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,URIBL_BLOCKED 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 B36F1C43219 for ; Fri, 3 May 2019 19:24:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E8BD2075E for ; Fri, 3 May 2019 19:24:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726572AbfECTYK (ORCPT ); Fri, 3 May 2019 15:24:10 -0400 Received: from mail.kernel.org ([198.145.29.99]:33752 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725789AbfECTYK (ORCPT ); Fri, 3 May 2019 15:24:10 -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 DC5E02075C; Fri, 3 May 2019 19:24:06 +0000 (UTC) Date: Fri, 3 May 2019 15:24:05 -0400 From: Steven Rostedt To: Linus Torvalds Cc: Peter Zijlstra , 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: <20190503152405.2d741af8@gandalf.local.home> In-Reply-To: References: <20190501202830.347656894@goodmis.org> <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> 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=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Thu, 2 May 2019 13:49:29 -0700 Linus Torvalds wrote: > On Thu, May 2, 2019 at 1:22 PM Peter Zijlstra wrote: > > > > Something like so; it boots; but I could've made some horrible mistake > > (again). > > This actually looks much better to me. > > Maybe it's more lines (I didn't check), but it's a lot simpler in that > now the magic of the int3 stack doesn't get exposed to anything else. > > We *could* also make this kernel-mode-only do_int3() be a special > function, and do something like > > # args: pt_regs pointer (no error code for int3) > movl %esp,%eax > # allocate a bit of extra room on the stack, so that > 'kernel_int3' can move the pt_regs > subl $8,%esp > call kernel_int3 > movl %eax,%esp > > and not do any stack switching magic in the asm code AT ALL. We'd do > > struct pt_regs *kernel_int3(struct pt_regs *regs) > { > .. > return regs; > } > > and now you the rule for call emulation ends up being that you need to > "memmove()" the ptregs up and down properly, and return the new > pt_regs pointer. > > Hmm? That would simplify the asm code further, but some people might > find it objectionable? > The problem with this approach is that it would require doing the same for x86_64, as the int3 C code is the same for both. And that may be a bit more difficult on the x86_64 side because it's all done with a simple flag in the idtentry macro to add the gap. -- Steve