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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 30256C43381 for ; Sat, 16 Feb 2019 14:01:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02CC0222E0 for ; Sat, 16 Feb 2019 14:01:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726999AbfBPOBg (ORCPT ); Sat, 16 Feb 2019 09:01:36 -0500 Received: from mx1.redhat.com ([209.132.183.28]:53592 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725294AbfBPOBg (ORCPT ); Sat, 16 Feb 2019 09:01:36 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 199922FE552; Sat, 16 Feb 2019 14:01:36 +0000 (UTC) Received: from MiWiFi-R3L-srv.redhat.com (ovpn-12-24.pek2.redhat.com [10.72.12.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id B03F6608E2; Sat, 16 Feb 2019 14:00:55 +0000 (UTC) From: Baoquan He To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, x86@kernel.org, travis@sgi.com, thgarnie@google.com, keescook@chromium.org, akpm@linux-foundation.org, yamada.masahiro@socionext.com, kirill@shutemov.name, Baoquan He Subject: [PATCH v3 1/6] x86/mm/KASLR: Improve code comments about struct kaslr_memory_region Date: Sat, 16 Feb 2019 22:00:03 +0800 Message-Id: <20190216140008.28671-2-bhe@redhat.com> In-Reply-To: <20190216140008.28671-1-bhe@redhat.com> References: <20190216140008.28671-1-bhe@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Sat, 16 Feb 2019 14:01:36 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The old comment above kaslr_memory_region is not clear enough to explain the concepts of memory region KASLR. [Ingo suggested this and helped to prettify the text] Signed-off-by: Baoquan He --- arch/x86/mm/kaslr.c | 55 ++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 52 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 3f452ffed7e9..d7c6e4e8e48e 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -42,10 +42,59 @@ 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. + * 'struct kasl_memory_region' entries represent continuous chunks of + * kernel virtual memory regions, to be randomized by KASLR. + * + * ( The exception is the module space virtual memory window which + * uses separate logic earlier during bootup. ) + * + * Currently there are three such regions: the physical memory mapping, + * vmalloc and vmemmap regions. + * + * The array below has the entries ordered based on virtual addresses. + * The order is kept after randomization, i.e. the randomized + * virtual addresses of these regions are still ascending. + * + * Here are the fields: + * + * @base: points to a global variable used by the MM to get the + * virtual base address of any of the above regions. This allows the + * early KASLR code to modify these base addresses early during bootup, + * on a per bootup basis, without the MM code even being aware of whether + * it got changed and to what value. + * + * When KASLR is active then the MM code makes sure that for each region + * there's such a single, dynamic, global base address 'unsigned long' + * variable available for the KASLR code to point to and modify directly: + * + * { &page_offset_base, 0 }, + * { &vmalloc_base, 0 }, + * { &vmemmap_base, 1 }, + * + * @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. + * + * @size_tb: is the size of each memory region after randomization, and + * its unit is TB. + * + * Physical memory mapping: (actual RAM size + 10 TB padding) + * Vmalloc: 32 TB + * Vmemmap: 1 TB + * + * When randomize the layout, their order are kept, still the physical + * memory mapping region is handled fistly, next vmalloc and vmemmap. + * E.g the physical memory region, we limit the starting address to be + * taken from the 1st 1/3 part of the whole available virtual address + * space which is from 0xffff880000000000 to 0xfffffe0000000000, namely + * the original starting address of the physical memory mapping region + * to the starting address of cpu_entry_area mapping region. Once a random + * address is chosen for the physical memory mapping, we jump over the + * region and add 1G to begin the next region handling with the remaining + * available space. */ + static __initdata struct kaslr_memory_region { unsigned long *base; unsigned long size_tb; -- 2.17.2