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=-19.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=ham 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 DC759C433ED for ; Mon, 19 Apr 2021 18:16:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B626061246 for ; Mon, 19 Apr 2021 18:16:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234035AbhDSSR3 (ORCPT ); Mon, 19 Apr 2021 14:17:29 -0400 Received: from linux.microsoft.com ([13.77.154.182]:41012 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233907AbhDSSR2 (ORCPT ); Mon, 19 Apr 2021 14:17:28 -0400 Received: from [192.168.254.32] (unknown [47.187.223.33]) by linux.microsoft.com (Postfix) with ESMTPSA id DB03320B8000; Mon, 19 Apr 2021 11:16:57 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com DB03320B8000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1618856218; bh=cRJmWH03/XKOttU3OaDRbl+mvZMfWqX2u8y+9sokYqs=; h=Subject:To:References:Cc:From:Date:In-Reply-To:From; b=ptdT+5pNQXQ5X8C8cgYoQOv4klVxRcD3Vo9K86GurDgWobBYYu5HCKvkR5h4g6ECi MoJiH1y5lWTQBYt+RuYLvfM2P5ZT2AzsEwrpBexZENPxXNUQUHsB8Ndv0IWDQRiM1D JBTLKWH8dlsTq6NAD8WBjSWbnxp/pfzO6rf4Ifp0= Subject: Re: [RFC PATCH v2 0/1] arm64: Implement stack trace termination record To: mark.rutland@arm.com, broonie@kernel.org, jpoimboe@redhat.com, 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 References: <659f3d5cc025896ba4c49aea431aa8b1abc2b741> <20210402032404.47239-1-madvenka@linux.microsoft.com> Cc: pasha.tatashin@soleen.com From: "Madhavan T. Venkataraman" Message-ID: <96b4deb8-c841-b0fd-f1f9-ad0b737ec8a7@linux.microsoft.com> Date: Mon, 19 Apr 2021 13:16:57 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210402032404.47239-1-madvenka@linux.microsoft.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org CCing Pavel Tatashin on request. Pasha, This is v2. v1 is here: https://lore.kernel.org/linux-arm-kernel/20210324184607.120948-1-madvenka@linux.microsoft.com/ Thanks! Madhavan On 4/1/21 10:24 PM, madvenka@linux.microsoft.com wrote: > From: "Madhavan T. Venkataraman" > > Reliable stacktracing requires that we identify when a stacktrace is > terminated early. We can do this by ensuring all tasks have a final > frame record at a known location on their task stack, and checking > that this is the final frame record in the chain. > > All tasks have a pt_regs structure right after the task stack in the stack > page. The pt_regs structure contains a stackframe field. Make this stackframe > field the final frame in the task stack so all stack traces end at a fixed > stack offset. > > For kernel tasks, this is simple to understand. For user tasks, there is > some extra detail. User tasks get created via fork() et al. Once they return > from fork, they enter the kernel only on an EL0 exception. In arm64, > system calls are also EL0 exceptions. > > The EL0 exception handler uses the task pt_regs mentioned above to save > register state and call different exception functions. All stack traces > from EL0 exception code must end at the pt_regs. So, make pt_regs->stackframe > the final frame in the EL0 exception stack. > > To summarize, task_pt_regs(task)->stackframe will always be the final frame > in a stack trace. > > Sample stack traces > =================== > > The final frame for the idle tasks is different from v1. The rest of the > stack traces are the same. > > Primary CPU's idle task (changed from v1) > ======================= > > [ 0.022365] arch_stack_walk+0x0/0xd0 > [ 0.022376] callfd_stack+0x30/0x60 > [ 0.022387] rest_init+0xd8/0xf8 > [ 0.022397] arch_call_rest_init+0x18/0x24 > [ 0.022411] start_kernel+0x5b8/0x5f4 > [ 0.022424] __primary_switched+0xa8/0xac > > Secondary CPU's idle task (changed from v1) > ========================= > > [ 0.022484] arch_stack_walk+0x0/0xd0 > [ 0.022494] callfd_stack+0x30/0x60 > [ 0.022502] secondary_start_kernel+0x188/0x1e0 > [ 0.022513] __secondary_switched+0x80/0x84 > > --- > Changelog: > > v1 > - Set up task_pt_regs(current)->stackframe as the final frame > when a new task is initialized in copy_thread(). > > - Create pt_regs for the idle tasks and set up pt_regs->stackframe > as the final frame for the idle tasks. > > - Set up task_pt_regs(current)->stackframe as the final frame in > the EL0 exception handler so the EL0 exception stack trace ends > there. > > - Terminate the stack trace successfully in unwind_frame() when > the FP reaches task_pt_regs(current)->stackframe. > > - The stack traces (above) in the kernel will terminate at the > correct place. Debuggers may show an extra record 0x0 at the end > for pt_regs->stackframe. That said, I did not see that extra frame > when I did stack traces using gdb. > v2 > - Changed some wordings as suggested by Mark Rutland. > > - Removed the synthetic return PC for idle tasks. Changed the > branches to start_kernel() and secondary_start_kernel() to > calls so that they will have a proper return PC. > > Madhavan T. Venkataraman (1): > arm64: Implement stack trace termination record > > arch/arm64/kernel/entry.S | 8 +++++--- > arch/arm64/kernel/head.S | 29 +++++++++++++++++++++++------ > arch/arm64/kernel/process.c | 5 +++++ > arch/arm64/kernel/stacktrace.c | 10 +++++----- > 4 files changed, 38 insertions(+), 14 deletions(-) > > > base-commit: 0d02ec6b3136c73c09e7859f0d0e4e2c4c07b49b >