s390/sclp: rework sclp boundary checks

Rework the SCLP boundary check to account for different SCLP commands
(eventually) allowing different boundary sizes.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20200915194416.107460-3-walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

hw/s390x/sclp.c

@@ -49,6 +49,18 @@ static inline bool sclp_command_code_valid(uint32_t code)
     return false;
 }
 
+static bool sccb_verify_boundary(uint64_t sccb_addr, uint16_t sccb_len)
+{
+    uint64_t sccb_max_addr = sccb_addr + sccb_len - 1;
+    uint64_t sccb_boundary = (sccb_addr & PAGE_MASK) + PAGE_SIZE;
+
+    if (sccb_max_addr < sccb_boundary) {
+        return true;
+    }
+
+    return false;
+}
+
 static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int *count)
 {
     uint8_t features[SCCB_CPU_FEATURE_LEN] = { 0 };
@@ -229,6 +241,11 @@ int sclp_service_call_protected(CPUS390XState *env, uint64_t sccb,
         goto out_write;
     }
 
+    if (!sccb_verify_boundary(sccb, be16_to_cpu(work_sccb.h.length))) {
+        work_sccb.h.response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
+        goto out_write;
+    }
+
     sclp_c->execute(sclp, &work_sccb, code);
 out_write:
     s390_cpu_pv_mem_write(env_archcpu(env), 0, &work_sccb,
@@ -274,7 +291,7 @@ int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code)
         goto out_write;
     }
 
-    if ((sccb + be16_to_cpu(work_sccb.h.length)) > ((sccb & PAGE_MASK) + PAGE_SIZE)) {
+    if (!sccb_verify_boundary(sccb, be16_to_cpu(work_sccb.h.length))) {
         work_sccb.h.response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
         goto out_write;
     }