Message-ID: <4F2C1AC9.7090509@zytor.com>
Date: Fri, 03 Feb 2012 09:35:05 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org, Pavel Emelyanov <xemul@parallels.com>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Kees Cook <keescook@chromium.org>, Tejun Heo <tj@kernel.org>,
        Andrew Vagin <avagin@openvz.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andi Kleen <andi@firstfloor.org>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Glauber Costa <glommer@parallels.com>,
        Matt Helsley <matthltc@us.ibm.com>, Pekka Enberg <penberg@kernel.org>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Vasiliy Kulikov <segoon@openwall.com>, Valdis.Kletnieks@vt.edu
Subject: Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7
References: <20120130140905.441199885@openvz.org> <20120130141852.309402052@openvz.org> <20120203074656.GC30543@elte.hu> <20120203083530.GD1968@moon> <20120203090929.GA23996@elte.hu> <20120203012241.bcd3d0c8.akpm@linux-foundation.org> <20120203092823.GE1968@moon> <4F2C1A46.4010105@zytor.com>
In-Reply-To: <4F2C1A46.4010105@zytor.com>
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On 02/03/2012 09:32 AM, H. Peter Anvin wrote:
> On 02/03/2012 01:28 AM, Cyrill Gorcunov wrote:
>> static __init int kcmp_cookie_init(void)
>> {
>> int i, j;
>>
>> for (i = 0; i< KCMP_TYPES; i++) {
>> for (j = 0; j< 2; j++)
>> get_random_bytes(&cookies[i][j], sizeof(long));
>> cookies[i][1] |= (~(~0UL>> 1) | 1);
>> }
>>
>> return 0;
>> }
>>
>> I thought in first place that sizeof(cookies[i][j]) would allow me
>> to change type of cookies in one place (ie at declaration) but
>> if cookies type will be changed -- the code will need careful review
>> anway, so sizeof(long) will be enough I think.
>>
>> On the other hands, maybe more clean variant will be
>>
>> static __init int kcmp_cookie_init(void)
>> {
>> const int size = sizeof(cookies[0][0]);
>> int i, j;
>>
>> for (i = 0; i< KCMP_TYPES; i++) {
>> for (j = 0; j< 2; j++)
>> get_random_bytes(&cookies[i][j], size);
>> cookies[i][1] |= (~(~0UL>> 1) | 1);
>> }
>>
>
> How about:
>
> const int size = sizeof(cookies[0]);
>
> get_random_bytes(&cookies[i], size);
>
> ... and skip the completely unnecessary for loop?
>

Even better:

static __init int kcmp_cookie_init(void)
{
	int i;

	get_random_bytes(cookies, sizeof cookies);

	for (i = 0; i < KCMP_TYPES; i++)
		cookies[i][1] |= ~(~0UL >> 1) | 1;
}

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