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=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 8D3FCC43461 for ; Mon, 7 Sep 2020 10:24:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5045D204FD for ; Mon, 7 Sep 2020 10:24:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728658AbgIGKYO (ORCPT ); Mon, 7 Sep 2020 06:24:14 -0400 Received: from foss.arm.com ([217.140.110.172]:59986 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728424AbgIGKYC (ORCPT ); Mon, 7 Sep 2020 06:24:02 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 35F29106F; Mon, 7 Sep 2020 03:24:01 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D9BA73F66E; Mon, 7 Sep 2020 03:23:59 -0700 (PDT) Date: Mon, 7 Sep 2020 11:23:57 +0100 From: Dave Martin To: Boyan Karatotev Cc: Shuah Khan , boian4o1@gmail.com, Catalin Marinas , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, amit.kachhap@arm.com, vincenzo.frascino@arm.com, Will Deacon , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 1/4] kselftests/arm64: add a basic Pointer Authentication test Message-ID: <20200907102354.GL6642@arm.com> References: <20200828131606.7946-1-boyan.karatotev@arm.com> <20200828131606.7946-2-boyan.karatotev@arm.com> <20200902164858.GI6642@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 03, 2020 at 11:12:02AM +0100, Boyan Karatotev wrote: > On 02/09/2020 17:49, Dave Martin wrote: > > On Fri, Aug 28, 2020 at 02:16:03PM +0100, Boyan Karatotev wrote: > >> PAuth signs and verifies return addresses on the stack. It does so by > >> inserting a Pointer Authentication code (PAC) into some of the unused top > >> bits of an address. This is achieved by adding paciasp/autiasp instructions > >> at the beginning and end of a function. > >> > >> This feature is partially backwards compatible with earlier versions of the > >> ARM architecture. To coerce the compiler into emitting fully backwards > >> compatible code the main file is compiled to target an earlier ARM version. > >> This allows the tests to check for the feature and print meaningful error > >> messages instead of crashing. > >> > >> Add a test to verify that corrupting the return address results in a > >> SIGSEGV on return. > >> > >> Cc: Shuah Khan > >> Cc: Catalin Marinas > >> Cc: Will Deacon > >> Signed-off-by: Boyan Karatotev > >> --- [...] > >> diff --git a/tools/testing/selftests/arm64/pauth/pac_corruptor.S b/tools/testing/selftests/arm64/pauth/pac_corruptor.S > >> new file mode 100644 > >> index 000000000000..6a34ec23a034 > >> --- /dev/null > >> +++ b/tools/testing/selftests/arm64/pauth/pac_corruptor.S > >> @@ -0,0 +1,36 @@ > >> +/* SPDX-License-Identifier: GPL-2.0 */ > >> +/* Copyright (C) 2020 ARM Limited */ > >> + > >> +.global pac_corruptor > >> + > >> +.text > >> +/* > >> + * Corrupting a single bit of the PAC ensures the authentication will fail. It > >> + * also guarantees no possible collision. TCR_EL1.TBI0 is set by default so no > >> + * top byte PAC is tested > >> + */ > >> + pac_corruptor: > >> + paciasp > >> + > >> + /* make stack frame */ > >> + sub sp, sp, #16 > >> + stp x29, lr, [sp] > > > > Nit: if respinning, you can optimise a few sequences of this sort, e.g. > > > > stp x29, lr, [sp, #-16]! > > > >> + mov x29, sp > >> + > >> + /* prepare mask for bit to be corrupted (bit 54) */ > >> + mov x1, xzr > >> + add x1, x1, #1 > >> + lsl x1, x1, #54 > > > > Nit: > > > > mov x1, #1 << 54 > Thank you for this, didn't know I could do it this way. > > > > but anyway, the logic operations can encode most simple bitmasks > > directly as immediate operands, so you can skip this and just do > > > >> + > >> + /* get saved lr, corrupt selected bit, put it back */ > >> + ldr x0, [sp, #8] > >> + eor x0, x0, x1 > > > > eor x0, x0, #1 << 54 > > > >> + str x0, [sp, #8] > >> + > >> + /* remove stack frame */ > >> + ldp x29, lr, [sp] > >> + add sp, sp, #16 > > > > ldp x29, lr, [sp], #16 > > > > [...] > > > > Actually, since there are no leaf nested function calls and no trap is > > expected until the function returns (so backtracing in the middle of > > this function is unlikely to be needed), could we optimise this whole > > thing down to the following? > > > I suppose you're right. The intent was to emulate a c function but there > really is no point in doing all this extra work. Will change it. It's not critical either way, but this way it's at least less code to maintain / read. > > pac_corruptor: > > paciasp > > eor lr, lr, #1 << 53 > > autiasp > > ret > > > > Cheers > > ---Dave [...] Cheers ---Dave