CVE-2025-68171

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

x86/fpu: Ensure XFD state on signal delivery

Sean reported [1] the following splat when running KVM tests:

WARNING: CPU: 232 PID: 15391 at xfd_validate_state+0x65/0x70

Call Trace:

<TASK>

fpu__clear_user_states+0x9c/0x100

arch_do_signal_or_restart+0x142/0x210

exit_to_user_mode_loop+0x55/0x100

do_syscall_64+0x205/0x2c0

entry_SYSCALL_64_after_hwframe+0x4b/0x53

Chao further identified [2] a reproducible scenario involving signal

delivery: a non-AMX task is preempted by an AMX-enabled task which

modifies the XFD MSR.

When the non-AMX task resumes and reloads XSTATE with init values,

a warning is triggered due to a mismatch between fpstate::xfd and the

CPU's current XFD state. fpu__clear_user_states() does not currently

re-synchronize the XFD state after such preemption.

Invoke xfd_update_state() which detects and corrects the mismatch if

there is a dynamic feature.

This also benefits the

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References