kernel/livepatch/transition.c - third_party/linux - Git at Google

 /*
  * transition.c - Kernel Live Patching transition functions
  *
  * Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com>
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version 2
  * of the License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/cpu.h>
 #include <linux/stacktrace.h>
 #include "core.h"
 #include "patch.h"
 #include "transition.h"
 #include "../sched/sched.h"

 #define MAX_STACK_ENTRIES  100
 #define STACK_ERR_BUF_SIZE 128

 struct klp_patch *klp_transition_patch;

 static int klp_target_state = KLP_UNDEFINED;

 static bool klp_forced = false;

 /*
  * This work can be performed periodically to finish patching or unpatching any
  * "straggler" tasks which failed to transition in the first attempt.
  */
 static void klp_transition_work_fn(struct work_struct *work)
 {
 	mutex_lock(&klp_mutex);

 	if (klp_transition_patch)
 		klp_try_complete_transition();

 	mutex_unlock(&klp_mutex);
 }
 static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);

 /*
  * This function is just a stub to implement a hard force
  * of synchronize_sched(). This requires synchronizing
  * tasks even in userspace and idle.
  */
 static void klp_sync(struct work_struct *work)
 {
 }

 /*
  * We allow to patch also functions where RCU is not watching,
  * e.g. before user_exit(). We can not rely on the RCU infrastructure
  * to do the synchronization. Instead hard force the sched synchronization.
  *
  * This approach allows to use RCU functions for manipulating func_stack
  * safely.
  */
 static void klp_synchronize_transition(void)
 {
 	schedule_on_each_cpu(klp_sync);
 }

 /*
  * The transition to the target patch state is complete.  Clean up the data
  * structures.
  */
 static void klp_complete_transition(void)
 {
 	struct klp_object *obj;
 	struct klp_func *func;
 	struct task_struct *g, *task;
 	unsigned int cpu;

 	pr_debug("'%s': completing %s transition\n",
 		 klp_transition_patch->mod->name,
 		 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

 	if (klp_target_state == KLP_UNPATCHED) {
 		/*
 		 * All tasks have transitioned to KLP_UNPATCHED so we can now
 		 * remove the new functions from the func_stack.
 		 */
 		klp_unpatch_objects(klp_transition_patch);

 		/*
 		 * Make sure klp_ftrace_handler() can no longer see functions
 		 * from this patch on the ops->func_stack.  Otherwise, after
 		 * func->transition gets cleared, the handler may choose a
 		 * removed function.
 		 */
 		klp_synchronize_transition();
 	}

 	klp_for_each_object(klp_transition_patch, obj)
 		klp_for_each_func(obj, func)
 			func->transition = false;

 	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
 	if (klp_target_state == KLP_PATCHED)
 		klp_synchronize_transition();

 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task) {
 		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
 		task->patch_state = KLP_UNDEFINED;
 	}
 	read_unlock(&tasklist_lock);

 	for_each_possible_cpu(cpu) {
 		task = idle_task(cpu);
 		WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
 		task->patch_state = KLP_UNDEFINED;
 	}

 	klp_for_each_object(klp_transition_patch, obj) {
 		if (!klp_is_object_loaded(obj))
 			continue;
 		if (klp_target_state == KLP_PATCHED)
 			klp_post_patch_callback(obj);
 		else if (klp_target_state == KLP_UNPATCHED)
 			klp_post_unpatch_callback(obj);
 	}

 	pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
 		  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

 	/*
 	 * klp_forced set implies unbounded increase of module's ref count if
 	 * the module is disabled/enabled in a loop.
 	 */
 	if (!klp_forced && klp_target_state == KLP_UNPATCHED)
 		module_put(klp_transition_patch->mod);

 	klp_target_state = KLP_UNDEFINED;
 	klp_transition_patch = NULL;
 }

 /*
  * This is called in the error path, to cancel a transition before it has
  * started, i.e. klp_init_transition() has been called but
  * klp_start_transition() hasn't.  If the transition *has* been started,
  * klp_reverse_transition() should be used instead.
  */
 void klp_cancel_transition(void)
 {
 	if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
 		return;

 	pr_debug("'%s': canceling patching transition, going to unpatch\n",
 		 klp_transition_patch->mod->name);

 	klp_target_state = KLP_UNPATCHED;
 	klp_complete_transition();
 }

 /*
  * Switch the patched state of the task to the set of functions in the target
  * patch state.
  *
  * NOTE: If task is not 'current', the caller must ensure the task is inactive.
  * Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value.
  */
 void klp_update_patch_state(struct task_struct *task)
 {
 	/*
 	 * A variant of synchronize_sched() is used to allow patching functions
 	 * where RCU is not watching, see klp_synchronize_transition().
 	 */
 	preempt_disable_notrace();

