Re: [PATCH v4 3/4] fpga: dfl: add basic support DFHv1

[matthew . gerlach]

On Mon, 31 Oct 2022, Andy Shevchenko wrote:

> On Mon, Oct 31, 2022 at 09:16:19AM +0800, Xu Yilun wrote:
> > On 2022-10-31 at 00:06:28 +0200, Andy Shevchenko wrote:
> > > On Sat, Oct 29, 2022 at 09:08:44PM +0800, Xu Yilun wrote:
> > > > On 2022-10-20 at 14:26:09 -0700, matthew.gerlach@xxxxxxxxxxxxxxx wrote:
> > >
> > > > >  struct dfl_feature_info {
> > > > >  	u16 fid;
> > > > >  	u8 revision;
> > > > > +	u8 dfh_version;
> > > > >  	struct resource mmio_res;
> > > > >  	void __iomem *ioaddr;
> > > > >  	struct list_head node;
> > > > >  	unsigned int irq_base;
> > > > >  	unsigned int nr_irqs;
> > > > > +	unsigned int param_size;
> > > > > +	u64 params[];
> > > > >  };
> > >
> > > ...
> > >
> > > > > +	finfo = kzalloc(sizeof(*finfo) + dfh_psize, GFP_KERNEL);
> > >
> > >
> > > This probably may use something from overflow.h.
> > >
> > > > The u64 flexible array in the structure, but seems dfh_get_psize could
> > > > not garantee 64bit aligned size.
> > > >
> > > > What's the mandatory alignment of param data? If 64bit aligned, bit 33-34
> > > > of PARAM_HDR should be reserved. If 32bit aligned, finfo:params should be
> > > > u32[].
> > >
> > > Isn't it guaranteed by the C standard / architecture ABI?
> >
> > I'm referring to the malloc size of the structure. It reserved dfh_psize
> > bytes for this u64 array, but there is no garantee dfh_psize should be a
> > multiple of 8. So there may be memory leak when accessing the last
> > array element?
>
> Have you looked at macros in the overflow.h? Would the use of it solve your
> concern?

By clarifying the definition of the next field in the parameter header 
as the number of 8-byte words, dfh_get_psize is guaranteed to be a multiple of 8.
This is fixed in the next revision of patches.

Matthew Gerlach

> --
> With Best Regards,
> Andy Shevchenko