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Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filt

To: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 13 May 2011 17:02:15 +0200
Cc: James Morris <jmorris@namei.org>, Will Drewry <wad@chromium.org>, linux-kernel@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>, Frederic Weisbecker <fweisbec@gmail.com>, Eric Paris <eparis@redhat.com>, kees.cook@canonical.com, agl@chromium.org, "Serge E. Hallyn" <serge@hallyn.com>, Ingo Molnar <mingo@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>, Michal Marek <mmarek@suse.cz>, Oleg Nesterov <oleg@redhat.com>, Roland McGrath <roland@redhat.com>, Jiri Slaby <jslaby@suse.cz>, David Howells <dhowells@redhat.com>, Russell King <linux@arm.linux.org.uk>, Michal Simek <monstr@monstr.eu>, Ralf Baechle <ralf@linux-mips.org>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux390@de.ibm.com, Paul Mundt <lethal@linux-sh.org>, "David S. Miller" <davem@davemloft.net>, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, linux-arm-kernel@lists.infradead.org, microblaze-uclinux@itee.uq.edu.au, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, Linus Torvalds <torvalds@linux-foundation.org>
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* Peter Zijlstra <peterz@infradead.org> wrote:

> On Fri, 2011-05-13 at 14:49 +0200, Ingo Molnar wrote:
> > 
> > So given that by your own admission it makes sense to share the facilities 
> > at 
> > the low level, i also argue that it makes sense to share as high up as 
> > possible. 
> 
> I'm not saying any such thing, I'm saying that it might make sense to
> observe active objects and auto-create these observation points. That
> doesn't make them similar or make them share anything.

Well, they would share the lowest level call site:

        result = check_event_vfs_getname(result);

You call it 'auto-generated call site', i call it a shared (single line) call 
site. The same thing as far as the lowest level goes.

Now (the way i understood it) you'd want to stop the sharing right after that. 
I argue that it should go all the way up.

Note: i fully agree that there should be events where filters can have no 
effect whatsoever. For example if this was written as:

        check_event_vfs_getname(result);

Then it would have no effect. This is decided by the subsystem developers, 
obviously. So whether an event is 'active' or 'passive' can be enforced at the 
subsystem level as well.

As far as the event facilities go, 'no effect observation' is a special-case of 
'active observation' - just like read-only files are a special case of 
read-write files.

Thanks,

        Ingo

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