High [CVE-2026-64287] Bound used_lrs when flushing the pKVM hyp vCPU

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Bound used_lrs when flushing the pKVM hyp vCPU flush_hyp_vcpu() copies the host vGIC state into the hyp's private vCPU on every run. The vGIC list register save and restore use used_lrs as their loop bound and expect it to stay within the number of implemented list registers.

While this is generally the case, flush_hyp_vcpu() copies vgic_v3 verbatim and does not enforce this, so a value provided by the host is used at EL2 to index vgic_lr[] and access ICH_LR_EL2 (host -> EL2). Fix by clamping used_lrs to the number of implemented list registers after the copy, as the trusted path already does in vgic_flush_lr_state().

The number of implemented list registers is constant after init, so it is replicated once from kvm_vgic_global_state.nr_lr into hyp_gicv3_nr_lr rather than read on every entry. A flaw was found in the Kernel-based Virtual Machine (KVM) component of the Linux kernel on ARM64 systems.

A highly privileged local attacker could exploit a vulnerability where the system fails to properly restrict memory access during a specific virtual machine operation.

This could allow the attacker to read or write to sensitive memory areas, potentially leading to privilege escalation, where they gain unauthorized higher access, or cause a system crash (denial of service).