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 1F9D6C433F5 for ; Thu, 12 May 2022 12:02:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353511AbiELMCn (ORCPT ); Thu, 12 May 2022 08:02:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50568 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353504AbiELMCi (ORCPT ); Thu, 12 May 2022 08:02:38 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D3CA822A898 for ; Thu, 12 May 2022 05:02:37 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 6C00761F08 for ; Thu, 12 May 2022 12:02:37 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8604C385B8; Thu, 12 May 2022 12:02:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1652356956; bh=GddqpRN5crcgCx8YyYPEmUnEbQms5XbDgQpHleOXt5g=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=A+3EACV/vZh+KTHIPAul+vmmzBm0FXizErZwBy2TdJ1Oo+tb0HvILt8g/Bplz/t0s HL5J0EXAC97h07CHoUz2lITPDdH8uKNYN+4Z6cJldpva19dBWNhqdtLrAgKNdKrtiw bKsxxNRUdR7YOF5AdxxxjfR5GQg9UM82s6w2Zx6p7J1iwh4KpZAv6HhRB9XoC2mGRf dwLK09QuNhuXaAG1JgsWkZZmsl/2snI6eTr69D4RxEt1EOv1hKWY9/knM0shAapyjK NQCL+a6F7QA816IVXm3hr4JsTbfqjZ3uF4/xiQcYDVrfCj8bt9hTGtQGjhL8l574je Na6lcWWmBbK+A== Date: Thu, 12 May 2022 21:02:31 +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: <20220512210231.f9178a98f20a37981b1e89e3@kernel.org> In-Reply-To: <20220511111207.25d1a693@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> <20220511233450.40136cdf6a53eb32cd825be8@kernel.org> <20220511111207.25d1a693@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 Wed, 11 May 2022 11:12:07 -0400 Steven Rostedt wrote: > On Wed, 11 May 2022 23:34:50 +0900 > Masami Hiramatsu wrote: > > > 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) > > Or something. I'd have to see the use case. > > > > > 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. > > Is there any other case without full regs that the user would want anything > other than the args, stack pointer and instruction pointer? For the kprobes APIs/events, yes, it needs to access to the registers which is used for local variables when probing inside the function body. However at the function entry, I think almost no use case. (BTW, pstate is a bit special, that may show the actual processor-level status (context), so for the debugging, user might want to read it.) Thus the BPF use case via fprobes, I think there is no usecase. My concern is that the BPF may allow user program to access any field of pt_regs. Thus if the user miss-programmed, they may see a wrong value (I guess the fregs is not zero-filled) for unsaved registers. > That is, have a flag that says "only_args" or something, that says they > will only get the registers for arguments, a stack pointer, and the > instruction pointer (note, the fregs may not have the instruction pointer > as that is passed to the the caller via the "ip" parameter. If the fregs > needs that, we can add a "ftrace_regs_set_ip()" before calling the > callback registered to the fprobe). Yes, that is what I'm thinking. If "only_args" flag is set, BPF runtime must check the user program. And if it finds the program access the unsaved registers, it should stop executing. BTW, "what register is saved" can be determined statically, thus I think we just need the offset for checking (for fprobe usecase, since it will set the ftrace_ops flag by itself.) Thank you, -- Masami Hiramatsu (Google)