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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 9B7F8C48BE6 for ; Wed, 16 Jun 2021 20:49:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CDC661076 for ; Wed, 16 Jun 2021 20:49:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233710AbhFPUwE (ORCPT ); Wed, 16 Jun 2021 16:52:04 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:49094 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233632AbhFPUwA (ORCPT ); Wed, 16 Jun 2021 16:52:00 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1ltcTw-00ASGj-NA; Wed, 16 Jun 2021 14:49:52 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=email.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1ltcTv-001WUp-L5; Wed, 16 Jun 2021 14:49:52 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Al Viro Cc: Linus Torvalds , Michael Schmitz , linux-arch , Jens Axboe , Oleg Nesterov , Linux Kernel Mailing List , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , Geert Uytterhoeven , linux-m68k , Arnd Bergmann , Ley Foon Tan , Tejun Heo , Kees Cook References: <924ec53c-2fd9-2e1c-bbb1-3fda49809be4@gmail.com> <87eed4v2dc.fsf@disp2133> <5929e116-fa61-b211-342a-c706dcb834ca@gmail.com> <87fsxjorgs.fsf@disp2133> <87zgvqor7d.fsf_-_@disp2133> <87mtrpg47k.fsf@disp2133> <87pmwlek8d.fsf_-_@disp2133> <87eed1ek31.fsf_-_@disp2133> Date: Wed, 16 Jun 2021 15:49:44 -0500 In-Reply-To: (Al Viro's message of "Wed, 16 Jun 2021 20:28:54 +0000") Message-ID: <87lf798rh3.fsf@disp2133> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1ltcTv-001WUp-L5;;;mid=<87lf798rh3.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+tvGfrhmCRiEkshSDUtMHfA0mFIPg5PpQ= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 2/2] alpha/ptrace: Add missing switch_stack frames X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Al Viro writes: > On Wed, Jun 16, 2021 at 08:25:35PM +0000, Al Viro wrote: >> On Wed, Jun 16, 2021 at 01:32:50PM -0500, Eric W. Biederman wrote: >> >> > -.macro fork_like name >> > +.macro allregs name >> > .align 4 >> > .globl alpha_\name >> > .ent alpha_\name >> > + .cfi_startproc >> > alpha_\name: >> > .prologue 0 >> > - bsr $1, do_switch_stack >> > + SAVE_SWITCH_STACK >> > jsr $26, sys_\name >> > - ldq $26, 56($sp) >> > - lda $sp, SWITCH_STACK_SIZE($sp) >> > + RESTORE_SWITCH_STACK >> >> No. You've just added one hell of an overhead to fork(2), >> for no reason whatsoever. sys_fork() et.al. does *NOT* modify the >> callee-saved registers; it's plain C. So this change is complete >> BS. >> >> > +allregs exit >> > +allregs exit_group >> >> Details, please - what exactly makes exit(2) different from >> e.g. open(2)? > > Ah... PTRACE_EVENT_EXIT garbage, fortunately having no counterparts in case of > open(2)... Still, WTF would you want to restore callee-saved registers for > in case of exit(2)? Someone might want or try to read them in the case of exit. Which without some change will result in a read of other kernel stack content on alpha. Plus there are coredumps which definitely want to read everything. Although admittedly that case no longer matters. Eric