8 files changed, 102 insertions, 9 deletions

diff --git a/Documentation/ABI/testing/sysfs-kernel-livepatch b/Documentation/ABI/testing/sysfs-kernel-livepatch
index d5d39748382f..3bb9d5bc1ce3 100644
--- a/Documentation/ABI/testing/sysfs-kernel-livepatch
+++ b/Documentation/ABI/testing/sysfs-kernel-livepatch
@@ -33,6 +33,18 @@ Description:
 		An attribute which indicates whether the patch is currently in
 		transition.
 
+What:		/sys/kernel/livepatch/<patch>/signal
+Date:		Nov 2017
+KernelVersion:	4.15.0
+Contact:	live-patching@vger.kernel.org
+Description:
+		A writable attribute that allows administrator to affect the
+		course of an existing transition. Writing 1 sends a fake
+		signal to all remaining blocking tasks. The fake signal
+		means that no proper signal is delivered (there is no data in
+		signal pending structures). Tasks are interrupted or woken up,
+		and forced to change their patched state.
+
 What:		/sys/kernel/livepatch/<patch>/<object>
 Date:		Nov 2014
 KernelVersion:	3.19.0
diff --git a/Documentation/livepatch/livepatch.txt b/Documentation/livepatch/livepatch.txt
index ecdb18104ab0..9bcdef277a36 100644
--- a/Documentation/livepatch/livepatch.txt
+++ b/Documentation/livepatch/livepatch.txt
@@ -176,8 +176,12 @@ If a patch is in transition, this file shows 0 to indicate the task is
 unpatched and 1 to indicate it's patched.  Otherwise, if no patch is in
 transition, it shows -1.  Any tasks which are blocking the transition
 can be signaled with SIGSTOP and SIGCONT to force them to change their
-patched state.
-
+patched state. This may be harmful to the system though.
+/sys/kernel/livepatch/<patch>/signal attribute provides a better alternative.
+Writing 1 to the attribute sends a fake signal to all remaining blocking
+tasks. No proper signal is actually delivered (there is no data in signal
+pending structures). Tasks are interrupted or woken up, and forced to change
+their patched state.
 
 3.1 Adding consistency model support to new architectures
 ---------------------------------------------------------
@@ -435,6 +439,9 @@ Information about the registered patches can be found under
 /sys/kernel/livepatch. The patches could be enabled and disabled
 by writing there.
 
+/sys/kernel/livepatch/<patch>/signal attribute allows administrator to affect a
+patching operation.
+
 See Documentation/ABI/testing/sysfs-kernel-livepatch for more details.
 
 
diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index e9436c5e1e09..bf9c4e7792d1 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -153,6 +153,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 	if (thread_info_flags & _TIF_UPROBE)
 		uprobe_notify_resume(regs);
 
+	if (thread_info_flags & _TIF_PATCH_PENDING)
+		klp_update_patch_state(current);
+
 	if (thread_info_flags & _TIF_SIGPENDING) {
 		BUG_ON(regs != current->thread.regs);
 		do_signal(current);
@@ -163,9 +166,6 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_info_flags)
 		tracehook_notify_resume(regs);
 	}
 
-	if (thread_info_flags & _TIF_PATCH_PENDING)
-		klp_update_patch_state(current);
-
 	user_enter();
 }
 
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index d7d3cc24baf4..1e3883e45687 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -153,6 +153,9 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_UPROBE)
 			uprobe_notify_resume(regs);
 
+		if (cached_flags & _TIF_PATCH_PENDING)
+			klp_update_patch_state(current);
+
 		/* deal with pending signal delivery */
 		if (cached_flags & _TIF_SIGPENDING)
 			do_signal(regs);
@@ -165,9 +168,6 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		if (cached_flags & _TIF_USER_RETURN_NOTIFY)
 			fire_user_return_notifiers();
 
-		if (cached_flags & _TIF_PATCH_PENDING)
-			klp_update_patch_state(current);
-
 		/* Disable IRQs and retry */
 		local_irq_disable();
 
