// SPDX-License-Identifier: GPL-2.0-or-later
/*
* transition.c - Kernel Live Patching transition functions
*
* Copyright (C) 2015-2016 Josh Poimboeuf <[email protected]>
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/cpu.h>
#include <linux/stacktrace.h>
#include <linux/static_call.h>
#include "core.h"
#include "patch.h"
#include "transition.h"
#define MAX_STACK_ENTRIES 100
static DEFINE_PER_CPU(unsigned long[MAX_STACK_ENTRIES], klp_stack_entries);
#define STACK_ERR_BUF_SIZE 128
#define SIGNALS_TIMEOUT 15
struct klp_patch *klp_transition_patch;
static int klp_target_state = KLP_TRANSITION_IDLE;
static unsigned int klp_signals_cnt;
/*
* When a livepatch is in progress, enable klp stack checking in
* cond_resched(). This helps CPU-bound kthreads get patched.
*/
#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define klp_cond_resched_enable() sched_dynamic_klp_enable()
#define klp_cond_resched_disable() sched_dynamic_klp_disable()
#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
EXPORT_SYMBOL(klp_sched_try_switch_key);
#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
/*
* This work can be performed periodically to finish patching or unpatching any
* "straggler" tasks which failed to transition in the first attempt.
*/
static void klp_transition_work_fn(struct work_struct *work)
{
mutex_lock(&klp_mutex);
if (klp_transition_patch)
klp_try_complete_transition();
mutex_unlock(&klp_mutex);
}
static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
/*
* This function is just a stub to implement a hard force
* of synchronize_rcu(). This requires synchronizing
* tasks even in userspace and idle.
*/
static void klp_sync(struct work_struct *work)
{
}
/*
* We allow to patch also functions where RCU is not watching,
* e.g. before user_exit(). We can not rely on the RCU infrastructure
* to do the synchronization. Instead hard force the sched synchronization.
*
* This approach allows to use RCU functions for manipulating func_stack
* safely.
*/
static void klp_synchronize_transition(void)
{
schedule_on_each_cpu(klp_sync);
}
/*
* The transition to the target patch state is complete. Clean up the data
* structures.
*/
static void klp_complete_transition(void)
{
struct klp_object *obj;
struct klp_func *func;
struct task_struct *g, *task;
unsigned int cpu;
pr_debug("'%s': completing %s transition\n",
klp_transition_patch->mod->name,
klp_target_state == KLP_TRANSITION_PATCHED ? "patching" : "unpatching");
if (klp_transition_patch->replace && klp_target_state == KLP_TRANSITION_PATCHED) {
klp_unpatch_replaced_patches(klp_transition_patch);
klp_discard_nops(klp_transition_patch);
}
if (klp_target_state == KLP_TRANSITION_UNPATCHED) {
/*
* All tasks have transitioned to KLP_TRANSITION_UNPATCHED so we can now
* remove the new functions from the func_stack.
*/
klp_unpatch_objects(klp_transition_patch);
/*
* Make sure klp_ftrace_handler() can no longer see functions
* from this patch on the ops->func_stack. Otherwise, after
* func->transition gets cleared, the handler may choose a
* removed function.
*/
klp_synchronize_transition();
}
klp_for_each_object(klp_transition_patch, obj)
klp_for_each_func(obj, func)
func->transition = false;
/* Prevent klp_ftrace_handler() from seeing KLP_TRANSITION_IDLE state */
if (klp_target_state == KLP_TRANSITION_PATCHED)
klp_synchronize_transition();
read_lock(&tasklist_lock);
for_each_process_thread(g, task) {
WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
task->patch_state = KLP_TRANSITION_IDLE;
}
read_unlock(&tasklist_lock);
for_each_possible_cpu(cpu) {
task = idle_task(cpu);
WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
task->patch_state = KLP_TRANSITION_IDLE;
}
klp_for_each_object(klp_transition_patch, obj) {
if (!klp_is_object_loaded(obj))
continue;
if (klp_target_state == KLP_TRANSITION_PATCHED)
klp_post_patch_callback(obj);
else if (klp_target_state == KLP_TRANSITION_UNPATCHED)
klp_post_unpatch_callback(obj);
}
pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
klp_target_state == KLP_TRANSITION_PATCHED ? "patching" : "unpatching");
klp_target_state = KLP_TRANSITION_IDLE;
klp_transition_patch = NULL;
}
/*
* This is called in the error path, to cancel a transition before it has
* started, i.e. klp_init_transition() has been called but
* klp_start_transition() hasn't. If the transition *has* been started,
* klp_reverse_transition() should be used instead.
