Re: [PATCH v5 01/12] integrity: Introduce a Linux keyring called machine

Mimi Zohar
2021-09-09T15:20:35Z

On Tue, 2021-09-07 at 12:00 -0400, Eric Snowberg wrote:
> Many UEFI Linux distributions boot using shim. The UEFI shim provides
> what is called Machine Owner Keys (MOK). Shim uses both the UEFI Secure
> Boot DB and MOK keys to validate the next step in the boot chain. The
> MOK facility can be used to import user generated keys. These keys can
> be used to sign an end-users development kernel build. When Linux
> boots, both UEFI Secure Boot DB and MOK keys get loaded in the Linux
> .platform keyring.
>
> Add a new Linux keyring called machine. This keyring shall contain just

^Define

> MOK CA keys and not the remaining keys in the platform keyring. This new
> machine keyring will be used in follow on patches. Unlike keys in the
> platform keyring, keys contained in the machine keyring will be trusted
> within the kernel if the end-user has chosen to do so.
>
> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
> ---
> v1: Initial version
> v2: Removed destory keyring code
> v3: Unmodified from v2
> v4: Add Kconfig, merged in "integrity: add add_to_mok_keyring"
> v5: Rename to machine keyring
> ---
> security/integrity/Kconfig | 11 +++++
> security/integrity/Makefile | 1 +
> security/integrity/digsig.c | 1 +
> security/integrity/integrity.h | 12 +++++-
> .../platform_certs/machine_keyring.c | 42 +++++++++++++++++++
> 5 files changed, 66 insertions(+), 1 deletion(-)
> create mode 100644 security/integrity/platform_certs/machine_keyring.c
>
> diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig
> index 71f0177e8716..52193b86768a 100644
> --- a/security/integrity/Kconfig
> +++ b/security/integrity/Kconfig
> @@ -62,6 +62,17 @@ config INTEGRITY_PLATFORM_KEYRING
> provided by the platform for verifying the kexec'ed kerned image
> and, possibly, the initramfs signature.
>
> +config INTEGRITY_MACHINE_KEYRING
> + bool "Provide a keyring to which CA Machine Owner Keys may be added"
> + depends on SECONDARY_TRUSTED_KEYRING
> + depends on INTEGRITY_ASYMMETRIC_KEYS
> + depends on SYSTEM_BLACKLIST_KEYRING
> + help
> + If set, provide a keyring to which CA Machine Owner Keys (MOK) may
> + be added. This keyring shall contain just CA MOK keys. Unlike keys
> + in the platform keyring, keys contained in the .machine keyring will
> + be trusted within the kernel.

No sense in creating the ".machine" keyring, unless it is possible to
safely load CA certificates on it. At least for the time being, this
should also be dependent on EFI.

<snip>

> +++ b/security/integrity/platform_certs/machine_keyring.c
> @@ -0,0 +1,42 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Machine keyring routines.
> + *
> + * Copyright (c) 2021, Oracle and/or its affiliates.
> + */
> +
> +#include "../integrity.h"
> +
> +static __init int machine_keyring_init(void)
> +{
> + int rc;
> +
> + rc = integrity_init_keyring(INTEGRITY_KEYRING_MACHINE);
> + if (rc)
> + return rc;
> +
> + pr_notice("Machine keyring initialized\n");
> + return 0;
> +}
> +device_initcall(machine_keyring_init);
> +
> +void __init add_to_machine_keyring(const char *source, const void *data, size_t len)
> +{
> + key_perm_t perm;
> + int rc;
> +
> + perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW;
> + rc = integrity_load_cert(INTEGRITY_KEYRING_MACHINE, source, data, len, perm);
> +
> + /*
> + * Some MOKList keys may not pass the machine keyring restrictions.
> + * If the restriction check does not pass and the platform keyring
> + * is configured, try to add it into that keyring instead.
> + */
> + if (rc)

In addition to the comment, also test to see if the ".platform" keyring
is configured.

thanks,

Mimi

> + rc = integrity_load_cert(INTEGRITY_KEYRING_PLATFORM, source,
> + data, len, perm);
> +
> + if (rc)
> + pr_info("Error adding keys to machine keyring %s\n", source);
> +}