From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from zeniv.linux.org.uk ([195.92.253.2]:42980 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726261AbeIMHPO (ORCPT ); Thu, 13 Sep 2018 03:15:14 -0400 Date: Thu, 13 Sep 2018 03:07:57 +0100 From: Al Viro To: Arnd Bergmann Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 01/17] compat_ioctl: add generic_compat_ioctl_ptrarg() Message-ID: <20180913020757.GP19965@ZenIV.linux.org.uk> References: <20180912150142.157913-1-arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180912150142.157913-1-arnd@arndb.de> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Sep 12, 2018 at 05:01:02PM +0200, Arnd Bergmann wrote: > Many drivers have ioctl() handlers that are completely compatible > between 32-bit and 64-bit architectures, except for the argument > that is passed down from user space and may have to be passed > through compat_ptr() in order to become a valid 64-bit pointer. > > Using ".compat_ptr=generic_compat_ioctl_ptrarg" in file operations > should let us simplify a lot of those drivers to avoid #ifdef > checks, and convert additional drivers that don't have proper > compat handling yet. Just keep in mind that this should *only* be used when all ioctls implemented in a given instance do take pointers. Because otherwise you are asking for trouble - e.g. if one of them takes an u32 used as a bitmap, this will run into trouble as soon as somebody uses bit 31. With no visible warnings. IOW, it shouldn't be used blindly and it should come with big fat warning.