kernel/livepatch/patch.c - linux - Git at Google

 /*
  * patch.c - livepatch patching functions
  *
  * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
  * Copyright (C) 2014 SUSE
  * Copyright (C) 2015 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/livepatch.h>
 #include <linux/list.h>
 #include <linux/ftrace.h>
 #include <linux/rculist.h>
 #include <linux/slab.h>
 #include <linux/bug.h>
 #include <linux/printk.h>
 #include "core.h"
 #include "patch.h"
 #include "transition.h"

 static LIST_HEAD(klp_ops);

 struct klp_ops *klp_find_ops(unsigned long old_addr)
 {
 	struct klp_ops *ops;
 	struct klp_func *func;

 	list_for_each_entry(ops, &klp_ops, node) {
 		func = list_first_entry(&ops->func_stack, struct klp_func,
 					stack_node);
 		if (func->old_addr == old_addr)
 			return ops;
 	}

 	return NULL;
 }

 static void notrace klp_ftrace_handler(unsigned long ip,
 				       unsigned long parent_ip,
 				       struct ftrace_ops *fops,
 				       struct pt_regs *regs)
 {
 	struct klp_ops *ops;
 	struct klp_func *func;
 	int patch_state;

 	ops = container_of(fops, struct klp_ops, fops);

 	/*
 	 * A variant of synchronize_rcu() is used to allow patching functions
 	 * where RCU is not watching, see klp_synchronize_transition().
 	 */
 	preempt_disable_notrace();

 	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
 				      stack_node);

 	/*
 	 * func should never be NULL because preemption should be disabled here
 	 * and unregister_ftrace_function() does the equivalent of a
 	 * synchronize_rcu() before the func_stack removal.
 	 */
 	if (WARN_ON_ONCE(!func))
 		goto unlock;

 	/*
 	 * In the enable path, enforce the order of the ops->func_stack and
 	 * func->transition reads.  The corresponding write barrier is in
 	 * __klp_enable_patch().
 	 *
 	 * (Note that this barrier technically isn't needed in the disable
 	 * path.  In the rare case where klp_update_patch_state() runs before
 	 * this handler, its TIF_PATCH_PENDING read and this func->transition
 	 * read need to be ordered.  But klp_update_patch_state() already
 	 * enforces that.)
 	 */
 	smp_rmb();

 	if (unlikely(func->transition)) {

 		/*
 		 * Enforce the order of the func->transition and
 		 * current->patch_state reads.  Otherwise we could read an
 		 * out-of-date task state and pick the wrong function.  The
 		 * corresponding write barrier is in klp_init_transition().
 		 */
 		smp_rmb();

 		patch_state = current->patch_state;

 		WARN_ON_ONCE(patch_state == KLP_UNDEFINED);

 		if (patch_state == KLP_UNPATCHED) {
 			/*
 			 * Use the previously patched version of the function.
 			 * If no previous patches exist, continue with the
 			 * original function.
 			 */
 			func = list_entry_rcu(func->stack_node.next,
 					      struct klp_func, stack_node);

 			if (&func->stack_node == &ops->func_stack)
 				goto unlock;
 		}
 	}

 	klp_arch_set_pc(regs, (unsigned long)func->new_func);
 unlock:
 	preempt_enable_notrace();
 }

 /*
  * Convert a function address into the appropriate ftrace location.
  *
  * Usually this is just the address of the function, but on some architectures
  * it's more complicated so allow them to provide a custom behaviour.
  */
 #ifndef klp_get_ftrace_location
 static unsigned long klp_get_ftrace_location(unsigned long faddr)
 {
 	return faddr;
 }
 #endif

 static void klp_unpatch_func(struct klp_func *func)
 {
 	struct klp_ops *ops;

 	if (WARN_ON(!func->patched))
 		return;
 	if (WARN_ON(!func->old_addr))
 		return;

 	ops = klp_find_ops(func->old_addr);
 	if (WARN_ON(!ops))
 		return;

 	if (list_is_singular(&ops->func_stack)) {
 		unsigned long ftrace_loc;

 		ftrace_loc = klp_get_ftrace_location(func->old_addr);
 		if (WARN_ON(!ftrace_loc))
 			return;

