From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756375Ab1KHUBZ (ORCPT ); Tue, 8 Nov 2011 15:01:25 -0500 Received: from mail3.caviumnetworks.com ([12.108.191.235]:15850 "EHLO mail3.caviumnetworks.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751070Ab1KHUBY (ORCPT ); Tue, 8 Nov 2011 15:01:24 -0500 Message-ID: <4EB98A8E.4060900@cavium.com> Date: Tue, 08 Nov 2011 12:01:18 -0800 From: David Daney User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Fedora/3.0.10-1.fc12 Thunderbird/3.0.10 MIME-Version: 1.0 To: "manesoni@cisco.com" CC: Ralf Baechle , "ananth@in.ibm.com" , "kamensky@cisco.com" , "linux-kernel@vger.kernel.org" , "linux-mips@linux-mips.org" Subject: Re: [PATCH 2/4] MIPS Kprobes: Deny probes on ll/sc instructions References: <20111108170336.GA16526@cisco.com> <20111108170535.GC16526@cisco.com> In-Reply-To: <20111108170535.GC16526@cisco.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 08 Nov 2011 20:01:23.0746 (UTC) FILETIME=[30EFC020:01CC9E51] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/08/2011 09:05 AM, Maneesh Soni wrote: > > From: Maneesh Soni > > Deny probes on ll/sc instructions for MIPS kprobes > > As ll/sc instruction are for atomic read-modify-write operations, allowing > probes on top of these insturctions is a bad idea. > s/insturctions/instructions/ Not only is it a bad idea, it will probably make them fail 100% of the time. It is also an equally bad idea to place a probe between any LL and SC instructions. How do you prevent that? If you cannot prevent probes between LL and SC, why bother with this at all? David Daney > Signed-off-by: Victor Kamensky > Signed-off-by: Maneesh Soni > --- > arch/mips/kernel/kprobes.c | 31 +++++++++++++++++++++++++++++++ > 1 files changed, 31 insertions(+), 0 deletions(-) > > diff --git a/arch/mips/kernel/kprobes.c b/arch/mips/kernel/kprobes.c > index 9fb1876..0ab1a5f 100644 > --- a/arch/mips/kernel/kprobes.c > +++ b/arch/mips/kernel/kprobes.c > @@ -113,6 +113,30 @@ insn_ok: > return 0; > } > > +/* > + * insn_has_ll_or_sc function checks whether instruction is ll or sc > + * one; putting breakpoint on top of atomic ll/sc pair is bad idea; > + * so we need to prevent it and refuse kprobes insertion for such > + * instructions; cannot do much about breakpoint in the middle of > + * ll/sc pair; it is upto user to avoid those places > + */ > +static int __kprobes insn_has_ll_or_sc(union mips_instruction insn) > +{ > + int ret = 0; > + > + switch (insn.i_format.opcode) { > + case ll_op: > + case lld_op: > + case sc_op: > + case scd_op: > + ret = 1; > + break; > + default: > + break; > + } > + return ret; > +} > + > int __kprobes arch_prepare_kprobe(struct kprobe *p) > { > union mips_instruction insn; > @@ -121,6 +145,13 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p) > > insn = p->addr[0]; > > + if (insn_has_ll_or_sc(insn)) { > + pr_notice("Kprobes for ll and sc instructions are not" > + "supported\n"); > + ret = -EINVAL; > + goto out; > + } > + > if (insn_has_delayslot(insn)) { > pr_notice("Kprobes for branch and jump instructions are not" > "supported\n");