Hi,
On Wed, May 24, 2017 at 03:46:03PM +0100, David Howells wrote:
> From: Kyle McMartin <kyle@xxxxxxxxxx>
>
> Make sysrq+x exit secure boot mode on x86_64, thereby allowing the running
> kernel image to be modified. This lifts the lockdown.
>
> Signed-off-by: Kyle McMartin <kyle@xxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: x86@xxxxxxxxxx
> ---
>
> arch/x86/include/asm/efi.h | 2 ++
> drivers/firmware/efi/Kconfig | 10 ++++++++++
> drivers/firmware/efi/secureboot.c | 37 +++++++++++++++++++++++++++++++++++++
> 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 +-
> 8 files changed, 76 insertions(+), 8 deletions(-)
>
[...snip]
> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
> index 3ffc1ce29023..8b766dbad6dd 100644
> --- a/drivers/tty/sysrq.c
> +++ b/drivers/tty/sysrq.c
> @@ -481,6 +481,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = {
> /* x: May be registered on mips for TLB dump */
> /* x: May be registered on ppc/powerpc for xmon */
> /* x: May be registered on sparc64 for global PMU dump */
> + /* x: May be registered on x86_64 for disabling secure boot */
> NULL, /* x */
I suggest that add this key to the "What are the 'command' keys?"
session in Documentation/admin-guide/sysrq.rst.
> /* y: May be registered on sparc64 for global register dump */
> NULL, /* y */
> @@ -524,7 +525,7 @@ static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
> sysrq_key_table[i] = op_p;
> }
>
> -void __handle_sysrq(int key, bool check_mask)
> +void __handle_sysrq(int key, unsigned int from)
> {
> struct sysrq_key_op *op_p;
> int orig_log_level;
> @@ -544,11 +545,15 @@ void __handle_sysrq(int key, bool check_mask)
>
> op_p = __sysrq_get_key_op(key);
> if (op_p) {
> + /* Ban synthetic events from some sysrq functionality */
> + if ((from == SYSRQ_FROM_PROC || from == SYSRQ_FROM_SYNTHETIC) &&
> + op_p->enable_mask & SYSRQ_DISABLE_USERSPACE)
> + printk("This sysrq operation is disabled from userspace.\n");
> /*
> * Should we check for enabled operations (/proc/sysrq-trigger
> * should not) and is the invoked operation enabled?
> */
> - if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
> + if (from == SYSRQ_FROM_KERNEL || sysrq_on_mask(op_p->enable_mask)) {
> pr_cont("%s\n", op_p->action_msg);
> console_loglevel = orig_log_level;
> op_p->handler(key);
Looking at sysrq_on_mask():
static bool sysrq_on_mask(int mask)
{
return sysrq_always_enabled ||
sysrq_enabled == 1 ||
(sysrq_enabled & mask);
}
The SYSRQ_DISABLE_USERSPACE can be ignored by sysrq_always_enabled or
sysrq_enabled (the default value is CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x1).
Kernel should checks the locked down flag here when secure boot ON. Will we
have another lock down patch against this? Or I missed something?
Thanks a lot!
Joey Lee
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