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 E8EB4C433F5 for ; Thu, 24 Feb 2022 04:02:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229886AbiBXEDD (ORCPT ); Wed, 23 Feb 2022 23:03:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229481AbiBXEDB (ORCPT ); Wed, 23 Feb 2022 23:03:01 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 631DD165C0C; Wed, 23 Feb 2022 20:02:30 -0800 (PST) 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 E341EB8239B; Thu, 24 Feb 2022 04:02:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 386CFC340E9; Thu, 24 Feb 2022 04:02:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1645675347; bh=3vCCFqBbB+V46g9xXrlXgv9ohgrCK1afy9Vw/vL8ThU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=WNE2BzTEn51E0IHTFwRFu6XfIU0A6GdoVVgU8T0LMsV/nSlKjY+GXeAcRyStTSS1C I1givN5OHQx1Cw3Pu4WUGbCSkCC28ofPypyJF/A7ctbmy708cLnY/7BV/2NfDkgEaX 4eXYpX7vCbWz61gSlSp7jf3qwJN+VPmwXs0EZW0HQ3yX2c/0V++47CCDums1Gnxs6K FOUMwvBfh95dY9SP++5TEFhdIFBuQpXP2+QNzO8Jkz6EdW3nLrQW1tecUm/2Db6sBJ eNz9N2B90jtMbVk45XUU4ZzacxB+BD7ZodxRurUrhY+TUjTcZSG4cnGWs4TXJnq7aB biMnu1IMnFGKQ== Date: Thu, 24 Feb 2022 13:02:23 +0900 From: Masami Hiramatsu To: Jiri Olsa Cc: Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , netdev@vger.kernel.org, bpf@vger.kernel.org, lkml , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Steven Rostedt Subject: Re: [PATCH 02/10] bpf: Add multi kprobe link Message-Id: <20220224130223.70cd09a9f0fe1209bf36bad0@kernel.org> In-Reply-To: References: <20220222170600.611515-1-jolsa@kernel.org> <20220222170600.611515-3-jolsa@kernel.org> <20220223145840.64f708ed2357c89039f55f07@kernel.org> 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, 23 Feb 2022 18:44:33 +0100 Jiri Olsa wrote: > On Wed, Feb 23, 2022 at 02:58:40PM +0900, Masami Hiramatsu wrote: > > Hi Jiri, > > > > On Tue, 22 Feb 2022 18:05:52 +0100 > > Jiri Olsa wrote: > > > > [snip] > > > + > > > +static void > > > +kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip, > > > + struct pt_regs *regs) > > > +{ > > > + unsigned long saved_ip = instruction_pointer(regs); > > > + struct bpf_kprobe_multi_link *link; > > > + > > > + /* > > > + * Because fprobe's regs->ip is set to the next instruction of > > > + * dynamic-ftrace instruction, correct entry ip must be set, so > > > + * that the bpf program can access entry address via regs as same > > > + * as kprobes. > > > + */ > > > + instruction_pointer_set(regs, entry_ip); > > > > This is true for the entry_handler, but false for the exit_handler, > > because entry_ip points the probed function address, not the > > return address. Thus, when this is done in the exit_handler, > > the bpf prog seems to be called from the entry of the function, > > not return. > > > > If it is what you expected, please explictly comment it to > > avoid confusion. Or, make another handler function for exit > > probing. > > yes we want the ip of the function we are tracing, so it's correct, > I'll adjust the comment > > > > > > + > > > + link = container_of(fp, struct bpf_kprobe_multi_link, fp); > > > + kprobe_multi_link_prog_run(link, regs); > > > + > > > + instruction_pointer_set(regs, saved_ip); > > > +} > > > + > > > +static int > > > +kprobe_multi_resolve_syms(const void *usyms, u32 cnt, > > > + unsigned long *addrs) > > > +{ > > > + unsigned long addr, size; > > > + const char **syms; > > > + int err = -ENOMEM; > > > + unsigned int i; > > > + char *func; > > > + > > > + size = cnt * sizeof(*syms); > > > + syms = kvzalloc(size, GFP_KERNEL); > > > + if (!syms) > > > + return -ENOMEM; > > > + > > > + func = kmalloc(KSYM_NAME_LEN, GFP_KERNEL); > > > + if (!func) > > > + goto error; > > > + > > > + if (copy_from_user(syms, usyms, size)) { > > > + err = -EFAULT; > > > + goto error; > > > + } > > > + > > > + for (i = 0; i < cnt; i++) { > > > + err = strncpy_from_user(func, syms[i], KSYM_NAME_LEN); > > > + if (err == KSYM_NAME_LEN) > > > + err = -E2BIG; > > > + if (err < 0) > > > + goto error; > > > + > > > + err = -EINVAL; > > > + if (func[0] == '\0') > > > + goto error; > > > + addr = kallsyms_lookup_name(func); > > > + if (!addr) > > > + goto error; > > > + if (!kallsyms_lookup_size_offset(addr, &size, NULL)) > > > + size = MCOUNT_INSN_SIZE; > > > > Note that this is good for x86, but may not be good for other arch > > which use some preparation instructions before mcount call. Maybe you > > can just reject it if kallsyms_lookup_size_offset() fails. > > I 'borrowed' this from fprobe's get_ftrace_locations function, > and it still seems to match.. do you plan to change that? Oops, indeed, I need to fix my code too! Thank you! > > thanks, > jirka -- Masami Hiramatsu