linux-kernel - Re: [PATCH] mm, hugetlb: correct bit shift in hstate

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Message-id: <544743D6.6040103@samsung.com>
Date:	Wed, 22 Oct 2014 09:42:46 +0400
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	Sasha Levin <sasha.levin@...cle.com>, akpm@...ux-foundation.org
Cc:	n-horiguchi@...jp.nec.com, aarcange@...hat.com, mgorman@...e.de,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm, hugetlb: correct bit shift in hstate_sizelog

On 10/21/2014 10:15 PM, Sasha Levin wrote:
> hstate_sizelog() would shift left an int rather than long, triggering
> undefined behaviour and passing an incorrect value when the requested
> page size was more than 4GB, thus breaking >4GB pages.

> 
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> ---
>  include/linux/hugetlb.h |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 65e12a2..57e0dfd 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -312,7 +312,8 @@ static inline struct hstate *hstate_sizelog(int page_size_log)
>  {
>  	if (!page_size_log)
>  		return &default_hstate;
> -	return size_to_hstate(1 << page_size_log);
> +
> +	return size_to_hstate(1UL << page_size_log);

That still could be undefined on 32-bits. Either use 1ULL or reduce SHM_HUGE_MASK on 32bits.


>  }
>  
>  static inline struct hstate *hstate_vma(struct vm_area_struct *vma)
> 

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