*/
void klp_cancel_transition(void)
{
if (WARN_ON_ONCE(klp_target_state != KLP_TRANSITION_PATCHED))
return;
pr_debug("'%s': canceling patching transition, going to unpatch\n",
klp_transition_patch->mod->name);
klp_target_state = KLP_TRANSITION_UNPATCHED;
klp_complete_transition();
}
/*
* Switch the patched state of the task to the set of functions in the target
* patch state.
*
* NOTE: If task is not 'current', the caller must ensure the task is inactive.
* Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value.
*/
void klp_update_patch_state(struct task_struct *task)
{
/*
* A variant of synchronize_rcu() is used to allow patching functions
* where RCU is not watching, see klp_synchronize_transition().
*/
preempt_disable_notrace();
/*
* This test_and_clear_tsk_thread_flag() call also serves as a read
* barrier (smp_rmb) for two cases:
*
* 1) Enforce the order of the TIF_PATCH_PENDING read and the
* klp_target_state read. The corresponding write barriers are in
* klp_init_transition() and klp_reverse_transition().
*
* 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
* of func->transition, if klp_ftrace_handler() is called later on
* the same CPU. See __klp_disable_patch().
*/
if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
task->patch_state = READ_ONCE(klp_target_state);
preempt_enable_notrace();
}
/*
* Determine whether the given stack trace includes any references to a
* to-be-patched or to-be-unpatched function.
*/
static int klp_check_stack_func(struct klp_func *func, unsigned long *entries,
unsigned int nr_entries)
{
unsigned long func_addr, func_size, address;
struct klp_ops *ops;
int i;
if (klp_target_state == KLP_TRANSITION_UNPATCHED) {
/*
* Check for the to-be-unpatched function
* (the func itself).
*/
func_addr = (unsigned long)func->new_func;
func_size = func->new_size;
} else {
/*
* Check for the to-be-patched function
* (the previous func).
*/
ops = klp_find_ops(func->old_func);
if (list_is_singular(&ops->func_stack)) {
/* original function */
func_addr = (unsigned long)func->old_func;
func_size = func->old_size;
} else {
/* previously patched function */
struct klp_func *prev;
prev = list_next_entry(func, stack_node);
func_addr = (unsigned long)prev->new_func;
func_size = prev->new_size;
}
}
for (i = 0; i < nr_entries; i++) {
address = entries[i];
if (address >= func_addr && address < func_addr + func_size)
return -EAGAIN;
}
return 0;
}
/*
* Determine whether it's safe to transition the task to the target patch state
* by looking for any to-be-patched or to-be-unpatched functions on its stack.
*/
static int klp_check_stack(struct task_struct *task, const char **oldname)
{
unsigned long *entries = this_cpu_ptr(klp_stack_entries);
struct klp_object *obj;
struct klp_func *func;
int ret, nr_entries;
/* Protect 'klp_stack_entries' */
lockdep_assert_preemption_disabled();
ret = stack_trace_save_tsk_reliable(task, entries, MAX_STACK_ENTRIES);
if (ret < 0)
return -EINVAL;
nr_entries = ret;
klp_for_each_object(klp_transition_patch, obj) {
if (!obj->patched)
continue;
klp_for_each_func(obj, func) {
ret = klp_check_stack_func(func, entries, nr_entries);
if (ret) {
*oldname = func->old_name;
return -EADDRINUSE;
}
}
}
return 0;
}
static int klp_check_and_switch_task(struct task_struct *task, void *arg)
{
int ret;
if (task_curr(task) && task != current)
return -EBUSY;
ret = klp_check_stack(task, arg);
if (ret)
return ret;
clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
task->patch_state = klp_target_state;
return 0;
}
/*
* Try to safely switch a task to the target patch state. If it's currently
* running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
* if the stack is unreliable, return false.
