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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 4A460C64E7A for ; Tue, 1 Dec 2020 19:01:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E1F432151B for ; Tue, 1 Dec 2020 19:01:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729737AbgLATBj (ORCPT ); Tue, 1 Dec 2020 14:01:39 -0500 Received: from mail.kernel.org ([198.145.29.99]:44494 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725933AbgLATBj (ORCPT ); Tue, 1 Dec 2020 14:01:39 -0500 Received: from gaia (unknown [95.146.230.165]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AD93720643; Tue, 1 Dec 2020 19:00:54 +0000 (UTC) Date: Tue, 1 Dec 2020 19:00:52 +0000 From: Catalin Marinas To: Andy Lutomirski Cc: linux-arch , Brian Gerst , LKML , X86 ML , Borislav Petkov , Thomas Gleixner , Jan Kara , =?utf-8?B?UGF3ZcWC?= Jasiak , Russell King Subject: Re: [PATCH] fanotify: Fix sys_fanotify_mark() on native x86-32 Message-ID: <20201201190051.GB2502@gaia> References: <20201130223059.101286-1-brgerst@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Tue, Dec 01, 2020 at 09:34:32AM -0800, Andy Lutomirski wrote: > On Tue, Dec 1, 2020 at 9:23 AM Andy Lutomirski wrote: > > On Mon, Nov 30, 2020 at 2:31 PM Brian Gerst wrote: > > > Commit 121b32a58a3a converted native x86-32 which take 64-bit arguments to > > > use the compat handlers to allow conversion to passing args via pt_regs. > > > sys_fanotify_mark() was however missed, as it has a general compat handler. > > > Add a config option that will use the syscall wrapper that takes the split > > > args for native 32-bit. > > > > > > Reported-by: Paweł Jasiak > > > Fixes: 121b32a58a3a ("x86/entry/32: Use IA32-specific wrappers for syscalls taking 64-bit arguments") > > > Signed-off-by: Brian Gerst > > > --- > > > arch/Kconfig | 6 ++++++ > > > arch/x86/Kconfig | 1 + > > > fs/notify/fanotify/fanotify_user.c | 17 +++++++---------- > > > include/linux/syscalls.h | 24 ++++++++++++++++++++++++ > > > 4 files changed, 38 insertions(+), 10 deletions(-) > > > > > > diff --git a/arch/Kconfig b/arch/Kconfig > > > index 090ef3566c56..452cc127c285 100644 > > > --- a/arch/Kconfig > > > +++ b/arch/Kconfig > > > @@ -1045,6 +1045,12 @@ config HAVE_STATIC_CALL_INLINE > > > bool > > > depends on HAVE_STATIC_CALL > > > > > > +config ARCH_SPLIT_ARG64 > > > + bool > > > + help > > > + If a 32-bit architecture requires 64-bit arguments to be split into > > > + pairs of 32-bit arguemtns, select this option. > > > > You misspelled arguments. You might also want to clarify that, for > > 64-bit arches, this means that compat syscalls split their arguments. > > No, that's backwards. Maybe it should be depends !64BIT instead. > > But I'm really quite confused about something: what's special about > x86 here? Are there really Linux arches (compat or 32-bit native) > that *don't* split arguments like this? Sure, some arches probably > work the same way that x86 used to in which the compiler did the > splitting by magic for us, but that was always a bit of a kludge. On arm32 we rely on the compiler splitting a 64-bit argument in two consecutive registers. But I wouldn't say it's a kludge (well, mostly) as that's part of the arm procedure calling standard. Currently arm32 doesn't pass the syscall arguments through a read from pt_regs, so all is handled transparently. On arm64 compat, we need to re-assemble the arguments with some wrappers explicitly (arch/arm64/kernel/sys32.c) or call the generic wrapper like in the compat_sys_fanotify_mark() case. > Could this change maybe be made unconditional? I think it's fine in this particular case. I don't think it's valid in general because of the arm (and maybe others) requirement that the first register of a 64-bit argument is an even number (IIRC, Russell should know better). If the u64 mask was an argument before or after the current position, the compiler would have introduced a pad register but not if the arg is split in two u32. -- Catalin