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 6C17AC43381 for ; Thu, 14 Mar 2019 09:47:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FBA221019 for ; Thu, 14 Mar 2019 09:47:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727210AbfCNJrC (ORCPT ); Thu, 14 Mar 2019 05:47:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43716 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726712AbfCNJrB (ORCPT ); Thu, 14 Mar 2019 05:47:01 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1DC286857A; Thu, 14 Mar 2019 09:47:01 +0000 (UTC) Received: from MiWiFi-R3L-srv.redhat.com (ovpn-12-22.pek2.redhat.com [10.72.12.22]) by smtp.corp.redhat.com (Postfix) with ESMTP id E556269300; Thu, 14 Mar 2019 09:46:55 +0000 (UTC) From: Baoquan He To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, keescook@chromium.org, kirill@shutemov.name, yamada.masahiro@socionext.com, tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, x86@kernel.org, thgarnie@google.com, Baoquan He Subject: [PATCH v4 1/6] x86/mm/KASLR: Improve code comments about struct kaslr_memory_region Date: Thu, 14 Mar 2019 17:46:40 +0800 Message-Id: <20190314094645.4883-2-bhe@redhat.com> In-Reply-To: <20190314094645.4883-1-bhe@redhat.com> References: <20190314094645.4883-1-bhe@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Thu, 14 Mar 2019 09:47:01 +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 | 51 +++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 47 insertions(+), 4 deletions(-) diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c index 9a8756517504..5debf82ab06a 100644 --- a/arch/x86/mm/kaslr.c +++ b/arch/x86/mm/kaslr.c @@ -42,9 +42,46 @@ 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 kaslr_memory_region - 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 + * 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. E.g, the sizes in 4-level + * pageing mode are: + * + * - Physical memory mapping: (actual RAM size + 10 TB padding) + * - Vmalloc: 32 TB + * - Vmemmap: 1 TB + * + * As seen, 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; @@ -70,7 +107,13 @@ static inline bool kaslr_memory_enabled(void) return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN); } -/* Initialize base and padding for each memory region randomized with KASLR */ +/* + * kernel_randomize_memory - initialize base and padding for each + * memory region randomized with KASLR. + * + * When randomize the layout, their order are kept, still the physical + * memory mapping region is handled firstly, next vmalloc and vmemmap. + */ void __init kernel_randomize_memory(void) { size_t i; -- 2.17.2