mirror of https://gitee.com/openkylin/linux.git
647 lines
18 KiB
C
647 lines
18 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* transition.c - Kernel Live Patching transition functions
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*
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* Copyright (C) 2015-2016 Josh Poimboeuf <jpoimboe@redhat.com>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/cpu.h>
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#include <linux/stacktrace.h>
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#include "core.h"
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#include "patch.h"
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#include "transition.h"
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#include "../sched/sched.h"
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#define MAX_STACK_ENTRIES 100
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#define STACK_ERR_BUF_SIZE 128
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#define SIGNALS_TIMEOUT 15
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struct klp_patch *klp_transition_patch;
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static int klp_target_state = KLP_UNDEFINED;
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static unsigned int klp_signals_cnt;
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/*
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* This work can be performed periodically to finish patching or unpatching any
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* "straggler" tasks which failed to transition in the first attempt.
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*/
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static void klp_transition_work_fn(struct work_struct *work)
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{
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mutex_lock(&klp_mutex);
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if (klp_transition_patch)
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klp_try_complete_transition();
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mutex_unlock(&klp_mutex);
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}
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static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn);
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/*
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* This function is just a stub to implement a hard force
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* of synchronize_rcu(). This requires synchronizing
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* tasks even in userspace and idle.
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*/
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static void klp_sync(struct work_struct *work)
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{
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}
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/*
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* We allow to patch also functions where RCU is not watching,
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* e.g. before user_exit(). We can not rely on the RCU infrastructure
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* to do the synchronization. Instead hard force the sched synchronization.
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*
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* This approach allows to use RCU functions for manipulating func_stack
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* safely.
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*/
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static void klp_synchronize_transition(void)
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{
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schedule_on_each_cpu(klp_sync);
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}
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/*
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* The transition to the target patch state is complete. Clean up the data
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* structures.
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*/
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static void klp_complete_transition(void)
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{
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struct klp_object *obj;
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struct klp_func *func;
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struct task_struct *g, *task;
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unsigned int cpu;
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pr_debug("'%s': completing %s transition\n",
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klp_transition_patch->mod->name,
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klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
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if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) {
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klp_unpatch_replaced_patches(klp_transition_patch);
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klp_discard_nops(klp_transition_patch);
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}
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if (klp_target_state == KLP_UNPATCHED) {
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/*
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* All tasks have transitioned to KLP_UNPATCHED so we can now
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* remove the new functions from the func_stack.
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*/
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klp_unpatch_objects(klp_transition_patch);
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/*
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* Make sure klp_ftrace_handler() can no longer see functions
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* from this patch on the ops->func_stack. Otherwise, after
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* func->transition gets cleared, the handler may choose a
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* removed function.
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*/
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klp_synchronize_transition();
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}
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klp_for_each_object(klp_transition_patch, obj)
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klp_for_each_func(obj, func)
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func->transition = false;
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/* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */
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if (klp_target_state == KLP_PATCHED)
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klp_synchronize_transition();
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read_lock(&tasklist_lock);
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for_each_process_thread(g, task) {
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WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
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task->patch_state = KLP_UNDEFINED;
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}
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read_unlock(&tasklist_lock);
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for_each_possible_cpu(cpu) {
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task = idle_task(cpu);
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WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
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task->patch_state = KLP_UNDEFINED;
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}
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klp_for_each_object(klp_transition_patch, obj) {
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if (!klp_is_object_loaded(obj))
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continue;
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if (klp_target_state == KLP_PATCHED)
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klp_post_patch_callback(obj);
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else if (klp_target_state == KLP_UNPATCHED)
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klp_post_unpatch_callback(obj);
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}
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pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name,
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klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
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klp_target_state = KLP_UNDEFINED;
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klp_transition_patch = NULL;
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}
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/*
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* This is called in the error path, to cancel a transition before it has
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* started, i.e. klp_init_transition() has been called but
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* klp_start_transition() hasn't. If the transition *has* been started,
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* klp_reverse_transition() should be used instead.
