Re: [PATCH] hw/nubus/nubus-virtio-mmio: Fix missing ERRP_GUARD() in nubus_virtio_mmio_realize()

[Zhao Liu]

Hi Markus,

On Tue, Jul 23, 2024 at 12:21:17PM +0200, Markus Armbruster wrote:
> Date: Tue, 23 Jul 2024 12:21:17 +0200
> From: Markus Armbruster <armbru@redhat.com>
> Subject: Re: [PATCH] hw/nubus/nubus-virtio-mmio: Fix missing ERRP_GUARD()
>  in nubus_virtio_mmio_realize()
> 
> Zhao Liu <zhao1.liu@intel.com> writes:
> 
> > As the comment in qapi/error, dereferencing @errp requires
> 
> Suggest "According to the comment in qapi/error.h".
 
Thanks! Good words.

> > 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.
> > ...
> > * 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.
> >
> > But in nubus_virtio_mmio_realize(), @errp is dereferenced without
> > ERRP_GUARD().
> 
> Suggest to scratch "But".

No problem, will do.

> > Although nubus_virtio_mmio_realize() - as a DeviceClass.realize()
> > method - doesn't get the NULL @errp parameter, it hasn't triggered the
> > bug that dereferencing the NULL @errp. It's still necessary to follow
> > the requirement of @errp, so add missing ERRP_GUARD() in
> > nubus_virtio_mmio_realize().
> 
> Suggest
> 
>   Although nubus_virtio_mmio_realize() - as a DeviceClass.realize()
>   method - is never passed a null @errp argument, it should follow the
>   rules on @errp usage.  Add the ERRP_GUARD() there.

Thanks for the text! It sounds much more authentic!

> > Cc: Laurent Vivier <laurent@vivier.eu>
> > Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
> > Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
> > ---
> >  hw/nubus/nubus-virtio-mmio.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/hw/nubus/nubus-virtio-mmio.c b/hw/nubus/nubus-virtio-mmio.c
> > index 58a63c84d0be..a5558d3ec28b 100644
> > --- a/hw/nubus/nubus-virtio-mmio.c
> > +++ b/hw/nubus/nubus-virtio-mmio.c
> > @@ -23,6 +23,7 @@ static void nubus_virtio_mmio_set_input_irq(void *opaque, 
> > int n, int level)
> >  
> >  static void nubus_virtio_mmio_realize(DeviceState *dev, Error **errp)
> >  {
> > +    ERRP_GUARD();
> >      NubusVirtioMMIODeviceClass *nvmdc = NUBUS_VIRTIO_MMIO_GET_CLASS(dev);
> >      NubusVirtioMMIO *s = NUBUS_VIRTIO_MMIO(dev);
> >      NubusDevice *nd = NUBUS_DEVICE(dev);
>        SysBusDevice *sbd;
>        int i, offset;
> 
>        nvmdc->parent_realize(dev, errp);
> 
> Here's the dereference:
> 
>        if (*errp) {
>            return;
>        }
> 
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
> 

Thanks! Will refresh a v2 soon.

Regards,
Zhao