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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 B137AC10F14 for ; Thu, 3 Oct 2019 08:28:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 852862070B for ; Thu, 3 Oct 2019 08:28:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="u2FxOR8z" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728750AbfJCI2H (ORCPT ); Thu, 3 Oct 2019 04:28:07 -0400 Received: from merlin.infradead.org ([205.233.59.134]:48874 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726523AbfJCI2H (ORCPT ); Thu, 3 Oct 2019 04:28:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Fbgpkb4ZrN1nGnmGwSYFUAda/iVeR399X2dHLFAYocs=; b=u2FxOR8zeqCulSg/8YpUzgwQO Beao2Hmrly9ZYW+VfZvMRZ4k4HpOUqcdLBMRL4Y7ypmW2fLem5CHKlCysRIxUhMFEDtEqLz2968GE +QFtzp+tsF8sU78eCsGFwhvYUfkXqF2YD1O9RJocBCGIqFBn/AaAeQJPaaulycC9881geyqkNu1Yn gKlQHPDl42UJQFiUHL8qdebafFSZIVuGF0OhesLpW75rspRgeqX/Cv+oFTMSTHjCrebGFSFLp04Jy mu7NyNJyK1gcq/0q0Ioj/gN+RY4QMFN4ONx/4CpyPt9dDxwsAC33MogCYDPqFbKMyfdfFE0t2AxJr Dfc/bLbcg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.2 #3 (Red Hat Linux)) id 1iFwSn-0004Hq-8X; Thu, 03 Oct 2019 08:27:53 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 105E0301A79; Thu, 3 Oct 2019 10:27:02 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 3415320D8F669; Thu, 3 Oct 2019 10:27:51 +0200 (CEST) Date: Thu, 3 Oct 2019 10:27:51 +0200 From: Peter Zijlstra To: Masami Hiramatsu Cc: linux-kernel@vger.kernel.org, x86@kernel.org, Nadav Amit , Andy Lutomirski , Dave Hansen , Song Liu , Steven Rostedt , Daniel Bristot de Oliveira Subject: Re: [PATCH 1/3] x86/alternatives: Teach text_poke_bp() to emulate instructions Message-ID: <20191003082751.GQ4536@hirez.programming.kicks-ass.net> References: <20190827180622.159326993@infradead.org> <20190827181147.053490768@infradead.org> <20191003140050.1d4cf59d3de8b5396d36c269@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191003140050.1d4cf59d3de8b5396d36c269@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 03, 2019 at 02:00:50PM +0900, Masami Hiramatsu wrote: > > This fits almost all text_poke_bp() users, except > > arch_unoptimize_kprobe() which restores random text, and for that site > > we have to build an explicit emulate instruction. > > OK, and in this case, I would like to change RELATIVEJUMP_OPCODE > to JMP32_INSN_OPCODE for readability. (or at least > making RELATIVEJUMP_OPCODE as an alias of JMP32_INSN_OPCODE) > > @@ -448,12 +447,18 @@ void arch_optimize_kprobes(struct list_h > > void arch_unoptimize_kprobe(struct optimized_kprobe *op) > > { > > u8 insn_buff[RELATIVEJUMP_SIZE]; > > + u8 emulate_buff[RELATIVEJUMP_SIZE]; > > > > /* Set int3 to first byte for kprobes */ > > insn_buff[0] = BREAKPOINT_INSTRUCTION; > > memcpy(insn_buff + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE); > > + > > + emulate_buff[0] = RELATIVEJUMP_OPCODE; > > + *(s32 *)(&emulate_buff[1]) = (s32)((long)op->optinsn.insn - > > + ((long)op->kp.addr + RELATIVEJUMP_SIZE)); I'm halfway through a patch introducing: union text_poke_insn { u8 code[POKE_MAX_OPCODE_SUZE]; struct { u8 opcode; s32 disp; } __attribute__((packed)); }; to text-patching.h to unify all such custom unions we have all over the place. I'll mob up the above in that. > > + > > text_poke_bp(op->kp.addr, insn_buff, RELATIVEJUMP_SIZE, > > - op->optinsn.insn); > > + emulate_buff); > > } As argued in a previous thread, text_poke_bp() is broken when it changes more than a single instruction at a time. Now, ISTR optimized kprobes does something like: poke INT3 synchronize_rcu_tasks() /* waits for all tasks to schedule guarantees instructions after INT3 are unused */ install optimized probe /* overwrites multiple instrctions with JMP.d32 */ And the above then undoes that by: poke INT3 on top of the optimzed probe poke tail instructions back /* guaranteed safe because the above INT3 poke ensures the JMP.d32 instruction is unused */ poke head byte back Is this correct? If so, we should probably put a comment in there explaining how all this is unusual but safe.