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=-2.5 required=3.0 tests=MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT 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 BCDC0C04E87 for ; Fri, 17 May 2019 17:11:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 83D5F20848 for ; Fri, 17 May 2019 17:11:19 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 83D5F20848 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2415F6B0006; Fri, 17 May 2019 13:11:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1F1F96B0008; Fri, 17 May 2019 13:11:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0BB576B000A; Fri, 17 May 2019 13:11:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id B66766B0006 for ; Fri, 17 May 2019 13:11:18 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id n23so11578343edv.9 for ; Fri, 17 May 2019 10:11:18 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-original-authentication-results:x-gm-message-state:date:from:to :cc:subject:message-id:references:mime-version:content-disposition :in-reply-to:user-agent; bh=+4ze6Vjw9iqrs5snaXgX/vh42SSBU+Q84gO01wZY6oI=; b=SVNlK4r8qLFp9Bo265rHLXlIPJnEPjJi60LRIhZpkTltjvZNW8mil5SvBnPYjOdwys bPDTgelfXyXCQN/8F1QhKuMsv0HW8ZW4OwaRAwPwrLJVax6xgP5pOeJcGurBwVsMKERk wgavEhHZjfjfcB1t13ekTugEV9weTXaOiILhFnj0QSL0MCeRqLPvhMYDQbYyl/J/gYRi VE6F58+ZXoGGTx06/NHN4zMYH/Na3VckaMmVx3Kv8GetvNpQw6j6nNHgfyQ8Z6HQhuPR vEMcKSjX+tFsJpSn2E1VEJz7Ti66yQ6umkEe+ZqNxS8PL7eiHvFjZ+Abs9cG13ntMygP xe5Q== X-Original-Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Gm-Message-State: APjAAAXzxkU29nv+CpzWaReNjIxlB0aFX6lrRNafjo8ju7rr24CpnYET jXam0prWuLb9hu1bCI/ym0G0oJvGQ/mrKhVOzzoNZf3wfpDZEOcxFcfvmjAJkavG1dW/SzroHin CAFf7y6BrFQBDsf6/my/NH831TeQTuWWb5P1heaeMsZG+BRTMVPZ0VZ/kFTdhQnA= X-Received: by 2002:a17:906:4ed1:: with SMTP id i17mr45497403ejv.118.1558113078296; Fri, 17 May 2019 10:11:18 -0700 (PDT) X-Google-Smtp-Source: APXvYqw/NS53+GR7UGWnlOjckIXjvoZ4Ifi89ECmtw9luXtooBj7r2jpiEDrR8KKngUJaxagEy2r X-Received: by 2002:a17:906:4ed1:: with SMTP id i17mr45497274ejv.118.1558113076633; Fri, 17 May 2019 10:11:16 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1558113076; cv=none; d=google.com; s=arc-20160816; b=ss2Y6GVRldldBkGK+MSFkonZ88iKd+gXFzRKySPw45l2wQ5jgiMHammKZO7X8O28Va 1FDgaDpdDp9OIIi2PPMwYBsHS1NSEmSnd05iQ8yvLJWLfw5c8L3P0U0XAyKfgEDAIHi/ ywpozR3MEyCrBVOawT8fCcxqNostbiNJpBQ6jsnB2X0elMOeBFhZEVENWUANlTeRZO7F M5kE9XB1C5E4hQnVa8GJMEselvZncLWsqVPjIV4hzkNaafOye3j6EoLXxyK+/5J3GlwD zvVDdAGk4p3i9BXPz0mbNxXghbQWEAXHLdQ1Iah1VKlpc7JbPDHaU5zYuKQpH75hXseJ Zhjw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date; bh=+4ze6Vjw9iqrs5snaXgX/vh42SSBU+Q84gO01wZY6oI=; b=idZDt2jkgWVOX31bD0r6DJaHcfpgbibDW801ebSCmQreONtmtZMkJjh/04I87Aiwel ASMx8e5rOM47D+If/sgNigVkoUBEyNGMWVxgJq7BgH5ymcttjmK3oZeMAvG2GQ9a/zEO kf0LJM2TvWZWb1/+Puv3LYrtpekVANBNAxW5Vj4fdk9EMLAyGd1f+/eeXZRhYLX8xFxR PDKwidRyVPizEfhIaoLUMS738Qlm5Aste8/UY54UVpRaP0wGRacnQsBSOdy3LBlxIsEa pxRJ14FwqZvp11h/Z7lWWbKYAOHRBfPqYvezy7wArX/YKa76uNb4JIVx/AqQjcJ2vck2 zL4g== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id p56si4942345eda.176.2019.05.17.10.11.