From 836b2fe544a5e9b5ce116622cb36fba33838c6fd Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Fri, 4 Sep 2026 01:33:23 -0700 Subject: selftests/bpf: Check that JMP32 pointer vs zero jumps are not predicted Add jmp32_ptr_vs_zero_jne: the fall-through of the 32-bit compare, which the verifier used to skip, contains an out of bounds map value access, hence w/o the previous patch the program is accepted. See previous patch for detailed description. Reported-by: Nicholas Carlini Suggested-by: Nicholas Carlini Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260904083325.2083493-6-eddyz87@gmail.com Signed-off-by: Kumar Kartikeya Dwivedi --- lib/is_single_threaded.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 54 insertions(+) create mode 100644 lib/is_single_threaded.c (limited to 'lib/is_single_threaded.c') diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c new file mode 100644 index 000000000..8c98b20bf --- /dev/null +++ b/lib/is_single_threaded.c @@ -0,0 +1,54 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* Function to determine if a thread group is single threaded or not + * + * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + * - Derived from security/selinux/hooks.c + */ +#include +#include +#include + +/* + * Returns true if the task does not share ->mm with another thread/process. + */ +bool current_is_single_threaded(void) +{ + struct task_struct *task = current; + struct mm_struct *mm = task->mm; + struct task_struct *p, *t; + bool ret; + + if (atomic_read(&task->signal->live) != 1) + return false; + + if (atomic_read(&mm->mm_users) == 1) + return true; + + ret = false; + rcu_read_lock(); + for_each_process(p) { + if (unlikely(p->flags & PF_KTHREAD)) + continue; + if (unlikely(p == task->group_leader)) + continue; + + for_each_thread(p, t) { + if (unlikely(t->mm == mm)) + goto found; + if (likely(t->mm)) + break; + /* + * t->mm == NULL. Make sure next_thread/next_task + * will see other CLONE_VM tasks which might be + * forked before exiting. + */ + smp_rmb(); + } + } + ret = true; +found: + rcu_read_unlock(); + + return ret; +} -- cgit v1.3.1