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=-5.8 required=3.0 tests=BAYES_00,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 B9956C433E6 for ; Tue, 26 Jan 2021 09:50:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 805EF22B37 for ; Tue, 26 Jan 2021 09:50:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726891AbhAZJuT (ORCPT ); Tue, 26 Jan 2021 04:50:19 -0500 Received: from mx2.suse.de ([195.135.220.15]:51674 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391617AbhAZJtv (ORCPT ); Tue, 26 Jan 2021 04:49:51 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611654544; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=osw4L0DyfBtcvVTgNeZhtou4RLCF+glHhzfn0pNfjYg=; b=umFtaF7Xp+88tywWv+IHw+GChi1pbTz5a0a/jUxktvgzyCsZINaZZCBo497bleXWAM+EaU GR3gp9zDi+MvoS/Bfup9r+ocJQrD+2eLOJm6arv0yMnJpQ/n5l0mmiAHda+EzLGkIzOcSy pFLJXF60F17xvk+8Oxor/2Ezl2/NIsE= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D1727AC4F; Tue, 26 Jan 2021 09:49:03 +0000 (UTC) Date: Tue, 26 Jan 2021 10:49:03 +0100 From: Michal Hocko To: Mike Rapoport Cc: Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , David Hildenbrand , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org, Hagen Paul Pfeifer , Palmer Dabbelt Subject: Re: [PATCH v16 06/11] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20210126094903.GI827@dhcp22.suse.cz> References: <20210121122723.3446-1-rppt@kernel.org> <20210121122723.3446-7-rppt@kernel.org> <20210125170122.GU827@dhcp22.suse.cz> <20210125213618.GL6332@kernel.org> <20210126071614.GX827@dhcp22.suse.cz> <20210126083311.GN6332@kernel.org> <20210126090013.GF827@dhcp22.suse.cz> <20210126092011.GP6332@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210126092011.GP6332@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Tue 26-01-21 11:20:11, Mike Rapoport wrote: > On Tue, Jan 26, 2021 at 10:00:13AM +0100, Michal Hocko wrote: > > On Tue 26-01-21 10:33:11, Mike Rapoport wrote: > > > On Tue, Jan 26, 2021 at 08:16:14AM +0100, Michal Hocko wrote: > > > > On Mon 25-01-21 23:36:18, Mike Rapoport wrote: > > > > > On Mon, Jan 25, 2021 at 06:01:22PM +0100, Michal Hocko wrote: > > > > > > On Thu 21-01-21 14:27:18, Mike Rapoport wrote: > > > > > > > From: Mike Rapoport > > > > > > > > > > > > > > Introduce "memfd_secret" system call with the ability to create memory > > > > > > > areas visible only in the context of the owning process and not mapped not > > > > > > > only to other processes but in the kernel page tables as well. > > > > > > > > > > > > > > The user will create a file descriptor using the memfd_secret() system > > > > > > > call. The memory areas created by mmap() calls from this file descriptor > > > > > > > will be unmapped from the kernel direct map and they will be only mapped in > > > > > > > the page table of the owning mm. > > > > > > > > > > > > > > The secret memory remains accessible in the process context using uaccess > > > > > > > primitives, but it is not accessible using direct/linear map addresses. > > > > > > > > > > > > > > Functions in the follow_page()/get_user_page() family will refuse to return > > > > > > > a page that belongs to the secret memory area. > > > > > > > > > > > > > > A page that was a part of the secret memory area is cleared when it is > > > > > > > freed. > > > > > > > > > > > > > > The following example demonstrates creation of a secret mapping (error > > > > > > > handling is omitted): > > > > > > > > > > > > > > fd = memfd_secret(0); > > > > > > > ftruncate(fd, MAP_SIZE); > > > > > > > ptr = mmap(NULL, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); > > > > > > > > > > > > I do not see any access control or permission model for this feature. > > > > > > Is this feature generally safe to anybody? > > > > > > > > > > The mappings obey memlock limit. Besides, this feature should be enabled > > > > > explicitly at boot with the kernel parameter that says what is the maximal > > > > > memory size secretmem can consume. > > > > > > > > Why is such a model sufficient and future proof? I mean even when it has > > > > to be enabled by an admin it is still all or nothing approach. Mlock > > > > limit is not really useful because it is per mm rather than per user. > > > > > > > > Is there any reason why this is allowed for non-privileged processes? > > > > Maybe this has been discussed in the past but is there any reason why > > > > this cannot be done by a special device which will allow to provide at > > > > least some permission policy? > > > > > > Why this should not be allowed for non-privileged processes? This behaves > > > similarly to mlocked memory, so I don't see a reason why secretmem should > > > have different permissions model. > > > > Because appart from the reclaim aspect it fragments the direct mapping > > IIUC. That might have an impact on all others, right? > > It does fragment the direct map, but first it only splits 1G pages to 2M > pages and as was discussed several times already it's not that clear which > page size in the direct map is the best and this is very much workload > dependent. I do appreciate this has been discussed but this changelog is not specific on any of that reasoning and I am pretty sure nobody will remember details in few years in the future. Also some numbers would be appropriate. > These are the results of the benchmarks I've run with the default direct > mapping covered with 1G pages, with disabled 1G pages using "nogbpages" in > the kernel command line and with the entire direct map forced to use 4K > pages using a simple patch to arch/x86/mm/init.c. > > https://docs.google.com/spreadsheets/d/1tdD-cu8e93vnfGsTFxZ5YdaEfs2E1GELlvWNOGkJV2U/edit?usp=sharing A good start for the data I am asking above. -- Michal Hocko SUSE Labs