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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 26C57C2D0E7 for ; Wed, 25 Mar 2020 20:27:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0F532076F for ; Wed, 25 Mar 2020 20:27:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="V04eeOZm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727395AbgCYU1G (ORCPT ); Wed, 25 Mar 2020 16:27:06 -0400 Received: from mail-pl1-f195.google.com ([209.85.214.195]:39402 "EHLO mail-pl1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727236AbgCYU1F (ORCPT ); Wed, 25 Mar 2020 16:27:05 -0400 Received: by mail-pl1-f195.google.com with SMTP id m1so1252719pll.6 for ; Wed, 25 Mar 2020 13:27:05 -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=6SzOvwdTQqkZQCjlviRpZUVdzAyX4BMCYO6WRGnsRMg=; b=V04eeOZmpXZz9+n2K8s89RAUlNtFI2i3/IBt6L+R3HaP2VRpUcKrX06reMGWIzc2c+ XwtCJxYWfVvX423KhbuO1h44rQttz9YLq0WAz9cdrMlR19jmIZbXEYme+Erycyi1IU2U 88GPKoBsjo0xyDjf5T8gvQ6OIx9M3dosv2wAo= 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=6SzOvwdTQqkZQCjlviRpZUVdzAyX4BMCYO6WRGnsRMg=; b=HbjsVlx7XPkzyKEDrHNZxOgxe7jQTgopYwkXe00td2eV7e+Q+EX+iIYPwAqmsxvsBs IEakTM7O+JveXTk4xWuY3hxRw+LhNb+liHG6Uh5yGYaPLTNlRAmVvPRjD2kSWcQgU8mX R1I8ftfPOp/qI9Y7/svHmcd3n7Kl93pvEGWWZLLeMcOSK2LUIt+oRHgspt9qbYZiq103 TYCXM5C7V7x4kqLlb2dfFjCtGUGlfbVCI2v6wwmQ/fZoJt2af+sa660aO5R+OXvt2Mdp 0B6iPXuESRdyan36cJ1f6Y+G+eE6UbaQ8JohYg3JXTgY1ZYm5mMnbExXve/pX97h1sU3 sNvA== X-Gm-Message-State: ANhLgQ2b71pCsv+PLiLmsruh8OMqELF9e2JKpGnvimpUDNG0fiXiSxwK EvV80znhRMqMWfg9R1YgJmp5Gw== X-Google-Smtp-Source: ADFU+vswtN+46ClgfmDrS2YQ0+gwH0oaxyACQpe8SmgU+n/NeZSp3mJwpEGmc/BXB2B7g4eNvcGW5w== X-Received: by 2002:a17:902:fe97:: with SMTP id x23mr4918671plm.167.1585168024550; Wed, 25 Mar 2020 13:27:04 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id n22sm100777pjq.36.2020.03.25.13.27.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2020 13:27:03 -0700 (PDT) Date: Wed, 25 Mar 2020 13:27:02 -0700 From: Kees Cook To: "Reshetova, Elena" Cc: Jann Horn , Thomas Gleixner , the arch/x86 maintainers , Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Mark Rutland , Alexander Potapenko , Ard Biesheuvel , Kernel Hardening , "linux-arm-kernel@lists.infradead.org" , Linux-MM , kernel list Subject: Re: [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Message-ID: <202003251322.180F2536E@keescook> References: <20200324203231.64324-1-keescook@chromium.org> <202003241604.7269C810B@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 25, 2020 at 12:15:12PM +0000, Reshetova, Elena wrote: > > > Also, are you sure that it isn't possible to make the syscall that > > > leaked its stack pointer never return to userspace (via ptrace or > > > SIGSTOP or something like that), and therefore never realign its > > > stack, while keeping some controlled data present on the syscall's > > > stack? > > How would you reliably detect that a stack pointer has been leaked > to userspace while it has been in a syscall? Does not seem to be a trivial > task to me. Well, my expectation is that folks using this defense are also using panic_on_warn sysctl, etc, so attackers don't get a chance to actually _use_ register values spilled to dmesg. -- Kees Cook