On Thu, 2019-06-20 at 18:19 -0700, Matthew Garrett wrote:
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2239,6 +2239,15 @@
> lockd.nlm_udpport=M [NFS] Assign UDP port.
> Format: <integer>
>
> + lockdown= [SECURITY]
> + { integrity | confidentiality }
> + Enable the kernel lockdown feature. If set to
> + integrity, kernel features that allow userland to
> + modify the running kernel are disabled. If set to
> + confidentiality, kernel features that allow userland
> + to extract confidential information from the kernel
> + are also disabled.
> +
Does "also" imply "integrity" is a prereq for "confidentiality"?
> diff --git a/security/lockdown/Kconfig b/security/lockdown/Kconfig
> new file mode 100644
> index 000000000000..431cd2b9a14e
> --- /dev/null
> +++ b/security/lockdown/Kconfig
> @@ -0,0 +1,46 @@
> +config SECURITY_LOCKDOWN_LSM
> + bool "Basic module for enforcing kernel lockdown"
> + depends on SECURITY
> + help
> + Build support for an LSM that enforces a coarse kernel lockdown
> + behaviour.
> +
> +config SECURITY_LOCKDOWN_LSM_EARLY
> + bool "Enable lockdown LSM early in init"
> + depends on SECURITY_LOCKDOWN_LSM
> + help
> + Enable the lockdown LSM early in boot. This is necessary in order
> + to ensure that lockdown enforcement can be carried out on kernel
> + boot parameters that are otherwise parsed before the security
> + subsystem is fully initialised.
> +
> +choice
> + prompt "Kernel default lockdown mode"
> + default LOCK_DOWN_KERNEL_FORCE_NONE
> + depends on SECURITY_LOCKDOWN_LSM
> + help
> + The kernel can be configured to default to differing levels of
> + lockdown.
> +
> +config LOCK_DOWN_KERNEL_FORCE_NONE
> + bool "None"
> + help
> + No lockdown functionality is enabled by default. Lockdown may be
> + enabled via the kernel commandline or /sys/kernel/security/lockdown.
> +
> +config LOCK_DOWN_KERNEL_FORCE_INTEGRITY
> + bool "Integrity"
> + help
> + The kernel runs in integrity mode by default. Features that allow
> + the kernel to be modified at runtime are disabled.
> +
> +config LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY
> + bool "Confidentiality"
> + help
> + The kernel runs in confidentiality mode by default. Features that
> + allow the kernel to be modified at runtime or that permit userland
> + code to read confidential material held inside the kernel are
> + disabled.
> +
Is there a missing dependency on LOCK_DOWN_KERNEL_FORCE_INTEGRITY
here?
> +endchoice
> +
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> new file mode 100644
> index 000000000000..1ecb2eecb245
> --- /dev/null
> +++ b/security/lockdown/lockdown.c
> +
> +static int __init lockdown_lsm_init(void)
> +{
> +#if defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY)
> + lock_kernel_down("Kernel configuration", LOCKDOWN_INTEGRITY_MAX);
> +#elif defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY)
> + lock_kernel_down("Kernel configuration", LOCKDOWN_CONFIDENTIALITY_MAX);
> +#endif
> + security_add_hooks(lockdown_hooks, ARRAY_SIZE(lockdown_hooks),
> + "lockdown");
> + return 0;
> +}
If there is a dependency on
"defined(CONFIG_LOCK_DOWN_KERNEL_FORCE_INTEGRITY" for
"CONFIG_LOCK_DOWN_KERNEL_FORCE_CONFIDENTIALITY", then the ordering
should be reversed. If there isn't a dependency of one on the other,
then replace the "elif" with "endif".
Mimi
