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Date: Tue, 13 Mar 2018 18:16:51 -0700
From: Laura Abbott <labbott@...hat.com>
To: Phil Reid <preid@...ctromag.com.au>,
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: [PATCH 4/4] gpio: Remove VLA from stmpe driver
On 03/13/2018 05:18 PM, Laura Abbott wrote:
> On 03/13/2018 02:13 AM, Phil Reid wrote:
>> On 10/03/2018 08:10, 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>
>>> ---
>>> 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..b7854850bcdb 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_ATOMIC);
>>> + 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;
>>> }
>>>
>>
>> Doing this in an irq handler seems wrong.
>> Perhaps better if a buffer is pre-allocated in stmpe_gpio
>>
>>
>
> Sure, I can pre-allocate the buffer in the probe.
>
> Thanks,
> Laura
Actually I wonder if there would be concurrency problems if we
tried to pre-allocate a global buffer. But the IRQ handler
calls stmpe_block_read which takes a mutex to sleep so I think
doing the (small) kmalloc should be fine and I can change it to
a GFP_KERNEL.
Thanks,
Laura
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