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]. 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@xxxxxxxxxxxxxxxxxx/ [3] https://lore.kernel.org/lkml/1556221605.24945.3.camel@xxxxxxxxxxxxxxxxxxxxx/ [4] https://lore.kernel.org/linux-integrity/1e41f22b1f11784f1e943f32bf62034d4e054cdb.camel@xxxxxxxxxxxxxxxxxxxxx/ [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 (17): KEYS: Create static version of public_key_verify_signature integrity: Fix warning about missing prototypes integrity: Introduce a Linux keyring called machine integrity: Do not allow machine keyring updates following init X.509: Parse Basic Constraints for CA KEYS: CA link restriction integrity: restrict INTEGRITY_KEYRING_MACHINE to restrict_link_by_ca 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 integrity: store reference to machine keyring KEYS: link machine trusted keys to secondary_trusted_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 | 48 +++++++++++- 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 | 25 ++++++ 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, 287 insertions(+), 11 deletions(-) create mode 100644 security/integrity/platform_certs/machine_keyring.c base-commit: 136057256686de39cc3a07c2e39ef6bc43003ff6 -- 2.18.4