 		WARN_ON(unregister_ftrace_function(&ops->fops));
 		WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));

 		list_del_rcu(&func->stack_node);
 		list_del(&ops->node);
 		kfree(ops);
 	} else {
 		list_del_rcu(&func->stack_node);
 	}

 	func->patched = false;
 }

 static int klp_patch_func(struct klp_func *func)
 {
 	struct klp_ops *ops;
 	int ret;

 	if (WARN_ON(!func->old_addr))
 		return -EINVAL;

 	if (WARN_ON(func->patched))
 		return -EINVAL;

 	ops = klp_find_ops(func->old_addr);
 	if (!ops) {
 		unsigned long ftrace_loc;

 		ftrace_loc = klp_get_ftrace_location(func->old_addr);
 		if (!ftrace_loc) {
 			pr_err("failed to find location for function '%s'\n",
 				func->old_name);
 			return -EINVAL;
 		}

 		ops = kzalloc(sizeof(*ops), GFP_KERNEL);
 		if (!ops)
 			return -ENOMEM;

 		ops->fops.func = klp_ftrace_handler;
 		ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
 				  FTRACE_OPS_FL_DYNAMIC |
 				  FTRACE_OPS_FL_IPMODIFY;

 		list_add(&ops->node, &klp_ops);

 		INIT_LIST_HEAD(&ops->func_stack);
 		list_add_rcu(&func->stack_node, &ops->func_stack);

 		ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
 		if (ret) {
 			pr_err("failed to set ftrace filter for function '%s' (%d)\n",
 			       func->old_name, ret);
 			goto err;
 		}

 		ret = register_ftrace_function(&ops->fops);
 		if (ret) {
 			pr_err("failed to register ftrace handler for function '%s' (%d)\n",
 			       func->old_name, ret);
 			ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
 			goto err;
 		}


 	} else {
 		list_add_rcu(&func->stack_node, &ops->func_stack);
 	}

 	func->patched = true;

 	return 0;

 err:
 	list_del_rcu(&func->stack_node);
 	list_del(&ops->node);
 	kfree(ops);
 	return ret;
 }

 void klp_unpatch_object(struct klp_object *obj)
 {
 	struct klp_func *func;

 	klp_for_each_func(obj, func)
 		if (func->patched)
 			klp_unpatch_func(func);

 	obj->patched = false;
 }

 int klp_patch_object(struct klp_object *obj)
 {
 	struct klp_func *func;
 	int ret;

 	if (WARN_ON(obj->patched))
 		return -EINVAL;

 	klp_for_each_func(obj, func) {
 		ret = klp_patch_func(func);
 		if (ret) {
 			klp_unpatch_object(obj);
 			return ret;
 		}
 	}
 	obj->patched = true;

 	return 0;
 }

 void klp_unpatch_objects(struct klp_patch *patch)
 {
 	struct klp_object *obj;

 	klp_for_each_object(patch, obj)
 		if (obj->patched)
 			klp_unpatch_object(obj);
 }
	/*
	* patch.c - livepatch patching functions
	*
	* Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
	* Copyright (C) 2014 SUSE
	* Copyright (C) 2015 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/livepatch.h>
	#include <linux/list.h>
	#include <linux/ftrace.h>
	#include <linux/rculist.h>
	#include <linux/slab.h>
	#include <linux/bug.h>
	#include <linux/printk.h>
	#include "core.h"
	#include "patch.h"
	#include "transition.h"

	static LIST_HEAD(klp_ops);

	struct klp_ops *klp_find_ops(unsigned long old_addr)
	{
	struct klp_ops *ops;
	struct klp_func *func;

	list_for_each_entry(ops, &klp_ops, node) {
	func = list_first_entry(&ops->func_stack, struct klp_func,
	stack_node);
	if (func->old_addr == old_addr)
	return ops;
	}

	return NULL;
	}

	static void notrace klp_ftrace_handler(unsigned long ip,
	unsigned long parent_ip,
	struct ftrace_ops *fops,
	struct pt_regs *regs)
	{
	struct klp_ops *ops;
	struct klp_func *func;
	int patch_state;

	ops = container_of(fops, struct klp_ops, fops);

	/*
	* A variant of synchronize_rcu() is used to allow patching functions
	* where RCU is not watching, see klp_synchronize_transition().
	*/
	preempt_disable_notrace();

	func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
	stack_node);

	/*
	* func should never be NULL because preemption should be disabled here
	* and unregister_ftrace_function() does the equivalent of a
	* synchronize_rcu() before the func_stack removal.
	*/
	if (WARN_ON_ONCE(!func))
	goto unlock;

	/*
	* In the enable path, enforce the order of the ops->func_stack and
	* func->transition reads. The corresponding write barrier is in
	* __klp_enable_patch().
	*
	* (Note that this barrier technically isn't needed in the disable
	* path. In the rare case where klp_update_patch_state() runs before
	* this handler, its TIF_PATCH_PENDING read and this func->transition
	* read need to be ordered. But klp_update_patch_state() already
	* enforces that.)
	*/
	smp_rmb();

	if (unlikely(func->transition)) {

	/*
	* Enforce the order of the func->transition and
	* current->patch_state reads. Otherwise we could read an
	* out-of-date task state and pick the wrong function. The
	* corresponding write barrier is in klp_init_transition().
	*/
	smp_rmb();

	patch_state = current->patch_state;

