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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham 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 0C191ECDE44 for ; Wed, 31 Oct 2018 09:37:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C389620821 for ; Wed, 31 Oct 2018 09:37:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="ScM0FWYk" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C389620821 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728102AbeJaSeg (ORCPT ); Wed, 31 Oct 2018 14:34:36 -0400 Received: from merlin.infradead.org ([205.233.59.134]:35302 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727436AbeJaSef (ORCPT ); Wed, 31 Oct 2018 14:34:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=G0893bgA/y7iXzmJuJJEVe9WVnnsrWSG6x1JuEa+NgM=; b=ScM0FWYkYbf/CLCPPDd73lfwM 897SU9uP4fuMmkc9waT5p56RwxfAgMpMFZEo1aJjb6mf8eFn3vODDpK5CocZEdpWjxbhxWNQ9uEHN IUEcJYfBJhm/V3GC8ZHWXyEPB2YWe8G/YlmpuZ1JCLoxVZdNxCflEYq3vVVNDJZpRFAB4ahh5Wf5v /uGE9HR0w6FrbHPodGKHfAkkj6QmcD/5TFPce9EUlvPoPXwkSlHlGRyS36E3qfhb6MbbFpyrqqQdb FP/++d19zyCqKfej6Tvz7/rIlbCjb43R0TmwD18UWLrVEueyKU7cYWRB0Ln2Xl0bleGY+FZfP9sGp eZghIjyCQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gHmvt-0002ZX-9f; Wed, 31 Oct 2018 09:37:01 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BF0032029FA14; Wed, 31 Oct 2018 10:36:59 +0100 (CET) Date: Wed, 31 Oct 2018 10:36:59 +0100 From: Peter Zijlstra To: Matthew Wilcox Cc: Andy Lutomirski , Kees Cook , Igor Stoppa , Mimi Zohar , Dave Chinner , James Morris , Michal Hocko , Kernel Hardening , linux-integrity , linux-security-module , Igor Stoppa , Dave Hansen , Jonathan Corbet , Laura Abbott , Randy Dunlap , Mike Rapoport , "open list:DOCUMENTATION" , LKML , Thomas Gleixner Subject: Re: [PATCH 10/17] prmem: documentation Message-ID: <20181031093659.GL744@hirez.programming.kicks-ass.net> References: <20181023213504.28905-1-igor.stoppa@huawei.com> <20181023213504.28905-11-igor.stoppa@huawei.com> <20181026092609.GB3159@worktop.c.hoisthospitality.com> <20181028183126.GB744@hirez.programming.kicks-ass.net> <40cd77ce-f234-3213-f3cb-0c3137c5e201@gmail.com> <20181030152641.GE8177@hirez.programming.kicks-ass.net> <0A7AFB50-9ADE-4E12-B541-EC7839223B65@amacapital.net> <20181030175814.GB10491@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181030175814.GB10491@bombadil.infradead.org> 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 Tue, Oct 30, 2018 at 10:58:14AM -0700, Matthew Wilcox wrote: > On Tue, Oct 30, 2018 at 10:06:51AM -0700, Andy Lutomirski wrote: > > > On Oct 30, 2018, at 9:37 AM, Kees Cook wrote: > > I support the addition of a rare-write mechanism to the upstream kernel. > > And I think that there is only one sane way to implement it: using an > > mm_struct. That mm_struct, just like any sane mm_struct, should only > > differ from init_mm in that it has extra mappings in the *user* region. > > I'd like to understand this approach a little better. In a syscall path, > we run with the user task's mm. What you're proposing is that when we > want to modify rare data, we switch to rare_mm which contains a > writable mapping to all the kernel data which is rare-write. > > So the API might look something like this: > > void *p = rare_alloc(...); /* writable pointer */ > p->a = x; > q = rare_protect(p); /* read-only pointer */ > > To subsequently modify q, > > p = rare_modify(q); > q->a = y; > rare_protect(p); Why would you have rare_alloc() imply rare_modify() ? Would you have the allocator meta data inside the rare section?