From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262155AbVC2Cei (ORCPT ); Mon, 28 Mar 2005 21:34:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262156AbVC2Cei (ORCPT ); Mon, 28 Mar 2005 21:34:38 -0500 Received: from e35.co.us.ibm.com ([32.97.110.133]:10408 "EHLO e35.co.us.ibm.com") by vger.kernel.org with ESMTP id S262155AbVC2Cea (ORCPT ); Mon, 28 Mar 2005 21:34:30 -0500 Date: Mon, 28 Mar 2005 21:34:08 -0500 From: Ananth N Mavinakayanahalli To: William Cohen Cc: SystemTAP , akpm@osdl.org, prasanna@in.ibm.com, linux-kernel@vger.kernel.org, davem@davemloft.net Subject: Re: kprobe_handler should check pre_handler function Message-ID: <20050329023408.GA4847@in.ibm.com> Reply-To: ananth@in.ibm.com References: <424872C8.6080207@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <424872C8.6080207@redhat.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 28, 2005 at 04:10:32PM -0500, William Cohen wrote: Hi Will, > I found kprobes expects there to be a pre_handler function in the > structure. I was writing a probe that only needed a post_handler > function, no pre_handler function. The probe was tracking the > destinations of indirect calls and jumps, the probe needs to fire after > the instruction single steps to get the target address. The probe > crashed the machine because arch/i386/kernel/kprobe.c:kprobe_handler() > blindly calls p->pre_handler(). There should be a check to verify that > the pointer is non-null. There are cases where the pre_handler is not > needed and it would make sense to set it to NULL. Thus, a check should > be done for pre_handler like post_handler and fault_handler. You are right. The check for pre_handler is needed and here is a patch against 2.6.12-rc1-mm3 that does this. Thanks, Ananth Signed-off-by: Ananth N Mavinakayanahalli diff -Narup temp/linux-2.6.12-rc1/arch/i386/kernel/kprobes.c linux-2.6.12-rc1/arch/i386/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/i386/kernel/kprobes.c 2005-03-17 20:34:10.000000000 -0500 +++ linux-2.6.12-rc1/arch/i386/kernel/kprobes.c 2005-03-28 17:51:21.000000000 -0500 @@ -159,17 +159,16 @@ static int kprobe_handler(struct pt_regs if (is_IF_modifier(p->opcode)) kprobe_saved_eflags &= ~IF_MASK; - if (p->pre_handler(p, regs)) { + if (p->pre_handler && p->pre_handler(p, regs)) /* handler has already set things up, so skip ss setup */ return 1; - } - ss_probe: +ss_probe: prepare_singlestep(p, regs); kprobe_status = KPROBE_HIT_SS; return 1; - no_kprobe: +no_kprobe: preempt_enable_no_resched(); return ret; } diff -Narup temp/linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c 2005-03-28 17:48:56.000000000 -0500 +++ linux-2.6.12-rc1/arch/ppc64/kernel/kprobes.c 2005-03-28 17:51:31.000000000 -0500 @@ -128,10 +128,9 @@ static inline int kprobe_handler(struct kprobe_status = KPROBE_HIT_ACTIVE; current_kprobe = p; kprobe_saved_msr = regs->msr; - if (p->pre_handler(p, regs)) { + if (p->pre_handler && p->pre_handler(p, regs)) /* handler has already set things up, so skip ss setup */ return 1; - } ss_probe: prepare_singlestep(p, regs); diff -Narup temp/linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c 2005-03-17 20:34:33.000000000 -0500 +++ linux-2.6.12-rc1/arch/sparc64/kernel/kprobes.c 2005-03-28 17:50:55.000000000 -0500 @@ -128,7 +128,7 @@ static int kprobe_handler(struct pt_regs kprobe_status = KPROBE_HIT_ACTIVE; current_kprobe = p; - if (p->pre_handler(p, regs)) + if (p->pre_handler && p->pre_handler(p, regs)) return 1; ss_probe: diff -Narup temp/linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c --- temp/linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c 2005-03-28 17:48:57.000000000 -0500 +++ linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c 2005-03-28 17:51:10.000000000 -0500 @@ -293,17 +293,16 @@ int kprobe_handler(struct pt_regs *regs) if (is_IF_modifier(p->ainsn.insn)) kprobe_saved_rflags &= ~IF_MASK; - if (p->pre_handler(p, regs)) { + if (p->pre_handler && p->pre_handler(p, regs)) /* handler has already set things up, so skip ss setup */ return 1; - } - ss_probe: +ss_probe: prepare_singlestep(p, regs); kprobe_status = KPROBE_HIT_SS; return 1; - no_kprobe: +no_kprobe: preempt_enable_no_resched(); return ret; }