HansenPartnership.com/
> [5] https://github.com/esnowberg/mokutil/tree/mokvars-v3
> [6] https://github.com/rhboot/shim/commit/4e513405b4f1641710115780d19dcec130c5208f
>
> Eric Snowberg (17):
>   integrity: Introduce a Linux keyring called machine
>   integrity: Do not allow machine keyring updates following init
>   KEYS: Create static version of public_key_verify_signature
>   X.509: Parse Basic Constraints for CA
>   KEYS: CA link restriction
>   integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca
>   integrity: Fix warning about missing prototypes
>   integrity: add new keyring handler for mok keys
>   KEYS: Rename get_builtin_and_secondary_restriction
>   KEYS: add a reference to machine keyring
>   KEYS: Introduce link restriction for machine keys
>   KEYS: integrity: change link restriction to trust the machine keyring
>   KEYS: link secondary_trusted_keys to machine trusted keys
>   integrity: store reference to machine keyring
>   efi/mokvar: move up init order
>   integrity: Trust MOK keys if MokListTrustedRT found
>   integrity: Only use machine keyring when uefi_check_trust_mok_keys is
>     true
>
>  certs/system_keyring.c                        | 44 ++++++++++-
>  crypto/asymmetric_keys/restrict.c             | 43 +++++++++++
>  crypto/asymmetric_keys/x509_cert_parser.c     |  9 +++
>  drivers/firmware/efi/mokvar-table.c           |  2 +-
>  include/crypto/public_key.h                   | 15 ++++
>  include/keys/system_keyring.h                 | 14 ++++
>  security/integrity/Kconfig                    | 12 +++
>  security/integrity/Makefile                   |  1 +
>  security/integrity/digsig.c                   | 23 +++++-
>  security/integrity/integrity.h                | 17 +++-
>  .../platform_certs/keyring_handler.c          | 18 ++++-
>  .../platform_certs/keyring_handler.h          |  5 ++
>  security/integrity/platform_certs/load_uefi.c |  4 +-
>  .../platform_certs/machine_keyring.c          | 77 +++++++++++++++++++
>  14 files changed, 273 insertions(+), 11 deletions(-)
>  create mode 100644 security/integrity/platform_certs/machine_keyring.c
>
>
> base-commit: fa55b7dcdc43c1aa1ba12bca9d2dd4318c2a0dbf

Does shim have the necessary features in a release?

/Jarkko