// SPDX-License-Identifier: GPL-2.0-or-later
/*
* core.c - Kernel Live Patching Core
*
* Copyright (C) 2014 Seth Jennings <[email protected]>
* Copyright (C) 2014 SUSE
*/
#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/list.h>
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
#include <linux/elf.h>
#include <linux/moduleloader.h>
#include <linux/completion.h>
#include <linux/memory.h>
#include <linux/rcupdate.h>
#include <asm/cacheflush.h>
#include "core.h"
#include "patch.h"
#include "state.h"
#include "transition.h"
/*
* klp_mutex is a coarse lock which serializes access to klp data. All
* accesses to klp-related variables and structures must have mutex protection,
* except within the following functions which carefully avoid the need for it:
*
* - klp_ftrace_handler()
* - klp_update_patch_state()
* - __klp_sched_try_switch()
*/
DEFINE_MUTEX(klp_mutex);
/*
* Actively used patches: enabled or in transition. Note that replaced
* or disabled patches are not listed even though the related kernel
* module still can be loaded.
*/
LIST_HEAD(klp_patches);
static struct kobject *klp_root_kobj;
static bool klp_is_module(struct klp_object *obj)
{
return obj->name;
}
/* 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;
rcu_read_lock_sched();
/*
* We do not want to block removal of patched modules and therefore
* we do not take a reference here. The patches are removed by
* klp_module_going() instead.
*/
mod = find_module(obj->name);
/*
* Do not mess work of klp_module_coming() and klp_module_going().
* Note that the patch might still be needed before klp_module_going()
* 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;
rcu_read_unlock_sched();
}
static bool klp_initialized(void)
{
return !!klp_root_kobj;
}
static struct klp_func *klp_find_func(struct klp_object *obj,
struct klp_func *old_func)
{
struct klp_func *func;
klp_for_each_func(obj, func) {
if ((strcmp(old_func->old_name, func->old_name) == 0) &&
(old_func->old_sympos == func->old_sympos)) {
return func;
}
}
return NULL;
}
static struct klp_object *klp_find_object(struct klp_patch *patch,
struct klp_object *old_obj)
{
struct klp_object *obj;
klp_for_each_object(patch, obj) {
if (klp_is_module(old_obj)) {
if (klp_is_module(obj) &&
strcmp(old_obj->name, obj->name) == 0) {
return obj;
}
} else if (!klp_is_module(obj)) {
return obj;
}
}
return NULL;
}
struct klp_find_arg {
const char *name;
unsigned long addr;
unsigned long count;
unsigned long pos;
};
static int klp_match_callback(void *data, unsigned long addr)
{
struct klp_find_arg *args = data;
args->addr = addr;
args->count++;
/*
* Finish the search when the symbol is found for the desired position
* or the position is not defined for a non-unique symbol.
*/
if ((args->pos && (args->count == args->pos)) ||
(!args->pos && (args->count > 1)))
return 1;
return 0;
}
static int klp_find_callback(void *data, const char *name, unsigned long addr)
{
struct klp_find_arg *args = data;
if (strcmp(args->name, name))
return 0;
return klp_match_callback(data, addr);
}
static int klp_find_object_symbol(const char *objname, const char *name,
unsigned long sympos, unsigned long *addr)
{
struct klp_find_arg args = {
.name = name,
.addr = 0,
.count = 0,
.pos = sympos,
};
if (objname)
module_kallsyms_on_each_symbol(objname, klp_find_callback, &args);
else
kallsyms_on_each_match_symbol(klp_match_callback, name, &args);
/*
* Ensure an address was found. If sympos is 0, ensure symbol is unique;
* otherwise ensure the symbol position count matches sympos.
