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 DD47FC433DB for ; Tue, 26 Jan 2021 11:13:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A5E7723108 for ; Tue, 26 Jan 2021 11:13:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388076AbhAZLNS (ORCPT ); Tue, 26 Jan 2021 06:13:18 -0500 Received: from mx2.suse.de ([195.135.220.15]:44972 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727223AbhAZHRG (ORCPT ); Tue, 26 Jan 2021 02:17:06 -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=1611645376; 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=Rfz4YhgMdQKfWEhdPjTzowRS8ZrfPb0PZUsBEItApiI=; b=uSwnbNJryXqrtFn5ZDcik0uto2+MPvheE1cGTKIEOz6ZnfiLtVVNW3xYyy9RGpwnpMhlvH 1N3K5WJgiIeLyB1+A5OyZuJP2Jkezi6uvJEEzgHe7uQUCBH5hRl4x8iwIwlEA1xmTBtqZQ dR3KQIpKfgXY/BC62Y8U0m9xExJlGg8= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 5743EAE91; Tue, 26 Jan 2021 07:16:16 +0000 (UTC) Date: Tue, 26 Jan 2021 08:16:14 +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: <20210126071614.GX827@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210125213618.GL6332@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Please make sure to describe all those details in the changelog. -- Michal Hocko SUSE Labs