Subject: [PATCH v2 2/2] KVM: arm64: Bound used_lrs when flushing the pKVM hyp vCPU

From: Hyunwoo Kim <[email-masked]>
Date: Fri, 5 Jun 2026 00:12:03 +0900

flush_hyp_vcpu() copies the host vGIC state into the hyp's private vCPU
on every run. The vGIC list register save and restore use used_lrs as
their loop bound and expect it to stay within the number of implemented
list registers. While this is generally the case, flush_hyp_vcpu()
copies vgic_v3 verbatim and does not enforce this, so a value provided
by the host is used at EL2 to index vgic_lr[] and access ICH_LR<n>_EL2
(host -> EL2).

Fix by clamping used_lrs to the number of implemented list registers
after the copy, as the trusted path already does in
vgic_flush_lr_state().

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 | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 02c5d6e5abcbf..cd807fdb11ba8 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>
@@ -142,6 +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 used_lrs by the number of 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