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 D6C7FC433DB for ; Tue, 16 Mar 2021 06:31:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83F14651BE for ; Tue, 16 Mar 2021 06:31:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229775AbhCPGae (ORCPT ); Tue, 16 Mar 2021 02:30:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:52002 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230478AbhCPGa1 (ORCPT ); Tue, 16 Mar 2021 02:30:27 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 948EB65169; Tue, 16 Mar 2021 06:30:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615876227; bh=9V0KUrLMiXL6VT/H+rjc7n2huomnlDIWLOvYHtisMtE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=TpfY2jKZtLeiOYq1Du+xi8AJXy35Cfcxz2F1Q6RvKH/uA1WO2mt8SFIClfFrloM7T a90+TLD7l+lQIK24FVJ05nzEy9Z6qOU04fpWbAUg7KDtToKoLmJEDcANoyzbd7CsEc 6kEUScSjytuShT4qq8cyPmMeU3jgAHr8/8JaUPU2CkTKHmTfHYvSFX4NFxZDKVeLtY +RaS9hH/FYjb4+s282y2kwNb/72SksBWIrIDY3V+7WZ26kJgQHVgTmmZ9msmJJyyEm nBa6+uSqF6FU0wxlGZOAfFqq3/AZEYdPX665rfPfoTE/rnShwiqNFMZO2shPxbryd6 8BJFs84TZjt+A== Date: Tue, 16 Mar 2021 15:30:22 +0900 From: Masami Hiramatsu To: Josh Poimboeuf Cc: Steven Rostedt , Ingo Molnar , X86 ML , Daniel Xu , 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 v2 00/10] kprobes: Fix stacktrace with kretprobes Message-Id: <20210316153022.70cc181a2b3e0f73923e54da@kernel.org> In-Reply-To: <20210316023003.xbmgce3ndkouu65e@treble> References: <161553130371.1038734.7661319550287837734.stgit@devnote2> <20210316023003.xbmgce3ndkouu65e@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 Mon, 15 Mar 2021 21:30:03 -0500 Josh Poimboeuf wrote: > On Fri, Mar 12, 2021 at 03:41:44PM +0900, Masami Hiramatsu wrote: > > Hello, > > > > Here is the 2nd version of the series to fix the stacktrace with kretprobe. > > > > The 1st series is here; > > > > https://lore.kernel.org/bpf/161495873696.346821.10161501768906432924.stgit@devnote2/ > > > > In this version I merged the ORC unwinder fix for kretprobe which discussed in the > > previous thread. [3/10] is updated according to the Miroslav's comment. [4/10] is > > updated for simplify the code. [5/10]-[9/10] are discussed in the previsous tread > > and are introduced to the series. > > > > Daniel, can you also test this again? I and Josh discussed a bit different > > method and I've implemented it on this version. > > > > This actually changes the kretprobe behavisor a bit, now the instraction pointer in > > the pt_regs passed to kretprobe user handler is correctly set the real return > > address. So user handlers can get it via instruction_pointer() API. > > When I add WARN_ON(1) to a test kretprobe, it doesn't unwind properly. > > show_trace_log_lvl() reads the entire stack in lockstep with calls to > the unwinder so that it can decide which addresses get prefixed with > '?'. So it expects to find an actual return address on the stack. > Instead it finds %rsp. So it never syncs up with unwind_next_frame() > and shows all remaining addresses as unreliable. > > Call Trace: > __kretprobe_trampoline_handler+0xca/0x1a0 > trampoline_handler+0x3d/0x50 > kretprobe_trampoline+0x25/0x50 > ? init_test_probes.cold+0x323/0x387 > ? init_kprobes+0x144/0x14c > ? init_optprobes+0x15/0x15 > ? do_one_initcall+0x5b/0x300 > ? lock_is_held_type+0xe8/0x140 > ? kernel_init_freeable+0x174/0x2cd > ? rest_init+0x233/0x233 > ? kernel_init+0xa/0x11d > ? ret_from_fork+0x22/0x30 > > How about pushing 'kretprobe_trampoline' instead of %rsp for the return > address placeholder. That fixes the above test, and removes the need > for the weird 'state->ip == sp' check: > > Call Trace: > __kretprobe_trampoline_handler+0xca/0x150 > trampoline_handler+0x3d/0x50 > kretprobe_trampoline+0x29/0x50 > ? init_test_probes.cold+0x323/0x387 > elfcorehdr_read+0x10/0x10 > init_kprobes+0x144/0x14c > ? init_optprobes+0x15/0x15 > do_one_initcall+0x72/0x280 > kernel_init_freeable+0x174/0x2cd > ? rest_init+0x122/0x122 > kernel_init+0xa/0x10e > ret_from_fork+0x22/0x30 > > Though, init_test_probes.cold() (the real return address) is still > listed as unreliable. Maybe we need a call to kretprobe_find_ret_addr() > in show_trace_log_lvl(), similar to the ftrace_graph_ret_addr() call > there. Thanks for the test! OK, that could be acceptable. However, push %sp still needed for accessing stack address from kretprobe handler via pt_regs. (regs->sp must point the stack address) Anyway, with int3, it pushes one more entry for emulating call, so I think it is OK. Let me update the series! Thank you! > > > > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c > index 06f33bfebc50..70188fdd288e 100644 > --- a/arch/x86/kernel/kprobes/core.c > +++ b/arch/x86/kernel/kprobes/core.c > @@ -766,19 +766,19 @@ asm( > "kretprobe_trampoline:\n" > /* We don't bother saving the ss register */ > #ifdef CONFIG_X86_64 > - " pushq %rsp\n" > + /* Push fake return address to tell the unwinder it's a kretprobe */ > + " pushq $kretprobe_trampoline\n" > UNWIND_HINT_FUNC > " pushfq\n" > SAVE_REGS_STRING > " movq %rsp, %rdi\n" > " call trampoline_handler\n" > - /* Replace saved sp with true return address. */ > + /* Replace the fake return address with the real one. */ > " movq %rax, 19*8(%rsp)\n" > RESTORE_REGS_STRING > " popfq\n" > #else > " pushl %esp\n" > - UNWIND_HINT_FUNC > " pushfl\n" > SAVE_REGS_STRING > " movl %esp, %eax\n" > diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c > index 1d1b9388a1b1..1d3de84d2410 100644 > --- a/arch/x86/kernel/unwind_orc.c > +++ b/arch/x86/kernel/unwind_orc.c > @@ -548,8 +548,7 @@ bool unwind_next_frame(struct unwind_state *state) > * In those cases, find the correct return address from > * task->kretprobe_instances list. > */ > - if (state->ip == sp || > - is_kretprobe_trampoline(state->ip)) > + if (is_kretprobe_trampoline(state->ip)) > state->ip = kretprobe_find_ret_addr(state->task, > &state->kr_iter); > > > -- Masami Hiramatsu