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

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Date:	Fri, 22 Apr 2011 17:17:29 -0400
From:	Eric Paris <eparis@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.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>
Subject: Re: Make RCU dcache work with CONFIG_SECURITY=y

On Fri, 2011-04-22 at 11:26 -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).
> 
> And now I'm vacillating about the two later patches too. They look
> fine to me, but I really have _zero_ familiarity with selinux and
> smack internals, so unlike the first patch, I can't go "that looks
> like the obviously right thing, and it clearly catches all the RCU
> cases".
> 
> The "we can't use all the nifty RCU pathwalk in the config that most
> distros ship by default" is clearly a performance regression, and has
> meant that it's not been really showing its real advantages for most
> people. So in that sense, it's a regression fix and thus valid even
> though we're pretty late in the -rc series.
> 
> But at the same time, it's also a bit scary.
> 
> 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.

>>From an SELinux PoV (And I feel semi confident about SMACK) patch 1/3
can and should go in as soon as you want.  2/3 looked safe on first
glance, but I think I can make it smaller and better.  I'll try to get a
version of 2/3 on list in the next couple of days.  My first thought was
that it should probably go in via my SELinux tree next window......

-Eric

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