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![Petr Mladek](/assets/img/avatar_default.png)
klp_init_transition() does not set func->transition for immediate patches.
Then klp_ftrace_handler() could use the new code immediately. As a result,
it is not safe to put the livepatch module in klp_cancel_transition().
This patch reverts most of the last minute changes klp_cancel_transition().
It keeps the warning about a misuse because it still makes sense.
Fixes: 3ec24776bf
("livepatch: allow removal of a disabled patch")
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
553 lines
15 KiB
C
553 lines
15 KiB
C
/*
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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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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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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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struct klp_patch *klp_transition_patch;
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static int klp_target_state = KLP_UNDEFINED;
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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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* 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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bool immediate_func = false;
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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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synchronize_rcu();
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}
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if (klp_transition_patch->immediate)
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goto done;
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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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if (func->immediate)
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immediate_func = true;
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}
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}
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if (klp_target_state == KLP_UNPATCHED && !immediate_func)
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module_put(klp_transition_patch->mod);
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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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synchronize_rcu();
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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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done:
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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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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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rcu_read_lock();
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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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rcu_read_unlock();
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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,
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struct stack_trace *trace)
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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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if (func->immediate)
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return 0;
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for (i = 0; i < trace->nr_entries; i++) {
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address = trace->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_addr);
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if (list_is_singular(&ops->func_stack)) {
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/* original function */
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func_addr = func->old_addr;
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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 stack_trace trace;
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struct klp_object *obj;
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struct klp_func *func;
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int ret;
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trace.skip = 0;
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trace.nr_entries = 0;
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trace.max_entries = MAX_STACK_ENTRIES;
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trace.entries = entries;
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ret = save_stack_trace_tsk_reliable(task, &trace);
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WARN_ON_ONCE(ret == -ENOSYS);
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if (ret) {
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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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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, &trace);
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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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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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char err_buf[STACK_ERR_BUF_SIZE];
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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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* 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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bool complete = true;
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WARN_ON_ONCE(klp_target_state == KLP_UNDEFINED);
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/*
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* If the patch can be applied or reverted immediately, skip the
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* per-task transitions.
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*/
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if (klp_transition_patch->immediate)
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goto success;
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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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/*
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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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success:
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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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/* we're done, now cleanup the data structures */
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klp_complete_transition();
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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': %s...\n", klp_transition_patch->mod->name,
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klp_target_state == KLP_PATCHED ? "patching" : "unpatching");
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/*
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* If the patch can be applied or reverted immediately, skip the
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* per-task transitions.
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*/
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if (klp_transition_patch->immediate)
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return;
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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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}
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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;
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/*
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* If the patch can be applied or reverted immediately, skip the
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* per-task transitions.
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*/
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if (patch->immediate)
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return;
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/*
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* Initialize all tasks to the initial patch state to prepare them for
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* switching to the target state.
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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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WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
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task->patch_state = initial_state;
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}
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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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for_each_possible_cpu(cpu) {
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task = idle_task(cpu);
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WARN_ON_ONCE(task->patch_state != KLP_UNDEFINED);
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task->patch_state = initial_state;
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}
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/*
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* Enforce the order of the task->patch_state initializations and the
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* func->transition updates to ensure that klp_ftrace_handler() doesn't
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* see a func in transition with a task->patch_state of KLP_UNDEFINED.
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*
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* Also enforce the order of the klp_target_state write and future
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* TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
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* set a task->patch_state to KLP_UNDEFINED.
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*/
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smp_wmb();
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/*
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* Set the func transition states so klp_ftrace_handler() will know to
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* switch to the transition logic.
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*
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* When patching, the funcs aren't yet in the func_stack and will be
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* made visible to the ftrace handler shortly by the calls to
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* klp_patch_object().
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*
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* When unpatching, the funcs are already in the func_stack and so are
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* already visible to the ftrace handler.
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*/
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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;
|
|
|
|
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 */
|
|
synchronize_rcu();
|
|
|
|
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() */
|
|
}
|