Medium [CVE-2026-64555] Fix SPSR_EL2 restore in kvm_hyp_handle_mops

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: nv: Fix SPSR_EL2 restore in kvm_hyp_handle_mops() kvm_hyp_handle_mops() resets the single-step state machine as part of rewinding state for a MOPS exception by modifying vcpu_cpsr() and writing the result directly into hardware.

In the case of nested virtualization, vcpu_cpsr() is a synthetic value such that the rest of KVM can deal with vEL2 cleanly. That means the value requires translation before being written into hardware, which is unfortunately missing from the MOPS handler.

Fix it by directly modifying SPSR_EL2 and avoiding the synthetic state altogether, which will be resynchronized on the next 'full' exit back to KVM. A flaw was found in the Linux kernel's Kernel-based Virtual Machine (KVM) for ARM64 architecture, specifically affecting nested virtualization.

The kvm_hyp_handle_mops() function, responsible for handling certain virtualization operations, incorrectly restored the SPSR_EL2 register. This occurred because a synthetic value used for nested virtualization was written directly to hardware without proper translation, leading to an improper reset of the single-step state machine.

This could potentially impact the stability or security of nested virtualized environments. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).

Weakness: CWE-681.