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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 99CA8C5518B for ; Wed, 22 Apr 2020 17:51:18 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 699462098B for ; Wed, 22 Apr 2020 17:51:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="XKkNJn3s"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="SbiBDMBj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 699462098B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=BQ4ygPt7Ga+8M2Kp88XWFaiKqYDJVkF8cUjZNFzpSsw=; b=XKkNJn3slxolc+ +rUaBNu9eyY2DYlvegYyEnGtUrvUJKg/avscblE94+2AEgD+H1JiRmpybhw+7HAN2jRN774RV3Asm VzkmQ1ijIaY0c3p5nvJWff4YGmTbbV31TrxqeRJ3vnXOATuuetfpfIoBpeaQEK+Zs+gqzx+vgErmJ hkRfjY8kGWyykaTZUE15CLNE3IgYf5az5240t7bcQp1KOuODUuGSqeR5FsRhSxp0BEkXo41nlOcei I6qkTBNmZY40I1q+gS22QgyMohEBdJeO2QTJdiSmZAwyWEokEwd2HEUVRd7wKOkfILjIJJYVRlJuQ Ws968BQY2mKgFP2IvUSg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jRJWi-0000ve-9X; Wed, 22 Apr 2020 17:51:12 +0000 Received: from mail-pf1-x443.google.com ([2607:f8b0:4864:20::443]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jRJWc-0000uU-Bc for linux-arm-kernel@lists.infradead.org; Wed, 22 Apr 2020 17:51:10 +0000 Received: by mail-pf1-x443.google.com with SMTP id f7so1464234pfa.9 for ; Wed, 22 Apr 2020 10:51:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=ZF6h4B8lRkEW+PGdoi5ViWh9NdqvBm+plj3edg+BLxs=; b=SbiBDMBjNOJtZvz674h6CaZCEGdmafbK0qSIOSSMTCWnqd5jMXbDXqcct8K8mtTChe 4BmBYx34rurFf5imZkH6NB9jvIu0M0140rWbXixJsCfD/+8yfkJPCm/IHIsm3ZoRWfwb VIyeJQzY1bEBF+t0X5Jqa/2kR8k/V4WASdOqg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=ZF6h4B8lRkEW+PGdoi5ViWh9NdqvBm+plj3edg+BLxs=; b=JQhxV1KHvBhjJCmCgtzjEn1eVm2tG/7e+qfbpOakKUhe4/lllsc7Fne/6zNys1D1ZR RzmZxX2S6bHrTDRJs5jRS/7baXyPL98B9EvHKppKqMzPqajXk/6m92vgjKdFZkCXp82u eUN1Rj8ewhAPi3CdYdKggpGNtZh6aKco4s+nhz1tEAS8KSzVDEB/zu+4YnH4QIEn7yDZ /txLzIcz7BnJG8bmbSg/+2qsAnmJm0VEzR3hzn2V44ddaPgPODLbCxsSU0ifSgmYQGCZ iPW30O23EqVH0zKar8IcTf8r2M3pD2JXTFeXz3wzE7CSnXtXFyHzFcCVnN3QOMd/+oYn qqSA== X-Gm-Message-State: AGi0PuYNfKYBnKpdyyoGVqrd1ZdHUQHby5p7YPWr+kKLUpiOZfMHD9/t hKGWqeGXTPrLtXH+IUSXFvAkrA== X-Google-Smtp-Source: APiQypKgukJRS2MpdwcmV4gR8X/qlLkQhVOoNqLyqZFCT1UTaoEDKt7OxFkygmvQ9SLxUbFYDjP/kg== X-Received: by 2002:a63:9e54:: with SMTP id r20mr141098pgo.301.1587577864965; Wed, 22 Apr 2020 10:51:04 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id e4sm5917509pjv.30.2020.04.22.10.51.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Apr 2020 10:51:04 -0700 (PDT) Date: Wed, 22 Apr 2020 10:51:02 -0700 From: Kees Cook To: Will Deacon Subject: Re: [PATCH v11 01/12] add support for Clang's Shadow Call Stack (SCS) Message-ID: <202004221047.3AEAECC1@keescook> References: <20191018161033.261971-1-samitolvanen@google.com> <20200416161245.148813-1-samitolvanen@google.com> <20200416161245.148813-2-samitolvanen@google.com> <20200420171727.GB24386@willie-the-truck> <20200420211830.GA5081@google.com> <20200422173938.GA3069@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200422173938.GA3069@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200422_105106_419868_E3AB1C4B X-CRM114-Status: GOOD ( 19.45 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Juri Lelli , kernel-hardening@lists.openwall.com, Peter Zijlstra , Catalin Marinas , Marc Zyngier , Masahiro Yamada , clang-built-linux@googlegroups.com, Ingo Molnar , Sami Tolvanen , Laura Abbott , Dave Martin , Jann Horn , Steven Rostedt , linux-arm-kernel@lists.infradead.org, Michal Marek , Ard Biesheuvel , Nick Desaulniers , linux-kernel@vger.kernel.org, Miguel Ojeda , James Morse , Masami Hiramatsu Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Apr 22, 2020 at 06:39:47PM +0100, Will Deacon wrote: > On Mon, Apr 20, 2020 at 02:18:30PM -0700, Sami Tolvanen wrote: > > On Mon, Apr 20, 2020 at 06:17:28PM +0100, Will Deacon wrote: > > > > + * The shadow call stack is aligned to SCS_SIZE, and grows > > > > + * upwards, so we can mask out the low bits to extract the base > > > > + * when the task is not running. > > > > + */ > > > > + return (void *)((unsigned long)task_scs(tsk) & ~(SCS_SIZE - 1)); > > > > > > Could we avoid forcing this alignment it we stored the SCS pointer as a > > > (base,offset) pair instead? That might be friendlier on the allocations > > > later on. > > > > The idea is to avoid storing the current task's shadow stack address in > > memory, which is why I would rather not store the base address either. > > What I mean is that, instead of storing the current shadow stack pointer, > we instead store a base and an offset. We can still clear the base, as you > do with the pointer today, and I don't see that the offset is useful to > an attacker on its own. > > But more generally, is it really worthwhile to do this clearing at all? Can > you (or Kees?) provide some justification for it, please? We don't do it > for anything else, e.g. the pointer authentication keys, so something > feels amiss here. It's a hardening step to just reduce the lifetime of a valid address exposed in memory. In fact, since there is a cache, I think it should be wiped even in scs_release(). -- Kees Cook _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel