cregit-Linux how code gets into the kernel

Release 4.15 kernel/livepatch/transition.c

Directory: kernel/livepatch
 * transition.c - Kernel Live Patching transition functions
 * Copyright (C) 2015-2016 Josh Poimboeuf <>
 * 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
 * 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 <>.

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/cpu.h>
#include <linux/stacktrace.h>
#include "core.h"
#include "patch.h"
#include "transition.h"
#include "../sched/sched.h"

#define MAX_STACK_ENTRIES  100

#define STACK_ERR_BUF_SIZE 128

struct klp_patch *klp_transition_patch;

static int klp_target_state = KLP_UNDEFINED;

 * 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); }


Josh Poimboeuf30100.00%1100.00%

static DECLARE_DELAYED_WORK(klp_transition_work, klp_transition_work_fn); /* * This function is just a stub to implement a hard force * of synchronize_sched(). This requires synchronizing * tasks even in userspace and idle. */
static void klp_sync(struct work_struct *work) { }


Petr Mladek10100.00%1100.00%

/* * 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); }


Petr Mladek13100.00%1100.00%

/* * 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; bool immediate_func = false; pr_debug("'%s': completing %s transition\n", klp_transition_patch->mod->name, klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); if (klp_target_state == KLP_UNPATCHED) { /* * All tasks have transitioned to KLP_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(); } if (klp_transition_patch->immediate) goto done; klp_for_each_object(klp_transition_patch, obj) { klp_for_each_func(obj, func) { func->transition = false; if (func->immediate) immediate_func = true; } } /* Prevent klp_ftrace_handler() from seeing KLP_UNDEFINED state */ if (klp_target_state == KLP_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_UNDEFINED; } 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_UNDEFINED; } done: klp_for_each_object(klp_transition_patch, obj) { if (!klp_is_object_loaded(obj)) continue; if (klp_target_state == KLP_PATCHED) klp_post_patch_callback(obj); else if (klp_target_state == KLP_UNPATCHED) klp_post_unpatch_callback(obj); } pr_notice("'%s': %s complete\n", klp_transition_patch->mod->name, klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); /* * See complementary comment in __klp_enable_patch() for why we * keep the module reference for immediate patches. */ if (!klp_transition_patch->immediate && !immediate_func && klp_target_state == KLP_UNPATCHED) { module_put(klp_transition_patch->mod); } klp_target_state = KLP_UNDEFINED; klp_transition_patch = NULL; }


Josh Poimboeuf17762.99%233.33%
Joe Lawrence10236.30%350.00%
Petr Mladek20.71%116.67%

/* * 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_PATCHED)) return; pr_debug("'%s': canceling patching transition, going to unpatch\n", klp_transition_patch->mod->name); klp_target_state = KLP_UNPATCHED; klp_complete_transition(); }


Josh Poimboeuf2468.57%266.67%
Joe Lawrence1131.43%133.33%

/* * 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_sched() 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 barrier is in * klp_init_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(); }


Josh Poimboeuf3391.67%150.00%
Petr Mladek38.33%150.00%

/* * 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, struct stack_trace *trace) { unsigned long func_addr, func_size, address; struct klp_ops *ops; int i; if (func->immediate) return 0; for (i = 0; i < trace->nr_entries; i++) { address = trace->entries[i]; if (klp_target_state == KLP_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_addr); if (list_is_singular(&ops->func_stack)) { /* original function */ func_addr = func->old_addr; 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; } } if (address >= func_addr && address < func_addr + func_size) return -EAGAIN; } return 0; }


Josh Poimboeuf183100.00%1100.00%

/* * 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, char *err_buf) { static unsigned long entries[MAX_STACK_ENTRIES]; struct stack_trace trace; struct klp_object *obj; struct klp_func *func; int ret; trace.skip = 0; trace.nr_entries = 0; trace.max_entries = MAX_STACK_ENTRIES; trace.entries = entries; ret = save_stack_trace_tsk_reliable(task, &trace); WARN_ON_ONCE(ret == -ENOSYS); if (ret) { snprintf(err_buf, STACK_ERR_BUF_SIZE, "%s: %s:%d has an unreliable stack\n", __func__, task->comm, task->pid); return 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, &trace); if (ret) { snprintf(err_buf, STACK_ERR_BUF_SIZE, "%s: %s:%d is sleeping on function %s\n", __func__, task->comm, task->pid, func->old_name); return ret; } } } return 0; }


Josh Poimboeuf179100.00%1100.00%

/* * 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) { struct rq *rq; struct rq_flags flags; int ret; bool success = false; char err_buf[STACK_ERR_BUF_SIZE]; err_buf[0] = '\0'; /* 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. */ rq = task_rq_lock(task, &flags); if (task_running(rq, task) && task != current) { snprintf(err_buf, STACK_ERR_BUF_SIZE, "%s: %s:%d is running\n", __func__, task->comm, task->pid); goto done; } ret = klp_check_stack(task, err_buf); if (ret) goto done; success = true; clear_tsk_thread_flag(task, TIF_PATCH_PENDING); task->patch_state = klp_target_state; done: task_rq_unlock(rq, task, &flags); /* * Due to console deadlock issues, pr_debug() can't be used while * holding the task rq lock. Instead we have to use a temporary buffer * and print the debug message after releasing the lock. */ if (err_buf[0] != '\0') pr_debug("%s", err_buf); return success; }


Josh Poimboeuf176100.00%1100.00%

/* * 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; bool complete = true; WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED); /* * If the patch can be applied or reverted immediately, skip the * per-task transitions. */ if (klp_transition_patch->immediate) goto success; /* * 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. */ get_online_cpus(); for_each_possible_cpu(cpu) { task = idle_task(cpu); if (cpu_online(cpu)) { if (!klp_try_switch_task(task)) complete = false; } 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; } } put_online_cpus(); if (!complete) { /* * 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; } success: /* we're done, now cleanup the data structures */ klp_complete_transition(); }


Josh Poimboeuf164100.00%1100.00%

/* * 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_UNDEFINED); pr_notice("'%s': starting %s transition\n", klp_transition_patch->mod->name, klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); /* * If the patch can be applied or reverted immediately, skip the * per-task transitions. */ if (klp_transition_patch->immediate) return; /* * 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); } }


Josh Poimboeuf11599.14%150.00%
Joe Lawrence10.86%150.00%

/* * 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_UNDEFINED); 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_PATCHED ? "patching" : "unpatching"); /* * If the patch can be applied or reverted immediately, skip the * per-task transitions. */ if (patch->immediate) return; /* * 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; }


Josh Poimboeuf15388.95%150.00%
Joe Lawrence1911.05%150.00%

/* * 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(); }


Josh Poimboeuf7979.80%133.33%
Joe Lawrence1919.19%133.33%
Petr Mladek11.01%133.33%

/* 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() */ }


Josh Poimboeuf19100.00%1100.00%

Overall Contributors

Josh Poimboeuf139488.23%228.57%
Joe Lawrence1529.62%342.86%
Petr Mladek311.96%114.29%
Jiri Kosina30.19%114.29%
Directory: kernel/livepatch
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