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

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Date:   Tue, 1 Nov 2022 09:55:13 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     matthew.gerlach@...ux.intel.com, hao.wu@...el.com,
        russell.h.weight@...el.com, basheer.ahmed.muddebihal@...el.com,
        trix@...hat.com, mdf@...nel.org, linux-fpga@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        tianfei.zhang@...el.com, corbet@....net, jirislaby@...nel.org,
        geert+renesas@...der.be, niklas.soderlund+renesas@...natech.se,
        macro@...am.me.uk, johan@...nel.org, lukas@...ner.de,
        ilpo.jarvinen@...ux.intel.com, marpagan@...hat.com
Subject: Re: [PATCH v4 3/4] fpga: dfl: add basic support DFHv1

On 2022-10-31 at 17:34:20 +0200, 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@...ux.intel.com 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?

Yes, struct_size() or array_size() specifies the element size & count,
which solve the concern at the root.

> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>