From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964893AbbLGXXZ (ORCPT ); Mon, 7 Dec 2015 18:23:25 -0500 Received: from mail-oi0-f51.google.com ([209.85.218.51]:34930 "EHLO mail-oi0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932589AbbLGXXV convert rfc822-to-8bit (ORCPT ); Mon, 7 Dec 2015 18:23:21 -0500 MIME-Version: 1.0 In-Reply-To: <5634DD68.4090709@list.ru> References: <66cb936904b7ce56ddc1ce58119bd9683e4f3b43.1445822498.git.luto@kernel.org> <5634DD68.4090709@list.ru> From: Andy Lutomirski Date: Mon, 7 Dec 2015 15:23:01 -0800 Message-ID: Subject: Re: [PATCH v2 1/4] x86/signal/64: Add a comment about sigcontext->fs and gs To: Stas Sergeev Cc: Denys Vlasenko , Borislav Petkov , Brian Gerst , "linux-kernel@vger.kernel.org" , X86 ML , Linus Torvalds Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Oct 31, 2015 8:25 AM, "Stas Sergeev" wrote: > > 26.10.2015 04:25, Andy Lutomirski пишет: > >> These fields have a strange history. This tries to document it. >> >> This borrows from 9a036b93a344 ("x86/signal/64: Remove 'fs' and 'gs' >> from sigcontext"), which was reverted by ed596cde9425 ("Revert x86 >> sigcontext cleanups"). >> >> Signed-off-by: Andy Lutomirski > > Now the strategy about SS is to always save it to the sigcontext. > This is good because the syscall can clobber it, so the app had > to be very careful in the past trying to save it by hands. > How about saving also fs and gs? (without restoring yet) > If you do, you'll save dosemu a headache of doing any "pre-syscall" > work. Pre-syscall work is very nasty. > I haven't checked if the syscall clobber also these or only SS, > but perhaps saving them by the kernel won't hurt? There's a bunch of ongoing work about FS and GS. I want to wait and see.