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 76984C2BA2B for ; Sun, 19 Apr 2020 08:06:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A33421744 for ; Sun, 19 Apr 2020 08:06:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725970AbgDSIGs (ORCPT ); Sun, 19 Apr 2020 04:06:48 -0400 Received: from verein.lst.de ([213.95.11.211]:35721 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725903AbgDSIGs (ORCPT ); Sun, 19 Apr 2020 04:06:48 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 820AB68BEB; Sun, 19 Apr 2020 10:06:46 +0200 (CEST) Date: Sun, 19 Apr 2020 10:06:46 +0200 From: Christoph Hellwig To: Christophe Leroy Cc: Christoph Hellwig , Andrew Morton , Alexander Viro , Arnd Bergmann , linux-kernel@vger.kernel.org, Jeremy Kerr , linux-fsdevel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "Eric W . Biederman" Subject: Re: [PATCH 8/8] exec: open code copy_string_kernel Message-ID: <20200419080646.GE12222@lst.de> References: <20200414070142.288696-1-hch@lst.de> <20200414070142.288696-9-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 18, 2020 at 10:15:42AM +0200, Christophe Leroy wrote: > > > Le 14/04/2020 à 09:01, Christoph Hellwig a écrit : >> Currently copy_string_kernel is just a wrapper around copy_strings that >> simplifies the calling conventions and uses set_fs to allow passing a >> kernel pointer. But due to the fact the we only need to handle a single >> kernel argument pointer, the logic can be sigificantly simplified while >> getting rid of the set_fs. > > > Instead of duplicating almost identical code, can you write a function that > takes whether the source is from user or from kernel, then you just do > things like: > > if (from_user) > len = strnlen_user(str, MAX_ARG_STRLEN); > else > len = strnlen(str, MAX_ARG_STRLEN); > > > if (from_user) > copy_from_user(kaddr+offset, str, bytes_to_copy); > else > memcpy(kaddr+offset, str, bytes_to_copy); We'll need two different str variables then with and without __user annotations to keep type safety. And introduce a branch-y and unreadable mess in the exec fast path instead of adding a simple and well understood function for the kernel case that just deals with the much simpler case of just copying a single arg vector from a kernel address. 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 9B133C2BA2B for ; Sun, 19 Apr 2020 08:18:30 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4EC622145D for ; Sun, 19 Apr 2020 08:18:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4EC622145D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 494jQD5f0kzDrFD for ; Sun, 19 Apr 2020 18:18:28 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=lst.de (client-ip=213.95.11.211; helo=verein.lst.de; envelope-from=hch@lst.de; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=lst.de Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 494j8n6rnxzDrNR for ; Sun, 19 Apr 2020 18:06:49 +1000 (AEST) Received: by verein.lst.de (Postfix, from userid 2407) id 820AB68BEB; Sun, 19 Apr 2020 10:06:46 +0200 (CEST) Date: Sun, 19 Apr 2020 10:06:46 +0200 From: Christoph Hellwig To: Christophe Leroy Subject: Re: [PATCH 8/8] exec: open code copy_string_kernel Message-ID: <20200419080646.GE12222@lst.de> References: <20200414070142.288696-1-hch@lst.de> <20200414070142.288696-9-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Eric W . Biederman" , Arnd Bergmann , linux-kernel@vger.kernel.org, Jeremy Kerr , linux-fsdevel@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org, Christoph Hellwig , Alexander Viro Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Sat, Apr 18, 2020 at 10:15:42AM +0200, Christophe Leroy wrote: > > > Le 14/04/2020 à 09:01, Christoph Hellwig a écrit : >> Currently copy_string_kernel is just a wrapper around copy_strings that >> simplifies the calling conventions and uses set_fs to allow passing a >> kernel pointer. But due to the fact the we only need to handle a single >> kernel argument pointer, the logic can be sigificantly simplified while >> getting rid of the set_fs. > > > Instead of duplicating almost identical code, can you write a function that > takes whether the source is from user or from kernel, then you just do > things like: > > if (from_user) > len = strnlen_user(str, MAX_ARG_STRLEN); > else > len = strnlen(str, MAX_ARG_STRLEN); > > > if (from_user) > copy_from_user(kaddr+offset, str, bytes_to_copy); > else > memcpy(kaddr+offset, str, bytes_to_copy); We'll need two different str variables then with and without __user annotations to keep type safety. And introduce a branch-y and unreadable mess in the exec fast path instead of adding a simple and well understood function for the kernel case that just deals with the much simpler case of just copying a single arg vector from a kernel address.