linux/kernel/livepatch/core.c
Petr Mladek 8cb2c2dc47 livepatch: Fix subtle race with coming and going modules
There is a notifier that handles live patches for coming and going modules.
It takes klp_mutex lock to avoid races with coming and going patches but
it does not keep the lock all the time. Therefore the following races are
possible:

  1. The notifier is called sometime in STATE_MODULE_COMING. The module
     is visible by find_module() in this state all the time. It means that
     new patch can be registered and enabled even before the notifier is
     called. It might create wrong order of stacked patches, see below
     for an example.

   2. New patch could still see the module in the GOING state even after
      the notifier has been called. It will try to initialize the related
      object structures but the module could disappear at any time. There
      will stay mess in the structures. It might even cause an invalid
      memory access.

This patch solves the problem by adding a boolean variable into struct module.
The value is true after the coming and before the going handler is called.
New patches need to be applied when the value is true and they need to ignore
the module when the value is false.

Note that we need to know state of all modules on the system. The races are
related to new patches. Therefore we do not know what modules will get
patched.

Also note that we could not simply ignore going modules. The code from the
module could be called even in the GOING state until mod->exit() finishes.
If we start supporting patches with semantic changes between function
calls, we need to apply new patches to any still usable code.
See below for an example.

Finally note that the patch solves only the situation when a new patch is
registered. There are no such problems when the patch is being removed.
It does not matter who disable the patch first, whether the normal
disable_patch() or the module notifier. There is nothing to do
once the patch is disabled.

Alternative solutions:
======================

+ reject new patches when a patched module is coming or going; this is ugly

+ wait with adding new patch until the module leaves the COMING and GOING
  states; this might be dangerous and complicated; we would need to release
  kgr_lock in the middle of the patch registration to avoid a deadlock
  with the coming and going handlers; also we might need a waitqueue for
  each module which seems to be even bigger overhead than the boolean

+ stop modules from entering COMING and GOING states; wait until modules
  leave these states when they are already there; looks complicated; we would
  need to ignore the module that asked to stop the others to avoid a deadlock;
  also it is unclear what to do when two modules asked to stop others and
  both are in COMING state (situation when two new patches are applied)

+ always register/enable new patches and fix up the potential mess (registered
  patches order) in klp_module_init(); this is nasty and prone to regressions
  in the future development

+ add another MODULE_STATE where the kallsyms are visible but the module is not
  used yet; this looks too complex; the module states are checked on "many"
  locations

Example of patch stacking breakage:
===================================

The notifier could _not_ _simply_ ignore already initialized module objects.
For example, let's have three patches (P1, P2, P3) for functions a() and b()
where a() is from vmcore and b() is from a module M. Something like:

	a()	b()
P1	a1()	b1()
P2	a2()	b2()
P3	a3()	b3(3)

If you load the module M after all patches are registered and enabled.
The ftrace ops for function a() and b() has listed the functions in this
order:

	ops_a->func_stack -> list(a3,a2,a1)
	ops_b->func_stack -> list(b3,b2,b1)

, so the pointer to b3() is the first and will be used.

Then you might have the following scenario. Let's start with state when patches
P1 and P2 are registered and enabled but the module M is not loaded. Then ftrace
ops for b() does not exist. Then we get into the following race:

CPU0					CPU1

load_module(M)

  complete_formation()

  mod->state = MODULE_STATE_COMING;
  mutex_unlock(&module_mutex);

					klp_register_patch(P3);
					klp_enable_patch(P3);

					# STATE 1

  klp_module_notify(M)
    klp_module_notify_coming(P1);
    klp_module_notify_coming(P2);
    klp_module_notify_coming(P3);

					# STATE 2

The ftrace ops for a() and b() then looks:

  STATE1:

	ops_a->func_stack -> list(a3,a2,a1);
	ops_b->func_stack -> list(b3);

  STATE2:
	ops_a->func_stack -> list(a3,a2,a1);
	ops_b->func_stack -> list(b2,b1,b3);

therefore, b2() is used for the module but a3() is used for vmcore
because they were the last added.

Example of the race with going modules:
=======================================

CPU0					CPU1

delete_module()  #SYSCALL

   try_stop_module()
     mod->state = MODULE_STATE_GOING;

   mutex_unlock(&module_mutex);

					klp_register_patch()
					klp_enable_patch()

					#save place to switch universe

					b()     # from module that is going
					  a()   # from core (patched)

   mod->exit();

Note that the function b() can be called until we call mod->exit().

