[PATCH 5.12 122/677] KVM: arm/arm64: Fix KVM_VGIC_V3_ADDR_TYPE_REDIST read

[Greg Kroah-Hartman]

From: Eric Auger <eric.auger@xxxxxxxxxx>

commit 94ac0835391efc1a30feda6fc908913ec012951e upstream.

When reading the base address of the a REDIST region
through KVM_VGIC_V3_ADDR_TYPE_REDIST we expect the
redistributor region list to be populated with a single
element.

However list_first_entry() expects the list to be non empty.
Instead we should use list_first_entry_or_null which effectively
returns NULL if the list is empty.

Fixes: dbd9733ab674 ("KVM: arm/arm64: Replace the single rdist region by a list")
Cc: <Stable@xxxxxxxxxxxxxxx> # v4.18+
Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
Reported-by: Gavin Shan <gshan@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210412150034.29185-1-eric.auger@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kvm/vgic/vgic-kvm-device.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
+++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
@@ -87,8 +87,8 @@ int kvm_vgic_addr(struct kvm *kvm, unsig
 			r = vgic_v3_set_redist_base(kvm, 0, *addr, 0);
 			goto out;
 		}
-		rdreg = list_first_entry(&vgic->rd_regions,
-					 struct vgic_redist_region, list);
+		rdreg = list_first_entry_or_null(&vgic->rd_regions,
+						 struct vgic_redist_region, list);
 		if (!rdreg)
 			addr_ptr = &undef_value;
 		else