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

[Jonathan Cameron via <qemu-devel@nongnu.org>]

On Wed, 21 Feb 2024 23:04:23 +0800
Zhao Liu <zhao1.liu@linux.intel.com> wrote:

> 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.
Thanks for the explanation in the commit message and to Markus for
the cases it affected.

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> 
> Regards,
> Zhao
>