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,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 9BEB9C4338F for ; Thu, 12 Aug 2021 18:34:12 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 54B7561019 for ; Thu, 12 Aug 2021 18:34:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 54B7561019 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Cc:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=nDPAQPXhZcuCZukj4+sdstlvIzjgjjQJ2KK1L6FLY3U=; b=Tpd7KydSPvjzJx9UIgTeM7hidY ckJgOkdoftpz7najy+HNwfDFI/PjbRv8wpIiIjSIVu0vXtNSthURoBUxOtlCpLfqm76yT0ufYc5ey 76GFONbEd66XwGCQuzKsnctCClnrcVy+cmq1jb5+XNHnbtwa3ctMXJVJ8nXCCFkPPDkXl4aKYOr6F PXjpo+ix6dMVr1XMeXptLX5mcA4Ox3oyu7/PLERAZBEzsLGXdjd6nlgf3pUeshVB2DjJgSLWoZOTt 78kPGkMmR2IegKFBYOqjiQ29fyQt8bCjIBkFbe6XiFF9mMXKKXFXqU///3rdyOK8yIsAPMA6GjOsQ Ex4s021w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mEFUl-00As01-OO; Thu, 12 Aug 2021 18:31:59 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mEFUg-00AryH-JO for linux-arm-kernel@lists.infradead.org; Thu, 12 Aug 2021 18:31:57 +0000 Received: from [192.168.254.32] (unknown [47.187.212.181]) by linux.microsoft.com (Postfix) with ESMTPSA id 86F9F209A3B0; Thu, 12 Aug 2021 11:31:49 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 86F9F209A3B0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1628793110; bh=pkQbqTdl+/AZKnjeX+sJbAnQw1xnsGlyrS0T34UZnik=; h=Subject:To:References:From:Date:In-Reply-To:From; b=j1h1g0PF8YZ7gDVKimnoFOI37E5kP+2Jff0yGA12xSg/EfekAnFgYEr9/3XQZFkSl 3zXlXyGoYmhlrDiGRBGGJtEB0sQ3QeLLN5oL2wYUBmhrlP3UxcERnSJ5qTVZ+nkfVV YrodXTOevxRV38iC3xIe7lvAKgYmdaVng/H53BbM= Subject: Re: [RFC PATCH v7 0/4] arm64: Reorganize the unwinder and implement stack trace reliability checks To: mark.rutland@arm.com, broonie@kernel.org, jpoimboe@redhat.com, ardb@kernel.org, nobuta.keiya@fujitsu.com, sjitindarsingh@gmail.com, catalin.marinas@arm.com, will@kernel.org, jmorris@namei.org, pasha.tatashin@soleen.com, jthierry@redhat.com, linux-arm-kernel@lists.infradead.org, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org References: <3f2aab69a35c243c5e97f47c4ad84046355f5b90> <20210812132435.6143-1-madvenka@linux.microsoft.com> From: "Madhavan T. Venkataraman" Message-ID: <3a71bd4a-dc3c-eb66-6555-2f96877499f4@linux.microsoft.com> Date: Thu, 12 Aug 2021 13:31:48 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210812132435.6143-1-madvenka@linux.microsoft.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210812_113154_785547_1628C7D9 X-CRM114-Status: GOOD ( 65.03 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org The messages are not threaded properly. I will resend the whole series with proper threading. I apologize. Madhavan On 8/12/21 8:24 AM, madvenka@linux.microsoft.com wrote: > From: "Madhavan T. Venkataraman" > > Make all stack walking functions use arch_stack_walk() > ====================================================== > > Currently, there are multiple functions in ARM64 code that walk the > stack using start_backtrace() and unwind_frame(). Convert all of > them to use arch_stack_walk(). This makes maintenance easier. > > Reorganize the unwinder code for better consistency and maintenance > =================================================================== > > Rename unwinder functions to unwind_*() similar to other architectures > for naming consistency. > > Annotate all of the unwind_*() functions with notrace so they cannot be > ftraced and NOKPROBE_SYMBOL() so they cannot be kprobed. Ftrace and Kprobe > code can call the unwinder. > > Redefine the unwinder loop and make it similar to other architectures. > Define the following: > > unwind_start(&frame, task, fp, pc); > while (unwind_consume(&frame, consume_entry, cookie)) > unwind_next(&frame); > return !unwind_failed(&frame); > > unwind_start() > Same as the original start_backtrace(). > > unwind_consume() > This new function does two things: > > - Calls consume_entry() to consume the return PC. > > - Implements checks to determine whether the unwind should continue > or terminate. > > unwind_next() > Same as the original unwind_frame() except: > > - the stack trace termination check has been moved from here to > unwind_consume(). So, unwind_next() assumes that the fp is valid. > > - unwind_frame() used to return an error value. This function only > sets internal state and does not return anything. The state is > retrieved via a helper. See next. > > unwind_failed() > Return a boolean to indicate whether the stack trace completed > successfully or failed. arch_stack_walk() ignores the return > value. But arch_stack_walk_reliable() in the future will look > at the return value. > > Unwind status > Introduce a new flag called "failed" in struct stackframe. Set this > flag when an error is encountered. If this flag is set, terminate > the unwind. Also, let the unwinder return the status to the caller. > > Reliability checks > ================== > > There are some kernel features and conditions that make a stack trace > unreliable. Callers may require the unwinder to detect these cases. > E.g., livepatch. > > Introduce a new function called unwind_is_reliable() that will detect > these cases and return a boolean. > > Introduce a new argument to unwind() called "need_reliable" so a caller > can tell unwind() that it requires a reliable stack trace. For such a > caller, any unreliability in the stack trace must be treated as a fatal > error and the unwind must be aborted. > > Call unwind_is_reliable() from unwind_consume() like this: > > if (frame->need_reliable && !unwind_is_reliable(frame)) { > frame->failed = true; > return false; > } > > arch_stack_walk() passes "false" for need_reliable because its callers > don't care about reliability. arch_stack_walk() is used for debug and > test purposes. > > Introduce arch_stack_walk_reliable() for ARM64. This works like > arch_stack_walk() except for two things: > > - It passes "true" for need_reliable. > > - It returns -EINVAL if unwind() aborts. > > Introduce the first reliability check in unwind_is_reliable() - If > a return PC is not a valid kernel text address, consider the stack > trace unreliable. It could be some generated code. > > Other reliability checks will be added in the future. Until all of the > checks are in place, arch_stack_walk_reliable() may not be used by > livepatch. But it may be used by debug and test code. > > SYM_CODE check > ============== > > SYM_CODE functions do not follow normal calling conventions. They cannot > be unwound reliably using the frame pointer. Collect the address ranges > of these functions in a special section called "sym_code_functions". > > In unwind_is_reliable(), check the return PC against these ranges. If a > match is found, then consider the stack trace unreliable. This is the > second reliability check introduced by this work. > > Last stack frame > ---------------- > > If a SYM_CODE function occurs in the very last frame in the stack trace, > then the stack trace is not considered unreliable. This is because there > is no more unwinding to do. Examples: > > - EL0 exception stack traces end in the top level EL0 exception > handlers. > > - All kernel thread stack traces end in ret_from_fork(). > --- > Changelog: > > v7: > From Mark Rutland: > > - Make the unwinder loop similar to other architectures. > > - Keep details to within the unwinder functions and return a simple > boolean to the caller. > > - Convert some of the current code that contains unwinder logic to > simply use arch_stack_walk(). I have converted all of them. > > - Do not copy sym_code_functions[]. Just place it in rodata for now. > > - Have the main loop check for termination conditions rather than > having unwind_frame() check for them. In other words, let > unwind_frame() assume that the fp is valid. > > - Replace the big comment for SYM_CODE functions with a shorter > comment. > > /* > * As SYM_CODE functions don't follow the usual calling > * conventions, we assume by default that any SYM_CODE function > * cannot be unwound reliably. > * > * Note that this includes: > * > * - Exception handlers and entry assembly > * - Trampoline assembly (e.g., ftrace, kprobes) > * - Hypervisor-related assembly > * - Hibernation-related assembly > * - CPU start-stop, suspend-resume assembly > * - Kernel relocation assembly > */ > > v6: > From Mark Rutland: > > - The per-frame reliability concept and flag are acceptable. But more > work is needed to make the per-frame checks more accurate and more > complete. E.g., some code reorg is being worked on that will help. > > I have now removed the frame->reliable flag and deleted the whole > concept of per-frame status. This is orthogonal to this patch series. > Instead, I have improved the unwinder to return proper return codes > so a caller can take appropriate action without needing per-frame > status. > > - Remove the mention of PLTs and update the comment. > > I have replaced the comment above the call to __kernel_text_address() > with the comment suggested by Mark Rutland. > > Other comments: > > - Other comments on the per-frame stuff are not relevant because > that approach is not there anymore. > > v5: > From Keiya Nobuta: > > - The term blacklist(ed) is not to be used anymore. I have changed it > to unreliable. So, the function unwinder_blacklisted() has been > changed to unwinder_is_unreliable(). > > From Mark Brown: > > - Add a comment for the "reliable" flag in struct stackframe. The > reliability attribute is not complete until all the checks are > in place. Added a comment above struct stackframe. > > - Include some of the comments in the cover letter in the actual > code so that we can compare it with the reliable stack trace > requirements document for completeness. I have added a comment: > > - above unwinder_is_unreliable() that lists the requirements > that are addressed by the function. > > - above the __kernel_text_address() call about all the cases > the call covers. > > v4: > From Mark Brown: > > - I was checking the return PC with __kernel_text_address() before > the Function Graph trace handling. Mark Brown felt that all the > reliability checks should be performed on the original return PC > once that is obtained. So, I have moved all the reliability checks > to after the Function Graph Trace handling code in the unwinder. > Basically, the unwinder should perform PC translations first (for > rhe return trampoline for Function Graph Tracing, Kretprobes, etc). > Then, the reliability checks should be applied to the resulting > PC. > > - Mark said to