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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: Sat, 14 May 2011 09:05:42 +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>, 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 <linux-arm-kernel@lists.infradead.org>, 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 16:57 +0200, Ingo Molnar wrote:
> > this is a security mechanism
> 
> Who says? [...]

Kernel developers/maintainers of the affected code.

We have security hooks all around the kernel, which can deny/accept execution 
at various key points, but we do not have 'execute arbitrary user-space defined 
(safe) scripts' callbacks in general.

But yes, if a particular callback point is defined widely enough to allow much 
bigger intervention into the flow of execution, then more is possible as well.

> [...] and why would you want to unify two separate concepts only to them 
> limit it to security that just doesn't make sense.

I don't limit them to security - the callbacks themselves are either for 
passive observation or, at most, for security accept/deny callbacks.

It's decided by the subsystem maintainers what kind of user-space control power 
(or observation power) they want to allow, not me.

I would just like to not stop the facility itself at the 'observe only' level, 
like you suggest.

Thanks,

        Ingo

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