If we do not apply patch against b() because it is in MODULE_STATE_GOING,
it will call patched a() with modified semantic and things might get wrong.

[jpoimboe@redhat.com: use one boolean instead of two]
Signed-off-by: Petr Mladek <pmladek@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2015-03-17 10:31:54 +01:00

1039 lines
22 KiB
C

/*
* core.c - Kernel Live Patching Core
*
* Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
* Copyright (C) 2014 SUSE
*
* 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/module.h>
#include <linux/kernel.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/ftrace.h>
#include <linux/list.h>
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
/**
* struct klp_ops - structure for tracking registered ftrace ops structs
*
* A single ftrace_ops is shared between all enabled replacement functions
* (klp_func structs) which have the same old_addr. This allows the switch
* between function versions to happen instantaneously by updating the klp_ops
* struct's func_stack list. The winner is the klp_func at the top of the
* func_stack (front of the list).
*
* @node: node for the global klp_ops list
* @func_stack: list head for the stack of klp_func's (active func is on top)
* @fops: registered ftrace ops struct
*/
struct klp_ops {
struct list_head node;
struct list_head func_stack;
struct ftrace_ops fops;
};
/*
* The klp_mutex protects the global lists and state transitions of any
* structure reachable from them. References to any structure must be obtained
* under mutex protection (except in klp_ftrace_handler(), which uses RCU to
* ensure it gets consistent data).
*/
static DEFINE_MUTEX(klp_mutex);
static LIST_HEAD(klp_patches);
static LIST_HEAD(klp_ops);
static struct kobject *klp_root_kobj;
static 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 bool klp_is_module(struct klp_object *obj)
{
return obj->name;
}
static bool klp_is_object_loaded(struct klp_object *obj)
{
return !obj->name || obj->mod;
}
/* sets obj->mod if object is not vmlinux and module is found */
static void klp_find_object_module(struct klp_object *obj)
{
struct module *mod;
if (!klp_is_module(obj))
return;
mutex_lock(&module_mutex);
/*
* We do not want to block removal of patched modules and therefore
* we do not take a reference here. The patches are removed by
* a going module handler instead.
*/
mod = find_module(obj->name);
/*
* Do not mess work of the module coming and going notifiers.
* Note that the patch might still be needed before the going handler
* is called. Module functions can be called even in the GOING state
* until mod->exit() finishes. This is especially important for
* patches that modify semantic of the functions.
*/
if (mod && mod->klp_alive)
obj->mod = mod;
mutex_unlock(&module_mutex);
}
/* klp_mutex must be held by caller */
static bool klp_is_patch_registered(struct klp_patch *patch)
{
struct klp_patch *mypatch;
list_for_each_entry(mypatch, &klp_patches, list)
if (mypatch == patch)
return true;
return false;
}
static bool klp_initialized(void)
{
return klp_root_kobj;
}
struct klp_find_arg {
const char *objname;
const char *name;
unsigned long addr;
/*
* If count == 0, the symbol was not found. If count == 1, a unique
* match was found and addr is set. If count > 1, there is
* unresolvable ambiguity among "count" number of symbols with the same
* name in the same object.
*/
unsigned long count;
};
static int klp_find_callback(void *data, const char *name,
struct module *mod, unsigned long addr)
{
struct klp_find_arg *args = data;
if ((mod && !args->objname) || (!mod && args->objname))
return 0;
if (strcmp(args->name, name))
return 0;
if (args->objname && strcmp(args->objname, mod->name))
return 0;
/*
* args->addr might be overwritten if another match is found
* but klp_find_object_symbol() handles this and only returns the
* addr if count == 1.
*/
args->addr = addr;
args->count++;
return 0;
}
static int klp_find_object_symbol(const char *objname, const char *name,
unsigned long *addr)
