On Wed, Apr 11, 2018 at 6:24 PM, David Howells <dhowells@xxxxxxxxxx> wrote:
> Provide a single call to allow kernel code to determine whether the system
> should be locked down, thereby disallowing various accesses that might
> allow the running kernel image to be changed, including:
>
> - /dev/mem and similar
> - Loading of unauthorised modules
> - Fiddling with MSR registers
> - Suspend to disk managed by the kernel
> - Use of device DMA
>
> Two kernel configuration options are provided:
>
> (*) CONFIG_LOCK_DOWN_KERNEL
>
> This makes lockdown available and applies it to all the points that
> need to be locked down if the mode is set. Lockdown mode can be
> enabled by providing:
>
> lockdown=1
>
> on the command line.
>
> (*) CONFIG_LOCK_DOWN_MANDATORY
>
> This forces lockdown on at compile time, overriding the command line
> option.
>
> init_lockdown() is used as a hook from which lockdown can be managed in
> future. It has to be called from arch setup code before things like ACPI
> are enabled.
>
> Note that, with the other changes in this series, if lockdown mode is
> enabled, the kernel will not be able to use certain drivers as the ability
> to manually configure hardware parameters would then be prohibited. This
> primarily applies to ISA hardware devices.
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> ---
[...]
> diff --git a/security/lock_down.c b/security/lock_down.c
> new file mode 100644
> index 000000000000..f35ffdd096ad
> --- /dev/null
> +++ b/security/lock_down.c
[...]
> +/*
> + * Lock the kernel down from very early in the arch setup. This must happen
> + * prior to things like ACPI being initialised.
> + */
Pedantic nit: I think this comment is wrong now? This function
actually just prints stuff.
> +void __init init_lockdown(void)
> +{
> +#ifdef CONFIG_LOCK_DOWN_MANDATORY
> + pr_notice("Kernel is locked down from config; see man kernel_lockdown.7\n");
> +#endif
> +}
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