KVM: s390: sthyi: fix specification exception detection

sthyi should only generate a specification exception if the function
code is zero and the response buffer is not on a 4k boundary.

The current code would also test for unknown function codes if the
response buffer, that is currently only defined for function code 0,
is not on a 4k boundary and incorrectly inject a specification
exception instead of returning with condition code 3 and return code 4
(unsupported function code).

Fix this by moving the boundary check.

Fixes: 95ca2cb ("KVM: s390: Add sthyi emulation")
Cc: <[email protected]> # 4.8+
Reviewed-by: Janosch Frank <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Signed-off-by: Christian Borntraeger <[email protected]>

Author: heicarst

arch/s390/kvm/sthyi.c

@@ -425,14 +425,17 @@ int handle_sthyi(struct kvm_vcpu *vcpu)
 	VCPU_EVENT(vcpu, 3, "STHYI: fc: %llu addr: 0x%016llx", code, addr);
 	trace_kvm_s390_handle_sthyi(vcpu, code, addr);
 
-	if (reg1 == reg2 || reg1 & 1 || reg2 & 1 || addr & ~PAGE_MASK)
+	if (reg1 == reg2 || reg1 & 1 || reg2 & 1)
 		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
 
 	if (code & 0xffff) {
 		cc = 3;
 		goto out;
 	}
 
+	if (addr & ~PAGE_MASK)
+		return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
+
 	/*
 	 * If the page has not yet been faulted in, we want to do that
 	 * now and not after all the expensive calculations.