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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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#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 100static 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 * schedule(). This helps CPU-bound kthreads get patched. */
DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
#define klp_resched_enable() static_branch_enable(&klp_sched_try_switch_key)#define klp_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
/* * 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){ /* * This function is called from __schedule() while a context switch is * about to happen. Preemption is already disabled and klp_mutex * can't be acquired. * Disabled preemption is used to prevent racing with other callers of * klp_try_switch_task(). Thanks to task_call_func() they won't be * able to switch to this task while it's running. */ lockdep_assert_preemption_disabled();
if (likely(!klp_patch_pending(current))) return;
/* * 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);}
/* * 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_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_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; } }}