Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley
 Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United
 Kingdom.
 Registered in England and Wales under Company Registration No. 3798903
Subject: [PATCH 06/16] Add a sysrq option to exit secure boot mode
From: David Howells <dhowells@redhat.com>
To: keyrings@vger.kernel.org
Cc: dhowells@redhat.com, matthew.garrett@nebula.com,
        linux-security-module@vger.kernel.org, linux-efi@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date: Wed, 16 Nov 2016 21:48:00 +0000
Message-ID: <147933288015.19316.13883500379332751105.stgit@warthog.procyon.org.uk>
In-Reply-To: <147933283664.19316.12454053022687659937.stgit@warthog.procyon.org.uk>
References: <147933283664.19316.12454053022687659937.stgit@warthog.procyon.org.uk>
User-Agent: StGit/0.17.1-dirty
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 8148
Lines: 246

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: David Howells <dhowells@redhat.com>
---

 arch/x86/Kconfig            |   10 ++++++++++
 arch/x86/kernel/setup.c     |   31 +++++++++++++++++++++++++++++++
 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 +-
 7 files changed, 68 insertions(+), 8 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5b19997d88d0..c2b481b59931 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1798,6 +1798,16 @@ config EFI_SECURE_BOOT_LOCK_DOWN
 	  image.  Say Y here to automatically lock down the kernel when a
 	  system boots with UEFI Secure Boot enabled.
 
+config EFI_ALLOW_SECURE_BOOT_EXIT
+	def_bool n
+	depends on EFI_SECURE_BOOT_LOCK_DOWN && 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 SECCOMP
 	def_bool y
 	prompt "Enable seccomp to safely compute untrusted bytecode"
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 539f29587712..89786c2270bd 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -71,6 +71,11 @@
 #include <linux/jiffies.h>
 #include <linux/security.h>
 
+#include <linux/fips.h>
+#include <linux/cred.h>
+#include <linux/sysrq.h>
+#include <linux/init_task.h>
+
 #include <video/edid.h>
 
 #include <asm/mtrr.h>
@@ -1291,6 +1296,32 @@ void __init i386_reserve_resources(void)
 
 #endif /* CONFIG_X86_32 */
 
+#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 secure_boot_sysrq(void)
+{
+	if (efi_enabled(EFI_SECURE_BOOT))
+		register_sysrq_key('x', &secure_boot_sysrq_op);
+	return 0;
+}
+late_initcall(secure_boot_sysrq);
+#endif /*CONFIG_EFI_ALLOW_SECURE_BOOT_EXIT*/
+
+
 static struct notifier_block kernel_offset_notifier = {
 	.notifier_call = dump_kernel_offset
 };
diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 92595b98e7ed..894ed3f74f04 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -379,6 +379,7 @@ 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 52bbd27e93ae..72f46a1a2ce7 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -479,6 +479,7 @@ 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 */
@@ -522,7 +523,7 @@ 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;
@@ -542,11 +543,15 @@ 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);
@@ -578,7 +583,7 @@ 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(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,
@@ -810,8 +815,10 @@ 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;
 	}
@@ -1095,7 +1102,7 @@ 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 2a20c0dfdafc..d46d2e18a889 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1968,7 +1968,7 @@ 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;