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960 lines (784 loc) · 22 KB
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/*
* 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/list.h>
#include <linux/kallsyms.h>
#include <linux/livepatch.h>
#include <linux/elf.h>
#include <linux/moduleloader.h>
#include <linux/completion.h>
#include <asm/cacheflush.h>
#include "core.h"
#include "patch.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()
*/
DEFINE_MUTEX(klp_mutex);
static LIST_HEAD(klp_patches);
static struct kobject *klp_root_kobj;
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
* 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;
mutex_unlock(&module_mutex);
}
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;
unsigned long count;
unsigned long pos;
};
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 = 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_object_symbol(const char *objname, const char *name,
unsigned long sympos, unsigned long *addr)
{
struct klp_find_arg args = {
.objname = objname,
.name = name,
.addr = 0,
.count = 0,
.pos = sympos,
};
mutex_lock(&module_mutex);
if (objname)
module_kallsyms_on_each_symbol(klp_find_callback, &args);
else
kallsyms_on_each_symbol(klp_find_callback, &args);
mutex_unlock(&module_mutex);
/*
* 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 *relasec, struct module *pmod)
{
int i, cnt, vmlinux, ret;
char objname[MODULE_NAME_LEN];
char symname[KSYM_NAME_LEN];
char *strtab = pmod->core_kallsyms.strtab;
Elf_Rela *relas;
Elf_Sym *sym;
unsigned long sympos, addr;
/*
* Since the field widths for objname and symname 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 != 128);
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 = pmod->core_kallsyms.symtab + 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.objname.symname,sympos */
cnt = sscanf(strtab + sym->st_name,
".klp.sym.%55[^.].%127[^,],%lu",
objname, symname, &sympos);
if (cnt != 3) {
pr_err("symbol %s has an incorrectly formatted name\n",
strtab + sym->st_name);
return -EINVAL;
}
/* klp_find_object_symbol() treats a NULL objname as vmlinux */
vmlinux = !strcmp(objname, "vmlinux");
ret = klp_find_object_symbol(vmlinux ? NULL : objname,
symname, sympos, &addr);
if (ret)
return ret;
sym->st_value = addr;
}
return 0;
}
static int klp_write_object_relocations(struct module *pmod,
struct klp_object *obj)
{
int i, cnt, ret = 0;
const char *objname, *secname;
char sec_objname[MODULE_NAME_LEN];
Elf_Shdr *sec;
if (WARN_ON(!klp_is_object_loaded(obj)))
return -EINVAL;
objname = klp_is_module(obj) ? obj->name : "vmlinux";
/* For each klp relocation section */
for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
sec = pmod->klp_info->sechdrs + i;
secname = pmod->klp_info->secstrings + sec->sh_name;
if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
continue;
/*
* Format: .klp.rela.sec_objname.section_name
* See comment in klp_resolve_symbols() for an explanation
* of the selected field width value.
*/
cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
if (cnt != 1) {
pr_err("section %s has an incorrectly formatted name\n",
secname);
ret = -EINVAL;
break;
}
if (strcmp(objname, sec_objname))
continue;
ret = klp_resolve_symbols(sec, pmod);
if (ret)
break;
ret = apply_relocate_add(pmod->klp_info->sechdrs,
pmod->core_kallsyms.strtab,
pmod->klp_info->symndx, i, pmod);
if (ret)
break;
}
return ret;
}
static int __klp_disable_patch(struct klp_patch *patch)
{
if (klp_transition_patch)
return -EBUSY;
/* enforce stacking: only the last enabled patch can be disabled */
if (!list_is_last(&patch->list, &klp_patches) &&
list_next_entry(patch, list)->enabled)
return -EBUSY;
klp_init_transition(patch, KLP_UNPATCHED);
/*
* 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();
klp_try_complete_transition();
patch->enabled = false;
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->enabled) {
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 (klp_transition_patch)
return -EBUSY;
if (WARN_ON(patch->enabled))
return -EINVAL;
/* enforce stacking: only the first disabled patch can be enabled */
if (patch->list.prev != &klp_patches &&
!list_prev_entry(patch, list)->enabled)
return -EBUSY;
/*
* A reference is taken on the patch module to prevent it from being
* unloaded.
*
* Note: For immediate (no consistency model) patches we don't allow
* patch modules to unload since there is no safe/sane 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;
pr_notice("enabling patch '%s'\n", patch->mod->name);
klp_init_transition(patch, KLP_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_patch_object(obj);
if (ret) {
pr_warn("failed to enable patch '%s'\n",
patch->mod->name);
klp_cancel_transition();
return ret;
}
}
klp_start_transition();
klp_try_complete_transition();
patch->enabled = true;
return 0;
}
/**
* 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>/transition
* /sys/kernel/livepatch/<patch>/<object>
* /sys/kernel/livepatch/<patch>/<object>/<function,sympos>
*/
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 (!klp_is_patch_registered(patch)) {
/*
* Module with the patch could either disappear meanwhile or is
* not properly initialized yet.
