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=-14.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL 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 03C90C433DB for ; Tue, 23 Mar 2021 12:57:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A0DD6619C3 for ; Tue, 23 Mar 2021 12:57:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231401AbhCWM5O (ORCPT ); Tue, 23 Mar 2021 08:57:14 -0400 Received: from linux.microsoft.com ([13.77.154.182]:53430 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229675AbhCWM4n (ORCPT ); Tue, 23 Mar 2021 08:56:43 -0400 Received: from [192.168.254.32] (unknown [47.187.194.202]) by linux.microsoft.com (Postfix) with ESMTPSA id A21E320B5680; Tue, 23 Mar 2021 05:56:41 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com A21E320B5680 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1616504202; bh=9C5FVkGdJSAlL7ed0hNrX3OIMvNkBdBiqKHLwSxiMIE=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=BNO6uEk5h0LzM4a3Nkr1K2NycMd4M3Vh321R5LSJsP2GqLlQLO3uaM5CvD3Www1S5 Keb5+YKquEZbJdsjXh2HG53i89PcSnLqOECJDpYpRxWnWeApEtTkVIm4FR65d67Gq2 aYkCqzQ5JP69VonHbPc5JIdM+oN3yWKMuuSYw00U= Subject: Re: [RFC PATCH v2 5/8] arm64: Detect an FTRACE frame and mark a stack trace unreliable To: Mark Rutland Cc: 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: <5997dfe8d261a3a543667b83c902883c1e4bd270> <20210315165800.5948-1-madvenka@linux.microsoft.com> <20210315165800.5948-6-madvenka@linux.microsoft.com> <20210323105118.GE95840@C02TD0UTHF1T.local> From: "Madhavan T. Venkataraman" Message-ID: <2167f3c5-e7d0-40c8-99e3-ae89ceb2d60e@linux.microsoft.com> Date: Tue, 23 Mar 2021 07:56:40 -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: <20210323105118.GE95840@C02TD0UTHF1T.local> 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 On 3/23/21 5:51 AM, Mark Rutland wrote: > On Mon, Mar 15, 2021 at 11:57:57AM -0500, madvenka@linux.microsoft.com wrote: >> From: "Madhavan T. Venkataraman" >> >> When CONFIG_DYNAMIC_FTRACE_WITH_REGS is enabled and tracing is activated >> for a function, the ftrace infrastructure is called for the function at >> the very beginning. Ftrace creates two frames: >> >> - One for the traced function >> >> - One for the caller of the traced function >> >> That gives a reliable stack trace while executing in the ftrace >> infrastructure code. When ftrace returns to the traced function, the frames >> are popped and everything is back to normal. >> >> However, in cases like live patch, execution is redirected to a different >> function when ftrace returns. A stack trace taken while still in the ftrace >> infrastructure code will not show the target function. The target function >> is the real function that we want to track. >> >> So, if an FTRACE frame is detected on the stack, just mark the stack trace >> as unreliable. > > To identify this case, please identify the ftrace trampolines instead, > e.g. ftrace_regs_caller, return_to_handler. > Yes. As part of the return address checking, I will check this. IIUC, I think that I need to check for the inner labels that are defined at the point where the instructions are patched for ftrace. E.g., ftrace_call and ftrace_graph_call. SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL) bl ftrace_stub <==================================== #ifdef CONFIG_FUNCTION_GRAPH_TRACER SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller(); nop <======= // If enabled, this will be replaced // "b ftrace_graph_caller" #endif For instance, the stack trace I got while tracing do_mmap() with the stack trace tracer looks like this: ... [ 338.911793] trace_function+0xc4/0x160 [ 338.911801] function_stack_trace_call+0xac/0x130 [ 338.911807] ftrace_graph_call+0x0/0x4 [ 338.911813] do_mmap+0x8/0x598 [ 338.911820] vm_mmap_pgoff+0xf4/0x188 [ 338.911826] ksys_mmap_pgoff+0x1d8/0x220 [ 338.911832] __arm64_sys_mmap+0x38/0x50 [ 338.911839] el0_svc_common.constprop.0+0x70/0x1a8 [ 338.911846] do_el0_svc+0x2c/0x98 [ 338.911851] el0_svc+0x2c/0x70 [ 338.911859] el0_sync_handler+0xb0/0xb8 [ 338.911864] el0_sync+0x180/0x1c0 > It'd be good to check *exactly* when we need to reject, since IIUC when > we have a graph stack entry the unwind will be correct from livepatch's > PoV. > The current unwinder already handles this like this: #ifdef CONFIG_FUNCTION_GRAPH_TRACER if (tsk->ret_stack && (ptrauth_strip_insn_pac(frame->pc) == (unsigned long)return_to_handler)) { struct ftrace_ret_stack *ret_stack; /* * This is a case where function graph tracer has * modified a return address (LR) in a stack frame * to hook a function return. * So replace it to an original value. */ ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++); if (WARN_ON_ONCE(!ret_stack)) return -EINVAL; frame->pc = ret_stack->ret; } #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ Is there anything else that needs handling here? Thanks, Madhavan