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

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Date:   Mon, 31 Oct 2022 13:15:06 -0700 (PDT)
From:   matthew.gerlach@...ux.intel.com
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
cc:     Xu Yilun <yilun.xu@...el.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 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@...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?

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
>
>
>