linux-hardening - Re: [PATCH] iio: stmpe-adc: Use correctly sized arguments for bit field

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Date:   Thu, 3 Feb 2022 20:29:38 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] iio: stmpe-adc: Use correctly sized arguments for bit
 field

On Wed, Dec 15, 2021 at 03:25:13PM -0800, Kees Cook wrote:
> The find.h APIs are designed to be used only on unsigned long arguments.
> This can technically result in a over-read, but it is harmless in this
> case. Regardless, fix it to avoid the warning seen under -Warray-bounds,
> which we'd like to enable globally:
> 
> In file included from ./include/linux/bitmap.h:9,
>                  from ./include/linux/cpumask.h:12,
>                  from ./arch/x86/include/asm/cpumask.h:5,
>                  from ./arch/x86/include/asm/msr.h:11,
>                  from ./arch/x86/include/asm/processor.h:22,
>                  from ./arch/x86/include/asm/cpufeature.h:5,
>                  from ./arch/x86/include/asm/thread_info.h:53,
>                  from ./include/linux/thread_info.h:60,
>                  from ./arch/x86/include/asm/preempt.h:7,
>                  from ./include/linux/preempt.h:78,
>                  from ./include/linux/spinlock.h:55,
>                  from ./include/linux/swait.h:7,
>                  from ./include/linux/completion.h:12,
>                  from drivers/iio/adc/stmpe-adc.c:10:
> drivers/iio/adc/stmpe-adc.c: In function 'stmpe_adc_probe':
> ./include/linux/find.h:98:23: warning: array subscript 'long unsigned int[0]' is partly outside array bounds of 'u32[1]' {aka 'unsigned int[1]'} [-Warray-bounds]
>    98 |                 val = *addr | ~GENMASK(size - 1, offset);
>       |                       ^~~~~
> drivers/iio/adc/stmpe-adc.c:258:13: note: while referencing 'norequest_mask'
>   258 |         u32 norequest_mask = 0;
>       |             ^~~~~~~~~~~~~~
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/iio/adc/stmpe-adc.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/stmpe-adc.c b/drivers/iio/adc/stmpe-adc.c
> index fba659bfdb40..d2d405388499 100644
> --- a/drivers/iio/adc/stmpe-adc.c
> +++ b/drivers/iio/adc/stmpe-adc.c
> @@ -256,6 +256,7 @@ static int stmpe_adc_probe(struct platform_device *pdev)
>  	struct stmpe_adc *info;
>  	struct device_node *np;
>  	u32 norequest_mask = 0;
> +	unsigned long bits;
>  	int irq_temp, irq_adc;
>  	int num_chan = 0;
>  	int i = 0;
> @@ -309,8 +310,8 @@ static int stmpe_adc_probe(struct platform_device *pdev)
>  
>  	of_property_read_u32(np, "st,norequest-mask", &norequest_mask);
>  
> -	for_each_clear_bit(i, (unsigned long *) &norequest_mask,
> -			   (STMPE_ADC_LAST_NR + 1)) {
> +	bits = norequest_mask;

This would not work on 64-bit BE architecture. It should use bitmap_from_arr32()

> +	for_each_clear_bit(i, &bits, (STMPE_ADC_LAST_NR + 1)) {
>  		stmpe_adc_voltage_chan(&info->stmpe_adc_iio_channels[num_chan], i);
>  		num_chan++;
>  	}
> -- 
> 2.30.2