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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 7533FC55185 for ; Wed, 22 Apr 2020 18:00:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4EB312082E for ; Wed, 22 Apr 2020 18:00:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587578449; bh=NABYNKvs9sdWR1s9Ukqb7xA7e+KXEGWr4qmakQtX2oQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=e5iirHoedKiYXZg+8pfx9dzazQd1ho8TTGvdAYa1R2zlhsCa0kYEjn1SZtumt9aHH 9nZAkmHybB+14vYLelYqqli72UvemjjVRizxjGslvsGBgNz8Izh1OQcSB9Qd1EGRf2 GExe2QyCJhoQ5cENBJAIiRlo4W9H+1cDIC/5eWmc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726505AbgDVSAs (ORCPT ); Wed, 22 Apr 2020 14:00:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:54892 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726154AbgDVSAs (ORCPT ); Wed, 22 Apr 2020 14:00:48 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E90802076E; Wed, 22 Apr 2020 18:00:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587578447; bh=NABYNKvs9sdWR1s9Ukqb7xA7e+KXEGWr4qmakQtX2oQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bIWTCp0/uGUSMGuwWVLFng26QFFNEEyjpTIYnEYtTtH7rdtaX57uIzFs/BzvdR9ni ePP+N0LiLAOGVfPbD9BA0ZOSUWHgZJ8tEHTtYdx82R6CSL4NLvVuWj/VZ9123jk92Y AcNNFlBLukBMtR23rMiE1xDoXYGQUyefGhPfX8hc= Date: Wed, 22 Apr 2020 19:00:40 +0100 From: Will Deacon To: Kees Cook Cc: Sami Tolvanen , Catalin Marinas , James Morse , Steven Rostedt , Ard Biesheuvel , Mark Rutland , Masahiro Yamada , Michal Marek , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dave Martin , Laura Abbott , Marc Zyngier , Masami Hiramatsu , Nick Desaulniers , Jann Horn , Miguel Ojeda , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v12 01/12] add support for Clang's Shadow Call Stack (SCS) Message-ID: <20200422180040.GC3121@willie-the-truck> References: <20191018161033.261971-1-samitolvanen@google.com> <20200421021453.198187-1-samitolvanen@google.com> <20200421021453.198187-2-samitolvanen@google.com> <202004221052.489CCFEBC@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202004221052.489CCFEBC@keescook> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 22, 2020 at 10:54:45AM -0700, Kees Cook wrote: > On Mon, Apr 20, 2020 at 07:14:42PM -0700, Sami Tolvanen wrote: > > +void scs_release(struct task_struct *tsk) > > +{ > > + void *s; > > + > > + s = __scs_base(tsk); > > + if (!s) > > + return; > > + > > + WARN_ON(scs_corrupted(tsk)); > > + > > I'd like to have task_set_scs(tsk, NULL) retained here, to avoid need to > depend on the released task memory getting scrubbed at a later time. Hmm, doesn't it get zeroed almost immediately by kmem_cache_free() if INIT_ON_FREE_DEFAULT_ON is set? That seems much better than special-casing SCS, as there's a tonne of other useful stuff kicking around in the task_struct and treating this specially feels odd to me. Will