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 871EBC433E1 for ; Mon, 22 Mar 2021 17:28:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47BDE61994 for ; Mon, 22 Mar 2021 17:28:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231449AbhCVR2V (ORCPT ); Mon, 22 Mar 2021 13:28:21 -0400 Received: from mga02.intel.com ([134.134.136.20]:1524 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230146AbhCVR16 (ORCPT ); Mon, 22 Mar 2021 13:27:58 -0400 IronPort-SDR: R+Gt2MP1QDYzA+6cmHEi9+vAxD8pRIvB5qjY/zf29gX0gv/aF4NRCXL4LgyaI71A8JtQr2Xj4m 2hveqgt0hI0w== X-IronPort-AV: E=McAfee;i="6000,8403,9931"; a="177447416" X-IronPort-AV: E=Sophos;i="5.81,269,1610438400"; d="scan'208";a="177447416" Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Mar 2021 10:27:57 -0700 IronPort-SDR: /poCiz3iH8zbav4AUTruoJT/OU8lWJG21RxkY8P29L4ZNarEgYiS0oFCvkNqX2jXjm9t5M9f99 CAkt3Y15cttQ== X-IronPort-AV: E=Sophos;i="5.81,269,1610438400"; d="scan'208";a="592694134" Received: from yyu32-mobl1.amr.corp.intel.com (HELO [10.209.39.64]) ([10.209.39.64]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Mar 2021 10:27:53 -0700 Subject: Re: [PATCH v23 14/28] x86/mm: Shadow Stack page fault error checking To: "Kirill A. Shutemov" 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 , Borislav Petkov , 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: <20210316151054.5405-1-yu-cheng.yu@intel.com> <20210316151054.5405-15-yu-cheng.yu@intel.com> <20210322103858.evxun5bhw2i5sio6@box> From: "Yu, Yu-cheng" Message-ID: Date: Mon, 22 Mar 2021 10:27:53 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210322103858.evxun5bhw2i5sio6@box> 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 3/22/2021 3:38 AM, Kirill A. Shutemov wrote: > On Tue, Mar 16, 2021 at 08:10:40AM -0700, Yu-cheng Yu wrote: [...] >> >> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c >> index a73347e2cdfc..4316732a18c6 100644 >> --- a/arch/x86/mm/fault.c >> +++ b/arch/x86/mm/fault.c >> @@ -1100,6 +1100,17 @@ access_error(unsigned long error_code, struct vm_area_struct *vma) >> (error_code & X86_PF_INSTR), foreign)) >> return 1; >> >> + /* >> + * Verify a shadow stack access is within a shadow stack VMA. >> + * It is always an error otherwise. Normal data access to a >> + * shadow stack area is checked in the case followed. >> + */ >> + if (error_code & X86_PF_SHSTK) { >> + if (!(vma->vm_flags & VM_SHSTK)) >> + return 1; >> + return 0; > > Any reason to return 0 here? I would rather keep the single return 0 in > the function, after all checks are done. > For shadow stack fault, X86_PF_SHSTK and X86_PF_WRITE both can be set. So for shadow stack fault, return from here and don't go into the normal write fault case. Thanks, Yu-cheng >> + } >> + >> if (error_code & X86_PF_WRITE) { >> /* write, present and write, not present: */ >> if (unlikely(!(vma->vm_flags & VM_WRITE))) >> @@ -1293,6 +1304,14 @@ void do_user_addr_fault(struct pt_regs *regs, >> >> perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); >> >> + /* >> + * Clearing _PAGE_DIRTY is used to detect shadow stack access. >> + * This method cannot distinguish shadow stack read vs. write. >> + * For valid shadow stack accesses, set FAULT_FLAG_WRITE to effect >> + * copy-on-write. >> + */ >> + if (error_code & X86_PF_SHSTK) >> + flags |= FAULT_FLAG_WRITE; >> if (error_code & X86_PF_WRITE) >> flags |= FAULT_FLAG_WRITE; >> if (error_code & X86_PF_INSTR) >> -- >> 2.21.0 >> >