Re: [PATCH][next] gpio: xilinx: Fix potential integer overflow on shift of a u32 int

From: Dan Carpenter <dan.carpenter@oracle.com>
To: Colin King <colin.king@canonical.com>
Cc: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>,
	Srinivas Neeli <srinivas.neeli@xilinx.com>,
	Michal Simek <michal.simek@xilinx.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	linux-gpio@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH][next] gpio: xilinx: Fix potential integer overflow on shift of a u32 int
Date: Fri, 14 May 2021 08:37:54 +0300	[thread overview]
Message-ID: <20210514053754.GZ1955@kadam> (raw)
In-Reply-To: <20210513085227.54392-1-colin.king@canonical.com>

On Thu, May 13, 2021 at 09:52:27AM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> The left shift of the u32 integer v is evaluated using 32 bit
> arithmetic and then assigned to a u64 integer. There are cases
> where v will currently overflow on the shift. Avoid this by
> casting it to unsigned long (same type as map[]) before shifting
> it.
> 
> Addresses-Coverity: ("Unintentional integer overflow")
> Fixes: 02b3f84d9080 ("gpio: xilinx: Switch to use bitmap APIs")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/gpio/gpio-xilinx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpio/gpio-xilinx.c b/drivers/gpio/gpio-xilinx.c
> index 109b32104867..164a3a5a9393 100644
> --- a/drivers/gpio/gpio-xilinx.c
> +++ b/drivers/gpio/gpio-xilinx.c
> @@ -99,7 +99,7 @@ static inline void xgpio_set_value32(unsigned long *map, int bit, u32 v)
>  	const unsigned long offset = (bit % BITS_PER_LONG) & BIT(5);
>  
>  	map[index] &= ~(0xFFFFFFFFul << offset);
> -	map[index] |= v << offset;
> +	map[index] |= (unsigned long)v << offset;

Doing a shift by BIT(5) is super weird.  It looks like a double shift
bug and should probably trigger a static checker warning.  It's like
when people do BIT(BIT(5)).

It would be more readable to write it as:

	int shift = (bit % BITS_PER_LONG) ? 32 : 0;

regards,
dan carpenter