linux-kernel - Re: [PATCH] futex: avoid undefined behaviour when shift exponent is negative

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Message-ID: <59A0E237.1070501@huawei.com>
Date:   Sat, 26 Aug 2017 10:51:35 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Ingo Molnar <mingo@...nel.org>, <akpm@...ux-foundation.org>,
        <mingo@...hat.com>, <minchan@...nel.org>, <mhocko@...e.com>,
        <hpa@...or.com>, <x86@...nel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        "Zhen Lei" <thunder.leizhen@...wei.com>
Subject: Re: [PATCH] futex: avoid undefined behaviour when shift exponent
 is negative

On 2017/8/26 5:13, Thomas Gleixner wrote:
> On Fri, 25 Aug 2017, zhong jiang wrote:
>> From: zhong jiang <zhongjiang@...wei.com>
>> Date: Fri, 25 Aug 2017 12:05:56 +0800
>> Subject: [PATCH v2] futex: avoid undefined behaviour when shift exponent is
>>  negative
> Please do not send patches without changing the subject line so it's clear
> that there is a new patch.
  ok
>> using a shift value < 0 or > 31 will get crap as a result. because
>> it's just undefined. The issue still disturb me, so I try to fix
>> it again by excluding the especially condition.
> Which is obsolete now as this code is unified accross all architectures and
> the shift issue is addressed in the generic version of it. So all
> architectures get the same fix. See:
>
>  http://git.kernel.org/tip/30d6e0a4190d37740e9447e4e4815f06992dd8c3
  ok , I  miss the above patch.
> And no, we won't add that x86 fix before that unification hits mainline
> because that undefined behaviour is harmless as it only affects the user
> space value of the futex. IOW, the caller gets what it asked for: crap.
  Thank you for clarification.

  Regards
 zhongjiang
> Thanks,
>
> 	tglx
>
>
> .
>