*/
if (args.addr == 0)
pr_err("symbol '%s' not found in symbol table\n", name);
else if (args.count > 1 && sympos == 0) {
pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
name, objname);
} else if (sympos != args.count && sympos > 0) {
pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
sympos, name, objname ? objname : "vmlinux");
} else {
*addr = args.addr;
return 0;
}
*addr = 0;
return -EINVAL;
}
static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab,
unsigned int symndx, Elf_Shdr *relasec,
const char *sec_objname)
{
int i, cnt, ret;
char sym_objname[MODULE_NAME_LEN];
char sym_name[KSYM_NAME_LEN];
Elf_Rela *relas;
Elf_Sym *sym;
unsigned long sympos, addr;
bool sym_vmlinux;
bool sec_vmlinux = !strcmp(sec_objname, "vmlinux");
/*
* Since the field widths for sym_objname and sym_name in the sscanf()
* call are hard-coded and correspond to MODULE_NAME_LEN and
* KSYM_NAME_LEN respectively, we must make sure that MODULE_NAME_LEN
* and KSYM_NAME_LEN have the values we expect them to have.
*
* Because the value of MODULE_NAME_LEN can differ among architectures,
* we use the smallest/strictest upper bound possible (56, based on
* the current definition of MODULE_NAME_LEN) to prevent overflows.
*/
BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 512);
relas = (Elf_Rela *) relasec->sh_addr;
/* For each rela in this klp relocation section */
for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) {
sym = (Elf_Sym *)sechdrs[symndx].sh_addr + ELF_R_SYM(relas[i].r_info);
if (sym->st_shndx != SHN_LIVEPATCH) {
pr_err("symbol %s is not marked as a livepatch symbol\n",
strtab + sym->st_name);
return -EINVAL;
}
/* Format: .klp.sym.sym_objname.sym_name,sympos */
cnt = sscanf(strtab + sym->st_name,
".klp.sym.%55[^.].%511[^,],%lu",
sym_objname, sym_name, &sympos);
if (cnt != 3) {
pr_err("symbol %s has an incorrectly formatted name\n",
strtab + sym->st_name);
return -EINVAL;
}
sym_vmlinux = !strcmp(sym_objname, "vmlinux");
/*
* Prevent module-specific KLP rela sections from referencing
* vmlinux symbols. This helps prevent ordering issues with
* module special section initializations. Presumably such
* symbols are exported and normal relas can be used instead.
*/
if (!sec_vmlinux && sym_vmlinux) {
pr_err("invalid access to vmlinux symbol '%s' from module-specific livepatch relocation section\n",
sym_name);
return -EINVAL;
}
/* klp_find_object_symbol() treats a NULL objname as vmlinux */
ret = klp_find_object_symbol(sym_vmlinux ? NULL : sym_objname,
sym_name, sympos, &addr);
if (ret)
return ret;
sym->st_value = addr;
}
return 0;
}
void __weak clear_relocate_add(Elf_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me)
{
}
/*
* At a high-level, there are two types of klp relocation sections: those which
* reference symbols which live in vmlinux; and those which reference symbols
* which live in other modules. This function is called for both types:
*
* 1) When a klp module itself loads, the module code calls this function to
* write vmlinux-specific klp relocations (.klp.rela.vmlinux.* sections).
* These relocations are written to the klp module text to allow the patched
* code/data to reference unexported vmlinux symbols. They're written as
* early as possible to ensure that other module init code (.e.g.,
* jump_label_apply_nops) can access any unexported vmlinux symbols which
* might be referenced by the klp module's special sections.
*
* 2) When a to-be-patched module loads -- or is already loaded when a
* corresponding klp module loads -- klp code calls this function to write
* module-specific klp relocations (.klp.rela.{module}.* sections). These
* are written to the klp module text to allow the patched code/data to
* reference symbols which live in the to-be-patched module or one of its
* module dependencies. Exported symbols are supported, in addition to
* unexported symbols, in order to enable late module patching, which allows
* the to-be-patched module to be loaded and patched sometime *after* the
* klp module is loaded.
*/
static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
const char *shstrtab, const char *strtab,
unsigned int symndx, unsigned int secndx,
const char *objname, bool apply)
{
int cnt, ret;
char sec_objname[MODULE_NAME_LEN];
Elf_Shdr *sec = sechdrs + secndx;
/*
* Format: .klp.rela.sec_objname.section_name
* See comment in klp_resolve_symbols() for an explanation
* of the selected field width value.