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*/
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void klp_cancel_transition(void)
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{
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if (WARN_ON_ONCE(klp_target_state != KLP_PATCHED))
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return;
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pr_debug("'%s': canceling patching transition, going to unpatch\n",
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klp_transition_patch->mod->name);
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klp_target_state = KLP_UNPATCHED;
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klp_complete_transition();
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}
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/*
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* Switch the patched state of the task to the set of functions in the target
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* patch state.
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*
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* NOTE: If task is not 'current', the caller must ensure the task is inactive.
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* Otherwise klp_ftrace_handler() might read the wrong 'patch_state' value.
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*/
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void klp_update_patch_state(struct task_struct *task)
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{
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/*
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* A variant of synchronize_rcu() is used to allow patching functions
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* where RCU is not watching, see klp_synchronize_transition().
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*/
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preempt_disable_notrace();
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/*
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* This test_and_clear_tsk_thread_flag() call also serves as a read
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* barrier (smp_rmb) for two cases:
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*
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* 1) Enforce the order of the TIF_PATCH_PENDING read and the
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* klp_target_state read. The corresponding write barrier is in
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* klp_init_transition().
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*
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* 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
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* of func->transition, if klp_ftrace_handler() is called later on
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* the same CPU. See __klp_disable_patch().
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*/
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if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
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task->patch_state = READ_ONCE(klp_target_state);
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preempt_enable_notrace();
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}
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/*
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* Determine whether the given stack trace includes any references to a
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* to-be-patched or to-be-unpatched function.
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*/
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static int klp_check_stack_func(struct klp_func *func, unsigned long *entries,
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unsigned int nr_entries)
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{
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unsigned long func_addr, func_size, address;
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struct klp_ops *ops;
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int i;
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for (i = 0; i < nr_entries; i++) {
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address = entries[i];
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if (klp_target_state == KLP_UNPATCHED) {
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/*
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* Check for the to-be-unpatched function
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* (the func itself).
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*/
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func_addr = (unsigned long)func->new_func;
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func_size = func->new_size;
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} else {
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/*
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* Check for the to-be-patched function
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* (the previous func).
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*/
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ops = klp_find_ops(func->old_func);
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if (list_is_singular(&ops->func_stack)) {
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/* original function */
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func_addr = (unsigned long)func->old_func;
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func_size = func->old_size;
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} else {
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/* previously patched function */
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struct klp_func *prev;
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prev = list_next_entry(func, stack_node);
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func_addr = (unsigned long)prev->new_func;
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func_size = prev->new_size;
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}
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}
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if (address >= func_addr && address < func_addr + func_size)
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return -EAGAIN;
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}
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return 0;
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}
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/*
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* Determine whether it's safe to transition the task to the target patch state
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* by looking for any to-be-patched or to-be-unpatched functions on its stack.
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*/
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static int klp_check_stack(struct task_struct *task, char *err_buf)
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{
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static unsigned long entries[MAX_STACK_ENTRIES];
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struct klp_object *obj;
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struct klp_func *func;
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int ret, nr_entries;
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ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries));
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if (ret < 0) {
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snprintf(err_buf, STACK_ERR_BUF_SIZE,
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"%s: %s:%d has an unreliable stack\n",
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__func__, task->comm, task->pid);
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return ret;
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}
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nr_entries = ret;
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klp_for_each_object(klp_transition_patch, obj) {
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if (!obj->patched)
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continue;
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klp_for_each_func(obj, func) {
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ret = klp_check_stack_func(func, entries, nr_entries);
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if (ret) {
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snprintf(err_buf, STACK_ERR_BUF_SIZE,
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"%s: %s:%d is sleeping on function %s\n",
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__func__, task->comm, task->pid,
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func->old_name);
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return ret;
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}
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}
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}
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return 0;
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}
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/*
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* Try to safely switch a task to the target patch state. If it's currently
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* running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
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* if the stack is unreliable, return false.