*/
static bool klp_try_switch_task(struct task_struct *task)
{
const char *old_name;
int ret;
/* check if this task has already switched over */
if (task->patch_state == klp_target_state)
return true;
/*
* For arches which don't have reliable stack traces, we have to rely
* on other methods (e.g., switching tasks at kernel exit).
*/
if (!klp_have_reliable_stack())
return false;
/*
* Now try to check the stack for any to-be-patched or to-be-unpatched
* functions. If all goes well, switch the task to the target patch
* state.
*/
if (task == current)
ret = klp_check_and_switch_task(current, &old_name);
else
ret = task_call_func(task, klp_check_and_switch_task, &old_name);
switch (ret) {
case 0: /* success */
break;
case -EBUSY: /* klp_check_and_switch_task() */
pr_debug("%s: %s:%d is running\n",
__func__, task->comm, task->pid);
break;
case -EINVAL: /* klp_check_and_switch_task() */
pr_debug("%s: %s:%d has an unreliable stack\n",
__func__, task->comm, task->pid);
break;
case -EADDRINUSE: /* klp_check_and_switch_task() */
pr_debug("%s: %s:%d is sleeping on function %s\n",
__func__, task->comm, task->pid, old_name);
break;
default:
pr_debug("%s: Unknown error code (%d) when trying to switch %s:%d\n",
__func__, ret, task->comm, task->pid);
break;
}
return !ret;
}
void __klp_sched_try_switch(void)
{
if (likely(!klp_patch_pending(current)))
return;
/*
* This function is called from cond_resched() which is called in many
* places throughout the kernel. Using the klp_mutex here might
* deadlock.
*
* Instead, disable preemption to prevent racing with other callers of
* klp_try_switch_task(). Thanks to task_call_func() they won't be
* able to switch this task while it's running.
*/
preempt_disable();
/*
* Make sure current didn't get patched between the above check and
* preempt_disable().
*/
if (unlikely(!klp_patch_pending(current)))
goto out;
/*
* Enforce the order of the TIF_PATCH_PENDING read above and the
* klp_target_state read in klp_try_switch_task(). The corresponding
* write barriers are in klp_init_transition() and
* klp_reverse_transition().
*/
smp_rmb();
klp_try_switch_task(current);
out:
preempt_enable();
}
EXPORT_SYMBOL(__klp_sched_try_switch);
/*
* Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
* Kthreads with TIF_PATCH_PENDING set are woken up.
*/
static void klp_send_signals(void)
{
struct task_struct *g, *task;
if (klp_signals_cnt == SIGNALS_TIMEOUT)
pr_notice("signaling remaining tasks\n");
read_lock(&tasklist_lock);
for_each_process_thread(g, task) {
if (!klp_patch_pending(task))
continue;
/*
* There is a small race here. We could see TIF_PATCH_PENDING
* set and decide to wake up a kthread or send a fake signal.
* Meanwhile the task could migrate itself and the action
* would be meaningless. It is not serious though.
*/
if (task->flags & PF_KTHREAD) {
/*
* Wake up a kthread which sleeps interruptedly and
* still has not been migrated.
*/
wake_up_state(task, TASK_INTERRUPTIBLE);
} else {
/*
* Send fake signal to all non-kthread tasks which are
* still not migrated.
*/
set_notify_signal(task);
}
}
read_unlock(&tasklist_lock);
}
/*
* Try to switch all remaining tasks to the target patch state by walking the
* stacks of sleeping tasks and looking for any to-be-patched or
* to-be-unpatched functions. If such functions are found, the task can't be
* switched yet.
*
* If any tasks are still stuck in the initial patch state, schedule a retry.
*/
void klp_try_complete_transition(void)
{
unsigned int cpu;
struct task_struct *g, *task;
struct klp_patch *patch;
bool complete = true;
WARN_ON_ONCE(klp_target_state == KLP_TRANSITION_IDLE);
/*
* Try to switch the tasks to the target patch state by walking their
* stacks and looking for any to-be-patched or to-be-unpatched
* functions. If such functions are found on a stack, or if the stack
* is deemed unreliable, the task can't be switched yet.
