linux-kernel - Re: Make RCU dcache work with CONFIG

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Message-ID: <4DB1F404.1060504@schaufler-ca.com>
Date:	Fri, 22 Apr 2011 14:32:52 -0700
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, npiggin@...nel.dk,
	shaohua.li@...el.com, sds@...ho.nsa.gov, jmorris@...ei.org,
	linux-security-module@...r.kernel.org,
	Eric Paris <eparis@...isplace.org>,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: Make RCU dcache work with CONFIG_SECURITY=y

On 4/22/2011 2:16 PM, Andi Kleen wrote:
> On Fri, Apr 22, 2011 at 11:26:09AM -0700, Linus Torvalds wrote:
>> On Thu, Apr 21, 2011 at 5:23 PM, Andi Kleen <andi@...stfloor.org> wrote:
>>> I didn't find good test suites for the security modules, so
>>> there wasn't a lot of testing on this unfortunately
>>> (the selinux one for LTP doesn't seem to work). Some close
>>> review of these changes is needed.
>>>
>>> On the other hand the VFS changes itself are very straight forward
>>> and the 1/1 patch is very straight forward (and a win in itself)
>>>
>>> The bottom line is with this patchkit a CONFIG_SECURITY=y
>>> kernel has as good VFS performance as a kernel with CONFIG_SECURITY
>>> disabled.
>> Gaah. My immediate reaction to the patch-series was "This is great, I
>> was really hoping we could get all those annoying cases sorted out,
>> and I'll queue them for the next merge window".
>>
>> Having then actually read through the patches a bit more, I then got
>> convinced that at least the first patch should probably be applied
>> right away and be marked for stable, since it looks pretty damn
>> obvious to me, and it might already on its own fix the performance
>> regression for some configurations (although realistically I guess few
>> enough people really do the "selinux=0" thing, so the big advantage is
>> making easier to backport the other patches later if we don't do them
>> now).
> Yes I agree. The first patch is (nearly) a no-brainer and already
> has significant benefits. I would like to see it in .39.
>
>> Comments? I'd really like to see/hear feedback like "yeah, this looks
>> really obviously safe" vs "yeah, looks good, but I really don't feel
>> very comfortable with it" from the security people.
> Especially SMACK review is needed.

I am happy to get all the help I can on this. I am not now
nor have I ever been especially comfortable with sophisticated
locking models. Where possible I have written code with minimal
locking requirements, but sometimes you just can't avoid it. I
have been fortunate in that several people have offered advice
in the past.

> Or maybe selinux only for now,
> already got one ack for that.
>
> (BTW I have some doubts on the locking in smack in general, 
> but that's a separate issue -- see other thread)
>
> -Andi
>

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