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*/
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static bool klp_try_switch_task(struct task_struct *task)
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{
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static char err_buf[STACK_ERR_BUF_SIZE];
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struct rq *rq;
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struct rq_flags flags;
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int ret;
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bool success = false;
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err_buf[0] = '\0';
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/* check if this task has already switched over */
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if (task->patch_state == klp_target_state)
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return true;
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/*
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* For arches which don't have reliable stack traces, we have to rely
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* on other methods (e.g., switching tasks at kernel exit).
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*/
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if (!klp_have_reliable_stack())
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return false;
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/*
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* Now try to check the stack for any to-be-patched or to-be-unpatched
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* functions. If all goes well, switch the task to the target patch
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* state.
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*/
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rq = task_rq_lock(task, &flags);
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if (task_running(rq, task) && task != current) {
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snprintf(err_buf, STACK_ERR_BUF_SIZE,
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"%s: %s:%d is running\n", __func__, task->comm,
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task->pid);
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goto done;
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}
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ret = klp_check_stack(task, err_buf);
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if (ret)
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goto done;
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success = true;
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clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
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task->patch_state = klp_target_state;
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done:
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task_rq_unlock(rq, task, &flags);
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/*
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* Due to console deadlock issues, pr_debug() can't be used while
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* holding the task rq lock. Instead we have to use a temporary buffer
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* and print the debug message after releasing the lock.
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*/
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if (err_buf[0] != '\0')
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pr_debug("%s", err_buf);
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return success;
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}
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/*
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* Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
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* Kthreads with TIF_PATCH_PENDING set are woken up.
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*/
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static void klp_send_signals(void)
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{
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struct task_struct *g, *task;
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if (klp_signals_cnt == SIGNALS_TIMEOUT)
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pr_notice("signaling remaining tasks\n");
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read_lock(&tasklist_lock);
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for_each_process_thread(g, task) {
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if (!klp_patch_pending(task))
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continue;
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/*
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* There is a small race here. We could see TIF_PATCH_PENDING
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* set and decide to wake up a kthread or send a fake signal.
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* Meanwhile the task could migrate itself and the action
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* would be meaningless. It is not serious though.
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*/
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if (task->flags & PF_KTHREAD) {
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/*
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* Wake up a kthread which sleeps interruptedly and
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* still has not been migrated.
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*/
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wake_up_state(task, TASK_INTERRUPTIBLE);
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} else {
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/*
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* Send fake signal to all non-kthread tasks which are
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* still not migrated.
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*/
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spin_lock_irq(&task->sighand->siglock);
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signal_wake_up(task, 0);
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spin_unlock_irq(&task->sighand->siglock);
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}
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}
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read_unlock(&tasklist_lock);
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}
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/*
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* Try to switch all remaining tasks to the target patch state by walking the
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* stacks of sleeping tasks and looking for any to-be-patched or
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* to-be-unpatched functions. If such functions are found, the task can't be
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* switched yet.
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*
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* If any tasks are still stuck in the initial patch state, schedule a retry.
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*/
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void klp_try_complete_transition(void)
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{
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unsigned int cpu;
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struct task_struct *g, *task;
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struct klp_patch *patch;
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bool complete = true;
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WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
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/*
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* Try to switch the tasks to the target patch state by walking their
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* stacks and looking for any to-be-patched or to-be-unpatched
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* functions. If such functions are found on a stack, or if the stack
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* is deemed unreliable, the task can't be switched yet.
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*
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* Usually this will transition most (or all) of the tasks on a system
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* unless the patch includes changes to a very common function.
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*/
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read_lock(&tasklist_lock);
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for_each_process_thread(g, task)
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if (!klp_try_switch_task(task))
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complete = false;
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read_unlock(&tasklist_lock);
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/*
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* Ditto for the idle "swapper" tasks.
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*/
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get_online_cpus();
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for_each_possible_cpu(cpu) {
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task = idle_task(cpu);
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if (cpu_online(cpu)) {
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if (!klp_try_switch_task(task))
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complete = false;
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} else if (task->patch_state != klp_target_state) {
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/* offline idle tasks can be switched immediately */
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clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
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task->patch_state = klp_target_state;
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}
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}
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put_online_cpus();
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if (!complete) {
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if (klp_signals_cnt && !(klp_signals_cnt % SIGNALS_TIMEOUT))
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klp_send_signals();
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klp_signals_cnt++;
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/*
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* Some tasks weren't able to be switched over. Try again
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* later and/or wait for other methods like kernel exit
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* switching.
