Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752381AbeAFHzk (ORCPT + 1 other); Sat, 6 Jan 2018 02:55:40 -0500 Received: from mga11.intel.com ([192.55.52.93]:13474 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751670AbeAFHzj (ORCPT ); Sat, 6 Jan 2018 02:55:39 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,320,1511856000"; d="scan'208";a="24841378" Subject: Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch) To: Hanjun Guo , Jiri Kosina References: <20171123003438.48A0EEDE@viggo.jf.intel.com> <20171123003447.1DB395E3@viggo.jf.intel.com> <93776eb2-b6d4-679a-280c-8ba558a69c34@linux.intel.com> <20a54a5f-f4e5-2126-fb73-6a995d13d52d@linux.intel.com> <332f4eab-8a3d-8b29-04f2-7c075f81b85b@linux.intel.com> <6b076a05-22b6-ce3e-efba-02c65dd1438d@huawei.com> Cc: Yisheng Xie , linux-kernel@vger.kernel.org, linux-mm@kvack.org, richard.fellner@student.tugraz.at, moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, luto@kernel.org, Linus Torvalds , keescook@google.com, hughd@google.com, x86@kernel.org, Andrea Arcangeli From: Dave Hansen Message-ID: <80dbcf02-2035-94dc-ca29-4f17ad271fda@linux.intel.com> Date: Fri, 5 Jan 2018 23:55:38 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <6b076a05-22b6-ce3e-efba-02c65dd1438d@huawei.com> Content-Type: multipart/mixed; boundary="------------D0A5EE75B77BBD36D7B26952" Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: This is a multi-part message in MIME format. --------------D0A5EE75B77BBD36D7B26952 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit On 01/05/2018 10:53 PM, Hanjun Guo wrote: >> + /* >> + * PTI poisons low addresses in the kernel page tables in the >> + * name of making them unusable for userspace. To execute >> + * code at such a low address, the poison must be cleared. >> + */ >> + pgd->pgd &= ~_PAGE_NX; >> >> We will have a try in a minute, and report back later. > And it works，we can boot/reboot the system successfully, thank > you all the quick response and debug! I think I'll just submit the attached patch if there are no objections (and if it works, of course!). I just stuck the NX clearing at the bottom. --------------D0A5EE75B77BBD36D7B26952 Content-Type: text/x-patch; name="pti-tboot-fix.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="pti-tboot-fix.patch" From: Dave Hansen This is another case similar to what EFI does: create a new set of page tables, map some code at a low address, and jump to it. PTI mistakes this low address for userspace and mistakenly marks it non-executable in an effort to make it unusable for userspace. Undo the poison to allow execution. Signed-off-by: Dave Hansen Cc: Ning Sun Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: tboot-devel@lists.sourceforge.net Cc: linux-kernel@vger.kernel.org --- b/arch/x86/kernel/tboot.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff -puN arch/x86/kernel/tboot.c~pti-tboot-fix arch/x86/kernel/tboot.c --- a/arch/x86/kernel/tboot.c~pti-tboot-fix 2018-01-05 21:50:55.755554960 -0800 +++ b/arch/x86/kernel/tboot.c 2018-01-05 23:51:41.368536890 -0800 @@ -138,6 +138,17 @@ static int map_tboot_page(unsigned long return -1; set_pte_at(&tboot_mm, vaddr, pte, pfn_pte(pfn, prot)); pte_unmap(pte); + + /* + * PTI poisons low addresses in the kernel page tables in the + * name of making them unusable for userspace. To execute + * code at such a low address, the poison must be cleared. + * + * Note: 'pgd' actually gets set in p4d_alloc() _or_ + * pud_alloc() depending on 4/5-level paging. + */ + pgd->pgd &= ~_PAGE_NX; + return 0; } _ --------------D0A5EE75B77BBD36D7B26952--