 	/*
 	 * This test_and_clear_tsk_thread_flag() call also serves as a read
 	 * barrier (smp_rmb) for two cases:
 	 *
 	 * 1) Enforce the order of the TIF_PATCH_PENDING read and the
 	 *    klp_target_state read.  The corresponding write barrier is in
 	 *    klp_init_transition().
 	 *
 	 * 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
 	 *    of func->transition, if klp_ftrace_handler() is called later on
 	 *    the same CPU.  See __klp_disable_patch().
 	 */
 	if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
 		task->patch_state = READ_ONCE(klp_target_state);

 	preempt_enable_notrace();
 }

 /*
  * Determine whether the given stack trace includes any references to a
  * to-be-patched or to-be-unpatched function.
  */
 static int klp_check_stack_func(struct klp_func *func,
 				struct stack_trace *trace)
 {
 	unsigned long func_addr, func_size, address;
 	struct klp_ops *ops;
 	int i;

 	for (i = 0; i < trace->nr_entries; i++) {
 		address = trace->entries[i];

 		if (klp_target_state == KLP_UNPATCHED) {
 			 /*
 			  * Check for the to-be-unpatched function
 			  * (the func itself).
 			  */
 			func_addr = (unsigned long)func->new_func;
 			func_size = func->new_size;
 		} else {
 			/*
 			 * Check for the to-be-patched function
 			 * (the previous func).
 			 */
 			ops = klp_find_ops(func->old_addr);

 			if (list_is_singular(&ops->func_stack)) {
 				/* original function */
 				func_addr = func->old_addr;
 				func_size = func->old_size;
 			} else {
 				/* previously patched function */
 				struct klp_func *prev;

 				prev = list_next_entry(func, stack_node);
 				func_addr = (unsigned long)prev->new_func;
 				func_size = prev->new_size;
 			}
 		}

 		if (address >= func_addr && address < func_addr + func_size)
 			return -EAGAIN;
 	}

 	return 0;
 }

 /*
  * Determine whether it's safe to transition the task to the target patch state
  * by looking for any to-be-patched or to-be-unpatched functions on its stack.
  */
 static int klp_check_stack(struct task_struct *task, char *err_buf)
 {
 	static unsigned long entries[MAX_STACK_ENTRIES];
 	struct stack_trace trace;
 	struct klp_object *obj;
 	struct klp_func *func;
 	int ret;

 	trace.skip = 0;
 	trace.nr_entries = 0;
 	trace.max_entries = MAX_STACK_ENTRIES;
 	trace.entries = entries;
 	ret = save_stack_trace_tsk_reliable(task, &trace);
 	WARN_ON_ONCE(ret == -ENOSYS);
 	if (ret) {
 		snprintf(err_buf, STACK_ERR_BUF_SIZE,
 			 "%s: %s:%d has an unreliable stack\n",
 			 __func__, task->comm, task->pid);
 		return ret;
 	}

 	klp_for_each_object(klp_transition_patch, obj) {
 		if (!obj->patched)
 			continue;
 		klp_for_each_func(obj, func) {
 			ret = klp_check_stack_func(func, &trace);
 			if (ret) {
 				snprintf(err_buf, STACK_ERR_BUF_SIZE,
 					 "%s: %s:%d is sleeping on function %s\n",
 					 __func__, task->comm, task->pid,
 					 func->old_name);
 				return ret;
 			}
 		}
 	}

 	return 0;
 }

 /*
  * Try to safely switch a task to the target patch state.  If it's currently
  * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
  * if the stack is unreliable, return false.
  */
 static bool klp_try_switch_task(struct task_struct *task)
 {
 	struct rq *rq;
 	struct rq_flags flags;
 	int ret;
 	bool success = false;
 	char err_buf[STACK_ERR_BUF_SIZE];

 	err_buf[0] = '\0';