*
* Usually this will transition most (or all) of the tasks on a system
* unless the patch includes changes to a very common function.
*/
read_lock(&tasklist_lock);
for_each_process_thread(g, task)
if (!klp_try_switch_task(task))
complete = false;
read_unlock(&tasklist_lock);
/*
* Ditto for the idle "swapper" tasks.
*/
cpus_read_lock();
for_each_possible_cpu(cpu) {
task = idle_task(cpu);
if (cpu_online(cpu)) {
if (!klp_try_switch_task(task)) {
complete = false;
/* Make idle task go through the main loop. */
wake_up_if_idle(cpu);
}
} else if (task->patch_state != klp_target_state) {
/* offline idle tasks can be switched immediately */
clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
task->patch_state = klp_target_state;
}
}
cpus_read_unlock();
if (!complete) {
if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT))
klp_send_signals();
klp_signals_cnt++;
/*
* Some tasks weren't able to be switched over. Try again
* later and/or wait for other methods like kernel exit
* switching.
*/
schedule_delayed_work(&klp_transition_work,
round_jiffies_relative(HZ));
return;
}
/* Done! Now cleanup the data structures. */
klp_cond_resched_disable();
patch = klp_transition_patch;
klp_complete_transition();
/*
* It would make more sense to free the unused patches in
* klp_complete_transition() but it is called also
* from klp_cancel_transition().
*/
if (!patch->enabled)
klp_free_patch_async(patch);
else if (patch->replace)
klp_free_replaced_patches_async(patch);
}
/*
* Start the transition to the specified target patch state so tasks can begin
* switching to it.
*/
void klp_start_transition(void)
{
struct task_struct *g, *task;
unsigned int cpu;
WARN_ON_ONCE(klp_target_state == KLP_TRANSITION_IDLE);
pr_notice("'%s': starting %s transition\n",
klp_transition_patch->mod->name,
klp_target_state == KLP_TRANSITION_PATCHED ? "patching" : "unpatching");
/*
* Mark all normal tasks as needing a patch state update. They'll
* switch either in klp_try_complete_transition() or as they exit the
* kernel.
*/
read_lock(&tasklist_lock);
for_each_process_thread(g, task)
if (task->patch_state != klp_target_state)
set_tsk_thread_flag(task, TIF_PATCH_PENDING);
read_unlock(&tasklist_lock);
/*
* Mark all idle tasks as needing a patch state update. They'll switch
* either in klp_try_complete_transition() or at the idle loop switch
* point.
*/
for_each_possible_cpu(cpu) {
task = idle_task(cpu);
if (task->patch_state != klp_target_state)
set_tsk_thread_flag(task, TIF_PATCH_PENDING);
}
klp_cond_resched_enable();
klp_signals_cnt = 0;
}
/*
* Initialize the global target patch state and all tasks to the initial patch
* state, and initialize all function transition states to true in preparation
* for patching or unpatching.
*/
void klp_init_transition(struct klp_patch *patch, int state)
{
struct task_struct *g, *task;
unsigned int cpu;
struct klp_object *obj;
struct klp_func *func;
int initial_state = !state;
WARN_ON_ONCE(klp_target_state != KLP_TRANSITION_IDLE);
klp_transition_patch = patch;
/*
* Set the global target patch state which tasks will switch to. This
* has no effect until the TIF_PATCH_PENDING flags get set later.
*/
klp_target_state = state;
pr_debug("'%s': initializing %s transition\n", patch->mod->name,
klp_target_state == KLP_TRANSITION_PATCHED ? "patching" : "unpatching");
/*
* Initialize all tasks to the initial patch state to prepare them for
* switching to the target state.
*/
read_lock(&tasklist_lock);
for_each_process_thread(g, task) {
WARN_ON_ONCE(task->patch_state != KLP_TRANSITION_IDLE);
task->patch_state = initial_state;
}
read_unlock(&tasklist_lock);
/*
* Ditto for the idle "swapper" tasks.
*/
for_each_possible_cpu(cpu) {
task = idle_task(cpu);
WARN_ON_ONCE(task->patch_state != KLP_TRANSITION_IDLE);
task->patch_state = initial_state;
}
/*
* Enforce the order of the task->patch_state initializations and the
* func->transition updates to ensure that klp_ftrace_handler() doesn't
* see a func in transition with a task->patch_state of KLP_TRANSITION_IDLE.