{
struct klp_find_arg args = {
.objname = objname,
.name = name,
.addr = 0,
.count = 0
};
kallsyms_on_each_symbol(klp_find_callback, &args);
if (args.count == 0)
pr_err("symbol '%s' not found in symbol table\n", name);
else if (args.count > 1)
pr_err("unresolvable ambiguity (%lu matches) on symbol '%s' in object '%s'\n",
args.count, name, objname);
else {
*addr = args.addr;
return 0;
}
*addr = 0;
return -EINVAL;
}
struct klp_verify_args {
const char *name;
const unsigned long addr;
};
static int klp_verify_callback(void *data, const char *name,
struct module *mod, unsigned long addr)
{
struct klp_verify_args *args = data;
if (!mod &&
!strcmp(args->name, name) &&
args->addr == addr)
return 1;
return 0;
}
static int klp_verify_vmlinux_symbol(const char *name, unsigned long addr)
{
struct klp_verify_args args = {
.name = name,
.addr = addr,
};
if (kallsyms_on_each_symbol(klp_verify_callback, &args))
return 0;
pr_err("symbol '%s' not found at specified address 0x%016lx, kernel mismatch?\n",
name, addr);
return -EINVAL;
}
static int klp_find_verify_func_addr(struct klp_object *obj,
struct klp_func *func)
{
int ret;
#if defined(CONFIG_RANDOMIZE_BASE)
/* KASLR is enabled, disregard old_addr from user */
func->old_addr = 0;
#endif
if (!func->old_addr || klp_is_module(obj))
ret = klp_find_object_symbol(obj->name, func->old_name,
&func->old_addr);
else
ret = klp_verify_vmlinux_symbol(func->old_name,
func->old_addr);
return ret;
}
/*
* external symbols are located outside the parent object (where the parent
* object is either vmlinux or the kmod being patched).
*/
static int klp_find_external_symbol(struct module *pmod, const char *name,
unsigned long *addr)
{
const struct kernel_symbol *sym;
/* first, check if it's an exported symbol */
preempt_disable();
sym = find_symbol(name, NULL, NULL, true, true);
if (sym) {
*addr = sym->value;
preempt_enable();
return 0;
}
preempt_enable();
/* otherwise check if it's in another .o within the patch module */
return klp_find_object_symbol(pmod->name, name, addr);
}
static int klp_write_object_relocations(struct module *pmod,
struct klp_object *obj)
{
int ret;
struct klp_reloc *reloc;
if (WARN_ON(!klp_is_object_loaded(obj)))
return -EINVAL;
if (WARN_ON(!obj->relocs))
return -EINVAL;
for (reloc = obj->relocs; reloc->name; reloc++) {
if (!klp_is_module(obj)) {
ret = klp_verify_vmlinux_symbol(reloc->name,
reloc->val);
if (ret)
return ret;
} else {
/* module, reloc->val needs to be discovered */
if (reloc->external)
ret = klp_find_external_symbol(pmod,
reloc->name,
&reloc->val);
else
ret = klp_find_object_symbol(obj->mod->name,
reloc->name,
&reloc->val);
if (ret)
return ret;
}
ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
reloc->val + reloc->addend);
if (ret) {
pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
reloc->name, reloc->val, ret);
return ret;
}
}
return 0;
}
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;
ops = container_of(fops, struct klp_ops, fops);
rcu_read_lock();
func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
stack_node);
if (WARN_ON_ONCE(!func))
goto unlock;
klp_arch_set_pc(regs, (unsigned long)func->new_func);
unlock:
rcu_read_unlock();
}
static int klp_disable_func(struct klp_func *func)
{
struct klp_ops *ops;
int ret;
if (WARN_ON(func->state != KLP_ENABLED))
return -EINVAL;
if (WARN_ON(!func->old_addr))
return -EINVAL;
ops = klp_find_ops(func->old_addr);
if (WARN_ON(!ops))
return -EINVAL;
if (list_is_singular(&ops->func_stack)) {
ret = unregister_ftrace_function(&ops->fops);
if (ret) {
pr_err("failed to unregister ftrace handler for function '%s' (%d)\n",
func->old_name, ret);
return ret;
}
ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
if (ret)
pr_warn("function unregister succeeded but failed to clear the filter\n");
list_del_rcu(&func->stack_node);
list_del(&ops->node);
kfree(ops);
} else {
list_del_rcu(&func->stack_node);
}
func->state = KLP_DISABLED;
return 0;
}
static int klp_enable_func(struct klp_func *func)
{
struct klp_ops *ops;
