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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 0B5BFC433DF for ; Tue, 25 Aug 2020 14:15:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7D3F20665 for ; Tue, 25 Aug 2020 14:15:29 +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="F0NY4N2G" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726187AbgHYOP2 (ORCPT ); Tue, 25 Aug 2020 10:15:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59620 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725893AbgHYOP1 (ORCPT ); Tue, 25 Aug 2020 10:15:27 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 221A3C061574 for ; Tue, 25 Aug 2020 07:15:27 -0700 (PDT) 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; bh=rpL1dCRWpxTiOufY/e0NW96imqT+arMYCY2NNc5N7tI=; b=F0NY4N2GNGQonqtuLf8+pXPYAE bjuCTYw/ONtO2Qvnyf+jNRKZwQ3bR2dKT24TSlYfzlAUOQlpeZTLjCxfDafTvd5u82neTXWT31l7e Sfh77tx5cOK6GWZsia7FGvWV391oL/5CKXzWySJVgk5g03yg+SdW2xEBODaSd+QUZ6pe6PTXcH15v WxDw7Wivu+c1IWEcIdLMxzNh77Q3KCeg1hxNkjb95e5Ox9AFYiyTp/WQh3LTe3DKpEiOmDn4eruOk cdcurrCJRoNpoYAHAPTPVyeY+HDH4EXh3jd8w9bYmAUQluYksBOIP3viuLP1njhtrvVBw2QIICRM+ 7ZznDz6w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kAZjO-0003kh-IH; Tue, 25 Aug 2020 14:15:22 +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 615BB30280E; Tue, 25 Aug 2020 16:15:21 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 13B7120C19006; Tue, 25 Aug 2020 16:15:21 +0200 (CEST) Date: Tue, 25 Aug 2020 16:15:21 +0200 From: peterz@infradead.org To: Masami Hiramatsu Cc: "Eddy_Wu@trendmicro.com" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "David S. Miller" , Paul McKenney Subject: Re: x86/kprobes: kretprobe fails to triggered if kprobe at function entry is not optimized (trigger by int3 breakpoint) Message-ID: <20200825141521.GA1362448@hirez.programming.kicks-ass.net> References: <8816bdbbc55c4d2397e0b02aad2825d3@trendmicro.com> <20200825005426.f592075d13be740cb3c9aa77@kernel.org> <7396e7b2079644a6aafd9670a111232b@trendmicro.com> <20200825151538.f856d701a34f4e0561a64932@kernel.org> <20200825120911.GX1362448@hirez.programming.kicks-ass.net> <20200825221555.a2d72c9754284feced6a8536@kernel.org> <20200825133005.GY1362448@hirez.programming.kicks-ass.net> <20200825225954.2202d28b449f2354d5c88070@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200825225954.2202d28b449f2354d5c88070@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 25, 2020 at 10:59:54PM +0900, Masami Hiramatsu wrote: > On Tue, 25 Aug 2020 15:30:05 +0200 > peterz@infradead.org wrote: > > > On Tue, Aug 25, 2020 at 10:15:55PM +0900, Masami Hiramatsu wrote: > > > > > > damn... one last problem is dangling instances.. so close. > > > > We can apparently unregister a kretprobe while there's still active > > > > kretprobe_instance's out referencing it. > > > > > > Yeah, kretprobe already provided the per-instance data (as far as > > > I know, only systemtap depends on it). We need to provide it for > > > such users. > > > But if we only have one lock, we can avoid checking NMI because > > > we can check the recursion with trylock. It is needed only if the > > > kretprobe uses per-instance data. Or we can just pass a dummy > > > instance on the stack. > > > > I think it is true in general, you can unregister a rp while tasks are > > preempted. > > Would you mean the kretprobe handler (or trampoline handler) will be > preempted? All kprobes (including kretprobe) handler is running in > non-preemptive state, so it shouldn't happen... I was thinking about something like: for_each_process_thread(p, t) { if (!t->kretprobe_instances.first) continue; again: if (try_invoke_on_locked_down_task(t, unhook_rp_inst, tp)) continue; smp_function_call(...); if (!done) goto again; } So then for each task that has a kretprobe stack, we iterate the stack and set ri->rp = NULL, remotely when the task isn't running, locally if the task is running. I just need to change the semantics of try_invoke_on_locked_down_task() a bit -- they're a tad weird atm. > > Anyway,. I think I have a solution, just need to talk to paulmck for a > > bit. > > Ah, you mentioned that the removing the kfree() from the trampline > handler? I think we can make an rcu callback which will kfree() the > given instances. (If it works in NMI) Yes, calling kfree() from the trampoline seems dodgy at best. When !ri->rp rcu_free() is a good option.