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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 8F588C04AAA for ; Fri, 3 May 2019 16:31:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6A9F62081C for ; Fri, 3 May 2019 16:31:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728405AbfECQbb convert rfc822-to-8bit (ORCPT ); Fri, 3 May 2019 12:31:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:33238 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726633AbfECQbb (ORCPT ); Fri, 3 May 2019 12:31:31 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 322E620651; Fri, 3 May 2019 16:31:28 +0000 (UTC) Date: Fri, 3 May 2019 12:31:26 -0400 From: Steven Rostedt To: Andy Lutomirski Cc: Peter Zijlstra , Linus Torvalds , Linux List Kernel Mailing , Ingo Molnar , Andrew Morton , Andy Lutomirski , Nicolai Stange , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , the arch/x86 maintainers , Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Joe Lawrence , Shuah Khan , Konrad Rzeszutek Wilk , Tim Chen , Sebastian Andrzej Siewior , Mimi Zohar , Juergen Gross , Nick Desaulniers , Nayna Jain , Masahiro Yamada , Joerg Roedel , "open list:KERNEL SELFTEST FRAMEWORK" , stable Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions Message-ID: <20190503123126.3a2801be@gandalf.local.home> In-Reply-To: <2045370D-38D8-406C-9E94-C1D483E232C9@amacapital.net> References: <20190501203152.397154664@goodmis.org> <20190501232412.1196ef18@oasis.local.home> <20190502162133.GX2623@hirez.programming.kicks-ass.net> <20190502181811.GY2623@hirez.programming.kicks-ass.net> <20190502202146.GZ2623@hirez.programming.kicks-ass.net> <20190502185225.0cdfc8bc@gandalf.local.home> <20190502193129.664c5b2e@gandalf.local.home> <20190502195052.0af473cf@gandalf.local.home> <20190503092959.GB2623@hirez.programming.kicks-ass.net> <20190503092247.20cc1ff0@gandalf.local.home> <2045370D-38D8-406C-9E94-C1D483E232C9@amacapital.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 3 May 2019 09:20:55 -0700 Andy Lutomirski wrote: > So here’s a somewhat nutty suggestion: how about we tweak the 32-bit entry code to emulate the sane 64-bit frame, not just for int3 but always? Basically, the entry asm for entries from kernel mode would do, roughly: > > push $0 ;dummy for call emulation > push %ss > push $0 ;a dummy for ESP > push 3*4(%esp) ;EFLAGS > push 3*4(%esp) ;CS > push 3*4(%esp) ;EIP > push %rax > lea 7*4(%esp), %rax > mov %rax, 4*4(%esp) ;ESP > > And the exit asm would do a little dance to write EFLAGS, CS, and EIP to the right spot, then load ESP-3*4 into %esp and do IRET. > > Now the annoying kernel_stack_pointer() hack can just go away, since regs->sp is always correct! > > I probably screwed up some arithmetic there, but it’s the idea that counts :) Yeah, as it will end up with: $0 ; dummy for call emulation %ss $0 ; dummy for ESP EIP $0 %ss $0 As 3 only gets you over what you already pushed. I think 5*4 is what you want. I guess the real question is, what's the performance impact of doing that? Although, this is only needed for kernel -> kernel exceptions, which are hopefully a rarity. -- Steve