 	/* check if this task has already switched over */
 	if (task->patch_state == klp_target_state)
 		return true;

 	/*
 	 * For arches which don't have reliable stack traces, we have to rely
 	 * on other methods (e.g., switching tasks at kernel exit).
 	 */
 	if (!klp_have_reliable_stack())
 		return false;

 	/*
 	 * Now try to check the stack for any to-be-patched or to-be-unpatched
 	 * functions.  If all goes well, switch the task to the target patch
 	 * state.
 	 */
 	rq = task_rq_lock(task, &flags);

 	if (task_running(rq, task) && task != current) {
 		snprintf(err_buf, STACK_ERR_BUF_SIZE,
 			 "%s: %s:%d is running\n", __func__, task->comm,
 			 task->pid);
 		goto done;
 	}

 	ret = klp_check_stack(task, err_buf);
 	if (ret)
 		goto done;

 	success = true;

 	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	task->patch_state = klp_target_state;

 done:
 	task_rq_unlock(rq, task, &flags);

 	/*
 	 * Due to console deadlock issues, pr_debug() can't be used while
 	 * holding the task rq lock.  Instead we have to use a temporary buffer
 	 * and print the debug message after releasing the lock.
 	 */
 	if (err_buf[0] != '\0')
 		pr_debug("%s", err_buf);

 	return success;

 }

 /*
  * Try to switch all remaining tasks to the target patch state by walking the
  * stacks of sleeping tasks and looking for any to-be-patched or
  * to-be-unpatched functions.  If such functions are found, the task can't be
  * switched yet.
  *
  * If any tasks are still stuck in the initial patch state, schedule a retry.
  */
 void klp_try_complete_transition(void)
 {
 	unsigned int cpu;
 	struct task_struct *g, *task;
 	bool complete = true;

 	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);

 	/*
 	 * Try to switch the tasks to the target patch state by walking their
 	 * stacks and looking for any to-be-patched or to-be-unpatched
 	 * functions.  If such functions are found on a stack, or if the stack
 	 * is deemed unreliable, the task can't be switched yet.
 	 *
 	 * Usually this will transition most (or all) of the tasks on a system
 	 * unless the patch includes changes to a very common function.
 	 */
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task)
 		if (!klp_try_switch_task(task))
 			complete = false;
 	read_unlock(&tasklist_lock);

 	/*
 	 * Ditto for the idle "swapper" tasks.
 	 */
 	get_online_cpus();
 	for_each_possible_cpu(cpu) {
 		task = idle_task(cpu);
 		if (cpu_online(cpu)) {
 			if (!klp_try_switch_task(task))
 				complete = false;
 		} else if (task->patch_state != klp_target_state) {
 			/* offline idle tasks can be switched immediately */
 			clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
 			task->patch_state = klp_target_state;
 		}
 	}
 	put_online_cpus();

 	if (!complete) {
 		/*
 		 * Some tasks weren't able to be switched over.  Try again
 		 * later and/or wait for other methods like kernel exit
 		 * switching.
 		 */
 		schedule_delayed_work(&klp_transition_work,
 				      round_jiffies_relative(HZ));
 		return;
 	}

 	/* we're done, now cleanup the data structures */
 	klp_complete_transition();
 }

 /*
  * Start the transition to the specified target patch state so tasks can begin
  * switching to it.
  */
 void klp_start_transition(void)
 {
 	struct task_struct *g, *task;
 	unsigned int cpu;

 	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);

 	pr_notice("'%s': starting %s transition\n",
 		  klp_transition_patch->mod->name,
 		  klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

 	/*
 	 * Mark all normal tasks as needing a patch state update.  They'll
 	 * switch either in klp_try_complete_transition() or as they exit the
 	 * kernel.
 	 */
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task)
 		if (task->patch_state != klp_target_state)
 			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	read_unlock(&tasklist_lock);

