KVM: s390: pv: avoid double free of sida page

If kvm_s390_pv_destroy_cpu is called more than once, we risk calling
free_page on a random page, since the sidad field is aliased with the
gbea, which is not guaranteed to be zero.

This can happen, for example, if userspace calls the KVM_PV_DISABLE
IOCTL, and it fails, and then userspace calls the same IOCTL again.
This scenario is only possible if KVM has some serious bug or if the
hardware is broken.

The solution is to simply return successfully immediately if the vCPU
was already non secure.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes: 19e1227768863a1469797c13ef8fea1af7beac2c ("KVM: S390: protvirt: Introduce instruction data area bounce buffer")
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Message-Id: <20210920132502.36111-3-imbrenda@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index c8841f476e9132bca23c52828a27fb3cc7fdeadc..0a854115100b461ea3b5494ea9256c1f335e80ec 100644 (file)
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -16,18 +16,17 @@
 
 int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
 {
-       int cc = 0;
+       int cc;
 
-       if (kvm_s390_pv_cpu_get_handle(vcpu)) {
-               cc = uv_cmd_nodata(kvm_s390_pv_cpu_get_handle(vcpu),
-                                  UVC_CMD_DESTROY_SEC_CPU, rc, rrc);
+       if (!kvm_s390_pv_cpu_get_handle(vcpu))
+               return 0;
+
+       cc = uv_cmd_nodata(kvm_s390_pv_cpu_get_handle(vcpu), UVC_CMD_DESTROY_SEC_CPU, rc, rrc);
+
+       KVM_UV_EVENT(vcpu->kvm, 3, "PROTVIRT DESTROY VCPU %d: rc %x rrc %x",
+                    vcpu->vcpu_id, *rc, *rrc);
+       WARN_ONCE(cc, "protvirt destroy cpu failed rc %x rrc %x", *rc, *rrc);
 
-               KVM_UV_EVENT(vcpu->kvm, 3,
-                            "PROTVIRT DESTROY VCPU %d: rc %x rrc %x",
-                            vcpu->vcpu_id, *rc, *rrc);
-               WARN_ONCE(cc, "protvirt destroy cpu failed rc %x rrc %x",
-                         *rc, *rrc);
-       }
        /* Intended memory leak for something that should never happen. */
        if (!cc)
                free_pages(vcpu->arch.pv.stor_base,