From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.codeaurora.org by pdx-caf-mail.web.codeaurora.org (Dovecot) with LMTP id AGKFN4CAGVuQBAAAmS7hNA ; Thu, 07 Jun 2018 18:59:12 +0000 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id CCFE36089E; Thu, 7 Jun 2018 18:59:12 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on pdx-caf-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=unavailable autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by smtp.codeaurora.org (Postfix) with ESMTP id 45B8E601D2; Thu, 7 Jun 2018 18:59:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 45B8E601D2 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753612AbeFGS7J (ORCPT + 25 others); Thu, 7 Jun 2018 14:59:09 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39032 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751231AbeFGS7H (ORCPT ); Thu, 7 Jun 2018 14:59:07 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4386B40122A1; Thu, 7 Jun 2018 18:59:06 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-116-135.ams2.redhat.com [10.36.116.135]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C11081C65D; Thu, 7 Jun 2018 18:58:57 +0000 (UTC) Subject: Re: [PATCH 03/10] x86/cet: Signal handling for shadow stack To: Andy Lutomirski , Yu-cheng Yu , Dmitry Safonov , Cyrill Gorcunov Cc: LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , "H. J. Lu" , "Shanbhogue, Vedvyas" , "Ravi V. Shankar" , Dave Hansen , Jonathan Corbet , Oleg Nesterov , Arnd Bergmann , mike.kravetz@oracle.com References: <20180607143807.3611-1-yu-cheng.yu@intel.com> <20180607143807.3611-4-yu-cheng.yu@intel.com> From: Florian Weimer Message-ID: <2b920019-cf03-334c-3b6a-b2c6b7f4dfa3@redhat.com> Date: Thu, 7 Jun 2018 20:58:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Thu, 07 Jun 2018 18:59:06 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Thu, 07 Jun 2018 18:59:06 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'fweimer@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/07/2018 08:30 PM, Andy Lutomirski wrote: > On Thu, Jun 7, 2018 at 7:41 AM Yu-cheng Yu wrote: >> >> Set and restore shadow stack pointer for signals. > > How does this interact with siglongjmp()? We plan to use some unused signal mask bits in the jump buffer (we have a lot of those in glibc for some reason) to store the shadow stack pointer. > This patch makes me extremely nervous due to the possibility of ABI > issues and CRIU breakage. > >> diff --git a/arch/x86/include/uapi/asm/sigcontext.h b/arch/x86/include/uapi/asm/sigcontext.h >> index 844d60eb1882..6c8997a0156a 100644 >> --- a/arch/x86/include/uapi/asm/sigcontext.h >> +++ b/arch/x86/include/uapi/asm/sigcontext.h >> @@ -230,6 +230,7 @@ struct sigcontext_32 { >> __u32 fpstate; /* Zero when no FPU/extended context */ >> __u32 oldmask; >> __u32 cr2; >> + __u32 ssp; >> }; >> >> /* >> @@ -262,6 +263,7 @@ struct sigcontext_64 { >> __u64 trapno; >> __u64 oldmask; >> __u64 cr2; >> + __u64 ssp; >> >> /* >> * fpstate is really (struct _fpstate *) or (struct _xstate *) >> @@ -320,6 +322,7 @@ struct sigcontext { >> struct _fpstate __user *fpstate; >> __u32 oldmask; >> __u32 cr2; >> + __u32 ssp; > > Is it actually okay to modify these structures like this? They're > part of the user ABI, and I don't know whether any user code relies on > the size being constant. Probably not. Historically, these things have been tacked at the end of the floating point state, see struct _xstate: /* New processor state extensions go here: */ However, I'm not sure if this is really ideal because I doubt that everyone who needs the shadow stack pointer also wants to sacrifice space for the AVX-512 save area (which is already a backwards compatibility hazard). Other architectures have variable offsets and some TLV-style setup here. Thanks, Florian