 	/*
 	 * Mark all idle tasks as needing a patch state update.  They'll switch
 	 * either in klp_try_complete_transition() or at the idle loop switch
 	 * point.
 	 */
 	for_each_possible_cpu(cpu) {
 		task = idle_task(cpu);
 		if (task->patch_state != klp_target_state)
 			set_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	}
 }

 /*
  * Initialize the global target patch state and all tasks to the initial patch
  * state, and initialize all function transition states to true in preparation
  * for patching or unpatching.
  */
 void klp_init_transition(struct klp_patch *patch, int state)
 {
 	struct task_struct *g, *task;
 	unsigned int cpu;
 	struct klp_object *obj;
 	struct klp_func *func;
 	int initial_state = !state;

 	WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED);

 	klp_transition_patch = patch;

 	/*
 	 * Set the global target patch state which tasks will switch to.  This
 	 * has no effect until the TIF_PATCH_PENDING flags get set later.
 	 */
 	klp_target_state = state;

 	pr_debug("'%s': initializing %s transition\n", patch->mod->name,
 		 klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

 	/*
 	 * Initialize all tasks to the initial patch state to prepare them for
 	 * switching to the target state.
 	 */
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task) {
 		WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
 		task->patch_state = initial_state;
 	}
 	read_unlock(&tasklist_lock);

 	/*
 	 * Ditto for the idle "swapper" tasks.
 	 */
 	for_each_possible_cpu(cpu) {
 		task = idle_task(cpu);
 		WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
 		task->patch_state = initial_state;
 	}

 	/*
 	 * Enforce the order of the task->patch_state initializations and the
 	 * func->transition updates to ensure that klp_ftrace_handler() doesn't
 	 * see a func in transition with a task->patch_state of KLP_UNDEFINED.
 	 *
 	 * Also enforce the order of the klp_target_state write and future
 	 * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
 	 * set a task->patch_state to KLP_UNDEFINED.
 	 */
 	smp_wmb();

 	/*
 	 * Set the func transition states so klp_ftrace_handler() will know to
 	 * switch to the transition logic.
 	 *
 	 * When patching, the funcs aren't yet in the func_stack and will be
 	 * made visible to the ftrace handler shortly by the calls to
 	 * klp_patch_object().
 	 *
 	 * When unpatching, the funcs are already in the func_stack and so are
 	 * already visible to the ftrace handler.
 	 */
 	klp_for_each_object(patch, obj)
 		klp_for_each_func(obj, func)
 			func->transition = true;
 }

 /*
  * This function can be called in the middle of an existing transition to
  * reverse the direction of the target patch state.  This can be done to
  * effectively cancel an existing enable or disable operation if there are any
  * tasks which are stuck in the initial patch state.
  */
 void klp_reverse_transition(void)
 {
 	unsigned int cpu;
 	struct task_struct *g, *task;

 	pr_debug("'%s': reversing transition from %s\n",
 		 klp_transition_patch->mod->name,
 		 klp_target_state == KLP_PATCHED ? "patching to unpatching" :
 						   "unpatching to patching");

 	klp_transition_patch->enabled = !klp_transition_patch->enabled;

 	klp_target_state = !klp_target_state;

 	/*
 	 * Clear all TIF_PATCH_PENDING flags to prevent races caused by
 	 * klp_update_patch_state() running in parallel with
 	 * klp_start_transition().
 	 */
 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task)
 		clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
 	read_unlock(&tasklist_lock);

 	for_each_possible_cpu(cpu)
 		clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);

 	/* Let any remaining calls to klp_update_patch_state() complete */
 	klp_synchronize_transition();

 	klp_start_transition();
 }

 /* Called from copy_process() during fork */
 void klp_copy_process(struct task_struct *child)
 {
 	child->patch_state = current->patch_state;

