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_MUTT 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 49EEEC4321A for ; Tue, 11 Jun 2019 15:56:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1F3612080A for ; Tue, 11 Jun 2019 15:56:13 +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="UO4Up5c8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405486AbfFKP4M (ORCPT ); Tue, 11 Jun 2019 11:56:12 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:33226 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391859AbfFKP4L (ORCPT ); Tue, 11 Jun 2019 11:56:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=dYWF8dg5ZWwrOvlmpQU8/b1U7j2GS0cV9KF8ci48uQA=; b=UO4Up5c8sxzI2qusz/vGAYQOu +QwryOTTYPx6psOLJBQIF4rNOo6mPv28IbkjmvcvaR6QPL8LzVVW9D7fCKgOw5o0P3F+2EHE2S3lV feKBFI2c8bb8M2xx42ivpb/hRUsXPsVWHX5hYWDY1k/y7NP2G+hqyI8fe11VYhntf8EFYBidqSHou MAz97neHt3+nmuK60pH2EyctnEi4CxcIKmNRf7Qj3OMuCK52uOT5vKlgO6GuG7jbvcl9dlgUzX7DU WxuEzW3SPEJZK4FQVgW6m6QE/tM9hm/FJo+N9aQy/pSU/86ldKDldOIjUCrHd7K4KqdYC0c2m7OZF 5URSSNUUA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1haj7a-0008Fj-Sg; Tue, 11 Jun 2019 15:55:39 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 5E6A42023E4A7; Tue, 11 Jun 2019 17:55:37 +0200 (CEST) Date: Tue, 11 Jun 2019 17:55:37 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: Andy Lutomirski , Masami Hiramatsu , x86@kernel.org, linux-kernel@vger.kernel.org, Ard Biesheuvel , Andy Lutomirski , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Jason Baron , Jiri Kosina , David Laight , Borislav Petkov , Julia Cartwright , Jessica Yu , "H. Peter Anvin" , Nadav Amit , Rasmus Villemoes , Edward Cree , Daniel Bristot de Oliveira Subject: Re: [PATCH 08/15] x86/alternatives: Teach text_poke_bp() to emulate instructions Message-ID: <20190611155537.GB3436@hirez.programming.kicks-ass.net> References: <20190605130753.327195108@infradead.org> <20190605131945.005681046@infradead.org> <20190608004708.7646b287151cf613838ce05f@kernel.org> <20190607173427.GK3436@hirez.programming.kicks-ass.net> <3DA961AB-950B-4886-9656-C0D268D521F1@amacapital.net> <20190611080307.GN3436@hirez.programming.kicks-ass.net> <20190611112254.576226fe@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190611112254.576226fe@gandalf.local.home> 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 Tue, Jun 11, 2019 at 11:22:54AM -0400, Steven Rostedt wrote: > On Tue, 11 Jun 2019 10:03:07 +0200 > Peter Zijlstra wrote: > > > > So what happens is that arch_prepare_optimized_kprobe() <- > > copy_optimized_instructions() copies however much of the instruction > > stream is required such that we can overwrite the instruction at @addr > > with a 5 byte jump. > > > > arch_optimize_kprobe() then does the text_poke_bp() that replaces the > > instruction @addr with int3, copies the rel jump address and overwrites > > the int3 with jmp. > > > > And I'm thinking the problem is with something like: > > > > @addr: nop nop nop nop nop > > What would work would be to: > > add breakpoint to first opcode. > > call synchronize_tasks(); > > /* All tasks now hitting breakpoint and jumping over affected > code */ > > update the rest of the instructions. > > replace breakpoint with jmp. > > One caveat is that the replaced instructions must not be a call > function. As if the call function calls schedule then it will > circumvent the synchronize_tasks(). It would be OK if that call is the > last of the instructions. But I doubt we modify anything more then a > call size anyway, so this should still work for all current instances. Right, something like this could work (although I cannot currently find synchronize_tasks), but it would make the optprobe stuff fairly slow (iirc this sync_tasks() thing could be pretty horrible).