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=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 A3CC8C433E0 for ; Thu, 11 Mar 2021 01:55:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6218461585 for ; Thu, 11 Mar 2021 01:55:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229691AbhCKByr (ORCPT ); Wed, 10 Mar 2021 20:54:47 -0500 Received: from mail.kernel.org ([198.145.29.99]:35564 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229483AbhCKBym (ORCPT ); Wed, 10 Mar 2021 20:54:42 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 051E264DD1; Thu, 11 Mar 2021 01:54:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615427682; bh=IfzsfOitPrwLeGojJ6pZ8/YMYEJqzCh715+wQiVOIJI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=uT9vnpy/L6HQyZ5uMtMX8G6OxfAeKN2z1nMGdRCBkiQMlTFHihfew53N7Nd7GbJjd JCQE3TV4z4YdCQwURysOcU2I3fTouqAv3OxDns7ob4mNlHAAN8STcGNTh9/t0oI8Xi tap4YryV7nJsd/w7mg09thRMSNVF8C3GkZBAKmOFKL7bLHO7xfe/CqfnzXBpqXB4Aq hKJen0j0IXmO3BY5xAkuTwbYiwrj3btQEsQ+Icg5S/O9HrTEYv9lpJe8ghwVlwI0TY coKHtMsk9BI8vKU9bm9wEKeFyoyi+CQJzy0NN2X2sOFOJueLYE2BYwDhqNVOTuGEh5 F9zruhwnMh0aQ== Date: Thu, 11 Mar 2021 10:54:38 +0900 From: Masami Hiramatsu To: Josh Poimboeuf Cc: Daniel Xu , Steven Rostedt , Ingo Molnar , X86 ML , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kuba@kernel.org, mingo@redhat.com, ast@kernel.org, tglx@linutronix.de, kernel-team@fb.com, yhs@fb.com Subject: Re: [PATCH -tip 0/5] kprobes: Fix stacktrace in kretprobes Message-Id: <20210311105438.cca15ed7645c454294dc3e1f@kernel.org> In-Reply-To: <20210311010615.7pemfngxx7cy42fe@treble> References: <20210305191645.njvrsni3ztvhhvqw@maharaja.localdomain> <20210306101357.6f947b063a982da9c949f1ba@kernel.org> <20210307212333.7jqmdnahoohpxabn@maharaja.localdomain> <20210308115210.732f2c42bf347c15fbb2a828@kernel.org> <20210309011945.ky7v3pnbdpxhmxkh@treble> <20210310185734.332d9d52a26780ba02d09197@kernel.org> <20210310150845.7kctaox34yrfyjxt@treble> <20210311005509.0a1a65df0d2d6c7da73a9288@kernel.org> <20210310183113.xxverwh4qplr7xxb@treble> <20210311092018.2d0e54d2c891850e549d16fe@kernel.org> <20210311010615.7pemfngxx7cy42fe@treble> 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 Wed, 10 Mar 2021 19:06:15 -0600 Josh Poimboeuf wrote: > On Thu, Mar 11, 2021 at 09:20:18AM +0900, Masami Hiramatsu wrote: > > > > bool unwind_next_frame(struct unwind_state *state) > > > > { > > > > unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp; > > > > @@ -536,6 +561,18 @@ bool unwind_next_frame(struct unwind_state *state) > > > > > > > > state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx, > > > > state->ip, (void *)ip_p); > > > > + /* > > > > + * There are special cases when the stack unwinder is called > > > > + * from the kretprobe handler or the interrupt handler which > > > > + * occurs in the kretprobe trampoline code. In those cases, > > > > + * %sp is shown on the stack instead of the return address. > > > > + * Or, when the unwinder find the return address is replaced > > > > + * by kretprobe_trampoline. > > > > + * In those cases, correct address can be found in kretprobe. > > > > + */ > > > > + if (state->ip == sp || > > > > > > Why is the 'state->ip == sp' needed? > > > > As I commented above, until kretprobe_trampoline writes back the real > > address to the stack, sp value is there (which has been pushed by the > > 'pushq %rsp' at the entry of kretprobe_trampoline.) > > > > ".type kretprobe_trampoline, @function\n" > > "kretprobe_trampoline:\n" > > /* We don't bother saving the ss register */ > > " pushq %rsp\n" // THIS > > " pushfq\n" > > > > Thus, from inside the kretprobe handler, like ftrace, you'll see > > the sp value instead of the real return address. > > I see. If you change is_kretprobe_trampoline_address() to include the > entire function, like: > > static bool is_kretprobe_trampoline_address(unsigned long ip) > { > return (void *)ip >= kretprobe_trampoline && > (void *)ip < kretprobe_trampoline_end; > } > > then the unwinder won't ever read the bogus %rsp value into state->ip, > and the 'state->ip == sp' check can be removed. Hmm, I couldn't get your point. Since sp is the address of stack, it always out of text address. > > > > And it would make the unwinder just work automatically when unwinding > > > from the handler using the regs. > > > > > > It would also work when unwinding from the handler's stack, if we put an > > > UNWIND_HINT_REGS after saving the regs. > > > > At that moment, the real return address is not identified. So we can not > > put it. > > True, at the time the regs are originally saved, the real return address > isn't available. But by the time the user handler is called, the return > address *is* available. So if the real return address were placed in > regs->ip before calling the handler, the unwinder could find it there, > when called from the handler. OK, but this is not arch independent specification. I can make a hack only for x86, but that is not clean implementation, hmm. > > Then we wouldn't need the call to orc_kretprobe_correct_ip() in > __unwind_start(). What about the ORC implementation in other architecture? Is that for x86 only? > > But maybe it's not possible due to the regs->ip expectations of legacy > handlers? Usually, the legacy handlers will ignore it, the official way to access the correct return address is kretprobe_instance.ret_addr. Because it is arch independent. Nowadays there are instruction_pointer() and instruction_pointer_set() APIs in many (not all) architecutre, so I can try to replace to use it instead of the kretprobe_instance.ret_addr. (and it will break the out-of-tree codes) Thank you, -- Masami Hiramatsu