 	/* 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);
 }

 /*
  * Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an
  * existing transition to finish.
  *
  * NOTE: klp_update_patch_state(task) requires the task to be inactive or
  * 'current'. This is not the case here and the consistency model could be
  * broken. Administrator, who is the only one to execute the
  * klp_force_transitions(), has to be aware of this.
  */
 void klp_force_transition(void)
 {
 	struct task_struct *g, *task;
 	unsigned int cpu;

 	pr_warn("forcing remaining tasks to the patched state\n");

 	read_lock(&tasklist_lock);
 	for_each_process_thread(g, task)
 		klp_update_patch_state(task);
 	read_unlock(&tasklist_lock);

 	for_each_possible_cpu(cpu)
 		klp_update_patch_state(idle_task(cpu));

 	klp_forced = true;
 }
	/*
	* transition.c - Kernel Live Patching transition functions
	*
	* Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com>
	*
	* This program is free software; you can redistribute it and/or
	* modify it under the terms of the GNU General Public License
	* as published by the Free Software Foundation; either version 2
	* of the License, or (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, see <http://www.gnu.org/licenses/>.
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/cpu.h>
	#include <linux/stacktrace.h>
	#include "core.h"
	#include "patch.h"
	#include "transition.h"
	#include "../sched/sched.h"

	#define MAX_STACK_ENTRIES 100
	#define STACK_ERR_BUF_SIZE 128

	struct klp_patch *klp_transition_patch;

	static int klp_target_state = KLP_UNDEFINED;

	static bool klp_forced = false;

	/*
	* This work can be performed periodically to finish patching or unpatching any
	* "straggler" tasks which failed to transition in the first attempt.
	*/
	static void klp_transition_work_fn(struct work_struct *work)
	{
	mutex_lock(&klp_mutex);

	if (klp_transition_patch)
	klp_try_complete_transition();

	mutex_unlock(&klp_mutex);
	}
	static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);

	/*
	* This function is just a stub to implement a hard force
	* of synchronize_sched(). This requires synchronizing
	* tasks even in userspace and idle.
	*/
	static void klp_sync(struct work_struct *work)
	{
	}

	/*
	* We allow to patch also functions where RCU is not watching,
	* e.g. before user_exit(). We can not rely on the RCU infrastructure
	* to do the synchronization. Instead hard force the sched synchronization.
	*
	* This approach allows to use RCU functions for manipulating func_stack
	* safely.
	*/
	static void klp_synchronize_transition(void)
	{
	schedule_on_each_cpu(klp_sync);
	}

	/*
	* The transition to the target patch state is complete. Clean up the data
	* structures.
	*/
	static void klp_complete_transition(void)
	{
	struct klp_object *obj;
	struct klp_func *func;
	struct task_struct g, task;
	unsigned int cpu;

	pr_debug("'%s': completing %s transition\n",
	klp_transition_patch->mod->name,
	klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

	if (klp_target_state == KLP_UNPATCHED) {
	/*
	* All tasks have transitioned to KLP_UNPATCHED so we can now
	* remove the new functions from the func_stack.
	*/
	klp_unpatch_objects(klp_transition_patch);

	/*
	* Make sure klp_ftrace_handler() can no longer see functions
	* from this patch on the ops->func_stack. Otherwise, after
	* func->transition gets cleared, the handler may choose a
	* removed function.
	*/
	klp_synchronize_transition();
	}

	klp_for_each_object(klp_transition_patch, obj)
	klp_for_each_func(obj, func)
	func->transition = false;

	/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
	if (klp_target_state == KLP_PATCHED)
	klp_synchronize_transition();

	read_lock(&tasklist_lock);
	for_each_process_thread(g, task) {
	WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
	task->patch_state = KLP_UNDEFINED;
	}
	read_unlock(&tasklist_lock);

	for_each_possible_cpu(cpu) {
	task = idle_task(cpu);
	WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
	task->patch_state = KLP_UNDEFINED;
	}

	klp_for_each_object(klp_transition_patch, obj) {
	if (!klp_is_object_loaded(obj))
	continue;
	if (klp_target_state == KLP_PATCHED)
	klp_post_patch_callback(obj);
	else if (klp_target_state == KLP_UNPATCHED)
	klp_post_unpatch_callback(obj);
	}

	pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
	klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

