linux-kernel - Re: [PATCH v2] Security: smack: replace kzalloc with kmem_cache for inode

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <544D94C1.8010402@schaufler-ca.com>
Date:	Sun, 26 Oct 2014 17:41:37 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	PINTU KUMAR <pintu_agarwal@...oo.com>, Rohit <rohit.kr@...sung.com>
CC:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"james.l.morris@...cle.com" <james.l.morris@...cle.com>,
	"serge@...lyn.com" <serge@...lyn.com>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpgs@...sung.com" <cpgs@...sung.com>,
	"pintu.k@...sung.com" <pintu.k@...sung.com>,
	"vishnu.ps@...sung.com" <vishnu.ps@...sung.com>,
	"iqbal.ams@...sung.com" <iqbal.ams@...sung.com>,
	"ed.savinay@...sung.com" <ed.savinay@...sung.com>,
	"me.rohit@...e.com" <me.rohit@...e.com>
Subject: Re: [PATCH v2] Security: smack: replace kzalloc with kmem_cache for
 inode_smack

On 10/17/2014 10:37 AM, Casey Schaufler wrote:
> On 10/17/2014 9:34 AM, PINTU KUMAR wrote:
>> Hi,
>>
>>
>>> ________________________________
>>> From: Casey Schaufler <casey@...aufler-ca.com>
>>> To: Rohit <rohit.kr@...sung.com> 
>>> Cc: akpm@...ux-foundation.org; james.l.morris@...cle.com; serge@...lyn.com; linux-security-module@...r.kernel.org; linux-kernel@...r.kernel.org; cpgs@...sung.com; pintu.k@...sung.com; vishnu.ps@...sung.com; iqbal.ams@...sung.com; ed.savinay@...sung.com; me.rohit@...e.com; pintu_agarwal@...oo.com; Casey Schaufler <casey@...aufler-ca.com> 
>>> Sent: Friday, 17 October 2014 8:08 PM
>>> Subject: Re: [PATCH v2] Security: smack: replace kzalloc with kmem_cache for inode_smack
>>>
>>>
>>> On 10/17/2014 4:42 AM, Rohit wrote:
>>>> On Thu, 16 Oct 2014 09:24:01 -0700
>>>> Casey Schaufler <casey@...aufler-ca.com> wrote:
>>>>
>>>>> On 10/15/2014 5:10 AM, Rohit wrote:
>>>>>> The patch use kmem_cache to allocate/free inode_smack since they are
>>>>>> alloced in high volumes making it a perfect case for kmem_cache.
>>>>>>
>>>>>> As per analysis, 24 bytes of memory is wasted per allocation due
>>>>>> to internal fragmentation. With kmem_cache, this can be avoided.
>>>>> What impact does this have on performance? I am much more
>>>>> concerned with speed than with small amount of memory.
>>>>>
>>>> I think there should not be any performance problem as such.
>>>> However, please let me know how to check the performance in this case.
>>> Any inode intensive benchmark would suffice. Even the classic
>>> kernel build would do.
>>>
>>>> As far as i know, kzalloc first finds the kmalloc_index corresponding to
>>>> the size to get the kmem_cache_object and then calls kmem_cache_alloc
>>>> with the kmalloc_index(kmem_cache object). Here, we create kmem_cache
>>>> object specific for inode_smack and directly calls kmem_cache_alloc()
>>>> which should give better performance as compared to kzalloc.
>>> That would be my guess as well, but performance is tricky. Sometimes
>>> things that "obviously" make performance better make it worse. There can
>>> be unanticipated side effects.
>>>
>>>
>>>> Please let me know your comments.
>>> If you can run any sort of test that demonstrates this change
>>> does not have performance impact, I'm fine with it. Smack is being
>>> used in small devices, and both memory use and performance are critical
>>> to the success of these devices. Of the two, performance is currently
>>> more of an issue.
>>>
>> SMACK is used heavily in Tizen. We verified these changes for one of Tizen project.
>> During boot time we observed that this object is used heavily, as identified by kmalloc-accounting.
>> After replacing this we did not observe any difference in boot time. Also there was no side-effects seen so far.
>> If you know of any other tests, please let us know.
>> We will also try to gather some performance stats and present here.
> We need to be somewhat more precise than "did not observe any
> difference in boot time". The ideal benchmark would perform lots
> of changes to the filesystem without doing lots of IO. One process
> that matches that profile fairly well is a kernel make. I would be
> satisfied with something as crude as using time(1) on a small (5?)
> number of clean kernel makes each with and without the patch on the
> running kernel. At the level of accuracy you usually get from time(1)
> you won't find trivial differences, but if the change is a big problem
> (or a big win) we'll know.

I have not seen anything indicating that the requested performance
measurements have been done. I have no intention of accepting this
without assurance that performance has not been damaged. I request
that no one else carry this forward, either. The performance impact
of security facilities comes under too much scrutiny to ignore it.

> ... 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/