linux-kernel - Re: [PATCH] linux/bitmap.h: fix potential sign-extension overflow

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Date:   Tue, 15 Oct 2019 12:44:52 -0700
From:   Joe Perches <joe@...ches.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] linux/bitmap.h: fix potential sign-extension overflow

On Tue, 2019-10-15 at 13:46 -0500, Gustavo A. R. Silva wrote:
> In expression 0xff << offset, left shifting by more than 31 bits has
> undefined behavior. Notice that the shift amount, *offset*, can be as
> much as 63.
> 
> Fix this by adding suffix ULL to integer 0xFF.
[]
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
[]
> @@ -520,7 +520,7 @@ static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
>  	const size_t index = BIT_WORD(start);
>  	const unsigned long offset = start % BITS_PER_LONG;
>  
> -	map[index] &= ~(0xFF << offset);
> +	map[index] &= ~(0xFFULL << offset);

BITS_PER_LONG is 32 and 0xFFULL is 64 bit
when compiled for 32 bit arches.

This should just be 0xFFUL and not ULL.