	/*
	* klp_forced set implies unbounded increase of module's ref count if
	* the module is disabled/enabled in a loop.
	*/
	if (!klp_forced && klp_target_state == KLP_UNPATCHED)
	module_put(klp_transition_patch->mod);

	klp_target_state = KLP_UNDEFINED;
	klp_transition_patch = NULL;
	}

	/*
	* This is called in the error path, to cancel a transition before it has
	* started, i.e. klp_init_transition() has been called but
	* klp_start_transition() hasn't. If the transition has been started,
	* klp_reverse_transition() should be used instead.
	*/
	void klp_cancel_transition(void)
	{
	if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
	return;

	pr_debug("'%s': canceling patching transition, going to unpatch\n",
	klp_transition_patch->mod->name);

	klp_target_state = KLP_UNPATCHED;
	klp_complete_transition();
	}

	/*
	* Switch the patched state of the task to the set of functions in the target
	* patch state.
	*
	* NOTE: If task is not 'current', the caller must ensure the task is inactive.
	* Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value.
	*/
	void klp_update_patch_state(struct task_struct *task)
	{
	/*
	* A variant of synchronize_sched() is used to allow patching functions
	* where RCU is not watching, see klp_synchronize_transition().
	*/
	preempt_disable_notrace();

	/*
	* This test_and_clear_tsk_thread_flag() call also serves as a read
	* barrier (smp_rmb) for two cases:
	*
	* 1) Enforce the order of the TIF_PATCH_PENDING read and the
	* klp_target_state read. The corresponding write barrier is in
	* klp_init_transition().
	*
	* 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
	* of func->transition, if klp_ftrace_handler() is called later on
	* the same CPU. See __klp_disable_patch().
	*/
	if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
	task->patch_state = READ_ONCE(klp_target_state);

	preempt_enable_notrace();
	}

	/*
	* Determine whether the given stack trace includes any references to a
	* to-be-patched or to-be-unpatched function.
	*/
	static int klp_check_stack_func(struct klp_func *func,
	struct stack_trace *trace)
	{
	unsigned long func_addr, func_size, address;
	struct klp_ops *ops;
	int i;

	for (i = 0; i < trace->nr_entries; i++) {
	address = trace->entries[i];

	if (klp_target_state == KLP_UNPATCHED) {
	/*
	* Check for the to-be-unpatched function
	* (the func itself).
	*/
	func_addr = (unsigned long)func->new_func;
	func_size = func->new_size;
	} else {
	/*
	* Check for the to-be-patched function
	* (the previous func).
	*/
	ops = klp_find_ops(func->old_addr);

	if (list_is_singular(&ops->func_stack)) {
	/* original function */
	func_addr = func->old_addr;
	func_size = func->old_size;
	} else {
	/* previously patched function */
	struct klp_func *prev;

	prev = list_next_entry(func, stack_node);
	func_addr = (unsigned long)prev->new_func;
	func_size = prev->new_size;
	}
	}

	if (address >= func_addr && address < func_addr + func_size)
	return -EAGAIN;
	}

	return 0;
	}

	/*
	* Determine whether it's safe to transition the task to the target patch state
	* by looking for any to-be-patched or to-be-unpatched functions on its stack.
	*/
	static int klp_check_stack(struct task_struct task, char err_buf)
	{
	static unsigned long entries[MAX_STACK_ENTRIES];
	struct stack_trace trace;
	struct klp_object *obj;
	struct klp_func *func;
	int ret;

	trace.skip = 0;
	trace.nr_entries = 0;
	trace.max_entries = MAX_STACK_ENTRIES;
	trace.entries = entries;
	ret = save_stack_trace_tsk_reliable(task, &trace);
	WARN_ON_ONCE(ret == -ENOSYS);
	if (ret) {
	snprintf(err_buf, STACK_ERR_BUF_SIZE,
	"%s: %s:%d has an unreliable stack\n",
	__func__, task->comm, task->pid);
	return ret;
	}

	klp_for_each_object(klp_transition_patch, obj) {
	if (!obj->patched)
	continue;
	klp_for_each_func(obj, func) {
	ret = klp_check_stack_func(func, &trace);
	if (ret) {
	snprintf(err_buf, STACK_ERR_BUF_SIZE,
	"%s: %s:%d is sleeping on function %s\n",
	__func__, task->comm, task->pid,
	func->old_name);
	return ret;
	}
	}
	}

	return 0;
	}

	/*
	* Try to safely switch a task to the target patch state. If it's currently
	* running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
	* if the stack is unreliable, return false.
	*/
	static bool klp_try_switch_task(struct task_struct *task)
	{
	struct rq *rq;
	struct rq_flags flags;
	int ret;
	bool success = false;
	char err_buf[STACK_ERR_BUF_SIZE];

	err_buf[0] = '\0';

