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=-3.8 required=3.0 tests=BAYES_00, 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 7B293C4741F for ; Sun, 1 Nov 2020 11:09:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 34E222084C for ; Sun, 1 Nov 2020 11:09:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726440AbgKALJy (ORCPT ); Sun, 1 Nov 2020 06:09:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726303AbgKALJx (ORCPT ); Sun, 1 Nov 2020 06:09:53 -0500 Received: from mout-p-101.mailbox.org (mout-p-101.mailbox.org [IPv6:2001:67c:2050::465:101]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16D07C0617A6; Sun, 1 Nov 2020 03:09:53 -0800 (PST) Received: from smtp2.mailbox.org (smtp2.mailbox.org [IPv6:2001:67c:2050:105:465:1:2:0]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-101.mailbox.org (Postfix) with ESMTPS id 4CPCxT5LHFzQjy2; Sun, 1 Nov 2020 12:09:49 +0100 (CET) X-Virus-Scanned: amavisd-new at heinlein-support.de Received: from smtp2.mailbox.org ([80.241.60.241]) by gerste.heinlein-support.de (gerste.heinlein-support.de [91.198.250.173]) (amavisd-new, port 10030) with ESMTP id 0NqHY5bM4ywr; Sun, 1 Nov 2020 12:09:42 +0100 (CET) Date: Sun, 1 Nov 2020 12:09:35 +0100 From: Hagen Paul Pfeifer 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" , Idan Yaniv , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Thomas Gleixner , Shuah Khan , 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 Subject: Re: [PATCH v6 0/6] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20201101110935.GA4105325@laniakea> References: <20200924132904.1391-1-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200924132904.1391-1-rppt@kernel.org> X-Key-Id: 98350C22 X-Key-Fingerprint: 490F 557B 6C48 6D7E 5706 2EA2 4A22 8D45 9835 0C22 X-GPG-Key: gpg --recv-keys --keyserver wwwkeys.eu.pgp.net 98350C22 X-MBO-SPAM-Probability: * X-Rspamd-Score: 0.32 / 15.00 / 15.00 X-Rspamd-Queue-Id: EBDB416FE X-Rspamd-UID: bd1d51 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Mike Rapoport | 2020-09-24 16:28:58 [+0300]: >This is an implementation of "secret" mappings backed by a file descriptor. >I've dropped the boot time reservation patch for now as it is not strictly >required for the basic usage and can be easily added later either with or >without CMA. Isn't memfd_secret currently *unnecessarily* designed to be a "one task feature"? memfd_secret fulfills exactly two (generic) features: - address space isolation from kernel (aka SECRET_EXCLUSIVE, not in kernel's direct map) - hide from kernel, great - disabling processor's memory caches against speculative-execution vulnerabilities (spectre and friends, aka SECRET_UNCACHED), also great But, what about the following use-case: implementing a hardened IPC mechanism where even the kernel is not aware of any data and optionally via SECRET_UNCACHED even the hardware caches are bypassed! With the patches we are so close to achieving this. How? Shared, SECRET_EXCLUSIVE and SECRET_UNCACHED mmaped pages for IPC involved tasks required to know this mapping (and memfd_secret fd). After IPC is done, tasks can copy sensitive data from IPC pages into memfd_secret() pages, un-sensitive data can be used/copied everywhere. One missing piece is still the secure zeroization of the page(s) if the mapping is closed by last process to guarantee a secure cleanup. This can probably done as an general mmap feature, not coupled to memfd_secret() and can be done independently ("reverse" MAP_UNINITIALIZED feature). PS: thank you Mike for your effort! See the following pseudo-code as an example: // simple assume file-descriptor and mapping is inherited // by child for simplicity, ptr is int fd = memfd_secret(SECRETMEM_UNCACHED); ftruncate(fd, PAGE_SIZE); uint32_t *ptr = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); pid_t pid_other; void signal_handler(int sig) { // update IPC data on shared, uncachaed, exclusive mapped page *ptr += 1; // inform other sleep(1); kill(pid_other, SIGUSR1); } void ipc_loop(void) { signal(SIGUSR1, signal_handler); while (1) { sleep(1); } } int main(void) { pid_t child_pid; switch (child_pid = fork()) { case 0: pid_other = getppid(); break; default: pid_other = child_pid break; } ipc_loop(); } Hagen