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=-11.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 E95E7C433DB for ; Thu, 11 Mar 2021 01:07:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AE72564FC3 for ; Thu, 11 Mar 2021 01:07:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229633AbhCKBGc (ORCPT ); Wed, 10 Mar 2021 20:06:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:24692 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229578AbhCKBG3 (ORCPT ); Wed, 10 Mar 2021 20:06:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615424788; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NlNmI4tedf0ptWCOX9AN1BL2Q8MJrpCOVljUQI3bIm0=; b=FBAqsUFnhoPyDgW9Iz37vFNt1s2KWwlFOrZ66dbta4etyTKeBqMtN7sljSpYlrRi3UCXnE UZIavlSNEm/rYYCWBd2skpYjSjbJZWv9UVqBSWTgz03B7rZ0ZB12UKZXTO4apcCeT9rj7X dX+vosPpisncOFB1rUfhoEHToPU8Ysw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-556-OsMim5OTMCSQb5c4x9uz8A-1; Wed, 10 Mar 2021 20:06:24 -0500 X-MC-Unique: OsMim5OTMCSQb5c4x9uz8A-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 142091005D45; Thu, 11 Mar 2021 01:06:22 +0000 (UTC) Received: from treble (ovpn-118-249.rdu2.redhat.com [10.10.118.249]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BD45E1981B; Thu, 11 Mar 2021 01:06:18 +0000 (UTC) Date: Wed, 10 Mar 2021 19:06:15 -0600 From: Josh Poimboeuf To: Masami Hiramatsu 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: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210311092018.2d0e54d2c891850e549d16fe@kernel.org> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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. Then we wouldn't need the call to orc_kretprobe_correct_ip() in __unwind_start(). But maybe it's not possible due to the regs->ip expectations of legacy handlers? -- Josh