Re: [PATCH v2 3/5] KVM: arm64: Validate the host-provided vgic model in pKVM

[Suzuki K Poulose]

On 11/10/2026 15:36, Fuad Tabba wrote:
> EL2 copies vgic_model from the host's struct kvm unchecked, and the nVHE
> world switch dispatches on it with no cpucap guard. A host writing
> KVM_DEV_TYPE_ARM_VGIC_V5 makes EL2 access GICv5 CPU interface registers
> that are UNDEFINED without FEAT_GCIE, and panics the hypervisor on any
> GICv3 machine.
>
> Accept only GICv3, the one model pKVM supports, and force anything else
> to 0, as for a VM with no in-kernel irqchip. EL2 reads the model only to
> pick the GICv5 world switch and to emulate GICv3 CPU interface accesses,
> and the host's own copy is left alone.
>
> Fixes: 9b8e3d4ca0e73 ("KVM: arm64: gic-v5: Implement GICv5 load/put and save/restore")
> Signed-off-by: Fuad Tabba <fuad.tabba@xxxxxxxxx>
> ---
>   arch/arm64/kvm/hyp/nvhe/pkvm.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> index 459bd9eb7e4bc..a9d0e94709199 100644
> --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
> +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
> @@ -340,13 +340,19 @@ static void pkvm_init_features_from_host(struct pkvm_hyp_vm *hyp_vm, const struc
>   {
>   	struct kvm *kvm = &hyp_vm->kvm;
>   	unsigned long host_arch_flags = READ_ONCE(host_kvm->arch.flags);
> +	u32 vgic_model = READ_ONCE(host_kvm->arch.vgic.vgic_model);
>   	DECLARE_BITMAP(allowed_features, KVM_VCPU_MAX_FEATURES);
>   
>   	/* CTR_EL0 is always under host control, even for protected VMs. */
>   	hyp_vm->kvm.arch.ctr_el0 = host_kvm->arch.ctr_el0;
>   
> -	/* Preserve the vgic model so that GICv3 emulation works */
> -	hyp_vm->kvm.arch.vgic.vgic_model = host_kvm->arch.vgic.vgic_model;
> +	/*
> +	 * pKVM runs only GICv3. Anything else becomes 0, the model of a VM
> +	 * with no in-kernel irqchip, which keeps EL2 off the GICv5 registers.
> +	 */
> +	if (vgic_model != KVM_DEV_TYPE_ARM_VGIC_V3)
> +		vgic_model = 0;



> +	hyp_vm->kvm.arch.vgic.vgic_model = vgic_model;

0 is not a valid KVM_DEV_TYPE_*, so this looks good to me.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>