[PATCH 5/5] Add a sysrq option to exit secure boot mode

[David Howells <dhowells@redhat.com>]

From: Kyle McMartin <kyle@redhat.com>

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@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: x86@kernel.org
---

 arch/x86/include/asm/efi.h         |    2 ++
 drivers/firmware/efi/Kconfig       |   10 ++++++++++
 drivers/firmware/efi/secure_boot.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(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 2f77bcefe6b4..e86a2fa9af86 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -31,6 +31,8 @@
 
 #define ARCH_EFI_IRQ_FLAGS_MASK	X86_EFLAGS_IF
 
+#define EFI_SECURE_BOOT_EXIT_KEY 'x'
+
 #ifdef CONFIG_X86_32
 
 extern unsigned long asmlinkage efi_call_phys(void *, ...);
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 6da8345d8c49..0979716589be 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -108,6 +108,16 @@ config EFI_SECURE_BOOT
 	  - Loading unsigned modules
 	  - Kexec'ing unsigned images
 
+config EFI_ALLOW_SECURE_BOOT_EXIT
+	def_bool n
+	depends on EFI_SECURE_BOOT && MAGIC_SYSRQ
+	select ALLOW_LOCKDOWN_LIFT
+	prompt "Allow secure boot mode to be exited with SysRq+x on a keyboard"
+	---help---
+	  Allow secure boot mode to be exited and the kernel lockdown lifted by
+	  typing SysRq+x on a keyboard attached to the system (not permitted
+	  through procfs).
+
 config EFI_ARMSTUB
 	bool
 
diff --git a/drivers/firmware/efi/secure_boot.c b/drivers/firmware/efi/secure_boot.c
index 7292a3b832e3..be624a16996e 100644
--- a/drivers/firmware/efi/secure_boot.c
+++ b/drivers/firmware/efi/secure_boot.c
@@ -13,6 +13,8 @@
 #include <linux/kernel.h>
 #include <linux/printk.h>
 #include <linux/security.h>
+#include <linux/sysrq.h>
+#include <asm/efi.h>
 
 /*
  * Decide what to do when UEFI secure boot mode is enabled.
@@ -41,3 +43,38 @@ void __init efi_set_secure_boot(enum efi_secureboot_mode mode)
 		}
 	}
 }
+
+/*
+ * Allow secure boot to be lifted by pressing something like SysRq+x (and not
+ * by echoing the appropriate letter into the sysrq-trigger file).
+ */
+#ifdef CONFIG_EFI_ALLOW_SECURE_BOOT_EXIT
+
+static void sysrq_handle_secure_boot(int key)
+{
+	if (!efi_enabled(EFI_SECURE_BOOT))
+		return;
+
+	pr_info("Secure boot disabled\n");
+	lift_kernel_lockdown();
+}
+
+static struct sysrq_key_op secure_boot_sysrq_op = {
+	.handler	= sysrq_handle_secure_boot,
+	.help_msg	= "unSB(x)",
+	.action_msg	= "Disabling Secure Boot restrictions",
+	.enable_mask	= SYSRQ_DISABLE_USERSPACE,
+};
+
+static int __init efi_secure_boot_sysrq(void)
+{
+	if (efi_enabled(EFI_SECURE_BOOT)) {
+		secure_boot_sysrq_op.help_msg[5] = EFI_SECURE_BOOT_EXIT_KEY;
+		register_sysrq_key(EFI_SECURE_BOOT_EXIT_KEY, &secure_boot_sysrq_op);
+	}
+	return 0;
+}
+
+late_initcall(efi_secure_boot_sysrq);
+
+#endif /* CONFIG_EFI_ALLOW_SECURE_BOOT_EXIT */
diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 022be0e22eba..4a054a564636 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -387,6 +387,7 @@ static int uinput_allocate_device(struct uinput_device *udev)
 	if (!udev->dev)
 		return -ENOMEM;
 
+	udev->dev->flags |= INPUTDEV_FLAGS_SYNTHETIC;
 	udev->dev->event = uinput_dev_event;
 	input_set_drvdata(udev->dev, udev);
 
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index c6fc7141d7b2..0c96cf60f1a6 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 */
 	/* 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);
@@ -580,7 +585,7 @@ 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);
 
@@ -661,7 +666,7 @@ static void sysrq_do_reset(unsigned long _state)
 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;
 	}
@@ -1097,7 +1104,7 @@ 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 a65e3b24fb18..8b0357175049 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 387fa7d05c98..f7c52a9ea394 100644
--- a/include/linux/sysrq.h
+++ b/include/linux/sysrq.h
@@ -28,6 +28,8 @@
 #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;
@@ -42,8 +44,12 @@ 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 c8146d53ca67..b480cadf9272 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1970,7 +1970,7 @@ 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;