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

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

On Wed, 21 Feb 2024 23:11:12 +0800
Zhao Liu <zhao1.liu@linux.intel.com> wrote:

> 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.
> 
Agreed cleanup would be good, but this is fine if you don't want to
do that now.

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

> Regards,
> Zhao
> 
>