linux-kernel - Re: [PATCH] Fix an overflow in range_to

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Message-ID: <CAE9FiQV1ckyhy+cWVZC+=rU9s2nrBO6qV0Yt5xkYuv_gS9ZSWQ@mail.gmail.com>
Date:	Tue, 29 May 2012 10:18:43 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc:	mingo@...hat.com, x86@...nel.org, tglx@...utronix.de,
	hpa@...or.com, Feng Jin <joe.jin@...cle.com>,
	ethan.zhao@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix an overflow in range_to_mtrr func

On Mon, May 28, 2012 at 5:29 AM, Zhenzhong Duan
<zhenzhong.duan@...cle.com> wrote:
> When boot x86_64 kernel on sun G5+ with 4T mem, see an overflow in mtrr cleanup as below.
>
> *BAD*gran_size: 2G      chunk_size: 2G  num_reg: 10     lose cover RAM:
> -18014398505283592M
>
> This is because 1<<31 sign extended.
> Use explicit type conversion to force a 64bit constant to fix it.
> Useful for mem larger than or equal to 4T.
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
> ---
>  arch/x86/kernel/cpu/mtrr/cleanup.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mtrr/cleanup.c b/arch/x86/kernel/cpu/mtrr/cleanup.c
> index ac140c7..853a4c6 100644
> --- a/arch/x86/kernel/cpu/mtrr/cleanup.c
> +++ b/arch/x86/kernel/cpu/mtrr/cleanup.c
> @@ -266,7 +266,7 @@ range_to_mtrr(unsigned int reg, unsigned long range_startk,
>                if (align > max_align)
>                        align = max_align;
>
> -               sizek = 1 << align;
> +               sizek = (unsigned long)1 << align;

how about

            sizek = 1UL << align;


>                if (debug_print) {
>                        char start_factor = 'K', size_factor = 'K';
>                        unsigned long start_base, size_base;
> --
> 1.7.3
>
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