*/
cnt = sscanf(shstrtab + sec->sh_name, ".klp.rela.%55[^.]",
sec_objname);
if (cnt != 1) {
pr_err("section %s has an incorrectly formatted name\n",
shstrtab + sec->sh_name);
return -EINVAL;
}
if (strcmp(objname ? objname : "vmlinux", sec_objname))
return 0;
if (apply) {
ret = klp_resolve_symbols(sechdrs, strtab, symndx,
sec, sec_objname);
if (ret)
return ret;
return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
}
clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
return 0;
}
int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
const char *shstrtab, const char *strtab,
unsigned int symndx, unsigned int secndx,
const char *objname)
{
return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx,
secndx, objname, true);
}
/*
* Sysfs Interface
*
* /sys/kernel/livepatch
* /sys/kernel/livepatch/<patch>
* /sys/kernel/livepatch/<patch>/enabled
* /sys/kernel/livepatch/<patch>/transition
* /sys/kernel/livepatch/<patch>/force
* /sys/kernel/livepatch/<patch>/replace
* /sys/kernel/livepatch/<patch>/<object>
* /sys/kernel/livepatch/<patch>/<object>/patched
* /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
*/
static int __klp_disable_patch(struct klp_patch *patch);
static ssize_t enabled_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
struct klp_patch *patch;
int ret;
bool enabled;
ret = kstrtobool(buf, &enabled);
if (ret)
return ret;
patch = container_of(kobj, struct klp_patch, kobj);
mutex_lock(&klp_mutex);
if (patch->enabled == enabled) {
/* already in requested state */
ret = -EINVAL;
goto out;
}
/*
* Allow to reverse a pending transition in both ways. It might be
* necessary to complete the transition without forcing and breaking
* the system integrity.
*
* Do not allow to re-enable a disabled patch.
*/
if (patch == klp_transition_patch)
klp_reverse_transition();
else if (!enabled)
ret = __klp_disable_patch(patch);
else
ret = -EINVAL;
out:
mutex_unlock(&klp_mutex);
if (ret)
return ret;
return count;
}
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 sysfs_emit(buf, "%d\n", patch->enabled);
}
static ssize_t transition_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
struct klp_patch *patch;
patch = container_of(kobj, struct klp_patch, kobj);
return sysfs_emit(buf, "%d\n", patch == klp_transition_patch);
}
static ssize_t force_store(struct kobject *kobj, struct kobj_attribute *attr,
const char *buf, size_t count)
{
struct klp_patch *patch;
int ret;
bool val;
ret = kstrtobool(buf, &val);
if (ret)
return ret;
if (!val)
return count;
mutex_lock(&klp_mutex);
patch = container_of(kobj, struct klp_patch, kobj);
if (patch != klp_transition_patch) {
mutex_unlock(&klp_mutex);
return -EINVAL;
}
klp_force_transition();
mutex_unlock(&klp_mutex);
return count;
}
static ssize_t replace_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
struct klp_patch *patch;
patch = container_of(kobj, struct klp_patch, kobj);
return sysfs_emit(buf, "%d\n", patch->replace);
}
static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
static struct kobj_attribute force_kobj_attr = __ATTR_WO(force);
static struct kobj_attribute replace_kobj_attr = __ATTR_RO(replace);
static struct attribute *klp_patch_attrs[] = {
&enabled_kobj_attr.attr,
&transition_kobj_attr.attr,
&force_kobj_attr.attr,
&replace_kobj_attr.attr,
NULL
};
ATTRIBUTE_GROUPS(klp_patch);
static ssize_t patched_show(struct kobject *kobj,
struct kobj_attribute *attr, char *buf)
{
struct klp_object *obj;
obj = container_of(kobj, struct klp_object, kobj);
return sysfs_emit(buf, "%d\n", obj->patched);
}
static struct kobj_attribute patched_kobj_attr = __ATTR_RO(patched);
static struct attribute *klp_object_attrs[] = {
&patched_kobj_attr.attr,
NULL,
};
ATTRIBUTE_GROUPS(klp_object);
static void klp_free_object_dynamic(struct klp_object *obj)
{
kfree(obj->name);
kfree(obj);
}
static void klp_init_func_early(struct klp_object *obj,
struct klp_func *func);