*
* Also enforce the order of the klp_target_state write and future
* TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and
* __klp_sched_try_switch() don't set a task->patch_state to
* KLP_TRANSITION_IDLE.
*/
smp_wmb();
/*
* Set the func transition states so klp_ftrace_handler() will know to
* switch to the transition logic.
*
* When patching, the funcs aren't yet in the func_stack and will be
* made visible to the ftrace handler shortly by the calls to
* klp_patch_object().
*
* When unpatching, the funcs are already in the func_stack and so are
* already visible to the ftrace handler.
*/
klp_for_each_object(patch, obj)
klp_for_each_func(obj, func)
func->transition = true;
}
/*
* This function can be called in the middle of an existing transition to
* reverse the direction of the target patch state. This can be done to
* effectively cancel an existing enable or disable operation if there are any
* tasks which are stuck in the initial patch state.
*/
void klp_reverse_transition(void)
{
unsigned int cpu;
struct task_struct *g, *task;
pr_debug("'%s': reversing transition from %s\n",
klp_transition_patch->mod->name,
klp_target_state == KLP_TRANSITION_PATCHED ? "patching to unpatching" :
"unpatching to patching");
/*
* Clear all TIF_PATCH_PENDING flags to prevent races caused by
* klp_update_patch_state() or __klp_sched_try_switch() running in
* parallel with the reverse transition.
*/
read_lock(&tasklist_lock);
for_each_process_thread(g, task)
clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
read_unlock(&tasklist_lock);
for_each_possible_cpu(cpu)
clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
/*
* Make sure all existing invocations of klp_update_patch_state() and
* __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before
* starting the reverse transition.
*/
klp_synchronize_transition();
/*
* All patching has stopped, now re-initialize the global variables to
* prepare for the reverse transition.
*/
klp_transition_patch->enabled = !klp_transition_patch->enabled;
klp_target_state = !klp_target_state;
/*
* Enforce the order of the klp_target_state write and the
* TIF_PATCH_PENDING writes in klp_start_transition() to ensure
* klp_update_patch_state() and __klp_sched_try_switch() don't set
* task->patch_state to the wrong value.
*/
smp_wmb();
klp_start_transition();
}
/* Called from copy_process() during fork */
void klp_copy_process(struct task_struct *child)
{
/*
* The parent process may have gone through a KLP transition since
* the thread flag was copied in setup_thread_stack earlier. Bring
* the task flag up to date with the parent here.
*
* The operation is serialized against all klp_*_transition()
* operations by the tasklist_lock. The only exceptions are
* klp_update_patch_state(current) and __klp_sched_try_switch(), but we
* cannot race with them because we are current.
*/
if (test_tsk_thread_flag(current, TIF_PATCH_PENDING))
set_tsk_thread_flag(child, TIF_PATCH_PENDING);
else
clear_tsk_thread_flag(child, TIF_PATCH_PENDING);
child->patch_state = current->patch_state;
}
/*
* Drop TIF_PATCH_PENDING of all tasks on admin's request. This forces an
* existing transition to finish.
*
* NOTE: klp_update_patch_state(task) requires the task to be inactive or
* 'current'. This is not the case here and the consistency model could be
* broken. Administrator, who is the only one to execute the
* klp_force_transitions(), has to be aware of this.
*/
void klp_force_transition(void)
{
struct klp_patch *patch;
struct task_struct *g, *task;
unsigned int cpu;
pr_warn("forcing remaining tasks to the patched state\n");
read_lock(&tasklist_lock);
for_each_process_thread(g, task)
klp_update_patch_state(task);
read_unlock(&tasklist_lock);
for_each_possible_cpu(cpu)
klp_update_patch_state(idle_task(cpu));
/* Set forced flag for patches being removed. */
if (klp_target_state == KLP_TRANSITION_UNPATCHED)
klp_transition_patch->forced = true;
else if (klp_transition_patch->replace) {
klp_for_each_patch(patch) {
if (patch != klp_transition_patch)
patch->forced = true;
}
}
}
Codebase Browser
linux