CVE-2026-23425

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

KVM: arm64: Fix ID register initialization for non-protected pKVM guests

In protected mode, the hypervisor maintains a separate instance of

the `kvm` structure for each VM. For non-protected VMs, this structure is

initialized from the host's `kvm` state.

Currently, `pkvm_init_features_from_host()` copies the

`KVM_ARCH_FLAG_ID_REGS_INITIALIZED` flag from the host without the

underlying `id_regs` data being initialized. This results in the

hypervisor seeing the flag as set while the ID registers remain zeroed.

Consequently, `kvm_has_feat()` checks at EL2 fail (return 0) for

non-protected VMs. This breaks logic that relies on feature detection,

such as `ctxt_has_tcrx()` for TCR2_EL1 support. As a result, certain

system registers (e.g., TCR2_EL1, PIR_EL1, POR_EL1) are not

saved/restored during the world switch, which could lead to state

corruption.

Fix this by explicitly copying the ID registers from the host `kvm` to

the hypervisor `kvm` for non-protected VMs during initialization, since

we trust the host with its non-protected guests' features. Also ensure

`KVM_ARCH_FLAG_ID_REGS_INITIALIZED` is cleared initially in

`pkvm_init_features_from_host` so that `vm_copy_id_regs` can properly

initialize them and set the flag once done.