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=-6.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 80A53C433E0 for ; Tue, 26 Jan 2021 17:51:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 50DF822597 for ; Tue, 26 Jan 2021 17:51:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393508AbhAZRve (ORCPT ); Tue, 26 Jan 2021 12:51:34 -0500 Received: from mail.kernel.org ([198.145.29.99]:49116 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390210AbhAZIeJ (ORCPT ); Tue, 26 Jan 2021 03:34:09 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 80421221EB; Tue, 26 Jan 2021 08:33:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611650008; bh=H0L/s8b4ORCyoaJiNR4/K6IuwhLTXEpC4ZxQCe2ujf8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=EiBtPa6OHymra64Rxg1txloFiP5zjzCvuSlyIWVKmTvpUQdX/H67DIMK2i2Uuodnj +pJRik86ygJhPW3cqQpj8FV++iT2hrMKpDvLQYhvX44rTITRurUjen/zoJmMCQae3l Lcmo9GGwXJm85xFsIWywNeP7VUd2gTVus5ElWf7PtfH5tVV1lax9hRI14JSRV54lD0 87cNfRzXdbjKDvN/lHzsMDhXJYMYhdbs3ULnE6saF1L3DUJZ00q1I65E4c1szhEa/q NYwZ6iwhJfaJttOq3tbqFu9cHDCpuiTKRUJgeTaGGA94lPYwrOTfi1R7p0Odgfis+A brW+tXgU4OohQ== Date: Tue, 26 Jan 2021 10:33:11 +0200 From: Mike Rapoport To: Michal Hocko 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: <20210126083311.GN6332@kernel.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210126071614.GX827@dhcp22.suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > Please make sure to describe all those details in the changelog. -- Sincerely yours, Mike.