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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS 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 06D4DC433ED for ; Mon, 5 Apr 2021 23:40:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CD71A6135D for ; Mon, 5 Apr 2021 23:40:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238565AbhDEXlB (ORCPT ); Mon, 5 Apr 2021 19:41:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:55768 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232109AbhDEXk5 (ORCPT ); Mon, 5 Apr 2021 19:40:57 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id DE71261184; Mon, 5 Apr 2021 23:40:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1617666050; bh=wXcvCpV5lngQfAsxhsTeGFb1bpyuoynRwRXUiAxBCzs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=I4gn9Yon5sGPKvk7Mne/CxcIV8unoQeeNrAeKR/0MkHJp0MziBaIuiPtp/5KpJOPM 9wsbVj3Mgy/11NGt52I8i2WCXgIVzLlZzMBNNquporc3nprlf0X6iJ9ucM9FIp3lyB 5hIeLWd2qb6sn+mbpK9v/+UyG6tnRZ/aNCt+2E4EUPJDgMQCkhgpXEGLU+3SxYSQKt e5QVfGQlLicuQsbH8zAlJB0FCdwmmUAOLaTYSDPY1XIXPBRsbSOcPJ3s4GJ27mpPWS s658IHY/HMbzuw77ZTLbazhfer1NiCOosQPYgxlYOviiJnn4bZLW8N2kKPrPV83R9S B7uF/rKoc/ocQ== Date: Tue, 6 Apr 2021 08:40:46 +0900 From: Masami Hiramatsu To: "Madhavan T. Venkataraman" Cc: Josh Poimboeuf , mark.rutland@arm.com, broonie@kernel.org, jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v1 0/4] arm64: Implement stack trace reliability checks Message-Id: <20210406084046.4f0b946728dc01da09045338@kernel.org> In-Reply-To: <7dda9af3-1ecf-5e6f-1e46-8870a2a5e550@linux.microsoft.com> References: <77bd5edeea72d44533c769b1e8c0fea7a9d7eb3a> <20210330190955.13707-1-madvenka@linux.microsoft.com> <20210403170159.gegqjrsrg7jshlne@treble> <20210405222436.4fda9a930676d95e862744af@kernel.org> <7dda9af3-1ecf-5e6f-1e46-8870a2a5e550@linux.microsoft.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 5 Apr 2021 09:56:48 -0500 "Madhavan T. Venkataraman" wrote: > > > On 4/5/21 8:24 AM, Masami Hiramatsu wrote: > > Hi Madhaven, > > > > On Sat, 3 Apr 2021 22:29:12 -0500 > > "Madhavan T. Venkataraman" wrote: > > > > > >>>> Check for kretprobe > >>>> =================== > >>>> > >>>> For functions with a kretprobe set up, probe code executes on entry > >>>> to the function and replaces the return address in the stack frame with a > >>>> kretprobe trampoline. Whenever the function returns, control is > >>>> transferred to the trampoline. The trampoline eventually returns to the > >>>> original return address. > >>>> > >>>> A stack trace taken while executing in the function (or in functions that > >>>> get called from the function) will not show the original return address. > >>>> Similarly, a stack trace taken while executing in the trampoline itself > >>>> (and functions that get called from the trampoline) will not show the > >>>> original return address. This means that the caller of the probed function > >>>> will not show. This makes the stack trace unreliable. > >>>> > >>>> Add the kretprobe trampoline to special_functions[]. > >>>> > >>>> FYI, each task contains a task->kretprobe_instances list that can > >>>> theoretically be consulted to find the orginal return address. But I am > >>>> not entirely sure how to safely traverse that list for stack traces > >>>> not on the current process. So, I have taken the easy way out. > >>> > >>> For kretprobes, unwinding from the trampoline or kretprobe handler > >>> shouldn't be a reliability concern for live patching, for similar > >>> reasons as above. > >>> > >> > >> Please see previous answer. > >> > >>> Otherwise, when unwinding from a blocked task which has > >>> 'kretprobe_trampoline' on the stack, the unwinder needs a way to get the > >>> original return address. Masami has been working on an interface to > >>> make that possible for x86. I assume something similar could be done > >>> for arm64. > >>> > >> > >> OK. Until that is available, this case needs to be addressed. > > > > Actually, I've done that on arm64 :) See below patch. > > (and I also have a similar code for arm32, what I'm considering is how > > to unify x86/arm/arm64 kretprobe_find_ret_addr(), since those are very > > similar.) > > > > This is applicable on my x86 series v5 > > > > https://lore.kernel.org/bpf/161676170650.330141.6214727134265514123.stgit@devnote2/ > > > > Thank you, > > > > > > I took a brief look at your changes. Looks reasonable. > > However, for now, I am going to include the kretprobe_trampoline in the special_functions[] > array until your changes are merged. At that point, it is just a matter of deleting > kretprobe_trampoline from the special_functions[] array. That is all. > > I hope that is fine with everyone. Agreed, that is reasonable unless my series is merged. Thank you, -- Masami Hiramatsu