Subject: [PATCH] KVM: arm64: Sanitise host vCPU fields in flush_hyp_vcpu()

From: Hyunwoo Kim <[email-masked]>
Date: Thu, 4 Jun 2026 20:18:16 +0900

flush_hyp_vcpu() copies the host vCPU context and vGIC state into the
hyp's private vCPU on every run. ctxt_to_vcpu() expects a guest context
to have a NULL __hyp_running_vcpu, which is only ever set on the host
context, so that it resolves the vCPU via container_of(). The vGIC list
register save and restore expect used_lrs to stay within the number of
implemented list registers. While this is generally the case,
flush_hyp_vcpu() copies both fields verbatim from the host vCPU and
enforces neither expectation.

Fix by clearing __hyp_running_vcpu and clamping used_lrs after the copy.

Fixes: be66e67f1750 ("KVM: arm64: Use the pKVM hyp vCPU structure in handle___kvm_vcpu_run()")
Signed-off-by: Hyunwoo Kim <[email-masked]>
---
 arch/arm64/kvm/hyp/nvhe/hyp-main.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 06db299c37a89..ef9318ff0c25e 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -7,6 +7,7 @@
 #include <hyp/adjust_pc.h>
 #include <hyp/switch.h>
 
+#include <asm/arch_gicv3.h>
 #include <asm/pgtable-types.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_emulate.h>
@@ -128,6 +129,9 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 
 	hyp_vcpu->vcpu.arch.ctxt	= host_vcpu->arch.ctxt;
 
+	/* A guest context must keep a NULL __hyp_running_vcpu. */
+	hyp_vcpu->vcpu.arch.ctxt.__hyp_running_vcpu = NULL;
+
 	hyp_vcpu->vcpu.arch.mdcr_el2	= host_vcpu->arch.mdcr_el2;
 	hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWI | HCR_TWE);
 	hyp_vcpu->vcpu.arch.hcr_el2 |= READ_ONCE(host_vcpu->arch.hcr_el2) &
@@ -139,6 +143,13 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 
 	hyp_vcpu->vcpu.arch.vgic_cpu.vgic_v3 = host_vcpu->arch.vgic_cpu.vgic_v3;
 
+	/* Bound the host-provided used_lrs by the implemented list registers. */
+	if (static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
+		hyp_vcpu->vcpu.arch.vgic_cpu.vgic_v3.used_lrs =
+			min_t(unsigned int,
+			      hyp_vcpu->vcpu.arch.vgic_cpu.vgic_v3.used_lrs,
+			      (read_gicreg(ICH_VTR_EL2) & 0xf) + 1);
+
 	hyp_vcpu->vcpu.arch.pid = host_vcpu->arch.pid;
 }
 
-- 
2.43.0