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=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 64F9FC47420 for ; Thu, 1 Oct 2020 16:51:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2B3BF2075F for ; Thu, 1 Oct 2020 16:51:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732622AbgJAQvm (ORCPT ); Thu, 1 Oct 2020 12:51:42 -0400 Received: from mga01.intel.com ([192.55.52.88]:59840 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732016AbgJAQvl (ORCPT ); Thu, 1 Oct 2020 12:51:41 -0400 IronPort-SDR: jgp66Icb9SwbB6eEHv6R1yhBmm+K2sToWhrceCkSOhX1EkToiMCa1iRc4pE2mt+K3Sys9OcYJb g5FQxk1SXxkA== X-IronPort-AV: E=McAfee;i="6000,8403,9761"; a="180933792" X-IronPort-AV: E=Sophos;i="5.77,323,1596524400"; d="scan'208";a="180933792" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2020 09:51:38 -0700 IronPort-SDR: MI//hR/qDfigJQ/WhDVCXIhf6/vl8bAvbmWqe3dt+FZvFbfeHbaqAKVc7xnQKoOak2hvZBeZho A8V7kczDvZog== X-IronPort-AV: E=Sophos;i="5.77,323,1596524400"; d="scan'208";a="346148630" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.213.183.12]) ([10.213.183.12]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Oct 2020 09:51:35 -0700 Subject: Re: [PATCH v13 8/8] x86/vsyscall/64: Fixup Shadow Stack and Indirect Branch Tracking for vsyscall emulation To: Andy Lutomirski , "H.J. Lu" Cc: X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , "open list:DOCUMENTATION" , Linux-MM , linux-arch , Linux API , Arnd Bergmann , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu References: <99B32E59-CFF2-4756-89BD-AEA0021F355F@amacapital.net> From: "Yu, Yu-cheng" Message-ID: <79d1e67d-2394-1ce6-3bad-cce24ba792bd@intel.com> Date: Thu, 1 Oct 2020 09:51:35 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/30/2020 6:10 PM, Andy Lutomirski wrote: > On Wed, Sep 30, 2020 at 6:01 PM H.J. Lu wrote: >> >> On Wed, Sep 30, 2020 at 4:44 PM Andy Lutomirski wrote: [...] >>>>>>> From 09803e66dca38d7784e32687d0693550948199ed Mon Sep 17 00:00:00 2001 >>>>>>> From: Yu-cheng Yu >>>>>>> Date: Thu, 29 Nov 2018 14:15:38 -0800 >>>>>>> Subject: [PATCH v13 8/8] x86/vsyscall/64: Fixup Shadow Stack and >>>>>>> Indirect Branch >>>>>>> Tracking for vsyscall emulation >>>>>>> >>>>>>> Vsyscall entry points are effectively branch targets. Mark them with >>>>>>> ENDBR64 opcodes. When emulating the RET instruction, unwind shadow stack >>>>>>> and reset IBT state machine. >>>>>>> >>>>>>> Signed-off-by: Yu-cheng Yu >>>>>>> --- >>>>>>> v13: >>>>>>> - Check shadow stack address is canonical. >>>>>>> - Change from writing to MSRs to writing to CET xstate. >>>>>>> >>>>>>> arch/x86/entry/vsyscall/vsyscall_64.c | 34 +++++++++++++++++++++++ >>>>>>> arch/x86/entry/vsyscall/vsyscall_emu_64.S | 9 ++++++ >>>>>>> arch/x86/entry/vsyscall/vsyscall_trace.h | 1 + >>>>>>> 3 files changed, 44 insertions(+) >>>>>>> >>>>>>> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c >>>>>>> b/arch/x86/entry/vsyscall/vsyscall_64.c >>>>>>> index 44c33103a955..30b166091d46 100644 >>>>>>> --- a/arch/x86/entry/vsyscall/vsyscall_64.c >>>>>>> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c >>>>>>> @@ -38,6 +38,9 @@ >>>>>>> #include >>>>>>> #include >>>>>>> #include >>>>>>> +#include >>>>>>> +#include >>>>>>> +#include >>>>>>> >>>>>>> #define CREATE_TRACE_POINTS >>>>>>> #include "vsyscall_trace.h" >>>>>>> @@ -286,6 +289,44 @@ bool emulate_vsyscall(unsigned long error_code, >>>>>>> /* Emulate a ret instruction. */ >>>>>>> regs->ip = caller; >>>>>>> regs->sp += 8; >>>>>>> + >>>>>>> +#ifdef CONFIG_X86_CET >>>>>>> + if (tsk->thread.cet.shstk_size || tsk->thread.cet.ibt_enabled) { >>>>>>> + struct cet_user_state *cet; >>>>>>> + struct fpu *fpu; >>>>>>> + >>>>>>> + fpu = &tsk->thread.fpu; >>>>>>> + fpregs_lock(); >>>>>>> + >>>>>>> + if (!test_thread_flag(TIF_NEED_FPU_LOAD)) { >>>>>>> + copy_fpregs_to_fpstate(fpu); >>>>>>> + set_thread_flag(TIF_NEED_FPU_LOAD); >>>>>>> + } >>>>>>> + >>>>>>> + cet = get_xsave_addr(&fpu->state.xsave, XFEATURE_CET_USER); >>>>>>> + if (!cet) { >>>>>>> + /* >>>>>>> + * This should not happen. The task is >>>>>>> + * CET-enabled, but CET xstate is in INIT. >>>>>>> + */ >>>>>> [...] >>>>>> >>>>> >>>>> For what it's worth, I think there is an alternative. If you all >>>>> (userspace people, etc) can come up with a credible way for a user >>>>> program to statically declare that it doesn't need vsyscalls, then we >>>>> could make SHSTK depend on *that*, and we could avoid this mess. This >>>>> breaks orthogonality, but it's probably a decent outcome. >>>>> >>>> >>>> Would an arch_prctl(DISABLE_VSYSCALL) work? The kernel then sets a >>>> thread flag, and in emulate_vsyscall(), checks the flag. >>>> >>>> When CET is enabled, ld-linux will do DISABLE_VSYSCALL. >>>> >>>> How is that? >>> >>> Backwards, no? Presumably vsyscall needs to be disabled before or >>> concurrently with CET being enabled, not after. >>> >>> I think the solution of making vsyscall emulation work correctly with >>> CET is going to be better and possibly more straightforward. >>> >> >> We can do >> >> 1. Add ARCH_X86_DISABLE_VSYSCALL to disable the vsyscall page. >> 2. If CPU supports CET and the program is CET enabled: >> a. Disable the vsyscall page. >> b. Pass control to user. >> c. Enable the vsyscall page when ARCH_X86_CET_DISABLE is called. >> >> So when control is passed from kernel to user, the vsyscall page is >> disabled if the program >> is CET enabled. > > Let me say this one more time: > > If we have a per-process vsyscall disable control and a per-process > CET control, we are going to keep those settings orthogonal. I'm > willing to entertain an option in which enabling SHSTK without also > disabling vsyscalls is disallowed, We are *not* going to have any CET > flags magically disable vsyscalls, though, and we are not going to > have a situation where disabling vsyscalls on process startup requires > enabling SHSTK. > > Any possible static vsyscall controls (and CET controls, for that > matter) also need to come with some explanation of whether they are > properties set on the ELF loader, the ELF program being loaded, or > both. And this explanation needs to cover what happens when old > binaries link against new libc versions and vice versa. A new > CET-enabled binary linked against old libc running on a new kernel > that is expected to work on a non-CET CPU MUST work on a CET CPU, too. > > Right now, literally the only thing preventing vsyscall emulation from > coexisting with SHSTK is that the implementation eeds work. > > So your proposal is rejected. Sorry. > I think, even with shadow stack/ibt enabled, we can still allow XONLY without too much mess. What about this? Thanks, Yu-cheng ====== diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c index 8b0b32ac7791..d39da0a15521 100644 --- a/arch/x86/entry/vsyscall/vsyscall_64.c +++ b/arch/x86/entry/vsyscall/vsyscall_64.c @@ -48,16 +48,16 @@ static enum { EMULATE, XONLY, NONE } vsyscall_mode __ro_after_init = #ifdef CONFIG_LEGACY_VSYSCALL_NONE NONE; -#elif defined(CONFIG_LEGACY_VSYSCALL_XONLY) +#elif defined(CONFIG_LEGACY_VSYSCALL_XONLY) || defined(CONFIG_X86_CET) XONLY; -#else +#else EMULATE; #endif static int __init vsyscall_setup(char *str) { if (str) { - if (!strcmp("emulate", str)) + if (!strcmp("emulate", str) && !IS_ENABLED(CONFIG_X86_CET)) vsyscall_mode = EMULATE; else if (!strcmp("xonly", str)) vsyscall_mode = XONLY;