From mboxrd@z Thu Jan 1 00:00:00 1970 From: Suresh Siddha Subject: Re: [PATCH 1/4] [tip:x86/mm] Correcting improper large page preservation Date: Fri, 02 Apr 2010 23:43:20 -0700 Message-ID: <1270277000.2686.20.camel@sbs-t61> References: Reply-To: Suresh Siddha Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from mga02.intel.com ([134.134.136.20]:20507 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751675Ab0DCGoe (ORCPT ); Sat, 3 Apr 2010 02:44:34 -0400 In-Reply-To: Sender: linux-next-owner@vger.kernel.org List-ID: To: Siarhei Liakh Cc: "linux-kernel@vger.kernel.org" , "linux-security-module@vger.kernel.org" , "linux-next@vger.kernel.org" , Arjan van de Ven , James Morris , Andrew Morton , Andi Kleen , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , Rusty Russell , Stephen Rothwell , Dave Jones On Wed, 2010-03-31 at 18:59 -0700, Siarhei Liakh wrote: > + /* > + * .data and .bss should always be writable. > + */ > + if ((within(pfn, __pa((unsigned long)_sdata) >> PAGE_SHIFT, > + __pa((unsigned long)_edata) >> PAGE_SHIFT)) || > + (within(pfn, __pa((unsigned long)__bss_start) >> PAGE_SHIFT, > + __pa((unsigned long)__bss_stop) >> PAGE_SHIFT))) { > + pgprot_val(required) |= _PAGE_RW; > + } I have reviewed this patch and the only comment I have is: On 64bit kernels, kernel text/data mapping and kernel identity mappings are different virtual addresses mapping to same pfn ranges. For the data/bss pages, does it help (in identifying certain data corruptions more easily) in making the kernel identity mapping to be set to read-only and enforce the need of RW only for the kernel data mappings. Or is there some obscure code that uses something like __va(__pa(data_symbol)) and writes to it? If not, we can remove the __pa() constructs above and use the addr for comparisons. Otherwise this patch looks good to me. Reviewed-by: Suresh Siddha