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From: Frederic Weisbecker <firstname.lastname@example.org>
To: Eric Paris <email@example.com>
Cc: Ingo Molnar <firstname.lastname@example.org>,
Masami Hiramatsu <email@example.com>,
Eric Paris <firstname.lastname@example.org>,
email@example.com, firstname.lastname@example.org, email@example.com,
Jason Baron <firstname.lastname@example.org>,
Mathieu Desnoyers <email@example.com>,
Steven Rostedt <firstname.lastname@example.org>,
Arnaldo Carvalho de Melo <email@example.com>,
Peter Zijlstra <firstname.lastname@example.org>,
Thomas Gleixner <email@example.com>
Subject: Re: Using ftrace/perf as a basis for generic seccomp
Date: Thu, 3 Feb 2011 20:18:47 +0100 [thread overview]
Message-ID: <20110203191846.GD1769@nowhere> (raw)
On Thu, Feb 03, 2011 at 08:06:45PM +0100, Frederic Weisbecker wrote:
> On Wed, Feb 02, 2011 at 11:45:22AM -0500, Eric Paris wrote:
> > On Wed, 2011-02-02 at 13:26 +0100, Ingo Molnar wrote:
> > > * Masami Hiramatsu <firstname.lastname@example.org> wrote:
> > >
> > > > Hi Eric,
> > > >
> > > > (2011/02/01 23:58), Eric Paris wrote:
> > > > > On Wed, Jan 12, 2011 at 4:28 PM, Eric Paris <email@example.com> wrote:
> > > > >> Some time ago Adam posted a patch to allow for a generic seccomp
> > > > >> implementation (unlike the current seccomp where your choice is all
> > > > >> syscalls or only read, write, sigreturn, and exit) which got little
> > > > >> traction and it was suggested he instead do the same thing somehow using
> > > > >> the tracing code:
> > > > >> http://thread.gmane.org/gmane.linux.kernel/833556
> > > >
> > > > Hm, interesting idea :)
> > > > But why would you like to use tracing code? just for hooking?
> > >
> > > What I suggested before was to reuse the scripting engine and the tracepoints.
> > >
> > > I.e. the "seccomp restrictions" can be implemented via a filter expression - and the
> > > scripting engine could be generalized so that such 'sandboxing' code can make use of
> > > it.
> > >
> > > For example, if you want to restrict a process to only allow open() syscalls to fd 4
> > > (a very restrictive sandbox), it could be done via this filter expression:
> > >
> > > 'fd == 4'
> > >
> > > etc. Note that obviously the scripting engine needs to be abstracted out somewhat -
> > > but this is the basic idea, to reuse the callbacks and reuse the scripting engine
> > > for runtime filtering of syscall parameters.
> > Any pointers on what is involved in this abstraction? I can work out
> > the details, but I don't know the big picture well enough to even start
> > to move forwards.....
> In the big picture, the filtering code is very tight to the tracing code.
> Creation, initialization, removal of filters is all made on top of the
> trace events structures (struct ftrace_event_call) because we apply and
> interpret filters on the fields of trace events, which are what we save
> in a trace.
> If you look at the sched switch trace events, we have several fields
> like prev_comm and next_comm. These are defined in the TRACE_EVENT()
> macros calls. So when we apply a filter like "prev_comm == firefox-bin",
> we enter the filtering code with the trace_event structure for sched
> switch events and iterate through its fields to find one called
> prev_comm and then we work on top of that.
> I think you won't work with trace events, so you need to make the
> filtering code more tracing-agnostic.
> But I think it's quite workable and shouldn't be too hard to split that
> into a filtering backend. Many parts are already pretty standalone.
> Also I suspect the tracepoints are not what you need. Or may be
> they are. But as Masami said, the syscall tracepoint is called late.
> It's workable though. The other problem is that preemption is disabled
> when tracepoints are called, which is probably not what you want.
> One day I think we'll need to unify the tracepoints and notifier
> code but until then, better keep tracepoints for tracing.
> Now once you have the filtering code more generic, you still
> need an arch backend to map register contents and layout into syscall
> arguments name and type. On top of which you can finally use the filtering
> code. For that you can use, again, some code we use for tracing, which
> are syscalls metadata: informations generated on build time
> that have syscalls fields and type.
> And that also needs to be split up, but it's more trivial
> than the filtering part.
> Note for now, filtering + syscalls metadata only works on top
> of raw arguments value. Syscalls metadata don't know much
> about type semantics and won't help you to dereference
> syscall argument pointers. Only raw syscall parameter values.
> Similarly, the filtering code can't evaluate pointer dereferencing
> expression evaluation, only direct values comprehension.
Actually we have string comparison supported by the filtering code.
Still we need safe accessors (copy_from_user()) from filtering code
to use that safely on syscall parameters.
next prev parent reply other threads:[~2011-02-03 19:18 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-12 21:28 Eric Paris
2011-02-01 14:58 ` Eric Paris
2011-02-02 12:14 ` Masami Hiramatsu
2011-02-02 12:26 ` Ingo Molnar
2011-02-02 16:45 ` Eric Paris
2011-02-02 17:55 ` Ingo Molnar
2011-02-02 18:17 ` Steven Rostedt
2011-02-03 19:06 ` Frederic Weisbecker
2011-02-03 19:18 ` Frederic Weisbecker [this message]
2011-02-03 22:06 ` Stefan Fritsch
2011-02-03 23:10 ` Frederic Weisbecker
2011-02-04 1:50 ` Eric Paris
2011-02-04 14:31 ` Peter Zijlstra
2011-02-04 16:29 ` Eric Paris
2011-02-04 17:04 ` Frederic Weisbecker
2011-02-05 11:51 ` Stefan Fritsch
2011-02-07 12:26 ` Peter Zijlstra
2011-02-04 16:36 ` Eric Paris
2011-02-05 11:42 ` Stefan Fritsch
2011-02-06 16:51 ` Eric Paris
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