Re: [PATCH 5/6] hw/pci-bridge/cxl_upstream: Fix missing ERRP_GUARD() in cxl_usp_realize()

[Markus Armbruster]

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 cxl_usp_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
> cxl_usp_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/pci-bridge/cxl_upstream.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/pci-bridge/cxl_upstream.c b/hw/pci-bridge/cxl_upstream.c
> index e87eb4017713..03d123cca0ef 100644
> --- a/hw/pci-bridge/cxl_upstream.c
> +++ b/hw/pci-bridge/cxl_upstream.c
> @@ -289,6 +289,7 @@ static void free_default_cdat_table(CDATSubHeader 
> **cdat_table, int num,
>  
>  static void cxl_usp_realize(PCIDevice *d, Error **errp)
>  {
> +    ERRP_GUARD();
>      PCIEPort *p = PCIE_PORT(d);
>      CXLUpstreamPort *usp = CXL_USP(d);
>      CXLComponentState *cxl_cstate = &usp->cxl_cstate;

The dereference is

       cxl_doe_cdat_init(cxl_cstate, errp);
       if (*errp) {
           goto err_cap;
       }

As noted in review of PATCH 3, 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>