static void klp_init_object_early(struct klp_patch *patch,
struct klp_object *obj);
static struct klp_object *klp_alloc_object_dynamic(const char *name,
struct klp_patch *patch)
{
struct klp_object *obj;
obj = kzalloc(sizeof(*obj), GFP_KERNEL);
if (!obj)
return NULL;
if (name) {
obj->name = kstrdup(name, GFP_KERNEL);
if (!obj->name) {
kfree(obj);
return NULL;
}
}
klp_init_object_early(patch, obj);
obj->dynamic = true;
return obj;
}
static void klp_free_func_nop(struct klp_func *func)
{
kfree(func->old_name);
kfree(func);
}
static struct klp_func *klp_alloc_func_nop(struct klp_func *old_func,
struct klp_object *obj)
{
struct klp_func *func;
func = kzalloc(sizeof(*func), GFP_KERNEL);
if (!func)
return NULL;
if (old_func->old_name) {
func->old_name = kstrdup(old_func->old_name, GFP_KERNEL);
if (!func->old_name) {
kfree(func);
return NULL;
}
}
klp_init_func_early(obj, func);
/*
* func->new_func is same as func->old_func. These addresses are
* set when the object is loaded, see klp_init_object_loaded().
*/
func->old_sympos = old_func->old_sympos;
func->nop = true;
return func;
}
static int klp_add_object_nops(struct klp_patch *patch,
struct klp_object *old_obj)
{
struct klp_object *obj;
struct klp_func *func, *old_func;
obj = klp_find_object(patch, old_obj);
if (!obj) {
obj = klp_alloc_object_dynamic(old_obj->name, patch);
if (!obj)
return -ENOMEM;
}
klp_for_each_func(old_obj, old_func) {
func = klp_find_func(obj, old_func);
if (func)
continue;
func = klp_alloc_func_nop(old_func, obj);
if (!func)
return -ENOMEM;
}
return 0;
}
/*
* Add 'nop' functions which simply return to the caller to run
* the original function. The 'nop' functions are added to a
* patch to facilitate a 'replace' mode.
*/
static int klp_add_nops(struct klp_patch *patch)
{
struct klp_patch *old_patch;
struct klp_object *old_obj;
klp_for_each_patch(old_patch) {
klp_for_each_object(old_patch, old_obj) {
int err;
err = klp_add_object_nops(patch, old_obj);
if (err)
return err;
}
}
return 0;
}
static void klp_kobj_release_patch(struct kobject *kobj)
{
struct klp_patch *patch;
patch = container_of(kobj, struct klp_patch, kobj);
complete(&patch->finish);
}
static const struct kobj_type klp_ktype_patch = {
.release = klp_kobj_release_patch,
.sysfs_ops = &kobj_sysfs_ops,
.default_groups = klp_patch_groups,
};
static void klp_kobj_release_object(struct kobject *kobj)
{
struct klp_object *obj;
obj = container_of(kobj, struct klp_object, kobj);
if (obj->dynamic)
klp_free_object_dynamic(obj);
}
static const struct kobj_type klp_ktype_object = {
.release = klp_kobj_release_object,
.sysfs_ops = &kobj_sysfs_ops,
.default_groups = klp_object_groups,
};
static void klp_kobj_release_func(struct kobject *kobj)
{
struct klp_func *func;
func = container_of(kobj, struct klp_func, kobj);
if (func->nop)
klp_free_func_nop(func);
}
static const struct kobj_type klp_ktype_func = {
.release = klp_kobj_release_func,
.sysfs_ops = &kobj_sysfs_ops,
};
static void __klp_free_funcs(struct klp_object *obj, bool nops_only)
{
struct klp_func *func, *tmp_func;
klp_for_each_func_safe(obj, func, tmp_func) {
if (nops_only && !func->nop)
continue;
list_del(&func->node);
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;
klp_for_each_func(obj, func) {
func->old_func = NULL;
if (func->nop)
func->new_func = NULL;
}
}
static void __klp_free_objects(struct klp_patch *patch, bool nops_only)
{
struct klp_object *obj, *tmp_obj;
klp_for_each_object_safe(patch, obj, tmp_obj) {
__klp_free_funcs(obj, nops_only);
if (nops_only && !obj->dynamic)
continue;
list_del(&obj->node);
kobject_put(&obj->kobj);
}
}
static void klp_free_objects(struct klp_patch *patch)
{
__klp_free_objects(patch, false);
}
static void klp_free_objects_dynamic(struct klp_patch *patch)
{
__klp_free_objects(patch, true);
}
/*
* This function implements the free operations that can be called safely
* under klp_mutex.