improve the naming of the new functions so they don't > collide with existing ones. I have used a prefix "unwinder_" for > all the new functions. > > From Josh Poimboeuf: > > - In the error scenarios in the unwinder, the reliable flag in the > stack frame should be set. Implemented this. > > - Some of the other comments are not relevant to the new code as > I have taken a different approach in the new code. That is why > I have not made those changes. E.g., Ard wanted me to add the > "const" keyword to the global section array. That array does not > exist in v4. Similarly, Mark Brown said to use ARRAY_SIZE() for > the same array in a for loop. > > Other changes: > > - Add a new definition for SYM_CODE_END() that adds the address > range of the function to a special section called > "sym_code_functions". > > - Include the new section under initdata in vmlinux.lds.S. > > - Define an early_initcall() to copy the contents of the > "sym_code_functions" section to an array by the same name. > > - Define a function unwinder_blacklisted() that compares a return > PC against sym_code_sections[]. If there is a match, mark the > stack trace unreliable. Call this from unwind_frame(). > > v3: > - Implemented a sym_code_ranges[] array to contains sections bounds > for text sections that contain SYM_CODE_*() functions. The unwinder > checks each return PC against the sections. If it falls in any of > the sections, the stack trace is marked unreliable. > > - Moved SYM_CODE functions from .text and .init.text into a new > text section called ".code.text". Added this section to > vmlinux.lds.S and sym_code_ranges[]. > > - Fixed the logic in the unwinder that handles Function Graph > Tracer return trampoline. > > - Removed all the previous code that handles: > - ftrace entry code for traced function > - special_functions[] array that lists individual functions > - kretprobe_trampoline() special case > > v2 > - Removed the terminating entry { 0, 0 } in special_functions[] > and replaced it with the idiom { /* sentinel */ }. > > - Change the ftrace trampoline entry ftrace_graph_call in > special_functions[] to ftrace_call + 4 and added explanatory > comments. > > - Unnested #ifdefs in special_functions[] for FTRACE. > > v1 > - Define a bool field in struct stackframe. This will indicate if > a stack trace is reliable. > > - Implement a special_functions[] array that will be populated > with special functions in which the stack trace is considered > unreliable. > > - Using kallsyms_lookup(), get the address ranges for the special > functions and record them. > > - Implement an is_reliable_function(pc). This function will check > if a given return PC falls in any of the special functions. If > it does, the stack trace is unreliable. > > - Implement check_reliability() function that will check if a > stack frame is reliable. Call is_reliable_function() from > check_reliability(). > > - Before a return PC is checked against special_funtions[], it > must be validates as a proper kernel text address. Call > __kernel_text_address() from check_reliability(). > > - Finally, call check_reliability() from unwind_frame() for > each stack frame. > > - Add EL1 exception handlers to special_functions[]. > > el1_sync(); > el1_irq(); > el1_error(); > el1_sync_invalid(); > el1_irq_invalid(); > el1_fiq_invalid(); > el1_error_invalid(); > > - The above functions are currently defined as LOCAL symbols. > Make them global so that they can be referenced from the > unwinder code. > > - Add FTRACE trampolines to special_functions[]: > > ftrace_graph_call() > ftrace_graph_caller() > return_to_handler() > > - Add the kretprobe trampoline to special functions[]: > > kretprobe_trampoline() > > Previous versions and discussion > ================================ > > v6: https://lore.kernel.org/linux-arm-kernel/20210630223356.58714-1-madvenka@linux.microsoft.com/ > v5: https://lore.kernel.org/linux-arm-kernel/20210526214917.20099-1-madvenka@linux.microsoft.com/ > v4: https://lore.kernel.org/linux-arm-kernel/20210516040018.128105-1-madvenka@linux.microsoft.com/ > v3: https://lore.kernel.org/linux-arm-kernel/20210503173615.21576-1-madvenka@linux.microsoft.com/ > v2: https://lore.kernel.org/linux-arm-kernel/20210405204313.21346-1-madvenka@linux.microsoft.com/ > v1: https://lore.kernel.org/linux-arm-kernel/20210330190955.13707-1-madvenka@linux.microsoft.com/ > Madhavan T. Venkataraman (4): > arm64: Make all stack walking functions use arch_stack_walk() > arm64: Reorganize the unwinder code for better consistency and > maintenance > arm64: Introduce stack trace reliability checks in the unwinder > arm64: Create a list of SYM_CODE functions, check return PC against > list > > arch/arm64/include/asm/linkage.h | 12 ++ > arch/arm64/include/asm/sections.h | 1 + > arch/arm64/include/asm/stacktrace.h | 16 +- > arch/arm64/kernel/perf_callchain.c | 5 +- > arch/arm64/kernel/process.c | 39 ++-- > arch/arm64/kernel/return_address.c | 6 +- > arch/arm64/kernel/stacktrace.c | 291 ++++++++++++++++++++-------- > arch/arm64/kernel/time.c | 22 ++- > arch/arm64/kernel/vmlinux.lds.S | 10 + > 9 files changed, 277 insertions(+), 125 deletions(-) > > > base-commit: 36a21d51725af2ce0700c6ebcb6b9594aac658a6 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel