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

[Zhao Liu <zhao1.liu@linux.intel.com>]

On Wed, Feb 21, 2024 at 12:31:06PM +0100, Markus Armbruster wrote:
> Date: Wed, 21 Feb 2024 12:31:06 +0100
> From: Markus Armbruster <armbru@redhat.com>
> Subject: Re: [PATCH 1/6] hw/cxl/cxl-host: Fix missing ERRP_GUARD() in
>  cxl_fixed_memory_window_config()
> 
> 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>
>

Thanks! I'll attach your description to the commit message.

Regards,
Zhao