int ret;
if (WARN_ON(!func->old_addr))
return -EINVAL;
if (WARN_ON(func->state != KLP_DISABLED))
return -EINVAL;
ops = klp_find_ops(func->old_addr);
if (!ops) {
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, func->old_addr, 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, func->old_addr, 1, 0);
goto err;
}
} else {
list_add_rcu(&func->stack_node, &ops->func_stack);
}
func->state = KLP_ENABLED;
return 0;
err:
list_del_rcu(&func->stack_node);
list_del(&ops->node);
kfree(ops);
return ret;
}
static int klp_disable_object(struct klp_object *obj)
{
struct klp_func *func;
int ret;
for (func = obj->funcs; func->old_name; func++) {
if (func->state != KLP_ENABLED)
continue;
ret = klp_disable_func(func);
if (ret)
return ret;
}
obj->state = KLP_DISABLED;
return 0;
}
static int klp_enable_object(struct klp_object *obj)
{
struct klp_func *func;
int ret;
if (WARN_ON(obj->state != KLP_DISABLED))
return -EINVAL;
if (WARN_ON(!klp_is_object_loaded(obj)))
return -EINVAL;
for (func = obj->funcs; func->old_name; func++) {
ret = klp_enable_func(func);
if (ret)
goto unregister;
}
obj->state = KLP_ENABLED;
return 0;
unregister:
WARN_ON(klp_disable_object(obj));
return ret;
}
static int __klp_disable_patch(struct klp_patch *patch)
{
struct klp_object *obj;
int ret;
/* enforce stacking: only the last enabled patch can be disabled */
if (!list_is_last(&patch->list, &klp_patches) &&
list_next_entry(patch, list)->state == KLP_ENABLED)
return -EBUSY;
pr_notice("disabling patch '%s'\n", patch->mod->name);
for (obj = patch->objs; obj->funcs; obj++) {
if (obj->state != KLP_ENABLED)
continue;
ret = klp_disable_object(obj);
if (ret)
return ret;
}
patch->state = KLP_DISABLED;
return 0;
}
/**
* klp_disable_patch() - disables a registered patch
* @patch: The registered, enabled patch to be disabled
*
* Unregisters the patched functions from ftrace.
*
* Return: 0 on success, otherwise error
*/
int klp_disable_patch(struct klp_patch *patch)
{
int ret;
mutex_lock(&klp_mutex);
if (!klp_is_patch_registered(patch)) {
ret = -EINVAL;
goto err;
}
if (patch->state == KLP_DISABLED) {
ret = -EINVAL;
goto err;
}
ret = __klp_disable_patch(patch);
err:
mutex_unlock(&klp_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(klp_disable_patch);
static int __klp_enable_patch(struct klp_patch *patch)
{
struct klp_object *obj;
int ret;
if (WARN_ON(patch->state != KLP_DISABLED))
return -EINVAL;
/* enforce stacking: only the first disabled patch can be enabled */
if (patch->list.prev != &klp_patches &&
list_prev_entry(patch, list)->state == KLP_DISABLED)
return -EBUSY;
pr_notice_once("tainting kernel with TAINT_LIVEPATCH\n");
add_taint(TAINT_LIVEPATCH, LOCKDEP_STILL_OK);
pr_notice("enabling patch '%s'\n", patch->mod->name);
for (obj = patch->objs; obj->funcs; obj++) {
klp_find_object_module(obj);
if (!klp_is_object_loaded(obj))
continue;
ret = klp_enable_object(obj);
if (ret)
goto unregister;
}
patch->state = KLP_ENABLED;
return 0;
unregister:
WARN_ON(__klp_disable_patch(patch));
return ret;
}
/**
* klp_enable_patch() - enables a registered patch
* @patch: The registered, disabled patch to be enabled
*
* Performs the needed symbol lookups and code relocations,
* then registers the patched functions with ftrace.
*
* Return: 0 on success, otherwise error
*/
int klp_enable_patch(struct klp_patch *patch)
{
int ret;
mutex_lock(&klp_mutex);
if (!klp_is_patch_registered(patch)) {
ret = -EINVAL;
goto err;
}
ret = __klp_enable_patch(patch);
err:
mutex_unlock(&klp_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(klp_enable_patch);
/*
* Sysfs Interface
*
* /sys/kernel/livepatch
* /sys/kernel/livepatch/<patch>
* /sys/kernel/livepatch/<patch>/enabled
* /sys/kernel/livepatch/<patch>/<object>
* /sys/kernel/livepatch/<patch>/<object>/<func>
*/
static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
struct klp_patch *patch;
int ret;
unsigned long val;
ret = kstrtoul(buf, 10, &val);
if (ret)
return -EINVAL;
if (val != KLP_DISABLED && val != KLP_ENABLED)
return -EINVAL;
