From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King Subject: Re: Generic DMA - BUG_ON Date: Thu, 21 Jan 2010 17:53:17 +0000 Message-ID: <20100121175317.GA14752@flint.arm.linux.org.uk> References: <1263982111-24123-1-git-send-email-monstr@monstr.eu> <20100120105350.GA23394@flint.arm.linux.org.uk> <20100120110031.GD8665@amd.com> <1264089097.18869.0.camel@iscandar.digidescorp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1264089097.18869.0.camel@iscandar.digidescorp.com> Sender: linux-kernel-owner@vger.kernel.org To: "Steven J. Magnani" Cc: Joerg Roedel , monstr@monstr.eu, linux-kernel@vger.kernel.org, michal.simek@petalogix.com, arnd@arndb.de, linux-arch@vger.kernel.org, fujita.tomonori@lab.ntt.co.jp, akpm@linux-foundation.org, mingo@elte.hu List-Id: linux-arch.vger.kernel.org On Thu, Jan 21, 2010 at 09:51:37AM -0600, Steven J. Magnani wrote: > On Wed, 2010-01-20 at 12:00 +0100, Joerg Roedel wrote: > > On Wed, Jan 20, 2010 at 10:53:50AM +0000, Russell King wrote: > > > and ops is NULL, then this code will oops; you will get a full register > > > dump and backtrace. You can use this information along with markup_oops.pl > > > to find out where the problem is. > > > > You can't rely on the oops if the code runs in process context. The > > process may have address 0 mapped which would result in a security hole. > > We had two of these bugs last year. > > You also can't rely on an oops in a NOMMU environment. I don't see why implementations where NULL pointer derefs should be penalized by having additional NULL checks. Maybe this needs to be a conditional check which can be optimized away on architectures where NULL dereference always produces an oops. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from caramon.arm.linux.org.uk ([78.32.30.218]:58855 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754772Ab0AURyM (ORCPT ); Thu, 21 Jan 2010 12:54:12 -0500 Date: Thu, 21 Jan 2010 17:53:17 +0000 From: Russell King Subject: Re: Generic DMA - BUG_ON Message-ID: <20100121175317.GA14752@flint.arm.linux.org.uk> References: <1263982111-24123-1-git-send-email-monstr@monstr.eu> <20100120105350.GA23394@flint.arm.linux.org.uk> <20100120110031.GD8665@amd.com> <1264089097.18869.0.camel@iscandar.digidescorp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1264089097.18869.0.camel@iscandar.digidescorp.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: "Steven J. Magnani" Cc: Joerg Roedel , monstr@monstr.eu, linux-kernel@vger.kernel.org, michal.simek@petalogix.com, arnd@arndb.de, linux-arch@vger.kernel.org, fujita.tomonori@lab.ntt.co.jp, akpm@linux-foundation.org, mingo@elte.hu Message-ID: <20100121175317.g3NFsdcYR_w0PPlprQqxJvxs_TSmlmp8-Bfl1mnnTNY@z> On Thu, Jan 21, 2010 at 09:51:37AM -0600, Steven J. Magnani wrote: > On Wed, 2010-01-20 at 12:00 +0100, Joerg Roedel wrote: > > On Wed, Jan 20, 2010 at 10:53:50AM +0000, Russell King wrote: > > > and ops is NULL, then this code will oops; you will get a full register > > > dump and backtrace. You can use this information along with markup_oops.pl > > > to find out where the problem is. > > > > You can't rely on the oops if the code runs in process context. The > > process may have address 0 mapped which would result in a security hole. > > We had two of these bugs last year. > > You also can't rely on an oops in a NOMMU environment. I don't see why implementations where NULL pointer derefs should be penalized by having additional NULL checks. Maybe this needs to be a conditional check which can be optimized away on architectures where NULL dereference always produces an oops. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: