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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 046F8C43381 for ; Thu, 28 Feb 2019 00:35:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C94C3214D8 for ; Thu, 28 Feb 2019 00:35:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730323AbfB1Afc (ORCPT ); Wed, 27 Feb 2019 19:35:32 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39892 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729432AbfB1Afb (ORCPT ); Wed, 27 Feb 2019 19:35:31 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5F8C9C0240; Thu, 28 Feb 2019 00:35:31 +0000 (UTC) Received: from MiWiFi-R3L-srv.redhat.com (ovpn-12-40.pek2.redhat.com [10.72.12.40]) by smtp.corp.redhat.com (Postfix) with ESMTP id ECD6C619D2; Thu, 28 Feb 2019 00:35:25 +0000 (UTC) From: Baoquan He To: linux-kernel@vger.kernel.org, kirill.shutemov@linux.intel.com Cc: dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, keescook@chromium.org, thgarnie@google.com, Baoquan He Subject: [PATCH v2 0/2] x86/mm/KASLR: Change the granularity of randomization to PUD size in 5-level Date: Thu, 28 Feb 2019 08:35:20 +0800 Message-Id: <20190228003522.9957-1-bhe@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 28 Feb 2019 00:35:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is v2 post. v1 can be found here: http://lkml.kernel.org/r/20190224132231.4878-1-bhe@redhat.com Background: *** Earlier, during a series of KASLR patch reviewing, Ingo got the current memory region KASLR only has granularity of randomization in PUD size in 4-level paging mode, and P4D size in 5-level paging mode, He suggested me to try to change both of them to be PMD size at granularity: http://lkml.kernel.org/r/20180912100135.GB3333@gmail.com Later, I changed code to support PMD level of randomization for both 4-level and 5-level. https://github.com/baoquan-he/linux/commits/mm-kaslr-2m-aligned The test passed on my KVM guest with 1 GB RAM, but failed when I increased the RAM to 4 GB, and failed either on larger RAM. After analyzing, it's because that 1 GB page mapping need be mapped at 1 GB aligned physical address for intel CPU. The 2 MB level of randomization will break it and cause error. Please check below table in intel IA32 manual. Table 4-15. Format of an IA-32e Page-Directory-Pointer-Table Entry (PDPTE) that Maps a 1-GByte Page So PMD level of randomization for mm KASLR is not doable. However, during investigation and testing above code, it turns out that the current code is misleading to build identity mapping for the real mode trampoline in case KASLR enabled. From code, only a small area (which is smaller than 1 MB) need be identity mapped. Please check below patch which is from above mm-kaslr-2m-aligned patch series. it only builds up 2 MB identity maping for real mode trampoline, and test passed on machines with 32 GB RAM of 4-level and on KVM guest of 5-level. https://github.com/baoquan-he/linux/commit/e120e67fbf9a5aa818d20084d8dea5b4a27ecf97 Result: Make a patchset to: 1)change code to only build 1 GB of area for real mode trampoline, namely only copy one PUD entry where physical address 0 resides; 2)improve the randomization granularity of 5-level from P4D size to PUD size. Changelog: v1->v2: Improve patch according to Kirill's suggestions: *)Add more information to code comment for better understanding; *)Improve code to save one low memory page in 4-level; Baoquan He (2): x86/mm/KASLR: Only build one PUD entry of area for real mode trampoline x86/mm/KASLR: Change the granularity of randomization to PUD size in 5-level arch/x86/mm/kaslr.c | 92 ++++++++++++++++++++------------------------- 1 file changed, 40 insertions(+), 52 deletions(-) -- 2.17.2