patch = container_of(kobj, struct klp_patch, kobj);
mutex_lock(&klp_mutex);
if (val == patch->state) {
/* already in requested state */
ret = -EINVAL;
goto err;
}
if (val == KLP_ENABLED) {
ret = __klp_enable_patch(patch);
if (ret)
goto err;
} else {
ret = __klp_disable_patch(patch);
if (ret)
goto err;
}
mutex_unlock(&klp_mutex);
return count;
err:
mutex_unlock(&klp_mutex);
return ret;
}
static ssize_t enabled_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
struct klp_patch *patch;
patch = container_of(kobj, struct klp_patch, kobj);
return snprintf(buf, PAGE_SIZE-1, "%d\n", patch->state);
}
static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
static struct attribute *klp_patch_attrs[] = {
&enabled_kobj_attr.attr,
NULL
};
static void klp_kobj_release_patch(struct kobject *kobj)
{
/*
* Once we have a consistency model we'll need to module_put() the
* patch module here. See klp_register_patch() for more details.
*/
}
static struct kobj_type klp_ktype_patch = {
.release = klp_kobj_release_patch,
.sysfs_ops = &kobj_sysfs_ops,
.default_attrs = klp_patch_attrs,
};
static void klp_kobj_release_func(struct kobject *kobj)
{
}
static struct kobj_type klp_ktype_func = {
.release = klp_kobj_release_func,
.sysfs_ops = &kobj_sysfs_ops,
};
/*
* Free all functions' kobjects in the array up to some limit. When limit is
* NULL, all kobjects are freed.
*/
static void klp_free_funcs_limited(struct klp_object *obj,
struct klp_func *limit)
{
struct klp_func *func;
for (func = obj->funcs; func->old_name && func != limit; func++)
kobject_put(&func->kobj);
}
/* Clean up when a patched object is unloaded */
static void klp_free_object_loaded(struct klp_object *obj)
{
struct klp_func *func;
obj->mod = NULL;
for (func = obj->funcs; func->old_name; func++)
func->old_addr = 0;
}
/*
* Free all objects' kobjects in the array up to some limit. When limit is
* NULL, all kobjects are freed.
*/
static void klp_free_objects_limited(struct klp_patch *patch,
struct klp_object *limit)
{
struct klp_object *obj;
for (obj = patch->objs; obj->funcs && obj != limit; obj++) {
klp_free_funcs_limited(obj, NULL);
kobject_put(obj->kobj);
}
}
static void klp_free_patch(struct klp_patch *patch)
{
klp_free_objects_limited(patch, NULL);
if (!list_empty(&patch->list))
list_del(&patch->list);
kobject_put(&patch->kobj);
}
static int klp_init_func(struct klp_object *obj, struct klp_func *func)
{
INIT_LIST_HEAD(&func->stack_node);
func->state = KLP_DISABLED;
return kobject_init_and_add(&func->kobj, &klp_ktype_func,
obj->kobj, "%s", func->old_name);
}
/* parts of the initialization that is done only when the object is loaded */
static int klp_init_object_loaded(struct klp_patch *patch,
struct klp_object *obj)
{
struct klp_func *func;
int ret;
if (obj->relocs) {
ret = klp_write_object_relocations(patch->mod, obj);
if (ret)
return ret;
}
for (func = obj->funcs; func->old_name; func++) {
ret = klp_find_verify_func_addr(obj, func);
if (ret)
return ret;
}
return 0;
}
static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
{
struct klp_func *func;
int ret;
const char *name;
if (!obj->funcs)
return -EINVAL;
obj->state = KLP_DISABLED;
obj->mod = NULL;
klp_find_object_module(obj);
name = klp_is_module(obj) ? obj->name : "vmlinux";
obj->kobj = kobject_create_and_add(name, &patch->kobj);
if (!obj->kobj)
return -ENOMEM;
for (func = obj->funcs; func->old_name; func++) {
ret = klp_init_func(obj, func);
if (ret)
goto free;
}
if (klp_is_object_loaded(obj)) {
ret = klp_init_object_loaded(patch, obj);
if (ret)
goto free;
}
return 0;
free:
klp_free_funcs_limited(obj, func);
kobject_put(obj->kobj);
return ret;
}
static int klp_init_patch(struct klp_patch *patch)
{
struct klp_object *obj;
int ret;
if (!patch->objs)
return -EINVAL;
mutex_lock(&klp_mutex);
patch->state = KLP_DISABLED;
ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
klp_root_kobj, "%s", patch->mod->name);
if (ret)
goto unlock;
for (obj = patch->objs; obj->funcs; obj++) {
ret = klp_init_object(patch, obj);
if (ret)
goto free;
