Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752461AbaKXCnM (ORCPT ); Sun, 23 Nov 2014 21:43:12 -0500 Received: from mail4.hitachi.co.jp ([133.145.228.5]:39285 "EHLO mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751345AbaKXCnJ (ORCPT ); Sun, 23 Nov 2014 21:43:09 -0500 Message-ID: <54729B35.3040501@hitachi.com> Date: Mon, 24 Nov 2014 11:43:01 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Steven Rostedt Cc: Josh Poimboeuf , Ananth N Mavinakayanahalli , Jiri Kosina , Seth Jennings , Linux Kernel Mailing List , Petr Mladek , Vojtech Pavlik , Namhyung Kim , Miroslav Benes , Ingo Molnar Subject: Re: [PATCH ftrace/core v6 4/5] kprobes: Set IPMODIFY flag only if the probe can change regs->ip References: <20141121102502.11844.82696.stgit@localhost.localdomain> <20141121102530.11844.41626.stgit@localhost.localdomain> <20141121151548.7bd8bcd9@gandalf.local.home> In-Reply-To: <20141121151548.7bd8bcd9@gandalf.local.home> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2014/11/22 5:15), Steven Rostedt wrote: > On Fri, 21 Nov 2014 05:25:30 -0500 > Masami Hiramatsu wrote: > >> Set FTRACE_OPS_FL_IPMODIFY flag only for the probes which can change >> regs->ip, which has kprobe->break_handler. >> Currently we can not put jprobe and another ftrace handler which >> changes regs->ip on the same function because all kprobes have >> FTRACE_OPS_FL_IPMODIFY flag. This removes FTRACE_OPS_FL_IPMODIFY >> flag from kprobes and only when the user uses jprobe (or the >> kprobe.break_handler != NULL) we add additinal ftrace_ops with >> FTRACE_OPS_FL_IPMODIFY on target function. >> >> Note about the implementation: This uses a dummy ftrace_ops to >> reserve IPMODIFY flag on the given ftrace address, for the case >> that we have a enabled kprobe on a function entry and a jprobe >> is added on the same point. In that case, we already have a >> ftrace_ops without IPMODIFY flag on the entry, and we have to >> add another ftrace_ops with IPMODIFY on the same address. >> If we put a same handler on both ftrace_ops, the handler can >> be called twice on that entry until the first one is removed. >> This means that the kprobe and the jprobe are called twice too, >> and that will not what kprobes expected. >> Thus I added a dummy ftrace_ops just for reserving IPMODIFY flag. >> >> Signed-off-by: Masami Hiramatsu >> Cc: Ananth N Mavinakayanahalli >> Cc: Steven Rostedt >> Cc: Josh Poimboeuf >> Cc: Namhyung Kim >> --- >> Changes in v4: >> - Increment refcounter after succeeded to register ftrace_ops. >> >> Changes in v3: >> - Update __ftrace_add/remove_filter_ip() according to >> Namhyng's comments (thanks!) >> - Split out regs->ip recovering code from this patch. >> --- >> Documentation/kprobes.txt | 12 ++-- >> kernel/kprobes.c | 125 +++++++++++++++++++++++++++++++++++++++------ >> 2 files changed, 114 insertions(+), 23 deletions(-) >> >> diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt >> index 4227ec2..eb03efc 100644 >> --- a/Documentation/kprobes.txt >> +++ b/Documentation/kprobes.txt >> @@ -264,15 +264,13 @@ stop-machine method that ksplice uses for supporting a CONFIG_PREEMPT=y >> kernel. >> >> NOTE for geeks: >> -The jump optimization changes the kprobe's pre_handler behavior. >> -Without optimization, the pre_handler can change the kernel's execution >> +The jump optimization (and ftrace-based kprobes) changes the kprobe's >> +pre_handler behavior. >> +Without optimizations, the pre_handler can change the kernel's execution >> path by changing regs->ip and returning 1. However, when the probe >> is optimized, that modification is ignored. Thus, if you want to >> -tweak the kernel's execution path, you need to suppress optimization, >> -using one of the following techniques: >> -- Specify an empty function for the kprobe's post_handler or break_handler. >> - or >> -- Execute 'sysctl -w debug.kprobes_optimization=n' >> +tweak the kernel's execution path, you need to suppress optimization or >> +notify your handler will modify regs->ip by setting p->break_handler. >> >> 1.5 Blacklist >> >> diff --git a/kernel/kprobes.c b/kernel/kprobes.c >> index 831978c..4b4b7c5 100644 >> --- a/kernel/kprobes.c >> +++ b/kernel/kprobes.c >> @@ -915,10 +915,93 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe *p) >> #ifdef CONFIG_KPROBES_ON_FTRACE >> static struct ftrace_ops kprobe_ftrace_ops __read_mostly = { >> .func = kprobe_ftrace_handler, >> - .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_IPMODIFY, >> + .flags = FTRACE_OPS_FL_SAVE_REGS, >> }; >> static int kprobe_ftrace_enabled; >> >> +static void kprobe_ftrace_stub(unsigned long a0, unsigned long a1, >> + struct ftrace_ops *op, struct pt_regs *regs) >> +{ >> + /* Do nothing. This is just a dummy handler */ >> +} > > Feel free to just use ftrace_stub instead. That's what it's there for. Ah, I didn't know that. OK :) >> + >> +/* This is only for checking conflict with other ftrace users */ >> +static struct ftrace_ops kprobe_ipmod_ftrace_ops __read_mostly = { >> + .func = kprobe_ftrace_stub, >> + .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_IPMODIFY, >> +}; >> +static int kprobe_ipmod_ftrace_enabled; >> + >> +static int __ftrace_add_filter_ip(struct ftrace_ops *ops, unsigned long ip, >> + int *ref) >> +{ >> + int ret; >> + >> + /* Try to set given ip to filter */ >> + ret = ftrace_set_filter_ip(ops, ip, 0, 0); >> + if (ret < 0) >> + return ret; >> + >> + if (*ref == 0) { >> + ret = register_ftrace_function(ops); >> + if (ret < 0) { >> + /* Rollback the filter */ >> + ftrace_set_filter_ip(ops, ip, 1, 0); >> + goto out; > > Why the goto out, and not just return ret? > >> + } >> + } >> + (*ref)++; >> + >> +out: >> + return ret; > > Probably could just return 0 here. Agreed. > > Rest looks fine. Thank you! > > -- Steve > >> +} >> + >> +static int __ftrace_remove_filter_ip(struct ftrace_ops *ops, unsigned long ip, >> + int *ref) >> +{ >> + int ret; >> + >> + if (*ref == 1) { >> + ret = unregister_ftrace_function(ops); >> + if (ret < 0) >> + return ret; >> + /*Ignore failure, because it is already unregistered */ >> + ftrace_set_filter_ip(ops, ip, 1, 0); >> + } else { >> + /* Try to remove given ip to filter */ >> + ret = ftrace_set_filter_ip(ops, ip, 1, 0); >> + if (ret < 0) >> + return ret; >> + } >> + >> + (*ref)--; >> + >> + return 0; >> +} >> + > -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/