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 May 2019 10:11:16 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 29A57AEB0; Fri, 17 May 2019 17:11:16 +0000 (UTC) Date: Fri, 17 May 2019 19:11:15 +0200 From: Michal Hocko To: Kees Cook Cc: Alexander Potapenko , Andrew Morton , Christoph Lameter , Kernel Hardening , Masahiro Yamada , James Morris , "Serge E. Hallyn" , Nick Desaulniers , Kostya Serebryany , Dmitry Vyukov , Sandeep Patil , Laura Abbott , Randy Dunlap , Jann Horn , Mark Rutland , Linux Memory Management List , linux-security-module Subject: Re: [PATCH v2 1/4] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options Message-ID: <20190517170805.GS6836@dhcp22.suse.cz> References: <20190514143537.10435-1-glider@google.com> <20190514143537.10435-2-glider@google.com> <20190517140446.GA8846@dhcp22.suse.cz> <20190517142048.GM6836@dhcp22.suse.cz> <201905170928.A8F3BEC1B1@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201905170928.A8F3BEC1B1@keescook> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri 17-05-19 09:36:36, Kees Cook wrote: > On Fri, May 17, 2019 at 04:20:48PM +0200, Michal Hocko wrote: > > On Fri 17-05-19 16:11:32, Alexander Potapenko wrote: > > > On Fri, May 17, 2019 at 4:04 PM Michal Hocko wrote: > > > > > > > > On Tue 14-05-19 16:35:34, Alexander Potapenko wrote: > > > > > The new options are needed to prevent possible information leaks and > > > > > make control-flow bugs that depend on uninitialized values more > > > > > deterministic. > > > > > > > > > > init_on_alloc=1 makes the kernel initialize newly allocated pages and heap > > > > > objects with zeroes. Initialization is done at allocation time at the > > > > > places where checks for __GFP_ZERO are performed. > > > > > > > > > > init_on_free=1 makes the kernel initialize freed pages and heap objects > > > > > with zeroes upon their deletion. This helps to ensure sensitive data > > > > > doesn't leak via use-after-free accesses. > > > > > > > > Why do we need both? The later is more robust because even free memory > > > > cannot be sniffed and the overhead might be shifted from the allocation > > > > context (e.g. to RCU) but why cannot we stick to a single model? > > > init_on_free appears to be slower because of cache effects. It's > > > several % in the best case vs. <1% for init_on_alloc. > > > > This doesn't really explain why we need both. > > There are a couple reasons. The first is that once we have hardware with > memory tagging (e.g. arm64's MTE) we'll need both on_alloc and on_free > hooks to do change the tags. With MTE, zeroing comes for "free" with > tagging (though tagging is as slow as zeroing, so it's really the tagging > that is free...), so we'll need to re-use the init_on_free infrastructure. I am not sure I follow, but ... > > The second reason is for very paranoid use-cases where in-memory > data lifetime is desired to be minimized. There are various arguments > for/against the realism of the associated threat models, but given that > we'll need the infrastructre for MTE anyway, and there are people who > want wipe-on-free behavior no matter what the performance cost, it seems > reasonable to include it in this series. > > All that said, init_on_alloc looks desirable enough that distros will > likely build with it enabled by default (I hope), and the very paranoid > users will switch to (or additionally enable) init_on_free for their > systems. ... this should all be part of the changelog. -- Michal Hocko SUSE Labs