KVM: Check KVM_CAP_DIRTY_LOG_{RING, RING_ACQ_REL} prior to enabling them

There are two capabilities related to ring-based dirty page tracking:
KVM_CAP_DIRTY_LOG_RING and KVM_CAP_DIRTY_LOG_RING_ACQ_REL. Both are
supported by x86. However, arm64 supports KVM_CAP_DIRTY_LOG_RING_ACQ_REL
only when the feature is supported on arm64. The userspace doesn't have
to enable the advertised capability, meaning KVM_CAP_DIRTY_LOG_RING can
be enabled on arm64 by userspace and it's wrong.

Fix it by double checking if the capability has been advertised prior to
enabling it. It's rejected to enable the capability if it hasn't been
advertised.

Fixes: 17601bfe ("KVM: Add KVM_CAP_DIRTY_LOG_RING_ACQ_REL capability and config option")
Reported-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221031003621.164306-4-gshan@redhat.com

virt/kvm/kvm_main.c

@@ -4585,6 +4585,9 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm,
 	}
 	case KVM_CAP_DIRTY_LOG_RING:
 	case KVM_CAP_DIRTY_LOG_RING_ACQ_REL:
+		if (!kvm_vm_ioctl_check_extension_generic(kvm, cap->cap))
+			return -EINVAL;
+
 		return kvm_vm_ioctl_enable_dirty_log_ring(kvm, cap->args[0]);
 	default:
 		return kvm_vm_ioctl_enable_cap(kvm, cap);