On 3/6/19 3:58 PM, Matthew Garrett wrote: > From: Kyle McMartin <[email protected]> > > 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.
You still need to document this in Documentation/admin-guide/sysrq.rst, like I mentioned last week. > On x86 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. > Since this macro must be defined in an arch to be able to use this facility > for that arch, the Kconfig option is restricted to arches that support it. > > Signed-off-by: Kyle McMartin <[email protected]> > Signed-off-by: David Howells <[email protected]> > cc: [email protected] > Signed-off-by: Matthew Garrett <[email protected]> > --- > 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 | 9 +++++++ > security/lock_down.c | 47 ++++++++++++++++++++++++++++++++++++ > 8 files changed, 85 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h > index ed8ec011a9fd..8daf633a5347 100644 > --- a/arch/x86/include/asm/setup.h > +++ b/arch/x86/include/asm/setup.h > @@ -9,6 +9,8 @@ > #include <linux/linkage.h> > #include <asm/page_types.h> > > +#define LOCKDOWN_LIFT_KEY 'x' > + > #ifdef __i386__ > > #include <linux/pfn.h> > diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c > index 8ec483e8688b..c2a77dc73fa0 100644 > --- a/drivers/input/misc/uinput.c > +++ b/drivers/input/misc/uinput.c > @@ -365,6 +365,7 @@ static int uinput_create_device(struct uinput_device > *udev) > dev->flush = uinput_dev_flush; > } > > + dev->flags |= INPUTDEV_FLAGS_SYNTHETIC; > dev->event = uinput_dev_event; > > input_set_drvdata(udev->dev, udev); > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c > index 1f03078ec352..0a05d336008e 100644 > --- a/drivers/tty/sysrq.c > +++ b/drivers/tty/sysrq.c > @@ -480,6 +480,7 @@ 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 */ > /* y: May be registered on sparc64 for global register dump */ > NULL, /* y */ > @@ -523,7 +524,7 @@ 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; > @@ -543,11 +544,15 @@ 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); > @@ -579,7 +584,7 @@ void __handle_sysrq(int key, bool check_mask) > void handle_sysrq(int key) > { > if (sysrq_on()) > - __handle_sysrq(key, true); > + __handle_sysrq(key, SYSRQ_FROM_KERNEL); > } > EXPORT_SYMBOL(handle_sysrq); > > @@ -659,7 +664,7 @@ static void sysrq_do_reset(struct timer_list *t) > static void sysrq_handle_reset_request(struct sysrq_state *state) > { > if (state->reset_requested) > - __handle_sysrq(sysrq_xlate[KEY_B], false); > + __handle_sysrq(sysrq_xlate[KEY_B], SYSRQ_FROM_KERNEL); > > if (sysrq_reset_downtime_ms) > mod_timer(&state->keyreset_timer, > @@ -812,8 +817,10 @@ static bool sysrq_handle_keypress(struct sysrq_state > *sysrq, > > default: > if (sysrq->active && value && value != 2) { > + int from = sysrq->handle.dev->flags & > INPUTDEV_FLAGS_SYNTHETIC ? > + SYSRQ_FROM_SYNTHETIC : 0; > sysrq->need_reinject = false; > - __handle_sysrq(sysrq_xlate[code], true); > + __handle_sysrq(sysrq_xlate[code], from); > } > break; > } > @@ -1096,7 +1103,7 @@ static ssize_t write_sysrq_trigger(struct file *file, > const char __user *buf, > > if (get_user(c, buf)) > return -EFAULT; > - __handle_sysrq(c, false); > + __handle_sysrq(c, SYSRQ_FROM_PROC); > } > > return count; > diff --git a/include/linux/input.h b/include/linux/input.h > index 7c7516eb7d76..38cd0ea72c37 100644 > --- a/include/linux/input.h > +++ b/include/linux/input.h > @@ -42,6 +42,7 @@ struct input_value { > * @phys: physical path to the device in the system hierarchy > * @uniq: unique identification code for the device (if device has it) > * @id: id of the device (struct