From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx175.postini.com [74.125.245.175]) by kanga.kvack.org (Postfix) with SMTP id 614CE6B004A for ; Fri, 24 Feb 2012 15:55:21 -0500 (EST) Date: Fri, 24 Feb 2012 12:55:19 -0800 From: Andrew Morton Subject: Re: [PATCH] Ensure that walk_page_range()'s start and end are page-aligned Message-Id: <20120224125519.89120828.akpm@linux-foundation.org> In-Reply-To: <87obsoxcn6.fsf@danplanet.com> References: <1328902796-30389-1-git-send-email-danms@us.ibm.com> <87zkcm23az.fsf@caffeine.danplanet.com> <87obsoxcn6.fsf@danplanet.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dan Smith Cc: David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, dave@linux.vnet.ibm.com On Fri, 24 Feb 2012 11:19:25 -0800 Dan Smith wrote: > > ... > > The inner function walk_pte_range() increments "addr" by PAGE_SIZE after > each pte is processed, and only exits the loop if the result is equal to > "end". Current, if either (or both of) the starting or ending addresses > passed to walk_page_range() are not page-aligned, then we will never > satisfy that exit condition and begin calling the pte_entry handler with > bad data. > > To be sure that we will land in the right spot, this patch checks that > both "addr" and "end" are page-aligned in walk_page_range() before starting > the traversal. > > ... > > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -196,6 +196,11 @@ int walk_page_range(unsigned long addr, unsigned long end, > if (addr >= end) > return err; > > + if (WARN_ONCE((addr & ~PAGE_MASK) || (end & ~PAGE_MASK), > + "address range is not page-aligned")) { > + return -EINVAL; > + } > + > if (!walk->mm) > return -EINVAL; Well... why should we apply the patch? Is there some buggy code which is triggering the problem? Do you intend to write some buggy code to trigger the problem? ;) IOW, what benefit is there to this change? Also, as it's a developer-only thing we should arrange for the overhead to vanish when CONFIG_DEBUG_VM=n? -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org