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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3020FC433F5 for ; Wed, 11 May 2022 14:35:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244735AbiEKOfR (ORCPT ); Wed, 11 May 2022 10:35:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240207AbiEKOe7 (ORCPT ); Wed, 11 May 2022 10:34:59 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C8BAB6A02A for ; Wed, 11 May 2022 07:34:58 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 8B0C8B82073 for ; Wed, 11 May 2022 14:34:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3D091C34113; Wed, 11 May 2022 14:34:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652279696; bh=t7NtYe4g+ZzXlwVJbcVCuf8BrT1ifHZjftu0dkcPeDU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=To96SnoomjvJcuaMcVymixOJKBqwvB0ITJ+cp+vmiv8nwaFwLDwKSKJ/Sr+oLcrR5 TyQh9/nvJJtSIxdnQPCdaQkXOAxZGiMSemQmOsGMGmspApEEZuYY8eAnpZHNiEOJh2 bpiKc+VpbVcbtRQravcMqQ5F7cgSyzOiRHSxmdTqw60/TuZmyFIZBBWuWltVhIg/wk DWH8JzHRc0JiNYk0Ox5rmApFMwqjD6cTikfNyrQ6dFkNv1TD3RrveXHQtpdMY7apuK beMKIK9UmoQYfJqU/T3YtjEQTPCtKKJJ5fFRo6WpIPsD7RtQngDab7O2rctMyb20+M ti4O54qXJ/VNg== Date: Wed, 11 May 2022 23:34:50 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: Mark Rutland , Wang ShaoBo , cj.chengjian@huawei.com, huawei.libin@huawei.com, xiexiuqi@huawei.com, liwei391@huawei.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, will@kernel.org, zengshun.wu@outlook.com, Jiri Olsa Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines Message-Id: <20220511233450.40136cdf6a53eb32cd825be8@kernel.org> In-Reply-To: <20220510104446.6d23b596@gandalf.local.home> References: <20220421100639.03c0d123@gandalf.local.home> <20220421114201.21228eeb@gandalf.local.home> <20220421130648.56b21951@gandalf.local.home> <20220422114541.34d71ad9@gandalf.local.home> <20220426174749.b5372c5769af7bf901649a05@kernel.org> <20220505121538.04773ac98e2a8ba17f675d39@kernel.org> <20220509142203.6c4f2913@gandalf.local.home> <20220510181012.d5cba23a2547f14d14f016b9@kernel.org> <20220510104446.6d23b596@gandalf.local.home> 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 Tue, 10 May 2022 10:44:46 -0400 Steven Rostedt wrote: > On Tue, 10 May 2022 18:10:12 +0900 > Masami Hiramatsu wrote: > > > > > > > This was suggested by both Peter Zijlstra and Thomas Gleixner when I > > > introduced FTRACE_WITH_ARGS, where all functions can now get the arguments > > > from fregs, but not the full pt_regs. > > > > Hmm, I thought the ftrace_get_regs() is the all-or-nothing interface, or > > is there any way to get the arguments from fregs? > > Not yet generically. But that can easily be added. If you look at x86 live > patching, since it is arch specific, it just took the regs parameter > directly, knowing that the args were already set up. That is, ftrace_regs is > just a wrapper around pt_regs with just the regs for the arguments and stack > initialized. If you get regs from ftrace_get_regs(fregs) it will return > NULL if it wasn't full set of regs. But we can add generic functions to get > the parameters. > > That is, we can create a ftrace_get_kernel_argument() function that takes > fregs instead of pt_regs, and produce the same thing as > regs_get_kernel_argument(). > > x86 live kernel patching has this: > > arch/x86/include/asm/ftrace.h: > > #define ftrace_instruction_pointer_set(fregs, _ip) \ > do { (fregs)->regs.ip = (_ip); } while (0) > > > arch/x86/include/asm/livepatch.h: > > static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip) > { > ftrace_instruction_pointer_set(fregs, ip); > } > > Where fregs is not a full set of regs. OK, so fregs::regs will have a subset of pt_regs, and accessibility of the registers depends on the architecture. If we can have a checker like ftrace_regs_exist(fregs, reg_offset) kprobe on ftrace or fprobe user (BPF) can filter user's requests. I think I can introduce a flag for kprobes so that user can make a kprobe handler only using a subset of registers. Maybe similar filter code is also needed for BPF 'user space' library because this check must be done when compiling BPF. Thank you, > > > > > If a ftrace_ops has the REGS flag set > > > (using ftrace_regs_caller), the ftrace_get_regs(fregs) will return the > > > pt_regs, or it will return NULL if ftrace_regs_caller was not used. > > > > > > This way the same parameter can provide full pt_regs or a subset, and have > > > an generic interface to tell the difference. > > > > If it can provide a partial (subset of) pt_regs, that could be good for me > > too, since at least kprobe-events on ftrace can check the traced register > > is in the subset or not and reject it if it doesn't saved. > > That's exactly the use case for ftrace_regs. > > -- Steve -- Masami Hiramatsu