CVE-2025-40300

/// Technical description

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

x86/vmscape: Add conditional IBPB mitigation

VMSCAPE is a vulnerability that exploits insufficient branch predictor

isolation between a guest and a userspace hypervisor (like QEMU). Existing

mitigations already protect kernel/KVM from a malicious guest. Userspace

can additionally be protected by flushing the branch predictors after a

VMexit.

Since it is the userspace that consumes the poisoned branch predictors,

conditionally issue an IBPB after a VMexit and before returning to

userspace. Workloads that frequently switch between hypervisor and

userspace will incur the most overhead from the new IBPB.

This new IBPB is not integrated with the existing IBPB sites. For

instance, a task can use the existing speculation control prctl() to

get an IBPB at context switch time. With this implementation, the

IBPB is doubled up: one at context switch and another before running

userspace.

The intent is to integrate and optimiz

/// 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