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=-4.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_PASS,URIBL_BLOCKED autolearn=ham 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 57207C10F0E for ; Tue, 9 Apr 2019 20:43:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 189FC2084B for ; Tue, 9 Apr 2019 20:43:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="GZIlWj+F" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726627AbfDIUnp (ORCPT ); Tue, 9 Apr 2019 16:43:45 -0400 Received: from mail.efficios.com ([167.114.142.138]:55508 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726333AbfDIUnp (ORCPT ); Tue, 9 Apr 2019 16:43:45 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 92D837D6B5; Tue, 9 Apr 2019 16:43:43 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id 7KuMRDMaFv2W; Tue, 9 Apr 2019 16:43:43 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 166D97D6A8; Tue, 9 Apr 2019 16:43:43 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 166D97D6A8 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1554842623; bh=rpljNT4W03Re1hwIRD5UA8RXQeJsMbdUOXrWL26XfWc=; h=Date:From:To:Message-ID:MIME-Version; b=GZIlWj+Fjejq5UsSqSSpfNqadXVBDPLnqEOHyxdlUpi2Ky8+2aUl5KhjPzAG15Xqr 3CRfhgFzRZ9gv/hYnCXF5s8CDJivGSMvY4hbMSMwV2OphyV+64QWjHJJMYkOM+9n6T mhtT54nU9uKAbAx9LJCeMsTZC/ceyjHrPC5rLwLMB+9A/NdjtJz9+j/YLX/0jtgAli NP5HeQf7CUVkTrVVur4lrLVmyVjAU4vXEpbaoxJ697TTqILKBtRu/uRVQAGX/6eSWQ 2q4Q77G4vC6O+3OvuTRGf7nsNiMLyC2pPFJKdXMdkVhsos2WSaY1cxRHiMnkcxe3iA U8zZShhOPQFeQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id RRClCNAf68XO; Tue, 9 Apr 2019 16:43:42 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id EDDD57D6A0; Tue, 9 Apr 2019 16:43:42 -0400 (EDT) Date: Tue, 9 Apr 2019 16:43:42 -0400 (EDT) From: Mathieu Desnoyers To: Thomas Gleixner , Andy Lutomirski , Peter Zijlstra , "H. Peter Anvin" , Andi Kleen , Ingo Molnar , Borislav Petkov Cc: libc-alpha , linux-kernel , Carlos O'Donell , x86 Message-ID: <913288111.2663.1554842622822.JavaMail.zimbra@efficios.com> In-Reply-To: <11513896.2624.1554838336494.JavaMail.zimbra@efficios.com> References: <11513896.2624.1554838336494.JavaMail.zimbra@efficios.com> Subject: Re: rseq/x86: choosing rseq code signature MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.12_GA_3794 (ZimbraWebClient - FF66 (Linux)/8.8.12_GA_3794) Thread-Topic: rseq/x86: choosing rseq code signature Thread-Index: p8pmmV5FDxK+Lim3zGdIPg86Ryyj/a0NjlXh Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Apr 9, 2019, at 3:32 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote: > Hi, > > We are about to include the code signature required prior to restartable > sequences abort handlers into glibc, which will make this ABI choice final. > We need architecture maintainer input on that signature value. > > That code signature is placed before each abort handler, so the kernel can > validate that it is indeed jumping to an abort handler (and not some > arbitrary attacker-chosen code). The signature is never executed. > > Currently, tools/testing/selftests/rseq/rseq-x86.h defines RSEQ_SIG > as 0x53053053, and uses it as an immediate operand to the following > instruction opcodes (as suggested by Andy Lutomirski): > > x86-32: > - .byte 0x0f, 0x1f, 0x05: nopl > > x86-64: > - .byte 0x0f, 0x1f, 0x05: nopl (%rip) > > The current discussion thread on the glibc mailing list leads us towards > using a trap with uncommon immediate operand, which simplifies integration > with disassemblers, emulators, makes it easier to debug if the control > flow gets redirected there by mistake, and is nicer for some architecture's > speculative execution. > > The main advantage of choosing a trap instruction over a no-op is to ensure the > program traps if the execution flow gets redirected to the signature by mistake > (makes it easier to debug). It's not a hard requirement, but it would be a > bonus. > > Are there trap instructions that take an uncommon 4-byte immediate > operand you would recommend on x86 32/64 ? Or is the current choice of > nopl confirmed to be right one ? > > Here is an example of rseq signature definition template: > > /* > * TODO: document trap instruction objdump output on each sub-architecture > * instruction sets, as well as instruction set extensions. > */ > #define RSEQ_SIG 0x######## Peter Zijlstra suggested to use "invlpg" in user-space, which should generate a trap. The only concern would be emulators, but ideally they would not try to decode an instruction that is never executed. This would lead to the following patch. Any objections/ack ? diff --git a/tools/testing/selftests/rseq/rseq-x86.h b/tools/testing/selftests/rseq/rseq-x86.h index 2d4887b5d3f0..e9c8a9879e18 100644 --- a/tools/testing/selftests/rseq/rseq-x86.h +++ b/tools/testing/selftests/rseq/rseq-x86.h @@ -7,6 +7,11 @@ #include +/* + * RSEQ_SIG is used with the following privileged instructions, which trap in user-space: + * x86-32: 0f 01 3d 53 30 05 53 invlpg 0x53053053 + * x86-64: 0f 01 3d 53 30 05 53 invlpg 0x53053053(%rip) + */ #define RSEQ_SIG 0x53053053 #ifdef __x86_64__ @@ -78,8 +83,8 @@ do { \ #define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label) \ ".pushsection __rseq_failure, \"ax\"\n\t" \ - /* Disassembler-friendly signature: nopl (%rip). */\ - ".byte 0x0f, 0x1f, 0x05\n\t" \ + /* Disassembler-friendly signature: invlpg (%rip). */\ + ".byte 0x0f, 0x01, 0x3d\n\t" \ ".long " __rseq_str(RSEQ_SIG) "\n\t" \ __rseq_str(label) ":\n\t" \ teardown \ @@ -605,8 +610,8 @@ do { \ #define RSEQ_ASM_DEFINE_ABORT(label, teardown, abort_label) \ ".pushsection __rseq_failure, \"ax\"\n\t" \ - /* Disassembler-friendly signature: nopl . */ \ - ".byte 0x0f, 0x1f, 0x05\n\t" \ + /* Disassembler-friendly signature: invlpg . */ \ + ".byte 0x0f, 0x1f, 0x3d\n\t" \ ".long " __rseq_str(RSEQ_SIG) "\n\t" \ __rseq_str(label) ":\n\t" \ teardown \ -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com