[PATCH v1 1/4] KVM: arm64: Validate the host-provided vgic model in pKVM
From: Fuad Tabba <fuad.tabba@linux.dev>
Date: 2026-08-06 10:03:49
Also in:
kvmarm, lkml
Subsystem:
arm64 port (aarch64 architecture), kernel virtual machine for arm64 (kvm/arm64), the rest · Maintainers:
Catalin Marinas, Will Deacon, Marc Zyngier, Oliver Upton, Linus Torvalds
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,
which are UNDEFINED without FEAT_GCIE and panic the hypervisor on any
GICv3 machine.
Accept only the models pKVM can run, forcing anything else to 0.
Fixes: 9b8e3d4ca0e73 ("KVM: arm64: gic-v5: Implement GICv5 load/put and save/restore")
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
arch/arm64/kvm/hyp/nvhe/pkvm.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 24d6f164129ac..59bb15efdca42 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c@@ -340,13 +340,25 @@ 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; + /* + * Preserve the vgic model for GICv3 emulation, but only what pKVM can + * run: the GICv5 world switch touches registers UNDEFINED at EL2 + * without FEAT_GCIE. 0 is not a valid kvm_device_type: "no vgic". + */ + switch (vgic_model) { + case KVM_DEV_TYPE_ARM_VGIC_V2: + case KVM_DEV_TYPE_ARM_VGIC_V3: + break; + default: + vgic_model = 0; + } + hyp_vm->kvm.arch.vgic.vgic_model = vgic_model; /* No restrictions for non-protected VMs. */ if (!kvm_vm_is_protected(kvm)) {
--
2.39.5