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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 4752EC4360C for ; Wed, 25 Sep 2019 17:09:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 26F572146E for ; Wed, 25 Sep 2019 17:09:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408247AbfIYRJ0 (ORCPT ); Wed, 25 Sep 2019 13:09:26 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:50645 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731087AbfIYRJZ (ORCPT ); Wed, 25 Sep 2019 13:09:25 -0400 Received: from [185.81.138.21] (helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1iDAmo-0006nz-HU; Wed, 25 Sep 2019 17:09:06 +0000 Date: Wed, 25 Sep 2019 19:09:04 +0200 From: Christian Brauner To: Aleksa Sarai Cc: Ingo Molnar , Peter Zijlstra , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Rasmus Villemoes , Al Viro , Linus Torvalds , libc-alpha@sourceware.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1 0/4] lib: introduce copy_struct_from_user() helper Message-ID: <20190925170903.6ssligvk3gpbnwtq@wittgenstein> References: <20190925165915.8135-1-cyphar@cyphar.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190925165915.8135-1-cyphar@cyphar.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 25, 2019 at 06:59:11PM +0200, Aleksa Sarai wrote: > This series was split off from the openat2(2) syscall discussion[1]. > However, the copy_struct_to_user() helper has been dropped, because > after some discussion it appears that there is no really obvious > semantics for how copy_struct_to_user() should work on mixed-vintages > (for instance, whether [2] is the correct semantics for all syscalls). > > A common pattern for syscall extensions is increasing the size of a > struct passed from userspace, such that the zero-value of the new fields > result in the old kernel behaviour (allowing for a mix of userspace and > kernel vintages to operate on one another in most cases). > > Previously there was no common lib/ function that implemented > the necessary extension-checking semantics (and different syscalls > implemented them slightly differently or incompletely[3]). This series > implements the helper and ports several syscalls to use it. > > [1]: https://lore.kernel.org/lkml/20190904201933.10736-1-cyphar@cyphar.com/ > > [2]: commit 1251201c0d34 ("sched/core: Fix uclamp ABI bug, clean up and > robustify sched_read_attr() ABI logic and code") > > [3]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do > similar checks to copy_struct_from_user() while rt_sigprocmask(2) > always rejects differently-sized struct arguments. Thank for splitting this out! :) I should be able to review this tomorrow. Christian