[PATCH 01/12] KVM: arm64: Make ICC_*SGI*_EL1 undef in the absence of a vGICv3

[PATCH 01/12] KVM: arm64: Make ICC_*SGI*_EL1 undef in the absence of a vGICv3

[Marc Zyngier]

On a system with a GICv3, if a guest hasn't been configured with
GICv3 and that the host is not capable of GICv2 emulation,
a write to any of the ICC_*SGI*_EL1 registers is trapped to EL2.

We therefore try to emulate the SGI access, only to hit a NULL
pointer as no private interrupt is allocated (no GIC, remember?).

The obvious fix is to give the guest what it deserves, in the
shape of a UNDEF exception.

Reported-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
---
 arch/arm64/kvm/sys_regs.c  | 6 ++++++
 arch/arm64/kvm/vgic/vgic.h | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c90324060436..31e49da867ff 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -33,6 +33,7 @@
 #include <trace/events/kvm.h>
 
 #include "sys_regs.h"
+#include "vgic/vgic.h"
 
 #include "trace.h"
 
@@ -435,6 +436,11 @@ static bool access_gic_sgi(struct kvm_vcpu *vcpu,
 {
 	bool g1;
 
+	if (!kvm_has_gicv3(vcpu->kvm)) {
+		kvm_inject_undefined(vcpu);
+		return false;
+	}
+
 	if (!p->is_write)
 		return read_from_write_only(vcpu, p, r);
 
diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h
index ba8f790431bd..8532bfe3fed4 100644
--- a/arch/arm64/kvm/vgic/vgic.h
+++ b/arch/arm64/kvm/vgic/vgic.h
@@ -346,4 +346,11 @@ void vgic_v4_configure_vsgis(struct kvm *kvm);
 void vgic_v4_get_vlpi_state(struct vgic_irq *irq, bool *val);
 int vgic_v4_request_vpe_irq(struct kvm_vcpu *vcpu, int irq);
 
+static inline bool kvm_has_gicv3(struct kvm *kvm)
+{
+	return (static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif) &&
+		irqchip_in_kernel(kvm) &&
+		kvm->arch.vgic.vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3);
+}
+
 #endif
-- 
2.39.2

Re: [PATCH 01/12] KVM: arm64: Make ICC_*SGI*_EL1 undef in the absence of a vGICv3

[Oliver Upton]

On Tue, Aug 20, 2024 at 11:03:38AM +0100, Marc Zyngier wrote:
> On a system with a GICv3, if a guest hasn't been configured with
> GICv3 and that the host is not capable of GICv2 emulation,
> a write to any of the ICC_*SGI*_EL1 registers is trapped to EL2.
> 
> We therefore try to emulate the SGI access, only to hit a NULL
> pointer as no private interrupt is allocated (no GIC, remember?).
> 
> The obvious fix is to give the guest what it deserves, in the
> shape of a UNDEF exception.
> 
> Reported-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: stable@vger.kernel.org

LGTM, and just as an FYI I do plan on grabbing this for 6.11

-- 
Thanks,
Oliver

Re: [PATCH 01/12] KVM: arm64: Make ICC_*SGI*_EL1 undef in the absence of a vGICv3

[Marc Zyngier]

On Tue, 20 Aug 2024 22:46:30 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> On Tue, Aug 20, 2024 at 11:03:38AM +0100, Marc Zyngier wrote:
> > On a system with a GICv3, if a guest hasn't been configured with
> > GICv3 and that the host is not capable of GICv2 emulation,
> > a write to any of the ICC_*SGI*_EL1 registers is trapped to EL2.
> > 
> > We therefore try to emulate the SGI access, only to hit a NULL
> > pointer as no private interrupt is allocated (no GIC, remember?).
> > 
> > The obvious fix is to give the guest what it deserves, in the
> > shape of a UNDEF exception.
> > 
> > Reported-by: Alexander Potapenko <glider@google.com>
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > Cc: stable@vger.kernel.org
> 
> LGTM, and just as an FYI I do plan on grabbing this for 6.11

Great, thanks. Are you planning to route this via arm64, given that
Paolo is away for a bit?

	M.

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

Re: [PATCH 01/12] KVM: arm64: Make ICC_*SGI*_EL1 undef in the absence of a vGICv3

[Oliver Upton]

On Wed, Aug 21, 2024 at 11:59:52AM +0100, Marc Zyngier wrote:
> On Tue, 20 Aug 2024 22:46:30 +0100,
> Oliver Upton <oliver.upton@linux.dev> wrote:
> > 
> > On Tue, Aug 20, 2024 at 11:03:38AM +0100, Marc Zyngier wrote:
> > > On a system with a GICv3, if a guest hasn't been configured with
> > > GICv3 and that the host is not capable of GICv2 emulation,
> > > a write to any of the ICC_*SGI*_EL1 registers is trapped to EL2.
> > > 
> > > We therefore try to emulate the SGI access, only to hit a NULL
> > > pointer as no private interrupt is allocated (no GIC, remember?).
> > > 
> > > The obvious fix is to give the guest what it deserves, in the
> > > shape of a UNDEF exception.
> > > 
> > > Reported-by: Alexander Potapenko <glider@google.com>
> > > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > > Cc: stable@vger.kernel.org
> > 
> > LGTM, and just as an FYI I do plan on grabbing this for 6.11
> 
> Great, thanks. Are you planning to route this via arm64, given that
> Paolo is away for a bit?

Yup, exactly that. I'll send the PR in the next day or two when I have
some time to kick the tires on everything.

-- 
Thanks,
Oliver

Re: (subset) [PATCH 01/12] KVM: arm64: Make ICC_*SGI*_EL1 undef in the absence of a vGICv3

[Oliver Upton]

On Tue, 20 Aug 2024 11:03:38 +0100, Marc Zyngier wrote:
> On a system with a GICv3, if a guest hasn't been configured with
> GICv3 and that the host is not capable of GICv2 emulation,
> a write to any of the ICC_*SGI*_EL1 registers is trapped to EL2.
> 
> We therefore try to emulate the SGI access, only to hit a NULL
> pointer as no private interrupt is allocated (no GIC, remember?).
> 
> [...]

Applied to kvmarm/fixes, thanks!

[01/12] KVM: arm64: Make ICC_*SGI*_EL1 undef in the absence of a vGICv3
        https://git.kernel.org/kvmarm/kvmarm/c/3e6245ebe7ef

--
Best,
Oliver