From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f200.google.com (mail-io0-f200.google.com [209.85.223.200]) by kanga.kvack.org (Postfix) with ESMTP id 9B1FA6B007E for ; Mon, 2 May 2016 12:18:25 -0400 (EDT) Received: by mail-io0-f200.google.com with SMTP id k129so386117525iof.0 for ; Mon, 02 May 2016 09:18:25 -0700 (PDT) Received: from out4441.biz.mail.alibaba.com (out4441.biz.mail.alibaba.com. [47.88.44.41]) by mx.google.com with ESMTP id a3si9984069igy.69.2016.05.02.09.18.23 for ; Mon, 02 May 2016 09:18:24 -0700 (PDT) Message-ID: <57277EEA.6070909@emindsoft.com.cn> Date: Tue, 03 May 2016 00:23:06 +0800 From: Chen Gang MIME-Version: 1.0 Subject: Re: [PATCH] mm/kasan/kasan.h: Fix boolean checking issue for kasan_report_enabled() References: <1462167374-6321-1-git-send-email-chengang@emindsoft.com.cn> <572735EB.8030300@emindsoft.com.cn> <572747C2.5040009@emindsoft.com.cn> <57275B71.8000907@emindsoft.com.cn> <57276E95.1030201@emindsoft.com.cn> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Alexander Potapenko Cc: Dmitry Vyukov , Andrew Morton , Andrey Ryabinin , kasan-dev , LKML , "linux-mm@kvack.org" , Chen Gang On 5/2/16 23:35, Alexander Potapenko wrote: > On Mon, May 2, 2016 at 5:13 PM, Chen Gang wrote: >> >> OK. But it does not look quite easy to use kasan_disable_current() for >> INIT_KASAN which is used in INIT_TASK. >> >> If we have to set "kasan_depth == 1", we have to use kasan_depth-- in >> kasan_enable_current(). > Agreed, decrementing the counter in kasan_enable_current() is more natural. > I can fix this together with the comments. OK, thanks. And need I also send patch v2 for include/linux/kasan.h? (or you will fix them together). >> >> If we don't prevent the overflow, it will have negative effect with the >> caller. When we issue an warning, it means the caller's hope fail, but >> can not destroy the caller's original work. In our case: >> >> - Assume "kasan_depth-- for kasan_enable_current()", the first enable >> will let kasan_depth be 0. > Sorry, I'm not sure I follow. > If we start with kasan_depth=0 (which is the default case for every > task except for the init, which also gets kasan_depth=0 short after > the kernel starts), > then the first call to kasan_disable_current() will make kasan_depth > nonzero and will disable KASAN. > The subsequent call to kasan_enable_current() will enable KASAN back. > > There indeed is a problem when someone calls kasan_enable_current() > without previously calling kasan_disable_current(). > In this case we need to check that kasan_depth was zero and print a > warning if it was. > It actually does not matter whether we modify kasan_depth after that > warning or not, because we are already in inconsistent state. > But I think we should modify kasan_depth anyway to ease the debugging. > For me, BUG_ON() will be better for debugging, but it is really not well for using. For WARN_ON(), it already print warnings, so I am not quite sure "always modifying kasan_depth will be ease the debugging". When we are in inconsistent state, for me, what we can do is: - Still try to do correct things within our control: "when the caller make a mistake, if kasan_enable_current() notices about it, it need issue warning, and prevent itself to make mistake (causing disable). - "try to let negative effect smaller to user", e.g. let users "loose hope" (call enable has no effect) instead of destroying users' original work (call enable, but get disable). Thanks. -- Chen Gang (e??a??) Managing Natural Environments is the Duty of Human Beings. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754380AbcEBQSk (ORCPT ); Mon, 2 May 2016 12:18:40 -0400 Received: from out1134-251.mail.aliyun.com ([42.120.134.251]:36595 "EHLO out1134-251.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753965AbcEBQSe (ORCPT ); Mon, 2 May 2016 12:18:34 -0400 X-Greylist: delayed 38168 seconds by postgrey-1.27 at vger.kernel.org; Mon, 02 May 2016 12:18:32 EDT X-Alimail-AntiSpam: AC=CONTINUE;BC=0.07579863|-1;FP=0|0|0|0|0|-1|-1|-1;HT=e02c03311;MF=chengang@emindsoft.com.cn;NM=1;PH=DS;RN=8;RT=8;SR=0;TI=SMTPD_----4lBPBMI_1462205886; Message-ID: <57277EEA.6070909@emindsoft.com.cn> Date: Tue, 03 May 2016 00:23:06 +0800 From: Chen Gang User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Alexander Potapenko CC: Dmitry Vyukov , Andrew Morton , Andrey Ryabinin , kasan-dev , LKML , "linux-mm@kvack.org" , Chen Gang Subject: Re: [PATCH] mm/kasan/kasan.h: Fix boolean checking issue for kasan_report_enabled() References: <1462167374-6321-1-git-send-email-chengang@emindsoft.com.cn> <572735EB.8030300@emindsoft.com.cn> <572747C2.5040009@emindsoft.com.cn> <57275B71.8000907@emindsoft.com.cn> <57276E95.1030201@emindsoft.com.cn> In-Reply-To: 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 On 5/2/16 23:35, Alexander Potapenko wrote: > On Mon, May 2, 2016 at 5:13 PM, Chen Gang wrote: >> >> OK. But it does not look quite easy to use kasan_disable_current() for >> INIT_KASAN which is used in INIT_TASK. >> >> If we have to set "kasan_depth == 1", we have to use kasan_depth-- in >> kasan_enable_current(). > Agreed, decrementing the counter in kasan_enable_current() is more natural. > I can fix this together with the comments. OK, thanks. And need I also send patch v2 for include/linux/kasan.h? (or you will fix them together). >> >> If we don't prevent the overflow, it will have negative effect with the >> caller. When we issue an warning, it means the caller's hope fail, but >> can not destroy the caller's original work. In our case: >> >> - Assume "kasan_depth-- for kasan_enable_current()", the first enable >> will let kasan_depth be 0. > Sorry, I'm not sure I follow. > If we start with kasan_depth=0 (which is the default case for every > task except for the init, which also gets kasan_depth=0 short after > the kernel starts), > then the first call to kasan_disable_current() will make kasan_depth > nonzero and will disable KASAN. > The subsequent call to kasan_enable_current() will enable KASAN back. > > There indeed is a problem when someone calls kasan_enable_current() > without previously calling kasan_disable_current(). > In this case we need to check that kasan_depth was zero and print a > warning if it was. > It actually does not matter whether we modify kasan_depth after that > warning or not, because we are already in inconsistent state. > But I think we should modify kasan_depth anyway to ease the debugging. > For me, BUG_ON() will be better for debugging, but it is really not well for using. For WARN_ON(), it already print warnings, so I am not quite sure "always modifying kasan_depth will be ease the debugging". When we are in inconsistent state, for me, what we can do is: - Still try to do correct things within our control: "when the caller make a mistake, if kasan_enable_current() notices about it, it need issue warning, and prevent itself to make mistake (causing disable). - "try to let negative effect smaller to user", e.g. let users "loose hope" (call enable has no effect) instead of destroying users' original work (call enable, but get disable). Thanks. -- Chen Gang (陈刚) Managing Natural Environments is the Duty of Human Beings.