KVM: s390: Fix skey emulation permission check

All skey functions call skey_check_enable at their start, which checks
if we are in the PSTATE and injects a privileged operation exception
if we are.

Unfortunately they continue processing afterwards and perform the
operation anyhow as skey_check_enable does not deliver an error if the
exception injection was successful.

Let's move the PSTATE check into the skey functions and exit them on
such an occasion, also we now do not enable skey handling anymore in
such a case.

Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Fixes: a7e19ab ("KVM: s390: handle missing storage-key facility")
Cc: <stable@vger.kernel.org> # v4.8+
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/kvm/priv.c

@@ -232,8 +232,6 @@ static int try_handle_skey(struct kvm_vcpu *vcpu)
 		VCPU_EVENT(vcpu, 4, "%s", "retrying storage key operation");
 		return -EAGAIN;
 	}
-	if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
-		return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
 	return 0;
 }
 
@@ -244,6 +242,9 @@ static int handle_iske(struct kvm_vcpu *vcpu)
 	int reg1, reg2;
 	int rc;
 
+	if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
+		return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
+
 	rc = try_handle_skey(vcpu);
 	if (rc)
 		return rc != -EAGAIN ? rc : 0;
@@ -273,6 +274,9 @@ static int handle_rrbe(struct kvm_vcpu *vcpu)
 	int reg1, reg2;
 	int rc;
 
+	if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
+		return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
+
 	rc = try_handle_skey(vcpu);
 	if (rc)
 		return rc != -EAGAIN ? rc : 0;
@@ -308,6 +312,9 @@ static int handle_sske(struct kvm_vcpu *vcpu)
 	int reg1, reg2;
 	int rc;
 
+	if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
+		return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
+
 	rc = try_handle_skey(vcpu);
 	if (rc)
 		return rc != -EAGAIN ? rc : 0;