*
* The operation must be completed by calling klp_free_patch_finish()
* outside klp_mutex.
*/
static void klp_free_patch_start(struct klp_patch *patch)
{
if (!list_empty(&patch->list))
list_del(&patch->list);
klp_free_objects(patch);
}
/*
* This function implements the free part that must be called outside
* klp_mutex.
*
* It must be called after klp_free_patch_start(). And it has to be
* the last function accessing the livepatch structures when the patch
* gets disabled.
*/
static void klp_free_patch_finish(struct klp_patch *patch)
{
/*
* Avoid deadlock with enabled_store() sysfs callback by
* calling this outside klp_mutex. It is safe because
* this is called when the patch gets disabled and it
* cannot get enabled again.
*/
kobject_put(&patch->kobj);
wait_for_completion(&patch->finish);
/* Put the module after the last access to struct klp_patch. */
if (!patch->forced)
module_put(patch->mod);
}
/*
* The livepatch might be freed from sysfs interface created by the patch.
* This work allows to wait until the interface is destroyed in a separate
* context.
*/
static void klp_free_patch_work_fn(struct work_struct *work)
{
struct klp_patch *patch =
container_of(work, struct klp_patch, free_work);
klp_free_patch_finish(patch);
}
void klp_free_patch_async(struct klp_patch *patch)
{
klp_free_patch_start(patch);
schedule_work(&patch->free_work);
}
void klp_free_replaced_patches_async(struct klp_patch *new_patch)
{
struct klp_patch *old_patch, *tmp_patch;
klp_for_each_patch_safe(old_patch, tmp_patch) {
if (old_patch == new_patch)
return;
klp_free_patch_async(old_patch);
}
}
static int klp_init_func(struct klp_object *obj, struct klp_func *func)
{
if (!func->old_name)
return -EINVAL;
/*
* NOPs get the address later. The patched module must be loaded,
* see klp_init_object_loaded().
*/
if (!func->new_func && !func->nop)
return -EINVAL;
if (strlen(func->old_name) >= KSYM_NAME_LEN)
return -EINVAL;
INIT_LIST_HEAD(&func->stack_node);
func->patched = false;
func->transition = false;
/* The format for the sysfs directory is <function,sympos> where sympos
* is the nth occurrence of this symbol in kallsyms for the patched
* object. If the user selects 0 for old_sympos, then 1 will be used
* since a unique symbol will be the first occurrence.
*/
return kobject_add(&func->kobj, &obj->kobj, "%s,%lu",
func->old_name,
func->old_sympos ? func->old_sympos : 1);
}
static int klp_write_object_relocs(struct klp_patch *patch,
struct klp_object *obj,
bool apply)
{
int i, ret;
struct klp_modinfo *info = patch->mod->klp_info;
for (i = 1; i < info->hdr.e_shnum; i++) {
Elf_Shdr *sec = info->sechdrs + i;
if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
continue;
ret = klp_write_section_relocs(patch->mod, info->sechdrs,
info->secstrings,
patch->mod->core_kallsyms.strtab,
info->symndx, i, obj->name, apply);
if (ret)
return ret;
}
return 0;
}
static int klp_apply_object_relocs(struct klp_patch *patch,
struct klp_object *obj)
{
return klp_write_object_relocs(patch, obj, true);
}
static void klp_clear_object_relocs(struct klp_patch *patch,
struct klp_object *obj)
{
klp_write_object_relocs(patch, obj, false);
}
/* 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 (klp_is_module(obj)) {
/*
* Only write module-specific relocations here
* (.klp.rela.{module}.*). vmlinux-specific relocations were
* written earlier during the initialization of the klp module
* itself.
