From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 5D75E6B0005 for ; Thu, 29 Mar 2018 10:55:29 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id u68so2769822wmd.5 for ; Thu, 29 Mar 2018 07:55:29 -0700 (PDT) Received: from isilmar-4.linta.de (isilmar-4.linta.de. [136.243.71.142]) by mx.google.com with ESMTPS id f193si1468891wme.136.2018.03.29.07.55.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Mar 2018 07:55:27 -0700 (PDT) Date: Thu, 29 Mar 2018 16:55:26 +0200 From: Dominik Brodowski Subject: Re: [PATCH 000/109] remove in-kernel calls to syscalls Message-ID: <20180329145526.GA1414@isilmar-4.linta.de> References: <20180329112426.23043-1-linux@dominikbrodowski.net> <20180329142027.GA24860@bombadil.infradead.org> <20180329144209.GA25559@isilmar-4.linta.de> <07438b1e94ff42a184adb7134a680069@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <07438b1e94ff42a184adb7134a680069@AcuMS.aculab.com> Sender: owner-linux-mm@kvack.org List-ID: To: David Laight Cc: Matthew Wilcox , "linux-kernel@vger.kernel.org" , "viro@ZenIV.linux.org.uk" , "torvalds@linux-foundation.org" , "arnd@arndb.de" , "linux-arch@vger.kernel.org" , "hmclauchlan@fb.com" , "tautschn@amazon.co.uk" , Amir Goldstein , Andi Kleen , Andrew Morton , Christoph Hellwig , Darren Hart , "David S . Miller" , "Eric W . Biederman" , "H . Peter Anvin" , Ingo Molnar , Jaswinder Singh , Jeff Dike , Jiri Slaby , "kexec@lists.infradead.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-s390@vger.kernel.org" , "Luis R . Rodriguez" , "netdev@vger.kernel.org" , Peter Zijlstra , Thomas Gleixner , "user-mode-linux-devel@lists.sourceforge.net" , "x86@kernel.org" On Thu, Mar 29, 2018 at 02:46:44PM +0000, David Laight wrote: > From: Dominik Brodowski > > Sent: 29 March 2018 15:42 > > On Thu, Mar 29, 2018 at 07:20:27AM -0700, Matthew Wilcox wrote: > > > On Thu, Mar 29, 2018 at 01:22:37PM +0200, Dominik Brodowski wrote: > > > > At least on 64-bit x86, it will likely be a hard requirement from v4.17 > > > > onwards to not call system call functions in the kernel: It is better to > > > > use use a different calling convention for system calls there, where > > > > struct pt_regs is decoded on-the-fly in a syscall wrapper which then hands > > > > processing over to the actual syscall function. This means that only those > > > > parameters which are actually needed for a specific syscall are passed on > > > > during syscall entry, instead of filling in six CPU registers with random > > > > user space content all the time (which may cause serious trouble down the > > > > call chain).[*] > > > > > > How do we stop new ones from springing up? Some kind of linker trick > > > like was used to, er, "dissuade" people from using gets()? > > > > Once the patches which modify the syscall calling convention are merged, > > it won't compile on 64-bit x86, but bark loudly. That should frighten anyone. > > Meow. > > Should be pretty easy to ensure the prototypes aren't in any normal header. That's exactly why the compile will fail. > Renaming the global symbols (to not match the function name) will make it > much harder to call them as well. That still depends on the exact design of the patchset, which is still under review. Thanks, Dominik