[PATCH 6/8] KVM: arm64: Minimise EL2's exposure of host VGIC state during world switch

[Fuad Tabba <tabba@google.com>]

From: Marc Zyngier <maz@kernel.org>

The host passes a vgic_v3_cpu_if pointer to the __vgic_v3_save_aprs and
__vgic_v3_restore_vmcr_aprs hypercalls, which EL2 dereferences
wholesale. That exposes the host's full VGIC emulation state to the
hypervisor, against pKVM's isolation goals.

Recover the host vCPU from the supplied cpu_if via container_of() and
copy only vgic_vmcr and the active priority registers between EL2's
hyp-side state and the host vCPU, so EL2 no longer dereferences the
host's vgic_v3_cpu_if directly.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Co-developed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 67 ++++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 8923f594c264..f25ee3971528 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -7,6 +7,8 @@
 #include <hyp/adjust_pc.h>
 #include <hyp/switch.h>
 
+#include <linux/irqchip/arm-gic-v3.h>
+
 #include <asm/pgtable-types.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
@@ -237,6 +239,16 @@ static struct kvm_vcpu *__get_host_hyp_vcpus(struct kvm_vcpu *arg,
 		__get_host_hyp_vcpus(__vcpu, hyp_vcpup);		\
 	})
 
+#define get_host_hyp_vcpus_from_vgic_v3_cpu_if(ctxt, regnr, hyp_vcpup)		\
+	({									\
+		DECLARE_REG(struct vgic_v3_cpu_if *, cif, ctxt, regnr);\
+		struct kvm_vcpu *__vcpu = container_of(cif,			\
+						       struct kvm_vcpu,		\
+						       arch.vgic_cpu.vgic_v3);	\
+										\
+		__get_host_hyp_vcpus(__vcpu, hyp_vcpup);			\
+	})
+
 static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
 {
 	struct pkvm_hyp_vcpu *hyp_vcpu;
@@ -506,16 +518,63 @@ static void handle___vgic_v3_init_lrs(struct kvm_cpu_context *host_ctxt)
 
 static void handle___vgic_v3_save_aprs(struct kvm_cpu_context *host_ctxt)
 {
-	DECLARE_REG(struct vgic_v3_cpu_if *, cpu_if, host_ctxt, 1);
+	struct pkvm_hyp_vcpu *hyp_vcpu;
+	struct kvm_vcpu *host_vcpu;
 
-	__vgic_v3_save_aprs(kern_hyp_va(cpu_if));
+	host_vcpu = get_host_hyp_vcpus_from_vgic_v3_cpu_if(host_ctxt, 1,
+							   &hyp_vcpu);
+	if (!host_vcpu)
+		return;
+
+	if (unlikely(hyp_vcpu)) {
+		struct vgic_v3_cpu_if *hyp_cpu_if, *host_cpu_if;
+		int i;
+
+		hyp_cpu_if = &hyp_vcpu->vcpu.arch.vgic_cpu.vgic_v3;
+		__vgic_v3_save_aprs(hyp_cpu_if);
+
+		host_cpu_if = &host_vcpu->arch.vgic_cpu.vgic_v3;
+		host_cpu_if->vgic_vmcr = hyp_cpu_if->vgic_vmcr;
+		for (i = 0; i < ARRAY_SIZE(host_cpu_if->vgic_ap0r); i++) {
+			host_cpu_if->vgic_ap0r[i] = hyp_cpu_if->vgic_ap0r[i];
+			host_cpu_if->vgic_ap1r[i] = hyp_cpu_if->vgic_ap1r[i];
+		}
+	} else {
+		__vgic_v3_save_aprs(&host_vcpu->arch.vgic_cpu.vgic_v3);
+	}
 }
 
 static void handle___vgic_v3_restore_vmcr_aprs(struct kvm_cpu_context *host_ctxt)
 {
-	DECLARE_REG(struct vgic_v3_cpu_if *, cpu_if, host_ctxt, 1);
+	struct pkvm_hyp_vcpu *hyp_vcpu;
+	struct kvm_vcpu *host_vcpu;
 
-	__vgic_v3_restore_vmcr_aprs(kern_hyp_va(cpu_if));
+	host_vcpu = get_host_hyp_vcpus_from_vgic_v3_cpu_if(host_ctxt, 1,
+							   &hyp_vcpu);
+	if (!host_vcpu)
+		return;
+
+	if (unlikely(hyp_vcpu)) {
+		struct vgic_v3_cpu_if *hyp_cpu_if, *host_cpu_if;
+		int i;
+
+		hyp_cpu_if = &hyp_vcpu->vcpu.arch.vgic_cpu.vgic_v3;
+		host_cpu_if = &host_vcpu->arch.vgic_cpu.vgic_v3;
+
+		hyp_cpu_if->vgic_vmcr = host_cpu_if->vgic_vmcr;
+		/* Should be a one-off */
+		hyp_cpu_if->vgic_sre = (ICC_SRE_EL1_DIB |
+					ICC_SRE_EL1_DFB |
+					ICC_SRE_EL1_SRE);
+		for (i = 0; i < ARRAY_SIZE(host_cpu_if->vgic_ap0r); i++) {
+			hyp_cpu_if->vgic_ap0r[i] = host_cpu_if->vgic_ap0r[i];
+			hyp_cpu_if->vgic_ap1r[i] = host_cpu_if->vgic_ap1r[i];
+		}
+
+		__vgic_v3_restore_vmcr_aprs(hyp_cpu_if);
+	} else {
+		__vgic_v3_restore_vmcr_aprs(&host_vcpu->arch.vgic_cpu.vgic_v3);
+	}
 }
 
 static void handle___pkvm_init(struct kvm_cpu_context *host_ctxt)
-- 
2.55.0.rc0.738.g0c8ab3ebcc-goog