	WARN_ON_ONCE(patch_state == KLP_UNDEFINED);

	if (patch_state == KLP_UNPATCHED) {
	/*
	* Use the previously patched version of the function.
	* If no previous patches exist, continue with the
	* original function.
	*/
	func = list_entry_rcu(func->stack_node.next,
	struct klp_func, stack_node);

	if (&func->stack_node == &ops->func_stack)
	goto unlock;
	}
	}

	klp_arch_set_pc(regs, (unsigned long)func->new_func);
	unlock:
	preempt_enable_notrace();
	}

	/*
	* Convert a function address into the appropriate ftrace location.
	*
	* Usually this is just the address of the function, but on some architectures
	* it's more complicated so allow them to provide a custom behaviour.
	*/
	#ifndef klp_get_ftrace_location
	static unsigned long klp_get_ftrace_location(unsigned long faddr)
	{
	return faddr;
	}
	#endif

	static void klp_unpatch_func(struct klp_func *func)
	{
	struct klp_ops *ops;

	if (WARN_ON(!func->patched))
	return;
	if (WARN_ON(!func->old_addr))
	return;

	ops = klp_find_ops(func->old_addr);
	if (WARN_ON(!ops))
	return;

	if (list_is_singular(&ops->func_stack)) {
	unsigned long ftrace_loc;

	ftrace_loc = klp_get_ftrace_location(func->old_addr);
	if (WARN_ON(!ftrace_loc))
	return;

	WARN_ON(unregister_ftrace_function(&ops->fops));
	WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));

	list_del_rcu(&func->stack_node);
	list_del(&ops->node);
	kfree(ops);
	} else {
	list_del_rcu(&func->stack_node);
	}

	func->patched = false;
	}

	static int klp_patch_func(struct klp_func *func)
	{
	struct klp_ops *ops;
	int ret;

	if (WARN_ON(!func->old_addr))
	return -EINVAL;

	if (WARN_ON(func->patched))
	return -EINVAL;

	ops = klp_find_ops(func->old_addr);
	if (!ops) {
	unsigned long ftrace_loc;

	ftrace_loc = klp_get_ftrace_location(func->old_addr);
	if (!ftrace_loc) {
	pr_err("failed to find location for function '%s'\n",
	func->old_name);
	return -EINVAL;
	}

	ops = kzalloc(sizeof(*ops), GFP_KERNEL);
	if (!ops)
	return -ENOMEM;

	ops->fops.func = klp_ftrace_handler;
	ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS \|
	FTRACE_OPS_FL_DYNAMIC \|
	FTRACE_OPS_FL_IPMODIFY;

	list_add(&ops->node, &klp_ops);

	INIT_LIST_HEAD(&ops->func_stack);
	list_add_rcu(&func->stack_node, &ops->func_stack);

	ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
	if (ret) {
	pr_err("failed to set ftrace filter for function '%s' (%d)\n",
	func->old_name, ret);
	goto err;
	}

	ret = register_ftrace_function(&ops->fops);
	if (ret) {
	pr_err("failed to register ftrace handler for function '%s' (%d)\n",
	func->old_name, ret);
	ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
	goto err;
	}


	} else {
	list_add_rcu(&func->stack_node, &ops->func_stack);
	}

	func->patched = true;

	return 0;

	err:
	list_del_rcu(&func->stack_node);
	list_del(&ops->node);
	kfree(ops);
	return ret;
	}

	void klp_unpatch_object(struct klp_object *obj)
	{
	struct klp_func *func;

	klp_for_each_func(obj, func)
	if (func->patched)
	klp_unpatch_func(func);

	obj->patched = false;
	}

	int klp_patch_object(struct klp_object *obj)
	{
	struct klp_func *func;
	int ret;

	if (WARN_ON(obj->patched))
	return -EINVAL;

	klp_for_each_func(obj, func) {
	ret = klp_patch_func(func);
	if (ret) {
	klp_unpatch_object(obj);
	return ret;
	}
	}
	obj->patched = true;

	return 0;
	}

	void klp_unpatch_objects(struct klp_patch *patch)
	{
	struct klp_object *obj;

	klp_for_each_object(patch, obj)
	if (obj->patched)
	klp_unpatch_object(obj);
	}