*/
ret = klp_apply_object_relocs(patch, obj);
if (ret)
return ret;
}
klp_for_each_func(obj, func) {
ret = klp_find_object_symbol(obj->name, func->old_name,
func->old_sympos,
(unsigned long *)&func->old_func);
if (ret)
return ret;
ret = kallsyms_lookup_size_offset((unsigned long)func->old_func,
&func->old_size, NULL);
if (!ret) {
pr_err("kallsyms size lookup failed for '%s'\n",
func->old_name);
return -ENOENT;
}
if (func->nop)
func->new_func = func->old_func;
ret = kallsyms_lookup_size_offset((unsigned long)func->new_func,
&func->new_size, NULL);
if (!ret) {
pr_err("kallsyms size lookup failed for '%s' replacement\n",
func->old_name);
return -ENOENT;
}
}
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 (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
return -EINVAL;
obj->patched = false;
obj->mod = NULL;
klp_find_object_module(obj);
name = klp_is_module(obj) ? obj->name : "vmlinux";
ret = kobject_add(&obj->kobj, &patch->kobj, "%s", name);
if (ret)
return ret;
klp_for_each_func(obj, func) {
ret = klp_init_func(obj, func);
if (ret)
return ret;
}
if (klp_is_object_loaded(obj))
ret = klp_init_object_loaded(patch, obj);
return ret;
}
static void klp_init_func_early(struct klp_object *obj,
struct klp_func *func)
{
kobject_init(&func->kobj, &klp_ktype_func);
list_add_tail(&func->node, &obj->func_list);
}
static void klp_init_object_early(struct klp_patch *patch,
struct klp_object *obj)
{
INIT_LIST_HEAD(&obj->func_list);
kobject_init(&obj->kobj, &klp_ktype_object);
list_add_tail(&obj->node, &patch->obj_list);
}
static void klp_init_patch_early(struct klp_patch *patch)
{
struct klp_object *obj;
struct klp_func *func;
INIT_LIST_HEAD(&patch->list);
INIT_LIST_HEAD(&patch->obj_list);
kobject_init(&patch->kobj, &klp_ktype_patch);
patch->enabled = false;
patch->forced = false;
INIT_WORK(&patch->free_work, klp_free_patch_work_fn);
init_completion(&patch->finish);
klp_for_each_object_static(patch, obj) {
klp_init_object_early(patch, obj);
klp_for_each_func_static(obj, func) {
klp_init_func_early(obj, func);
}
}
}
static int klp_init_patch(struct klp_patch *patch)
{
struct klp_object *obj;
int ret;
ret = kobject_add(&patch->kobj, klp_root_kobj, "%s", patch->mod->name);
if (ret)
return ret;
if (patch->replace) {
ret = klp_add_nops(patch);
if (ret)
return ret;
}
klp_for_each_object(patch, obj) {
ret = klp_init_object(patch, obj);
if (ret)
return ret;
}
list_add_tail(&patch->list, &klp_patches);
return 0;
}
static int __klp_disable_patch(struct klp_patch *patch)
{
struct klp_object *obj;
if (WARN_ON(!patch->enabled))
return -EINVAL;
if (klp_transition_patch)
return -EBUSY;
klp_init_transition(patch, KLP_TRANSITION_UNPATCHED);
klp_for_each_object(patch, obj)
if (obj->patched)
klp_pre_unpatch_callback(obj);
/*
* Enforce the order of the func->transition writes in
* klp_init_transition() and the TIF_PATCH_PENDING writes in
* klp_start_transition(). In the rare case where klp_ftrace_handler()
* is called shortly after klp_update_patch_state() switches the task,
* this ensures the handler sees that func->transition is set.
