Re: [PATCH 1/6] hw/cxl/cxl-host: Fix missing ERRP_GUARD() in cxl_fixed_memory_window_config()

[Markus Armbruster]

Zhao Liu <zhao1.liu@linux.intel.com> writes:

> From: Zhao Liu <zhao1.liu@intel.com>
>
> As the comment in qapi/error, dereferencing @errp requires
> ERRP_GUARD():
>
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> * - It must not be dereferenced, because it may be null.
> * - It should not be passed to error_prepend() or
> *   error_append_hint(), because that doesn't work with &error_fatal.
> * ERRP_GUARD() lifts these restrictions.
> *
> * To use ERRP_GUARD(), add it right at the beginning of the function.
> * @errp can then be used without worrying about the argument being
> * NULL or &error_fatal.
> *
> * Using it when it's not needed is safe, but please avoid cluttering
> * the source with useless code.
>
> Currently, since machine_set_cfmw() - the caller of
> cxl_fixed_memory_window_config() - doesn't get the NULL errp parameter
> as the "set" method of object property, cxl_fixed_memory_window_config()
> doesn't trigger the dereference issue.
>
> To follow the requirement of errp, add missing ERRP_GUARD() in
> cxl_fixed_memory_window_config().
>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Suggested by credit:
>  Markus: Referred his explanation about ERRP_GUARD().
> ---
>  hw/cxl/cxl-host.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/cxl/cxl-host.c b/hw/cxl/cxl-host.c
> index 2aa776c79c74..c5f5fcfd64d0 100644
> --- a/hw/cxl/cxl-host.c
> +++ b/hw/cxl/cxl-host.c
> @@ -26,6 +26,7 @@ static void cxl_fixed_memory_window_config(CXLState 
> *cxl_state,
>                                             CXLFixedMemoryWindowOptions 
> *object,
>                                             Error **errp)
>  {
> +    ERRP_GUARD();
>      g_autofree CXLFixedWindow *fw = g_malloc0(sizeof(*fw));
>      strList *target;
>      int i;

The dereferences are

       fw->enc_int_ways = cxl_interleave_ways_enc(fw->num_targets, errp);
       if (*errp) {
           return;
       }

and

           fw->enc_int_gran =
               cxl_interleave_granularity_enc(object->interleave_granularity,
                                              errp);
           if (*errp) {
               return;
           }

We check *errp, because neither function returns a suitable error code.

Reviewed-by: Markus Armbruster <armbru@redhat.com>