Re: [PATCH v7 3/4] fpga: dfl: add basic support for DFHv1

[matthew . gerlach]

On Tue, 20 Dec 2022, Andy Shevchenko wrote:

> On Tue, Dec 20, 2022 at 08:36:51AM -0800, matthew.gerlach@xxxxxxxxxxxxxxx wrote:
> > From: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> >
> > Version 1 of the Device Feature Header (DFH) definition adds
> > functionality to the DFL bus.
> >
> > A DFHv1 header may have one or more parameter blocks that
> > further describes the HW to SW.  Add support to the DFL bus
> > to parse the MSI-X parameter.
> >
> > The location of a feature's register set is explicitly
> > described in DFHv1 and can be relative to the base of the DFHv1
> > or an absolute address.  Parse the location and pass the information
> > to DFL driver.
>
> ...
>
> > +/**
> > + * dfh_find_param() - find data for the given parameter id
> > + * @dfl_dev: dfl device
> > + * @param: id of dfl parameter
> > + *
> > + * Return: pointer to parameter header on success, NULL otherwise.
>
> header is a bit confusing here, does it mean we give and ID and we got
> something more than just a data as summary above suggests?

Yes, the summary is not correct.  It should say "find the parameter block 
for the given parameter id".

> In such case summary and this text should clarify what exactly we get
> and layout of the data. Since this is a pointer, who is responsible of
> checking out-of-boundary accesses? For instance, if the parameters are
> variadic by length the length should be returned as well. Otherwise it
> should be specified as a constant somewhere, right?

The parameter header has the next/size field; so the caller of 
dfh_find_param should perform boundary checking as part of interpreting 
the parameter data.  I think a function to perform this checking 
and data interpretation would help here.

> > + */
> > +u64 *dfh_find_param(struct dfl_device *dfl_dev, int param_id)
> > +{
> > +	return find_param(dfl_dev->params, dfl_dev->param_size, param_id);
> > +}
> > +EXPORT_SYMBOL_GPL(dfh_find_param);
>
> ...
>
> > +	finfo = kzalloc(sizeof(*finfo) + dfh_psize, GFP_KERNEL);
>
> It sounds like a candidate for struct_size() from overflow.h.
> I.o.w. check that header and come up with the best what can
> suit your case.

	finfo = kzalloc(struct_size(finfo, params, dfh_psize/sizeof(u64)), 
GFP_KERNEL);

Does seem better.

Thanks for the suggestion,
Matthew Gerlach


> >  	if (!finfo)
> >  		return -ENOMEM;
>
> --
> With Best Regards,
> Andy Shevchenko