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SubjectRe: [PATCH 02/27] Add a SysRq option to lift kernel lockdown
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On 10/19/17 07:50, David Howells wrote:
> From: Kyle McMartin <kyle@redhat.com>
>
> Make an option to provide a sysrq key that will lift the kernel lockdown,
> thereby allowing the running kernel image to be accessed and modified.
>
> On x86_64 this is triggered with SysRq+x, but this key may not be available
> on all arches, so it is set by setting LOCKDOWN_LIFT_KEY in asm/setup.h.
>
> Signed-off-by: Kyle McMartin <kyle@redhat.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: x86@kernel.org
> ---
>
> arch/x86/include/asm/setup.h | 2 ++
> drivers/input/misc/uinput.c | 1 +
> drivers/tty/sysrq.c | 19 +++++++++++------
> include/linux/input.h | 5 ++++
> include/linux/sysrq.h | 8 ++++++-
> kernel/debug/kdb/kdb_main.c | 2 +-
> security/Kconfig | 15 +++++++++++++
> security/lock_down.c | 48 ++++++++++++++++++++++++++++++++++++++++++
> 8 files changed, 92 insertions(+), 8 deletions(-)

> diff --git a/security/Kconfig b/security/Kconfig
> index 8e01fd59ae7e..4be6be71e075 100644
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -213,6 +213,21 @@ config LOCK_DOWN_KERNEL
> turns off various features that might otherwise allow access to the
> kernel image (eg. setting MSR registers).
>
> +config ALLOW_LOCKDOWN_LIFT
> + bool
> + help
> + Allow the lockdown on a kernel to be lifted, thereby restoring the
> + ability of userspace to access the kernel image (eg. by SysRq+x under

how about: on

> + x86).
> +
> +config ALLOW_LOCKDOWN_LIFT_BY_SYSRQ
> + bool "Allow the kernel lockdown to be lifted by SysRq"
> + depends on MAGIC_SYSRQ
> + help
> + Allow the lockdown on a kernel to be lifted, by pressing a SysRq key
> + combination on a wired keyboard.
> +
> +
> source security/selinux/Kconfig
> source security/smack/Kconfig
> source security/tomoyo/Kconfig
> diff --git a/security/lock_down.c b/security/lock_down.c
> index d8595c0e6673..f71118c340d2 100644
> --- a/security/lock_down.c
> +++ b/security/lock_down.c


> +
> +/*
> + * Allow lockdown to be lifted by pressing something like SysRq+x (and not by
> + * echoing the appropriate letter into the sysrq-trigger file).
> + */
> +#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT_BY_KEY

is that the same as: CONFIG_ALLOW_LOCKDOWN_LIFT_BY_SYSRQ ?
tested?

> +
> +static void sysrq_handle_lockdown_lift(int key)
> +{
> + if (kernel_locked_down)
> + lift_kernel_lockdown();
> +}
> +
> +static struct sysrq_key_op lockdown_lift_sysrq_op = {
> + .handler = sysrq_handle_lockdown_lift,
> + .help_msg = "unSB(x)",
> + .action_msg = "Disabling Secure Boot restrictions",
> + .enable_mask = SYSRQ_DISABLE_USERSPACE,
> +};
> +
> +static int __init lockdown_lift_sysrq(void)
> +{
> + if (kernel_locked_down) {
> + lockdown_lift_sysrq_op.help_msg[5] = LOCKDOWN_LIFT_KEY;
> + register_sysrq_key(LOCKDOWN_LIFT_KEY, &lockdown_lift_sysrq_op);
> + }
> + return 0;
> +}
> +
> +late_initcall(lockdown_lift_sysrq);
> +
> +#endif /* CONFIG_ALLOW_LOCKDOWN_LIFT_BY_KEY */

BY_SYSRQ


--
~Randy

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