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index de9e45dca70f..88766bd91803 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -454,6 +454,7 @@ EXPORT_SYMBOL_GPL(klp_enable_patch);
  * /sys/kernel/livepatch/<patch>
  * /sys/kernel/livepatch/<patch>/enabled
  * /sys/kernel/livepatch/<patch>/transition
+ * /sys/kernel/livepatch/<patch>/signal
  * /sys/kernel/livepatch/<patch>/<object>
  * /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
  */
@@ -528,11 +529,40 @@ static ssize_t transition_show(struct kobject *kobj,
 			patch == klp_transition_patch);
 }
 
+static ssize_t signal_store(struct kobject *kobj, struct kobj_attribute *attr,
+			    const char *buf, size_t count)
+{
+	struct klp_patch *patch;
+	int ret;
+	bool val;
+
+	patch = container_of(kobj, struct klp_patch, kobj);
+
+	/*
+	 * klp_mutex lock is not grabbed here intentionally. It is not really
+	 * needed. The race window is harmless and grabbing the lock would only
+	 * hold the action back.
+	 */
+	if (patch != klp_transition_patch)
+		return -EINVAL;
+
+	ret = kstrtobool(buf, &val);
+	if (ret)
+		return ret;
+
+	if (val)
+		klp_send_signals();
+
+	return count;
+}
+
 static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
 static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
+static struct kobj_attribute signal_kobj_attr = __ATTR_WO(signal);
 static struct attribute *klp_patch_attrs[] = {
 	&enabled_kobj_attr.attr,
 	&transition_kobj_attr.attr,
+	&signal_kobj_attr.attr,
 	NULL
 };
 
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 56add6327736..edcfcb8ebb2d 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -608,3 +608,44 @@ void klp_copy_process(struct task_struct *child)
 
 	/* TIF_PATCH_PENDING gets copied in setup_thread_stack() */
 }
+
+/*
+ * Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
+ * Kthreads with TIF_PATCH_PENDING set are woken up. Only admin can request this
+ * action currently.
+ */
+void klp_send_signals(void)
+{
+	struct task_struct *g, *task;
+
+	pr_notice("signaling remaining tasks\n");
+
+	read_lock(&tasklist_lock);
+	for_each_process_thread(g, task) {
+		if (!klp_patch_pending(task))
+			continue;
+
+		/*
+		 * There is a small race here. We could see TIF_PATCH_PENDING
+		 * set and decide to wake up a kthread or send a fake signal.
+		 * Meanwhile the task could migrate itself and the action
+		 * would be meaningless. It is not serious though.
+		 */
+		if (task->flags & PF_KTHREAD) {
+			/*
+			 * Wake up a kthread which sleeps interruptedly and
+			 * still has not been migrated.
+			 */
+			wake_up_state(task, TASK_INTERRUPTIBLE);
+		} else {
+			/*
+			 * Send fake signal to all non-kthread tasks which are
+			 * still not migrated.
+			 */
+			spin_lock_irq(&task->sighand->siglock);
+			signal_wake_up(task, 0);
+			spin_unlock_irq(&task->sighand->siglock);
+		}
+	}
+	read_unlock(&tasklist_lock);
+}
diff --git a/kernel/livepatch/transition.h b/kernel/livepatch/transition.h
index 0f6e27c481f9..40522795a5f6 100644
--- a/kernel/livepatch/transition.h
+++ b/kernel/livepatch/transition.h
@@ -11,5 +11,6 @@ void klp_cancel_transition(void);
 void klp_start_transition(void);
 void klp_try_complete_transition(void);
 void klp_reverse_transition(void);
+void klp_send_signals(void);
 
 #endif /* _LIVEPATCH_TRANSITION_H */
diff --git a/kernel/signal.c b/kernel/signal.c
index 8dcd8825b2de..186143b06d00 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -40,6 +40,7 @@
 #include <linux/cn_proc.h>
 #include <linux/compiler.h>
 #include <linux/posix-timers.h>
+#include <linux/livepatch.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/signal.h>
@@ -163,7 +164,8 @@ void recalc_sigpending_and_wake(struct task_struct *t)
 
 void recalc_sigpending(void)
 {
-	if (!recalc_sigpending_tsk(current) && !freezing(current))
+	if (!recalc_sigpending_tsk(current) && !freezing(current) &&
+	    !klp_patch_pending(current))
 		clear_thread_flag(TIF_SIGPENDING);
 
 }