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*/
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schedule_delayed_work(&klp_transition_work,
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round_jiffies_relative(HZ));
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return;
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}
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/* we're done, now cleanup the data structures */
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patch = klp_transition_patch;
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klp_complete_transition();
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/*
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* It would make more sense to free the unused patches in
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* klp_complete_transition() but it is called also
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* from klp_cancel_transition().
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*/
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if (!patch->enabled)
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klp_free_patch_async(patch);
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else if (patch->replace)
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klp_free_replaced_patches_async(patch);
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}
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/*
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* Start the transition to the specified target patch state so tasks can begin
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* switching to it.
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*/
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void klp_start_transition(void)
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{
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struct task_struct *g, *task;
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unsigned int cpu;
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WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
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pr_notice("'%s': starting %s transition\n",
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klp_transition_patch->mod->name,
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klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
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/*
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* Mark all normal tasks as needing a patch state update. They'll
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* switch either in klp_try_complete_transition() or as they exit the
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* kernel.
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*/
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read_lock(&tasklist_lock);
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for_each_process_thread(g, task)
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if (task->patch_state != klp_target_state)
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set_tsk_thread_flag(task, TIF_PATCH_PENDING);
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read_unlock(&tasklist_lock);
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/*
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* Mark all idle tasks as needing a patch state update. They'll switch
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* either in klp_try_complete_transition() or at the idle loop switch
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* point.
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*/
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for_each_possible_cpu(cpu) {
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task = idle_task(cpu);
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if (task->patch_state != klp_target_state)
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set_tsk_thread_flag(task, TIF_PATCH_PENDING);
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}
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klp_signals_cnt = 0;
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}
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/*
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* Initialize the global target patch state and all tasks to the initial patch
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* state, and initialize all function transition states to true in preparation
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* for patching or unpatching.
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*/
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void klp_init_transition(struct klp_patch *patch, int state)
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{
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struct task_struct *g, *task;
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unsigned int cpu;
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struct klp_object *obj;
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struct klp_func *func;
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int initial_state = !state;
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WARN_ON_ONCE(klp_target_state != KLP_UNDEFINED);
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klp_transition_patch = patch;
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/*
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* Set the global target patch state which tasks will switch to. This
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* has no effect until the TIF_PATCH_PENDING flags get set later.
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*/
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klp_target_state = state;
|
|
|
|
pr_debug("'%s': initializing %s transition\n", patch->mod->name,
|
|
klp_target_state == KLP_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_UNDEFINED);
|
|
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_UNDEFINED);
|
|
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_UNDEFINED.
|
|
*
|
|
* Also enforce the order of the klp_target_state write and future
|
|
* TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
|
|
* set a task->patch_state to KLP_UNDEFINED.
|
|
*/
|
|
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_PATCHED ? "patching to unpatching" :
|
|
"unpatching to patching");
|
|
|
|
klp_transition_patch->enabled = !klp_transition_patch->enabled;
|
|
|
|
klp_target_state = !klp_target_state;
|
|
|
|
/*
|
|
* Clear all TIF_PATCH_PENDING flags to prevent races caused by
|
|
* klp_update_patch_state() running in parallel with
|
|
* klp_start_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);
|
|
|
|
/* Let any remaining calls to klp_update_patch_state() complete */
|
|
klp_synchronize_transition();
|
|
|
|
klp_start_transition();
|
|
}
|
|
|
|
/* Called from copy_process() during fork */
|
|
void klp_copy_process(struct task_struct *child)
|
|
{
|
|
child->patch_state = current->patch_state;
|
|
|
|
/* TIF_PATCH_PENDING gets copied in setup_thread_stack() */
|
|
}
|
|
|
|
/*
|
|
* 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));
|
|
|
|
klp_for_each_patch(patch)
|
|
patch->forced = true;
|
|
}
|