*/
smp_wmb();
klp_start_transition();
patch->enabled = false;
klp_try_complete_transition();
return 0;
}
static int __klp_enable_patch(struct klp_patch *patch)
{
struct klp_object *obj;
int ret;
if (klp_transition_patch)
return -EBUSY;
if (WARN_ON(patch->enabled))
return -EINVAL;
pr_notice("enabling patch '%s'\n", patch->mod->name);
klp_init_transition(patch, KLP_TRANSITION_PATCHED);
/*
* Enforce the order of the func->transition writes in
* klp_init_transition() and the ops->func_stack writes in
* klp_patch_object(), so that klp_ftrace_handler() will see the
* func->transition updates before the handler is registered and the
* new funcs become visible to the handler.
*/
smp_wmb();
klp_for_each_object(patch, obj) {
if (!klp_is_object_loaded(obj))
continue;
ret = klp_pre_patch_callback(obj);
if (ret) {
pr_warn("pre-patch callback failed for object '%s'\n",
klp_is_module(obj) ? obj->name : "vmlinux");
goto err;
}
ret = klp_patch_object(obj);
if (ret) {
pr_warn("failed to patch object '%s'\n",
klp_is_module(obj) ? obj->name : "vmlinux");
goto err;
}
}
klp_start_transition();
patch->enabled = true;
klp_try_complete_transition();
return 0;
err:
pr_warn("failed to enable patch '%s'\n", patch->mod->name);
klp_cancel_transition();
return ret;
}
/**
* klp_enable_patch() - enable the livepatch
* @patch: patch to be enabled
*
* Initializes the data structure associated with the patch, creates the sysfs
* interface, performs the needed symbol lookups and code relocations,
* registers the patched functions with ftrace.
*
* This function is supposed to be called from the livepatch module_init()
* callback.
*
* Return: 0 on success, otherwise error
*/
int klp_enable_patch(struct klp_patch *patch)
{
int ret;
struct klp_object *obj;
if (!patch || !patch->mod || !patch->objs)
return -EINVAL;
klp_for_each_object_static(patch, obj) {
if (!obj->funcs)
return -EINVAL;
}
if (!is_livepatch_module(patch->mod)) {
pr_err("module %s is not marked as a livepatch module\n",
patch->mod->name);
return -EINVAL;
}
if (!klp_initialized())
return -ENODEV;
if (!klp_have_reliable_stack()) {
pr_warn("This architecture doesn't have support for the livepatch consistency model.\n");
pr_warn("The livepatch transition may never complete.\n");
}
mutex_lock(&klp_mutex);
if (!klp_is_patch_compatible(patch)) {
pr_err("Livepatch patch (%s) is not compatible with the already installed livepatches.\n",
patch->mod->name);
mutex_unlock(&klp_mutex);
return -EINVAL;
}
if (!try_module_get(patch->mod)) {
mutex_unlock(&klp_mutex);
return -ENODEV;
}
klp_init_patch_early(patch);
ret = klp_init_patch(patch);
if (ret)
goto err;
ret = __klp_enable_patch(patch);
if (ret)
goto err;
mutex_unlock(&klp_mutex);
return 0;
err:
klp_free_patch_start(patch);
mutex_unlock(&klp_mutex);
klp_free_patch_finish(patch);
return ret;
}
EXPORT_SYMBOL_GPL(klp_enable_patch);
/*
* This function unpatches objects from the replaced livepatches.
*
* We could be pretty aggressive here. It is called in the situation where
* these structures are no longer accessed from the ftrace handler.
* All functions are redirected by the klp_transition_patch. They
* use either a new code or they are in the original code because
* of the special nop function patches.
*
* The only exception is when the transition was forced. In this case,
* klp_ftrace_handler() might still see the replaced patch on the stack.
* Fortunately, it is carefully designed to work with removed functions
* thanks to RCU. We only have to keep the patches on the system. Also
* this is handled transparently by patch->module_put.
*/
void klp_unpatch_replaced_patches(struct klp_patch *new_patch)
{
struct klp_patch *old_patch;
klp_for_each_patch(old_patch) {
if (old_patch == new_patch)
return;
old_patch->enabled = false;
klp_unpatch_objects(old_patch);
}
}
/*
* This function removes the dynamically allocated 'nop' functions.
