From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753943AbaFMROI (ORCPT ); Fri, 13 Jun 2014 13:14:08 -0400 Received: from mail-lb0-f177.google.com ([209.85.217.177]:35679 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753423AbaFMROE convert rfc822-to-8bit (ORCPT ); Fri, 13 Jun 2014 13:14:04 -0400 MIME-Version: 1.0 In-Reply-To: References: <20140417081740.26341.10894.stgit@ltc230.yrl.intra.hitachi.co.jp> Date: Fri, 13 Jun 2014 19:14:02 +0200 Message-ID: Subject: Re: [tip:perf/kprobes] kprobes, x86: Call exception_enter after kprobes handled From: Frederic Weisbecker To: Ingo Molnar , "H. Peter Anvin" , LKML , Rusty Russell , seiji.aguchi@hds.com, Jiri Kosina , Kees Cook , Masami Hiramatsu , Andrew Morton , Steven Rostedt , Thomas Gleixner , Borislav Petkov Cc: linux-tip-commits@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Masami, 2014-04-24 12:59 GMT+02:00 tip-bot for Masami Hiramatsu : > Commit-ID: ecd50f714c421c759354632dd00f70c718c95b10 > Gitweb: http://git.kernel.org/tip/ecd50f714c421c759354632dd00f70c718c95b10 > Author: Masami Hiramatsu > AuthorDate: Thu, 17 Apr 2014 17:17:40 +0900 > Committer: Ingo Molnar > CommitDate: Thu, 24 Apr 2014 10:03:00 +0200 > > kprobes, x86: Call exception_enter after kprobes handled > > Move exception_enter() call after kprobes handler > is done. Since the exception_enter() involves > many other functions (like printk), it can cause > recursive int3/break loop when kprobes probe such > functions. > > Signed-off-by: Masami Hiramatsu > Reviewed-by: Steven Rostedt > Cc: Andrew Morton > Cc: Borislav Petkov > Cc: Jiri Kosina > Cc: Kees Cook > Cc: Rusty Russell > Cc: Seiji Aguchi > Link: http://lkml.kernel.org/r/20140417081740.26341.10894.stgit@ltc230.yrl.intra.hitachi.co.jp > Signed-off-by: Ingo Molnar This patch results in exception_enter/exception_exit imbalances: arch/x86/kernel/traps.c: In function ‘do_debug’: include/linux/context_tracking.h:46:6: warning: ‘prev_state’ may be used uninitialized in this function [-Wmaybe-uninitialized] if (prev_ctx == IN_USER) ^ arch/x86/kernel/traps.c:431:17: note: ‘prev_state’ was declared here enum ctx_state prev_state; An obvious solution would be to change all the goto exit before exception_enter() to return from do_debug(). But if there are any user of RCU before exception_enter() this won't work. Does kprobe_debug_handle() use RCU read side critical sections? I'm also worried about kmemcheck... > --- > arch/x86/kernel/traps.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c > index e5d4a70..ba9abe9 100644 > --- a/arch/x86/kernel/traps.c > +++ b/arch/x86/kernel/traps.c > @@ -327,7 +327,6 @@ dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_co > if (poke_int3_handler(regs)) > return; > > - prev_state = exception_enter(); > #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP > if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, > SIGTRAP) == NOTIFY_STOP) > @@ -338,6 +337,7 @@ dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_co > if (kprobe_int3_handler(regs)) > return; > #endif > + prev_state = exception_enter(); > > if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP, > SIGTRAP) == NOTIFY_STOP) > @@ -415,8 +415,6 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code) > unsigned long dr6; > int si_code; > > - prev_state = exception_enter(); > - > get_debugreg(dr6, 6); > > /* Filter out all the reserved bits which are preset to 1 */ > @@ -449,6 +447,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code) > if (kprobe_debug_handler(regs)) > goto exit; > #endif > + prev_state = exception_enter(); > > if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code, > SIGTRAP) == NOTIFY_STOP) > -- > To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html