From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B8694C04ABB for ; Tue, 11 Sep 2018 07:31:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6F1AC20865 for ; Tue, 11 Sep 2018 07:31:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F1AC20865 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726819AbeIKM3A (ORCPT ); Tue, 11 Sep 2018 08:29:00 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:52548 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726325AbeIKM3A (ORCPT ); Tue, 11 Sep 2018 08:29:00 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DAFC2401DEAF; Tue, 11 Sep 2018 07:31:00 +0000 (UTC) Received: from localhost (ovpn-8-16.pek2.redhat.com [10.72.8.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 220472027EA4; Tue, 11 Sep 2018 07:30:59 +0000 (UTC) Date: Tue, 11 Sep 2018 15:30:57 +0800 From: Baoquan He To: Ingo Molnar Cc: tglx@linutronix.de, hpa@zytor.com, thgarnie@google.com, kirill.shutemov@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Kees Cook Subject: Re: [PATCH v2 2/3] x86/mm/KASLR: Calculate the actual size of vmemmap region Message-ID: <20180911073057.GW1740@192.168.1.3> References: <20180909124946.17988-1-bhe@redhat.com> <20180909124946.17988-2-bhe@redhat.com> <20180910061151.GA85199@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180910061151.GA85199@gmail.com> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Tue, 11 Sep 2018 07:31:00 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Tue, 11 Sep 2018 07:31:00 +0000 (UTC) for IP:'10.11.54.4' DOMAIN:'int-mx04.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'bhe@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/10/18 at 08:11am, Ingo Molnar wrote: > > * Baoquan He wrote: > > > @@ -108,6 +109,14 @@ void __init kernel_randomize_memory(void) > > if (memory_tb < kaslr_regions[0].size_tb) > > kaslr_regions[0].size_tb = memory_tb; > > > > + /* > > + * Calculate how many TB vmemmap region needs, and align to > > + * 1TB boundary. > > + * */ > > Yeah, so that's not the standard comment style ... Sorry for this, Will change. Thanks. About clean up you suggested, I have made two patches and paste them at below. Please help check if it's OK. Thanks a lot. > So I get the part where the 'base' pointer is essentially pointers to various global variables > used by the MM to get the virtual base address of the kernel, vmalloc and vmemmap areas from, > which base addresses can thus be modified by the very early KASLR code to dynamically shape the > virtual memory layout of these kernel memory areas on a per bootup basis. > > (BTW., that would be a great piece of information to add for the uninitiated. It's not like > it's obvious!) > > But what does 'size_tb' do? Nothing explains it and your patch doesn't make it clearer either. > Also, get_padding() looks like an unnecessary layer of obfuscation: Yes, I agree. Have made an patch according to your suggestion, paste it here: >From c74b1e49eaa0e00335adbbb7e2d5df6d60518d4f Mon Sep 17 00:00:00 2001 From: Baoquan He Date: Tue, 11 Sep 2018 14:34:26 +0800 Subject: [PATCH] x86/mm/KASLR: Add code comments to explain fields of struct kaslr_memory_region Signed-off-by: Baoquan He Suggested-by: Ingo Molnar --- arch/x86/mm/kaslr.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 91053cee7648..402984d8d729 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -41,9 +41,21 @@ static const unsigned long vaddr_end = CPU_ENTRY_AREA_BASE; /* - * Memory regions randomized by KASLR (except modules that use a separate logic - * earlier during boot). The list is ordered based on virtual addresses. This - * order is kept after randomization. + * Memory regions randomized by KASLR (except modules that use a separate + * logic earlier during boot). Currently they are the physical memory + * mapping, vmalloc and vmemmap regions, are ordered based on virtual + * addresses. The order is kept after randomization. + * + * @base: points to various global variables used by the MM to get the + * virtual base address of the above regions, which base addresses can + * thus be modified by the very early KASLR code to dynamically shape + * the virtual memory layout of these kernel memory regions on a per + * bootup basis. + * + * @size_tb: size in TB of each memory region. Thereinto, the size of + * the physical memory mapping region is variable, calculated according + * to the actual size of system RAM in order to save more space for + * randomization. The rest are fixed values related to paging mode. */ static __initdata struct kaslr_memory_region { unsigned long *base; > /* Get size in bytes used by the memory region */ > static inline unsigned long get_padding(struct kaslr_memory_region *region) > { > return (region->size_tb << TB_SHIFT); > } Yes, we can open code get_padding() as the following patch. >From e4cababd630af06085cb79a0bae9c00acd5272c0 Mon Sep 17 00:00:00 2001 From: Baoquan He Date: Tue, 11 Sep 2018 14:39:38 +0800 Subject: [PATCH] x86/mm/KASLR: Open code unnecessary function get_padding It's used only twice and we do bit shifts in the parent function anyway so it's not like it's hiding some uninteresting detail. Signed-off-by: Baoquan He Suggested-by: Ingo Molnar --- arch/x86/mm/kaslr.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 9774b6e39f63..91053cee7648 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -54,12 +54,6 @@ static __initdata struct kaslr_memory_region { { &vmemmap_base, 0 }, }; -/* Get size in bytes used by the memory region */ -static inline unsigned long get_padding(struct kaslr_memory_region *region) -{ - return (region->size_tb << TB_SHIFT); -} - /* * Apply no randomization if KASLR was disabled at boot or if KASAN * is enabled. KASAN shadow mappings rely on regions being PGD aligned. @@ -120,7 +114,7 @@ void __init kernel_randomize_memory(void) /* Calculate entropy available between regions */ remain_entropy = vaddr_end - vaddr_start; for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++) - remain_entropy -= get_padding(&kaslr_regions[i]); + remain_entropy -= kaslr_regions[i].size_tb << TB_SHIFT; prandom_seed_state(&rand_state, kaslr_get_random_long("Memory")); @@ -144,7 +138,7 @@ void __init kernel_randomize_memory(void) * Jump the region and add a minimum padding based on * randomization alignment. */ - vaddr += get_padding(&kaslr_regions[i]); + vaddr += kaslr_regions[i].size_tb << TB_SHIFT; if (pgtable_l5_enabled()) vaddr = round_up(vaddr + 1, P4D_SIZE); else -- 2.13.6