*
* We could be pretty aggressive. NOPs do not change the existing
* behavior except for adding unnecessary delay by the ftrace handler.
*
* It is safe even when the transition was forced. The ftrace handler
* will see a valid ops->func_stack entry thanks to RCU.
*
* We could even free the NOPs structures. They must be the last entry
* in ops->func_stack. Therefore unregister_ftrace_function() is called.
* It does the same as klp_synchronize_transition() to make sure that
* nobody is inside the ftrace handler once the operation finishes.
*
* IMPORTANT: It must be called right after removing the replaced patches!
*/
void klp_discard_nops(struct klp_patch *new_patch)
{
klp_unpatch_objects_dynamic(klp_transition_patch);
klp_free_objects_dynamic(klp_transition_patch);
}
/*
* Remove parts of patches that touch a given kernel module. The list of
* patches processed might be limited. When limit is NULL, all patches
* will be handled.
*/
static void klp_cleanup_module_patches_limited(struct module *mod,
struct klp_patch *limit)
{
struct klp_patch *patch;
struct klp_object *obj;
klp_for_each_patch(patch) {
if (patch == limit)
break;
klp_for_each_object(patch, obj) {
if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
continue;
if (patch != klp_transition_patch)
klp_pre_unpatch_callback(obj);
pr_notice("reverting patch '%s' on unloading module '%s'\n",
patch->mod->name, obj->mod->name);
klp_unpatch_object(obj);
klp_post_unpatch_callback(obj);
klp_clear_object_relocs(patch, obj);
klp_free_object_loaded(obj);
break;
}
}
}
int klp_module_coming(struct module *mod)
{
int ret;
struct klp_patch *patch;
struct klp_object *obj;
if (WARN_ON(mod->state != MODULE_STATE_COMING))
return -EINVAL;
if (!strcmp(mod->name, "vmlinux")) {
pr_err("vmlinux.ko: invalid module name\n");
return -EINVAL;
}
mutex_lock(&klp_mutex);
/*
* Each module has to know that klp_module_coming()
* has been called. We never know what module will
* get patched by a new patch.
*/
mod->klp_alive = true;
klp_for_each_patch(patch) {
klp_for_each_object(patch, obj) {
if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
continue;
obj->mod = mod;
ret = klp_init_object_loaded(patch, obj);
if (ret) {
pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
patch->mod->name, obj->mod->name, ret);
goto err;
}
pr_notice("applying patch '%s' to loading module '%s'\n",
patch->mod->name, obj->mod->name);
ret = klp_pre_patch_callback(obj);
if (ret) {
pr_warn("pre-patch callback failed for object '%s'\n",
obj->name);
goto err;
}
ret = klp_patch_object(obj);
if (ret) {
pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
patch->mod->name, obj->mod->name, ret);
klp_post_unpatch_callback(obj);
goto err;
}
if (patch != klp_transition_patch)
klp_post_patch_callback(obj);
break;
}
}
mutex_unlock(&klp_mutex);
return 0;
err:
/*
* If a patch is unsuccessfully applied, return
* error to the module loader.
*/
pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
patch->mod->name, obj->mod->name, obj->mod->name);
mod->klp_alive = false;
obj->mod = NULL;
klp_cleanup_module_patches_limited(mod, patch);
mutex_unlock(&klp_mutex);
return ret;
}
void klp_module_going(struct module *mod)
{
if (WARN_ON(mod->state != MODULE_STATE_GOING &&
mod->state != MODULE_STATE_COMING))
return;
mutex_lock(&klp_mutex);
/*
* Each module has to know that klp_module_going()
* has been called. We never know what module will
* get patched by a new patch.
*/
mod->klp_alive = false;
klp_cleanup_module_patches_limited(mod, NULL);
mutex_unlock(&klp_mutex);
}
static int __init klp_init(void)
{
klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
if (!klp_root_kobj)
return -ENOMEM;
return 0;
}
module_init(klp_init);
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