cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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is_single_threaded.c (1202B)

      1// SPDX-License-Identifier: GPL-2.0-or-later
      2/* Function to determine if a thread group is single threaded or not
      3 *
      4 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
      5 * Written by David Howells (dhowells@redhat.com)
      6 * - Derived from security/selinux/hooks.c
      7 */
      8#include <linux/sched/signal.h>
      9#include <linux/sched/task.h>
     10#include <linux/sched/mm.h>
     11
     12/*
     13 * Returns true if the task does not share ->mm with another thread/process.
     14 */
     15bool current_is_single_threaded(void)
     16{
     17	struct task_struct *task = current;
     18	struct mm_struct *mm = task->mm;
     19	struct task_struct *p, *t;
     20	bool ret;
     21
     22	if (atomic_read(&task->signal->live) != 1)
     23		return false;
     24
     25	if (atomic_read(&mm->mm_users) == 1)
     26		return true;
     27
     28	ret = false;
     29	rcu_read_lock();
     30	for_each_process(p) {
     31		if (unlikely(p->flags & PF_KTHREAD))
     32			continue;
     33		if (unlikely(p == task->group_leader))
     34			continue;
     35
     36		for_each_thread(p, t) {
     37			if (unlikely(t->mm == mm))
     38				goto found;
     39			if (likely(t->mm))
     40				break;
     41			/*
     42			 * t->mm == NULL. Make sure next_thread/next_task
     43			 * will see other CLONE_VM tasks which might be
     44			 * forked before exiting.
     45			 */
     46			smp_rmb();
     47		}
     48	}
     49	ret = true;
     50found:
     51	rcu_read_unlock();
     52
     53	return ret;
     54}