Re: [PATCH v10 0/8] Enroll kernel keys thru MOK

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Jan 25, 2022 at 09:58:26PM -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. 
> 
> 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.
> 
> Unlike previous versions of this patch set, IMA support has been removed
> to simplify the series. After acceptance, a follow-on series will add IMA 
> support.
> 
> 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].
> 
> Upstream shim is located here [7], the build instructions are here [8].
> TLDR:
> 
> $ git clone --recurse-submodules https://github.com/rhboot/shim
> $ cd shim
> $ make
> 
> After building shim, move shimx64.efi and mmx64.efi to the vendor or 
> distribution specific directory on your EFI System Partition (assuming
> you are building on x86). The instructions above are the minimal
> steps needed to build shim to test this feature. It is assumed
> Secure Boot shall not be enabled for this testing. To do testing
> with Secure Boot enabled, all steps in the build instructions [8]
> must be followed.
> 
> Instructions for building mokutil (including the new changes):
> 
> $ git clone -b mokvars-v3 https://github.com/esnowberg/mokutil.git
> $ cd mokutil/
> $ ./autogen.sh
> $ make
> 
> [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
> [7] https://github.com/rhboot/shim
> [8] https://github.com/rhboot/shim/blob/main/BUILDING
> 
> Eric Snowberg (8):
>   integrity: Fix warning about missing prototypes
>   integrity: Introduce a Linux keyring called machine
>   integrity: add new keyring handler for mok keys
>   KEYS: store reference to machine keyring
>   KEYS: Introduce link restriction for machine keys
>   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 ++++++++++-
>  drivers/firmware/efi/mokvar-table.c           |  2 +-
>  include/keys/system_keyring.h                 | 14 ++++
>  security/integrity/Kconfig                    | 13 ++++
>  security/integrity/Makefile                   |  1 +
>  security/integrity/digsig.c                   | 15 +++-
>  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 +++++++++++++++++++
>  11 files changed, 202 insertions(+), 8 deletions(-)
>  create mode 100644 security/integrity/platform_certs/machine_keyring.c
> 
> 
> base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07
> -- 
> 2.18.4
> 

Thank you. I'll pick these soon. Is there any objections?

/Jarkko