*/
ret = -EINVAL;
goto err;
}
if (patch->enabled == enabled) {
/* already in requested state */
ret = -EINVAL;
goto err;
}
if (patch == klp_transition_patch) {
klp_reverse_transition();
} else if (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->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 snprintf(buf, PAGE_SIZE-1, "%d\n",
patch == klp_transition_patch);
}
static struct kobj_attribute enabled_kobj_attr = __ATTR_RW(enabled);
static struct kobj_attribute transition_kobj_attr = __ATTR_RO(transition);
static struct attribute *klp_patch_attrs[] = {
&enabled_kobj_attr.attr,
&transition_kobj_attr.attr,
NULL
};
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 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_object(struct kobject *kobj)
{
}
static struct kobj_type klp_ktype_object = {
.release = klp_kobj_release_object,
.sysfs_ops = &kobj_sysfs_ops,
};
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;
klp_for_each_func(obj, 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);
}
static int klp_init_func(struct klp_object *obj, struct klp_func *func)
{
if (!func->old_name || !func->new_func)
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_init_and_add(&func->kobj, &klp_ktype_func,
&obj->kobj, "%s,%lu", func->old_name,
func->old_sympos ? func->old_sympos : 1);
}
/* Arches may override this to finish any remaining arch-specific tasks */
void __weak arch_klp_init_object_loaded(struct klp_patch *patch,
struct klp_object *obj)
{
}
/* 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;
module_disable_ro(patch->mod);
ret = klp_write_object_relocations(patch->mod, obj);
if (ret) {
module_enable_ro(patch->mod, true);
return ret;
}
arch_klp_init_object_loaded(patch, obj);
module_enable_ro(patch->mod, true);
klp_for_each_func(obj, func) {
ret = klp_find_object_symbol(obj->name, func->old_name,
func->old_sympos,
&func->old_addr);
if (ret)
return ret;
ret = kallsyms_lookup_size_offset(func->old_addr,
&func->old_size, NULL);
if (!ret) {
pr_err("kallsyms size lookup failed for '%s'\n",
func->old_name);
return -ENOENT;
}
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 (!obj->funcs)
return -EINVAL;
obj->patched = false;
obj->mod = NULL;
klp_find_object_module(obj);
name = klp_is_module(obj) ? obj->name : "vmlinux";
ret = kobject_init_and_add(&obj->kobj, &klp_ktype_object,
&patch->kobj, "%s", name);
if (ret)
return ret;
klp_for_each_func(obj, 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->enabled = false;
init_completion(&patch->finish);
ret = kobject_init_and_add(&patch->kobj, &klp_ktype_patch,
klp_root_kobj, "%s", patch->mod->name);
if (ret) {
mutex_unlock(&klp_mutex);
return ret;
}
klp_for_each_object(patch, 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);
mutex_unlock(&klp_mutex);
kobject_put(&patch->kobj);
wait_for_completion(&patch->finish);
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;
mutex_lock(&klp_mutex);
if (!klp_is_patch_registered(patch)) {
ret = -EINVAL;
goto err;
}
if (patch->enabled) {
ret = -EBUSY;
goto err;
}
klp_free_patch(patch);
mutex_unlock(&klp_mutex);
kobject_put(&patch->kobj);
wait_for_completion(&patch->finish);
return 0;
err:
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.
*
* There is no need to take the reference on the patch module here. It is done
* later when the patch is enabled.
*
* Return: 0 on success, otherwise error
*/
int klp_register_patch(struct klp_patch *patch)
{
if (!patch || !patch->mod)
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;
/*
* Architectures without reliable stack traces have to set
* patch->immediate because there's currently no way to patch kthreads
* with the consistency model.
*/
if (!klp_have_reliable_stack() && !patch->immediate) {
pr_err("This architecture doesn't have support for the livepatch consistency model.\n");
return -ENOSYS;
}
return klp_init_patch(patch);
}
EXPORT_SYMBOL_GPL(klp_register_patch);
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;
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;
list_for_each_entry(patch, &klp_patches, list) {
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;
}
/*
* Only patch the module if the patch is enabled or is
* in transition.
*/
if (!patch->enabled && patch != klp_transition_patch)
break;
pr_notice("applying patch '%s' to loading module '%s'\n",
patch->mod->name, obj->mod->name);
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);
goto err;
}
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;
klp_free_object_loaded(obj);
mutex_unlock(&klp_mutex);
return ret;
}
void klp_module_going(struct module *mod)
{
struct klp_patch *patch;
struct klp_object *obj;
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;
list_for_each_entry(patch, &klp_patches, list) {
klp_for_each_object(patch, obj) {
if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
continue;
/*
* Only unpatch the module if the patch is enabled or
* is in transition.
*/
if (patch->enabled || patch == klp_transition_patch) {
pr_notice("reverting patch '%s' on unloading module '%s'\n",
patch->mod->name, obj->mod->name);
klp_unpatch_object(obj);
}
klp_free_object_loaded(obj);
break;
}
}
mutex_unlock(&klp_mutex);
}
static int __init klp_init(void)
{
int ret;
ret = klp_check_compiler_support();
if (ret) {
pr_info("Your compiler is too old; turning off.\n");
return -EINVAL;
}
klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
if (!klp_root_kobj)
return -ENOMEM;
return 0;
}
module_init(klp_init);