	/* check if this task has already switched over */
	if (task->patch_state == klp_target_state)
	return true;

	/*
	* For arches which don't have reliable stack traces, we have to rely
	* on other methods (e.g., switching tasks at kernel exit).
	*/
	if (!klp_have_reliable_stack())
	return false;

	/*
	* Now try to check the stack for any to-be-patched or to-be-unpatched
	* functions. If all goes well, switch the task to the target patch
	* state.
	*/
	rq = task_rq_lock(task, &flags);

	if (task_running(rq, task) && task != current) {
	snprintf(err_buf, STACK_ERR_BUF_SIZE,
	"%s: %s:%d is running\n", __func__, task->comm,
	task->pid);
	goto done;
	}

	ret = klp_check_stack(task, err_buf);
	if (ret)
	goto done;

	success = true;

	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
	task->patch_state = klp_target_state;

	done:
	task_rq_unlock(rq, task, &flags);

	/*
	* Due to console deadlock issues, pr_debug() can't be used while
	* holding the task rq lock. Instead we have to use a temporary buffer
	* and print the debug message after releasing the lock.
	*/
	if (err_buf[0] != '\0')
	pr_debug("%s", err_buf);

	return success;

	}

	/*
	* Try to switch all remaining tasks to the target patch state by walking the
	* stacks of sleeping tasks and looking for any to-be-patched or
	* to-be-unpatched functions. If such functions are found, the task can't be
	* switched yet.
	*
	* If any tasks are still stuck in the initial patch state, schedule a retry.
	*/
	void klp_try_complete_transition(void)
	{
	unsigned int cpu;
	struct task_struct g, task;
	bool complete = true;

	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);

	/*
	* Try to switch the tasks to the target patch state by walking their
	* stacks and looking for any to-be-patched or to-be-unpatched
	* functions. If such functions are found on a stack, or if the stack
	* is deemed unreliable, the task can't be switched yet.
	*
	* Usually this will transition most (or all) of the tasks on a system
	* unless the patch includes changes to a very common function.
	*/
	read_lock(&tasklist_lock);
	for_each_process_thread(g, task)
	if (!klp_try_switch_task(task))
	complete = false;
	read_unlock(&tasklist_lock);

	/*
	* Ditto for the idle "swapper" tasks.
	*/
	get_online_cpus();
	for_each_possible_cpu(cpu) {
	task = idle_task(cpu);
	if (cpu_online(cpu)) {
	if (!klp_try_switch_task(task))
	complete = false;
	} else if (task->patch_state != klp_target_state) {
	/* offline idle tasks can be switched immediately */
	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
	task->patch_state = klp_target_state;
	}
	}
	put_online_cpus();

	if (!complete) {
	/*
	* Some tasks weren't able to be switched over. Try again
	* later and/or wait for other methods like kernel exit
	* switching.
	*/
	schedule_delayed_work(&klp_transition_work,
	round_jiffies_relative(HZ));
	return;
	}

	/* we're done, now cleanup the data structures */
	klp_complete_transition();
	}

	/*
	* Start the transition to the specified target patch state so tasks can begin
	* switching to it.
	*/
	void klp_start_transition(void)
	{
	struct task_struct g, task;
	unsigned int cpu;

	WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);

	pr_notice("'%s': starting %s transition\n",
	klp_transition_patch->mod->name,
	klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

	/*
	* Mark all normal tasks as needing a patch state update. They'll
	* switch either in klp_try_complete_transition() or as they exit the
	* kernel.
	*/
	read_lock(&tasklist_lock);
	for_each_process_thread(g, task)
	if (task->patch_state != klp_target_state)
	set_tsk_thread_flag(task, TIF_PATCH_PENDING);
	read_unlock(&tasklist_lock);

	/*
	* Mark all idle tasks as needing a patch state update. They'll switch
	* either in klp_try_complete_transition() or at the idle loop switch
	* point.
	*/
	for_each_possible_cpu(cpu) {
	task = idle_task(cpu);
	if (task->patch_state != klp_target_state)
	set_tsk_thread_flag(task, TIF_PATCH_PENDING);
	}
	}

