linux-kernel - Re: [patch 1/8] Kprobes - do not use kprobes mutex in arch code

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20070716151220.GA23133@Krystal>
Date:	Mon, 16 Jul 2007 11:12:21 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc:	Christoph Hellwig <hch@...radead.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, prasanna@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net
Subject: Re: [patch 1/8] Kprobes - do not use kprobes mutex in arch code

* Ananth N Mavinakayanahalli (ananth@...ibm.com) wrote:
> On Sat, Jul 14, 2007 at 03:20:02PM -0400, Mathieu Desnoyers wrote:
> > * Christoph Hellwig (hch@...radead.org) wrote:
> > > On Fri, Jul 13, 2007 at 09:21:34PM -0400, Mathieu Desnoyers wrote:
> > > > Remove the kprobes mutex from kprobes.h, since it does not belong there. Also
> > > > remove all use of this mutex in the architecture specific code, replacing it by
> > > > a proper mutex lock/unlock in the architecture agnostic code.
> > > 
> > > This is not very nice for avr32/sparc64 which have a noop arch_remove_kprobe
> > > and now need to take a mutex to do nothing.  Maybe you can find a nice
> > > way to avoid that?
> > > 
> > > Except for this issue making kprobes_mutex static to kprobes.c sounds like
> > > a good improvement.
> > > 
> > 
> > Since only unregister_kprobe() calls arch_remove_kprobe(), and only
> > after having removed the struct kprobe from the kprobes list (while the
> > kprobes mutex is held), I wonder if there is any need to hold the
> > kprobes mutex at all when calling arch_remove_kprobe(). It turns out
> > that only get_insn_slot()/free_insn_slot() (which is in
> > kernel/kprobes.c, but called from arch specific code) seems to really
> > use protection of this mutex.
> 
> Right.
> 
> > Would it make sense to protect the kprobe_insn_pages list with a
> > new kprobe_insn_mutex, nestable in the kprobe_mutex ?
> 
> Do you think it is required after your change to make kprobe_mutex
> static? But yes, for architectures that don't need a arch_remove_kprobe,
> the situation is a bit odd... a mutex to do nothing. IIRC, that was the
> primary reason why we made the mutex visible outside of kernel/kprobes.c
> 

After making the kprobe_mutex static, the only alternative we have is to
protect the arch_remove_kprobe (empty on some architectures) call with
kprobe_mutex, which, as Christoph pointed out, is not so great. Besides,
I think the kprobe_insn_mutex would make more sense than taking a mutex
in the arch-specific arch_remove_kprobe() for a resource that is not
clearly identified.

Mathieu

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/