CVE-2022-49783: In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Drop fpregs lock before inheriting FPU permissions Mike Galbraith repor...

Description

In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Drop fpregs lock before inheriting FPU permissions Mike Galbraith reported the following against an old fork of preempt-rt but the same issue also applies to the current preempt-rt tree. BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd preempt_count: 1, expected: 0 RCU nest depth: 0, expected: 0 Preemption disabled at: fpu_clone CPU: 6 PID: 1 Comm: systemd Tainted: G E (unreleased) Call Trace: <TASK> dump_stack_lvl ? fpu_clone __might_resched rt_spin_lock fpu_clone ? copy_thread ? copy_process ? shmem_alloc_inode ? kmem_cache_alloc ? kernel_clone ? __do_sys_clone ? do_syscall_64 ? __x64_sys_rt_sigprocmask ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? exc_page_fault ? entry_SYSCALL_64_after_hwframe </TASK> Mike says: The splat comes from fpu_inherit_perms() being called under fpregs_lock(), and us reaching the spin_lock_irq() therein due to fpu_state_size_dynamic() returning true despite static key __fpu_state_size_dynamic having never been enabled. Mike's assessment looks correct. fpregs_lock on a PREEMPT_RT kernel disables preemption so calling spin_lock_irq() in fpu_inherit_perms() is unsafe. This problem exists since commit 9e798e9aa14c ("x86/fpu: Prepare fpu_clone() for dynamically enabled features"). Even though the original bug report should not have enabled the paths at all, the bug still exists. fpregs_lock is necessary when editing the FPU registers or a task's FP state but it is not necessary for fpu_inherit_perms(). The only write of any FP state in fpu_inherit_perms() is for the new child which is not running yet and cannot context switch or be borrowed by a kernel thread yet. Hence, fpregs_lock is not protecting anything in the new child until clone() completes and can be dropped earlier. The siglock still needs to be acquired by fpu_inherit_perms() as the read of the parent's permissions has to be serialised. [ bp: Cleanup splat. ]

Metrics

CVSS 3.1

5.5/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

0.14%

3.8th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions	Update
Linux	Linux Kernel	>= 5.16, < 6.0.10	—
Linux	Linux Kernel	6.1	Rc1

References

Timeline

Published: May 1, 2025
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2022-49783?

In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Drop fpregs lock before inheriting FPU permissions Mike Galbraith reported the following against an old fork of preempt-rt but the same issue also applies to the current preempt-rt tree. BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd preempt_count: 1, expected: 0 RCU nest depth: 0, expected: 0 Preemption disabled at: fpu_clone CPU: 6 PID: 1 Comm: systemd Tainted: G E (unreleased) Call Trace: <TASK> dump_stack_lvl ? fpu_clone __might_resched rt_spin_lock fpu_clone ? copy_thread ? copy_process ? shmem_alloc_inode ? kmem_cache_alloc ? kernel_clone ? __do_sys_clone ? do_syscall_64 ? __x64_sys_rt_sigprocmask ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? exc_page_fault ? entry_SYSCALL_64_after_hwframe </TASK> Mike says: The splat comes from fpu_inherit_perms() being called under fpregs_lock(), and us reaching the spin_lock_irq() therein due to fpu_state_size_dynamic() returning true despite static key __fpu_state_size_dynamic having never been enabled. Mike's assessment looks correct. fpregs_lock on a PREEMPT_RT kernel disables preemption so calling spin_lock_irq() in fpu_inherit_perms() is unsafe. This problem exists since commit 9e798e9aa14c ("x86/fpu: Prepare fpu_clone() for dynamically enabled features"). Even though the original bug report should not have enabled the paths at all, the bug still exists. fpregs_lock is necessary when editing the FPU registers or a task's FP state but it is not necessary for fpu_inherit_perms(). The only write of any FP state in fpu_inherit_perms() is for the new child which is not running yet and cannot context switch or be borrowed by a kernel thread yet. Hence, fpregs_lock is not protecting anything in the new child until clone() completes and can be dropped earlier. The siglock still needs to be acquired by fpu_inherit_perms() as the read of the parent's permissions has to be serialised. [ bp: Cleanup splat. ]

How severe is CVE-2022-49783?

CVE-2022-49783 has a CVSS score of 5.5/10 (MEDIUM severity). The EPSS model estimates a 0.14% probability of exploitation in the next 30 days.

How do I fix CVE-2022-49783?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.