Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752139AbeAFGyn (ORCPT + 1 other); Sat, 6 Jan 2018 01:54:43 -0500 Received: from szxga06-in.huawei.com ([45.249.212.32]:40498 "EHLO huawei.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1750980AbeAFGym (ORCPT ); Sat, 6 Jan 2018 01:54:42 -0500 Subject: Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch) From: Hanjun Guo To: Dave Hansen , Jiri Kosina CC: Yisheng Xie , , , , , , , , Linus Torvalds , , , , Andrea Arcangeli 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> Message-ID: <6b076a05-22b6-ce3e-efba-02c65dd1438d@huawei.com> Date: Sat, 6 Jan 2018 14:53:15 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.177.223.23] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On 2018/1/6 14:28, Hanjun Guo wrote: > Hi Dave, > > Thank you very much for the quick response! Minor comments inline. > > On 2018/1/6 14:06, Dave Hansen wrote: >> On 01/05/2018 08:54 PM, Hanjun Guo wrote: >>> Do you mean NX bit will be brought back later? I'm asking this because >>> I tested this patch which it fixed the boot panic issue but the system >>> will hang when rebooting the system, because rebooting will also call efi >>> then panic as NS bit is set. >> Wow, you're running a lot of very lighly-used code paths! You actually >> found a similar but totally separate issue from what I gather. Thank >> you immensely for the quick testing and bug reports! >> >> Could you test the attached fix? >> >> For those playing along at home, I think this will end up being needed >> for 4.15 and probably all the backports. I want to see if it works >> before I submit it for real, though. >> >> >> 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 | 7 +++++++ >> 1 file changed, 7 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 22:01:51.393553325 -0800 >> @@ -124,6 +124,13 @@ static int map_tboot_page(unsigned long >> pte_t *pte; >> >> pgd = pgd_offset(&tboot_mm, vaddr); >> + /* >> + * 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; > > ... > >> + >> p4d = p4d_alloc(&tboot_mm, pgd, vaddr); > > Seems pgd will be re-set after p4d_alloc(), so should > we put the code behind (or after pud_alloc())? > >> if (!p4d) >> return -1; > > + /* > + * 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! Thanks Hanjun