Re: [PATCH 3/6] hw/mem/cxl_type3: Fix missing ERRP_GUARD() in ct3_realize()

[Zhao Liu]

On Wed, Feb 21, 2024 at 12:35:47PM +0100, Markus Armbruster wrote:
> Date: Wed, 21 Feb 2024 12:35:47 +0100
> From: Markus Armbruster <armbru@redhat.com>
> Subject: Re: [PATCH 3/6] hw/mem/cxl_type3: Fix missing ERRP_GUARD() in
>  ct3_realize()
> 
> 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 ct3_realize() - as a PCIDeviceClass.realize() method -
> > doesn't get the NULL errp parameter, it doesn't trigger the dereference
> > issue.
> >
> > To follow the requirement of errp, add missing ERRP_GUARD() in
> > ct3_realize().
> >
> > 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/mem/cxl_type3.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/hw/mem/cxl_type3.c b/hw/mem/cxl_type3.c
> > index e8801805b90f..a3b0761f843b 100644
> > --- a/hw/mem/cxl_type3.c
> > +++ b/hw/mem/cxl_type3.c
> > @@ -645,6 +645,7 @@ static DOEProtocol doe_cdat_prot[] = {
> >  
> >  static void ct3_realize(PCIDevice *pci_dev, Error **errp)
> >  {
> > +    ERRP_GUARD();
> >      CXLType3Dev *ct3d = CXL_TYPE3(pci_dev);
> >      CXLComponentState *cxl_cstate = &ct3d->cxl_cstate;
> >      ComponentRegisters *regs = &cxl_cstate->crb;
> 
> The dereference is
> 
>        cxl_doe_cdat_init(cxl_cstate, errp);
>        if (*errp) {
>            goto err_free_special_ops;
>        }
> 
> We check *errp, because cxl_doe_cdat_init() returns void.  Could be
> improved to return bool, along with its callees ct3_load_cdat() and
> ct3_build_cdat(), but that's a slightly more ambitious cleanup, so
> 
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
>

Thanks! I can continue to consider such the cleanup in the follow up.

Will also add the dereference description in commit message to make
review easier.

Regards,
Zhao