}
list_add_tail(&patch->list, &klp_patches);
mutex_unlock(&klp_mutex);
return 0;
free:
klp_free_objects_limited(patch, obj);
kobject_put(&patch->kobj);
unlock:
mutex_unlock(&klp_mutex);
return ret;
}
/**
* klp_unregister_patch() - unregisters a patch
* @patch: Disabled patch to be unregistered
*
* Frees the data structures and removes the sysfs interface.
*
* Return: 0 on success, otherwise error
*/
int klp_unregister_patch(struct klp_patch *patch)
{
int ret = 0;
mutex_lock(&klp_mutex);
if (!klp_is_patch_registered(patch)) {
ret = -EINVAL;
goto out;
}
if (patch->state == KLP_ENABLED) {
ret = -EBUSY;
goto out;
}
klp_free_patch(patch);
out:
mutex_unlock(&klp_mutex);
return ret;
}
EXPORT_SYMBOL_GPL(klp_unregister_patch);
/**
* klp_register_patch() - registers a patch
* @patch: Patch to be registered
*
* Initializes the data structure associated with the patch and
* creates the sysfs interface.
*
* Return: 0 on success, otherwise error
*/
int klp_register_patch(struct klp_patch *patch)
{
int ret;
if (!klp_initialized())
return -ENODEV;
if (!patch || !patch->mod)
return -EINVAL;
/*
* A reference is taken on the patch module to prevent it from being
* unloaded. Right now, we don't allow patch modules to unload since
* there is currently no method to determine if a thread is still
* running in the patched code contained in the patch module once
* the ftrace registration is successful.
*/
if (!try_module_get(patch->mod))
return -ENODEV;
ret = klp_init_patch(patch);
if (ret)
module_put(patch->mod);
return ret;
}
EXPORT_SYMBOL_GPL(klp_register_patch);
static void klp_module_notify_coming(struct klp_patch *patch,
struct klp_object *obj)
{
struct module *pmod = patch->mod;
struct module *mod = obj->mod;
int ret;
ret = klp_init_object_loaded(patch, obj);
if (ret)
goto err;
if (patch->state == KLP_DISABLED)
return;
pr_notice("applying patch '%s' to loading module '%s'\n",
pmod->name, mod->name);
ret = klp_enable_object(obj);
if (!ret)
return;
err:
pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
pmod->name, mod->name, ret);
}
static void klp_module_notify_going(struct klp_patch *patch,
struct klp_object *obj)
{
struct module *pmod = patch->mod;
struct module *mod = obj->mod;
int ret;
if (patch->state == KLP_DISABLED)
goto disabled;
pr_notice("reverting patch '%s' on unloading module '%s'\n",
pmod->name, mod->name);
ret = klp_disable_object(obj);
if (ret)
pr_warn("failed to revert patch '%s' on module '%s' (%d)\n",
pmod->name, mod->name, ret);
disabled:
klp_free_object_loaded(obj);
}
static int klp_module_notify(struct notifier_block *nb, unsigned long action,
void *data)
{
struct module *mod = data;
struct klp_patch *patch;
struct klp_object *obj;
if (action != MODULE_STATE_COMING && action != MODULE_STATE_GOING)
return 0;
mutex_lock(&klp_mutex);
/*
* Each module has to know that the notifier has been called.
* We never know what module will get patched by a new patch.
*/
if (action == MODULE_STATE_COMING)
mod->klp_alive = true;
else /* MODULE_STATE_GOING */
mod->klp_alive = false;
list_for_each_entry(patch, &klp_patches, list) {
for (obj = patch->objs; obj->funcs; obj++) {
if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
continue;
if (action == MODULE_STATE_COMING) {
obj->mod = mod;
klp_module_notify_coming(patch, obj);
} else /* MODULE_STATE_GOING */
klp_module_notify_going(patch, obj);
break;
}
}
mutex_unlock(&klp_mutex);
return 0;
}
static struct notifier_block klp_module_nb = {
.notifier_call = klp_module_notify,
.priority = INT_MIN+1, /* called late but before ftrace notifier */
};
static int klp_init(void)
{
int ret;
ret = klp_check_compiler_support();
if (ret) {
pr_info("Your compiler is too old; turning off.\n");
return -EINVAL;
}
ret = register_module_notifier(&klp_module_nb);
if (ret)
return ret;
klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
if (!klp_root_kobj) {
ret = -ENOMEM;
goto unregister;
}
return 0;
unregister:
unregister_module_notifier(&klp_module_nb);
return ret;
}
module_init(klp_init);