cpu: crash fix (don't allow negative core id)

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Merge remote-tracking branch 'remotes/ehabkost/tags/machine-pull-request' into staging

cpu: crash fix (don't allow negative core id)

# gpg: Signature made Thu 03 Aug 2017 18:57:41 BST
# gpg:                using RSA key 0x2807936F984DC5A6
# gpg: Good signature from "Eduardo Habkost <ehabkost@redhat.com>"
# Primary key fingerprint: 5A32 2FD5 ABC4 D3DB ACCF  D1AA 2807 936F 984D C5A6

* remotes/ehabkost/tags/machine-pull-request:
  cpu: don't allow negative core id

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/cpu/core.c

@@ -33,6 +33,11 @@ static void core_prop_set_core_id(Object *obj, Visitor *v, const char *name,
         return;
     }
 
+    if (value < 0) {
+        error_setg(errp, "Invalid core id %"PRId64, value);
+        return;
+    }
+
     core->core_id = value;
 }