From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f72.google.com (mail-it0-f72.google.com [209.85.214.72]) by kanga.kvack.org (Postfix) with ESMTP id D1AFE280291 for ; Sat, 6 Jan 2018 03:43:18 -0500 (EST) Received: by mail-it0-f72.google.com with SMTP id f185so3384696itc.2 for ; Sat, 06 Jan 2018 00:43:18 -0800 (PST) Received: from huawei.com ([45.249.212.35]) by mx.google.com with ESMTPS id f32si5533375ioi.249.2018.01.06.00.43.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 06 Jan 2018 00:43:17 -0800 (PST) Subject: Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch) 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> <80dbcf02-2035-94dc-ca29-4f17ad271fda@linux.intel.com> From: Hanjun Guo Message-ID: <1e3fcdaa-75c9-99ef-3298-8015bb09b8cc@huawei.com> Date: Sat, 6 Jan 2018 16:42:06 +0800 MIME-Version: 1.0 In-Reply-To: <80dbcf02-2035-94dc-ca29-4f17ad271fda@linux.intel.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen , Jiri Kosina 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 On 2018/1/6 15:55, Dave Hansen wrote: > 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 worksi 1/4 ?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!). We tested that placing the NX clearing after pud_alloc(), and it works, patch below should work as well. > > I just stuck the NX clearing at the bottom. > > > 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; > } Thanks Hanjun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org