input_id) > + * @flags: input device flags (SYNTHETIC, etc.) > * @propbit: bitmap of device properties and quirks > * @evbit: bitmap of types of events supported by the device (EV_KEY, > * EV_REL, etc.) > @@ -124,6 +125,8 @@ struct input_dev { > const char *uniq; > struct input_id id; > > + unsigned int flags; > + > unsigned long propbit[BITS_TO_LONGS(INPUT_PROP_CNT)]; > > unsigned long evbit[BITS_TO_LONGS(EV_CNT)]; > @@ -190,6 +193,8 @@ struct input_dev { > }; > #define to_input_dev(d) container_of(d, struct input_dev, dev) > > +#define INPUTDEV_FLAGS_SYNTHETIC 0x000000001 > + > /* > * Verify that we are in sync with input_device_id mod_devicetable.h #defines > */ > diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h > index 8c71874e8485..7de1f08b60a9 100644 > --- a/include/linux/sysrq.h > +++ b/include/linux/sysrq.h > @@ -29,6 +29,8 @@ > #define SYSRQ_ENABLE_BOOT 0x0080 > #define SYSRQ_ENABLE_RTNICE 0x0100 > > +#define SYSRQ_DISABLE_USERSPACE 0x00010000 > + > struct sysrq_key_op { > void (*handler)(int); > char *help_msg; > @@ -43,8 +45,12 @@ struct sysrq_key_op { > * are available -- else NULL's). > */ > > +#define SYSRQ_FROM_KERNEL 0x0001 > +#define SYSRQ_FROM_PROC 0x0002 > +#define SYSRQ_FROM_SYNTHETIC 0x0004 > + > void handle_sysrq(int key); > -void __handle_sysrq(int key, bool check_mask); > +void __handle_sysrq(int key, unsigned int from); > int register_sysrq_key(int key, struct sysrq_key_op *op); > int unregister_sysrq_key(int key, struct sysrq_key_op *op); > struct sysrq_key_op *__sysrq_get_key_op(int key); > diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c > index 82a3b32a7cfc..efee1abf5e8e 100644 > --- a/kernel/debug/kdb/kdb_main.c > +++ b/kernel/debug/kdb/kdb_main.c > @@ -1981,7 +1981,7 @@ static int kdb_sr(int argc, const char **argv) > return KDB_ARGCOUNT; > > kdb_trap_printk++; > - __handle_sysrq(*argv[1], check_mask); > + __handle_sysrq(*argv[1], check_mask ? SYSRQ_FROM_KERNEL : 0); > kdb_trap_printk--; > > return 0; > diff --git a/security/Kconfig b/security/Kconfig > index 47dc3403b5af..8346eb883336 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -244,6 +244,15 @@ config LOCK_DOWN_KERNEL_FORCE > help > Enable the kernel lock down functionality automatically at boot. > > +config ALLOW_LOCKDOWN_LIFT_BY_SYSRQ > + bool "Allow the kernel lockdown to be lifted by SysRq" > + depends on LOCK_DOWN_KERNEL > + depends on MAGIC_SYSRQ > + depends on X86 > + 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 13a8228c1034..cfbc2c39712b 100644 > --- a/security/lock_down.c > +++ b/security/lock_down.c > @@ -11,8 +11,14 @@ > > #include <linux/security.h> > #include <linux/export.h> > +#include <linux/sysrq.h> > +#include <asm/setup.h> > > +#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT_BY_SYSRQ > +static __read_mostly bool kernel_locked_down; > +#else > static __ro_after_init bool kernel_locked_down; > +#endif > > /* > * Put the kernel into lock-down mode. > @@ -57,3 +63,44 @@ bool __kernel_is_locked_down(const char *what, bool first) > return kernel_locked_down; > } > EXPORT_SYMBOL(__kernel_is_locked_down); > + > +#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT_BY_SYSRQ > + > +/* > + * Take the kernel out of lockdown mode. > + */ > +static void lift_kernel_lockdown(void) > +{ > + pr_notice("Lifting lockdown\n"); > + kernel_locked_down = false; > +} > + > +/* > + * Allow lockdown to be lifted by pressing something like SysRq+x (and not by > + * echoing the appropriate letter into the sysrq-trigger file). > + */ > +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_SYSRQ */ > -- ~Randy