	/*
	* Initialize the global target patch state and all tasks to the initial patch
	* state, and initialize all function transition states to true in preparation
	* for patching or unpatching.
	*/
	void klp_init_transition(struct klp_patch *patch, int state)
	{
	struct task_struct g, task;
	unsigned int cpu;
	struct klp_object *obj;
	struct klp_func *func;
	int initial_state = !state;

	WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED);

	klp_transition_patch = patch;

	/*
	* Set the global target patch state which tasks will switch to. This
	* has no effect until the TIF_PATCH_PENDING flags get set later.
	*/
	klp_target_state = state;

	pr_debug("'%s': initializing %s transition\n", patch->mod->name,
	klp_target_state == KLP_PATCHED ? "patching" : "unpatching");

	/*
	* Initialize all tasks to the initial patch state to prepare them for
	* switching to the target state.
	*/
	read_lock(&tasklist_lock);
	for_each_process_thread(g, task) {
	WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
	task->patch_state = initial_state;
	}
	read_unlock(&tasklist_lock);

	/*
	* Ditto for the idle "swapper" tasks.
	*/
	for_each_possible_cpu(cpu) {
	task = idle_task(cpu);
	WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
	task->patch_state = initial_state;
	}

	/*
	* Enforce the order of the task->patch_state initializations and the
	* func->transition updates to ensure that klp_ftrace_handler() doesn't
	* see a func in transition with a task->patch_state of KLP_UNDEFINED.
	*
	* Also enforce the order of the klp_target_state write and future
	* TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
	* set a task->patch_state to KLP_UNDEFINED.
	*/
	smp_wmb();

	/*
	* Set the func transition states so klp_ftrace_handler() will know to
	* switch to the transition logic.
	*
	* When patching, the funcs aren't yet in the func_stack and will be
	* made visible to the ftrace handler shortly by the calls to
	* klp_patch_object().
	*
	* When unpatching, the funcs are already in the func_stack and so are
	* already visible to the ftrace handler.
	*/
	klp_for_each_object(patch, obj)
	klp_for_each_func(obj, func)
	func->transition = true;
	}

	/*
	* This function can be called in the middle of an existing transition to
	* reverse the direction of the target patch state. This can be done to
	* effectively cancel an existing enable or disable operation if there are any
	* tasks which are stuck in the initial patch state.
	*/
	void klp_reverse_transition(void)
	{
	unsigned int cpu;
	struct task_struct g, task;

	pr_debug("'%s': reversing transition from %s\n",
	klp_transition_patch->mod->name,
	klp_target_state == KLP_PATCHED ? "patching to unpatching" :
	"unpatching to patching");

	klp_transition_patch->enabled = !klp_transition_patch->enabled;

	klp_target_state = !klp_target_state;

	/*
	* Clear all TIF_PATCH_PENDING flags to prevent races caused by
	* klp_update_patch_state() running in parallel with
	* klp_start_transition().
	*/
	read_lock(&tasklist_lock);
	for_each_process_thread(g, task)
	clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
	read_unlock(&tasklist_lock);

	for_each_possible_cpu(cpu)
	clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);

	/* Let any remaining calls to klp_update_patch_state() complete */
	klp_synchronize_transition();

	klp_start_transition();
	}

	/* Called from copy_process() during fork */
	void klp_copy_process(struct task_struct *child)
	{
	child->patch_state = current->patch_state;

	/* 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);
	}

	/*
	* Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an
	* existing transition to finish.
	*
	* NOTE: klp_update_patch_state(task) requires the task to be inactive or
	* 'current'. This is not the case here and the consistency model could be
	* broken. Administrator, who is the only one to execute the
	* klp_force_transitions(), has to be aware of this.
	*/
	void klp_force_transition(void)
	{
	struct task_struct g, task;
	unsigned int cpu;

	pr_warn("forcing remaining tasks to the patched state\n");

	read_lock(&tasklist_lock);
	for_each_process_thread(g, task)
	klp_update_patch_state(task);
	read_unlock(&tasklist_lock);

	for_each_possible_cpu(cpu)
	klp_update_patch_state(idle_task(cpu));

	klp_forced = true;
	}