* [PATCH v2 1/2] KVM: arm64: Clear __hyp_running_vcpu when flushing the pKVM hyp vCPU
2026-06-04 15:12 [PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu() Hyunwoo Kim
@ 2026-06-04 15:12 ` Hyunwoo Kim
2026-06-04 15:12 ` [PATCH v2 2/2] KVM: arm64: Bound used_lrs " Hyunwoo Kim
2026-06-04 15:29 ` [PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu() Fuad Tabba
2 siblings, 0 replies; 4+ messages in thread
From: Hyunwoo Kim @ 2026-06-04 15:12 UTC (permalink / raw)
To: tabba, maz, oupton, joey.gouly, seiden, suzuki.poulose, yuzenghui,
catalin.marinas, will
Cc: linux-arm-kernel, kvmarm, imv4bel
flush_hyp_vcpu() copies the host vCPU context 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(). While this is generally
the case, flush_hyp_vcpu() copies the context verbatim and does not
enforce this, so a value provided by the host is dereferenced at EL2
(host -> EL2).
Fix by clearing __hyp_running_vcpu after the copy.
Fixes: be66e67f1750 ("KVM: arm64: Use the pKVM hyp vCPU structure in handle___kvm_vcpu_run()")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail•com>
---
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 06db299c37a89..02c5d6e5abcbf 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -128,6 +128,9 @@ static void flush_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
hyp_vcpu->vcpu.arch.ctxt = host_vcpu->arch.ctxt;
+ /* __hyp_running_vcpu must be NULL in a guest context. */
+ 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) &
--
2.43.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH v2 2/2] KVM: arm64: Bound used_lrs when flushing the pKVM hyp vCPU
2026-06-04 15:12 [PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu() Hyunwoo Kim
2026-06-04 15:12 ` [PATCH v2 1/2] KVM: arm64: Clear __hyp_running_vcpu when flushing the pKVM hyp vCPU Hyunwoo Kim
@ 2026-06-04 15:12 ` Hyunwoo Kim
2026-06-04 15:29 ` [PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu() Fuad Tabba
2 siblings, 0 replies; 4+ messages in thread
From: Hyunwoo Kim @ 2026-06-04 15:12 UTC (permalink / raw)
To: tabba, maz, oupton, joey.gouly, seiden, suzuki.poulose, yuzenghui,
catalin.marinas, will
Cc: linux-arm-kernel, kvmarm, imv4bel
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 <imv4bel@gmail•com>
---
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
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu()
2026-06-04 15:12 [PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu() Hyunwoo Kim
2026-06-04 15:12 ` [PATCH v2 1/2] KVM: arm64: Clear __hyp_running_vcpu when flushing the pKVM hyp vCPU Hyunwoo Kim
2026-06-04 15:12 ` [PATCH v2 2/2] KVM: arm64: Bound used_lrs " Hyunwoo Kim
@ 2026-06-04 15:29 ` Fuad Tabba
2 siblings, 0 replies; 4+ messages in thread
From: Fuad Tabba @ 2026-06-04 15:29 UTC (permalink / raw)
To: Hyunwoo Kim
Cc: maz, oupton, joey.gouly, seiden, suzuki.poulose, yuzenghui,
catalin.marinas, will, linux-arm-kernel, kvmarm
On Thu, 4 Jun 2026 at 16:12, Hyunwoo Kim <imv4bel@gmail•com> wrote:
>
> flush_hyp_vcpu() copies the host vCPU context and vGIC state into the
> hyp's private vCPU on every run. This series sanitises two fields that
> it currently copies verbatim (host -> EL2): __hyp_running_vcpu is
> cleared in the guest context, and used_lrs is bounded by the number of
> implemented list registers.
>
> v1 -> v2: split into two patches, one per field, per review.
For the series:
Reviewed-by: Fuad Tabba <tabba@google•com>
Tested-by: Fuad Tabba <tabba@google•com>
Cheers,
/fuad
>
> Hyunwoo Kim (2):
> KVM: arm64: Clear __hyp_running_vcpu when flushing the pKVM hyp vCPU
> KVM: arm64: Bound used_lrs when flushing the pKVM hyp vCPU
>
> arch/arm64/kvm/hyp/nvhe/hyp-main.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> --
> 2.43.0
>
^ permalink raw reply [flat|nested] 4+ messages in thread