[PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu()

[PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu()

[Hyunwoo Kim]

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.

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

[PATCH v2 1/2] KVM: arm64: Clear __hyp_running_vcpu when flushing the pKVM hyp vCPU

[Hyunwoo Kim]

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

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

[Hyunwoo Kim]

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

Re: [PATCH v2 0/2] KVM: arm64: Sanitise host vCPU fields copied in flush_hyp_vcpu()

[Fuad Tabba]

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
>

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

[Marc Zyngier]

On Thu, 04 Jun 2026 16:12:03 +0100,
Hyunwoo Kim <imv4bel@gmail.com> wrote:
> 
> 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))

There is no pKVM support without a GICv3 CPU interface, and absolutely
everything already assumes it. Why do we need this extra check?

> +		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);
> +

Reading ICH_VTR_EL2 on each entry is going to cause some really heavy
trapping under NV, and we should avoid this.

kvm_vgic_global_state.nr_lr contains this information, and it should
only be a matter of replicating it (or compute it once) at init time.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.