Add a sysrq option to exit secure boot mode

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>
[bwh: For 4.12, adjust context]

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0043-Add-a-sysrq-option-to-exit-secure-boot-mode.patch

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6bc8db6985f41f672f48c2f84c3c2f712f2710dd..d236c94f52980b1d62aadf0da0b1885c3d5dc413 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1899,6 +1899,16 @@ 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 e6a2155651cea8146fca98f1072008f350ff68e0..a8230bed45d1b079067197de079ab8e7912e0833 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -72,6 +72,11 @@
 #include <linux/mem_encrypt.h>
 #include <linux/security.h>
 
+#include <linux/fips.h>
+#include <linux/cred.h>
+#include <linux/sysrq.h>
+#include <linux/init_task.h>
+
 #include <linux/usb/xhci-dbgp.h>
 #include <video/edid.h>
 
@@ -1353,6 +1358,32 @@ 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 443151de90c6b506f6847b656a68d84577576ad1..45a1f5460805a42d71e44fd75c229e7db0e9b269 100644 (file)
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -408,6 +408,7 @@ 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 377b3592384e0d9421c86866f5609dd567c8dcc3..5ed20e0190f2c8b64dcf8e038456cab6971a1f89 100644 (file)
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -487,6 +487,7 @@ 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 */
@@ -530,7 +531,7 @@ 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;
@@ -550,11 +551,15 @@ 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);
@@ -586,7 +591,7 @@ 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);
 
@@ -667,7 +672,7 @@ 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,
@@ -818,8 +823,10 @@ 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;
        }
@@ -1103,7 +1110,7 @@ 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 7c7516eb7d76c64071e51c199fdb0fd0f4e3c934..38cd0ea72c376e0363f05e73683b2bea2d1a99fa 100644 (file)
--- 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 8c71874e84852b5cefb9b9bf0a06a877457eaf86..7de1f08b60a913dc1cf06fe86c3132982c6db8a8 100644 (file)
--- 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 c8146d53ca677a9ef28218ba5590fa3e28f530d7..b480cadf9272061306c122748a4fca6c167943dd 100644 (file)
--- 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;