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=-1.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 44E93C64EAD for ; Tue, 9 Oct 2018 03:44:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 084F5214C2 for ; Tue, 9 Oct 2018 03:44:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Y1PgeYG5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 084F5214C2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726529AbeJIK64 (ORCPT ); Tue, 9 Oct 2018 06:58:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:51924 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726393AbeJIK64 (ORCPT ); Tue, 9 Oct 2018 06:58:56 -0400 Received: from devbox (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 CA3F62077C; Tue, 9 Oct 2018 03:44:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1539056646; bh=7wj4aMoFQ0dYpT7wtlEKeVqG8wIOflWbhKLJCv9luNk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Y1PgeYG5IVT9H6gyM83PXZn8lQSLfraReBb5ckWXevYrByYzYMlX6fWNk+f+v4lKa ecalwgVY7UTeutfd/Elg0NuS5yn1bmAefERgN4eKwvcyQzytZNpIxSUDTIbaZuKI6e 1bTCmacTRhBymVM/ykS9iU5ad2XF85+ZkeeZe+HQ= Date: Tue, 9 Oct 2018 12:44:01 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Linus Torvalds , Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Masami Hiramatsu , Mathieu Desnoyers , Matthew Helsley , "Rafael J . Wysocki" , David Woodhouse , Paolo Bonzini , Josh Poimboeuf , Jason Baron , Jiri Kosina Subject: Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function" Message-Id: <20181009124401.6005e2a39c760851aa54e600@kernel.org> In-Reply-To: <20181006015720.634688468@goodmis.org> References: <20181006015110.653946300@goodmis.org> <20181006015720.634688468@goodmis.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 05 Oct 2018 21:51:11 -0400 Steven Rostedt wrote: > +typedef long dynfunc_t; > + > +struct dynfunc_struct; > + > +#define arch_dynfunc_trampoline(name, def) \ > + asm volatile ( \ > + ".globl dynfunc_" #name "; \n\t" \ > + "dynfunc_" #name ": \n\t" \ > + "jmp " #def " \n\t" \ > + ".balign 8 \n \t" \ > + : : : "memory" ) > + I have just a question, what is this different from livepatch? :) I think we can replace the first 5 bytes of the default function to jmp instruction (to alternative function) instead of making this trampoline. IOW, as far as I can see, this is changing ---- call %reg (or retpoline_reg) ---- to ---- call dynfunc_A dynfunc_A: jmp func_A or altered_func_A ---- If so, why don't we put the jmp on default func_A directly? ---- call func_A func_A: "jmp altered_func" or "original sequence" ---- (this is idealy same as jprobes did) Of course we have to arbitrate it with ftrace (fentry) but it may not so hard (simplest way is just adding "notrace" on the default function) BTW, I think "dynamic_function" may not correct name, it may be "alternative_function" or something like that, because this function must be replaced system-wide and this means we can not use this for generic function pointer usage which depends on thread context (like file_operations). But good for something pluggable code (LSM?). Thank you, -- Masami Hiramatsu