linux-kernel - Re: [PATCHv2 4/4] gpio: Remove VLA from stmpe driver

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Message-ID: <e7ec40ec-99cd-8078-3238-db024589d08b@electromag.com.au>
Date:   Fri, 23 Mar 2018 09:28:07 +0800
From:   Phil Reid <preid@...ctromag.com.au>
To:     Laura Abbott <labbott@...hat.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        Patrice Chotard <patrice.chotard@...com>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCHv2 4/4] gpio: Remove VLA from stmpe driver

On 23/03/2018 05:43, Laura Abbott wrote:
> On 03/18/2018 06:29 PM, Phil Reid wrote:
>> On 16/03/2018 02:00, Laura Abbott wrote:
>>> The new challenge is to remove VLAs from the kernel
>>> (see https://lkml.org/lkml/2018/3/7/621)
>>>
>>> This patch replaces a VLA with an appropriate call to kmalloc_array.
>>>
>>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>>> ---
>>> v2: Switch to GFP_KERNEL. There was some discussion about if we should
>>> be doing the allocation at all but given a) the allocation is pretty
>>> small and b) we can possibly take a mutex in a called function I think
>>> this is fine.
>>
>> I still think it's a bad idea. It's simple to preallocate the buffer.
>> But it's up to the maintainer.
>>
> 
> I'd feel a lot more confident about doing the global buffer with
> guidance from the maintainer. But looking at the platform data, the
> maximum number of GPIOs is 24, or 3 banks. Maybe we should just always
> stack allocate the maximum since it's fairly small.

That's the other way to go.


>>> ---
>>>   drivers/gpio/gpio-stmpe.c | 7 ++++++-
>>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpio/gpio-stmpe.c b/drivers/gpio/gpio-stmpe.c
>>> index f8d7d1cd8488..c2bb20ace6f5 100644
>>> --- a/drivers/gpio/gpio-stmpe.c
>>> +++ b/drivers/gpio/gpio-stmpe.c
>>> @@ -369,10 +369,14 @@ static irqreturn_t stmpe_gpio_irq(int irq, void *dev)
>>>       struct stmpe *stmpe = stmpe_gpio->stmpe;
>>>       u8 statmsbreg;
>>>       int num_banks = DIV_ROUND_UP(stmpe->num_gpios, 8);
>>> -    u8 status[num_banks];
>>> +    u8 *status;
>>>       int ret;
>>>       int i;
>>> +    status = kmalloc_array(num_banks, sizeof(*status), GFP_KERNEL);
>>> +    if (!status)
>>> +        return IRQ_NONE;
>>> +
>>>       /*
>>>        * the stmpe_block_read() call below, imposes to set statmsbreg
>>>        * with the register located at the lowest address. As STMPE1600
>>> @@ -424,6 +428,7 @@ static irqreturn_t stmpe_gpio_irq(int irq, void *dev)
>>>           }
>>>       }
>>> +    kfree(status);
>>>       return IRQ_HANDLED;
>>>   }
>>>
>>
>>
> 
> 
> 


-- 
Regards
Phil Reid