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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,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 39154C43461 for ; Mon, 10 May 2021 22:58:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F1CA613CF for ; Mon, 10 May 2021 22:58:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229937AbhEJW7O (ORCPT ); Mon, 10 May 2021 18:59:14 -0400 Received: from mga02.intel.com ([134.134.136.20]:14343 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229502AbhEJW7M (ORCPT ); Mon, 10 May 2021 18:59:12 -0400 IronPort-SDR: 5CCxM31DrQ8NpRCc57zhv8RqDO51fL6JXRIul4MJVkw5VTUsKQCY8WFY9rtcImWpqRy2Aq/LHQ EakplwnAGuvQ== X-IronPort-AV: E=McAfee;i="6200,9189,9980"; a="186440128" X-IronPort-AV: E=Sophos;i="5.82,288,1613462400"; d="scan'208";a="186440128" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 May 2021 15:58:06 -0700 IronPort-SDR: QsXO/4wRx+z3mdOQUqRrWo77zUAK8pyl2+PvaaF/SdE5zZB8LiimPlTFQZZ4cYaXz9oRpRzdWf iJ15TiTGHg8g== X-IronPort-AV: E=Sophos;i="5.82,288,1613462400"; d="scan'208";a="434014879" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.251.144.113]) ([10.251.144.113]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 May 2021 15:58:00 -0700 Subject: Re: [PATCH v26 23/30] x86/cet/shstk: Handle thread shadow stack To: Borislav Petkov Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , 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 , Haitao Huang References: <20210427204315.24153-1-yu-cheng.yu@intel.com> <20210427204315.24153-24-yu-cheng.yu@intel.com> From: "Yu, Yu-cheng" Message-ID: <89598d32-4bf8-b989-ee77-5b4b55a138a9@intel.com> Date: Mon, 10 May 2021 15:57:56 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 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 5/10/2021 7:15 AM, Borislav Petkov wrote: > On Tue, Apr 27, 2021 at 01:43:08PM -0700, Yu-cheng Yu wrote: [...] >> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c >> index c815c7507830..d387df84b7f1 100644 >> --- a/arch/x86/kernel/shstk.c >> +++ b/arch/x86/kernel/shstk.c >> @@ -70,6 +70,55 @@ int shstk_setup(void) >> return 0; >> } > >> +int shstk_setup_thread(struct task_struct *tsk, unsigned long clone_flags, > > Judging by what this function does, its name wants to be > > shstk_alloc_thread_stack() > > or so? > >> + unsigned long stack_size) >> +{ >> + unsigned long addr, size; >> + struct cet_user_state *state; >> + struct cet_status *cet = &tsk->thread.cet; > > The tip-tree preferred ordering of variable declarations at the > beginning of a function is reverse fir tree order:: > > struct long_struct_name *descriptive_name; > unsigned long foo, bar; > unsigned int tmp; > int ret; > > The above is faster to parse than the reverse ordering:: > > int ret; > unsigned int tmp; > unsigned long foo, bar; > struct long_struct_name *descriptive_name; > > And even more so than random ordering:: > > unsigned long foo, bar; > int ret; > struct long_struct_name *descriptive_name; > unsigned int tmp; > >> + >> + if (!cet->shstk_size) >> + return 0; >> + > > This check needs a comment. > >> + if ((clone_flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM) >> + return 0; >> + >> + state = get_xsave_addr(&tsk->thread.fpu.state.xsave, >> + XFEATURE_CET_USER); > > Let that line stick out. > >> + >> + if (!state) >> + return -EINVAL; >> + >> + if (stack_size == 0) > > if (!stack_size) > >> + return -EINVAL; > > and that test needs to be done first in the function. > >> + >> + /* Cap shadow stack size to 4 GB */ > > Why? > This is not necessary. I will make it just stack_size, which is passed in from copy_thread(). >> + size = min_t(unsigned long long, rlimit(RLIMIT_STACK), SZ_4G); >> + size = min(size, stack_size); >> + >> + /* >> + * Compat-mode pthreads share a limited address space. >> + * If each function call takes an average of four slots >> + * stack space, allocate 1/4 of stack size for shadow stack. >> + */ >> + if (in_compat_syscall()) >> + size /= 4; > > <---- newline here. > >> + size = round_up(size, PAGE_SIZE); >> + addr = alloc_shstk(size); >> + > > ^ Superfluous newline. > >> + if (IS_ERR_VALUE(addr)) { >> + cet->shstk_base = 0; >> + cet->shstk_size = 0; >> + return PTR_ERR((void *)addr); >> + } >> + >> + fpu__prepare_write(&tsk->thread.fpu); >> + state->user_ssp = (u64)(addr + size); > > cet_user_state has u64, cet_status has unsigned longs. Make them all u64. > > And since cet_status is per thread, but I had suggested struct > shstk_desc, I think now that that should be called > > struct thread_shstk > > or so to denote *exactly* what it is. > So this struct will be: struct thread_shstk { u64 shstk_base; u64 shstk_size; u64 locked:1; u64 ibt:1; }; Ok? Thanks, Yu-cheng