blob: 69bf3aa3bde8200b0a39665898c6cfeab8699cdb [file] [log] [blame]
/*
* 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)
{
if (!klp_is_module(obj))
return;
mutex_lock(&module_mutex);
/*
* We don't need to take a reference on the module here because we have
* the klp_mutex, which is also taken by the module notifier. This
* prevents any module from unloading until we release the klp_mutex.
*/
obj->mod = find_module(obj->name);
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);
preempt_enable();
if (sym) {
*addr = sym->value;
return 0;
}
/* 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);
rcu_read_unlock();
if (WARN_ON_ONCE(!func))
return;
klp_arch_set_pc(regs, (unsigned long)func->new_func);
}
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;
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);
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);