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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 6A0DCC43613 for ; Fri, 21 Jun 2019 14:50:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3DA50208C3 for ; Fri, 21 Jun 2019 14:50:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561128641; bh=S09RYkUMMxHYoHx76cTWh53Cqr6Fibp+qLvkSIpPItQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=MPDIxRtWG6eluoYt0P1VQfaIXvMEG5z4I2E1RL8D7WVr8IRGpYzX/3hsw3oaU41Fh CEBO7awlD3nR8DiElYFnC3oYdLTr1zqSUyBfWkiY8UsXBXPdJCUeFrSq2ImPKMUJ/R k0n7LnHc54rT8W/NSPZkCkfpnj2JqK53Oz4j596U= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726233AbfFUOuj (ORCPT ); Fri, 21 Jun 2019 10:50:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:39318 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726031AbfFUOuj (ORCPT ); Fri, 21 Jun 2019 10:50:39 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A8CC92089E; Fri, 21 Jun 2019 14:50:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561128638; bh=S09RYkUMMxHYoHx76cTWh53Cqr6Fibp+qLvkSIpPItQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=VTUHdnMaOZ0iDcqeySu7ks48hk5JDg+Vls1nObiTqE94DrxyTAcElQrmmD0FfzeE9 AwmbDFds/aoQsDKuurx+IyjCDHZpJZduH7+ddd7CTjxtE1jKJw5wlP3K/vPLj2FMDx wx5gT00rQzju9oABrDET2XzyIALVVE/Zxk+5tSlI= Date: Fri, 21 Jun 2019 23:50:34 +0900 From: Masami Hiramatsu To: "Naveen N. Rao" Cc: Michael Ellerman , Steven Rostedt , Ingo Molnar , Nicholas Piggin , , Subject: Re: [PATCH 7/7] powerpc/kprobes: Allow probing on any ftrace address Message-Id: <20190621235034.acc00fc3e2b2c7e89caa1fd5@kernel.org> In-Reply-To: References: X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 18 Jun 2019 20:17:06 +0530 "Naveen N. Rao" wrote: > With KPROBES_ON_FTRACE, kprobe is allowed to be inserted on instructions > that branch to _mcount (referred to as ftrace location). With > -mprofile-kernel, we now include the preceding 'mflr r0' as being part > of the ftrace location. > > However, by default, probing on an instruction that is not actually the > branch to _mcount() is prohibited, as that is considered to not be at an > instruction boundary. This is not the case on powerpc, so allow the same > by overriding arch_check_ftrace_location() > > In addition, we update kprobe_ftrace_handler() to detect this scenarios > and to pass the proper nip to the pre and post probe handlers. > > Signed-off-by: Naveen N. Rao > --- > arch/powerpc/kernel/kprobes-ftrace.c | 30 ++++++++++++++++++++++++++++ > 1 file changed, 30 insertions(+) > > diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c > index 972cb28174b2..6a0bd3c16cb6 100644 > --- a/arch/powerpc/kernel/kprobes-ftrace.c > +++ b/arch/powerpc/kernel/kprobes-ftrace.c > @@ -12,14 +12,34 @@ > #include > #include > > +/* > + * With -mprofile-kernel, we patch two instructions -- the branch to _mcount > + * as well as the preceding 'mflr r0'. Both these instructions are claimed > + * by ftrace and we should allow probing on either instruction. > + */ > +int arch_check_ftrace_location(struct kprobe *p) > +{ > + if (ftrace_location((unsigned long)p->addr)) > + p->flags |= KPROBE_FLAG_FTRACE; > + return 0; > +} > + > /* Ftrace callback handler for kprobes */ > void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, > struct ftrace_ops *ops, struct pt_regs *regs) > { > struct kprobe *p; > + int mflr_kprobe = 0; > struct kprobe_ctlblk *kcb; > > p = get_kprobe((kprobe_opcode_t *)nip); > + if (unlikely(!p)) { Hmm, is this really unlikely? If we put a kprobe on the second instruction address, we will see p == NULL always. > + p = get_kprobe((kprobe_opcode_t *)(nip - MCOUNT_INSN_SIZE)); > + if (!p) Here will be unlikely, because we can not find kprobe at both of nip and nip - MCOUNT_INSN_SIZE. > + return; > + mflr_kprobe = 1; > + } > + > if (unlikely(!p) || kprobe_disabled(p)) "unlikely(!p)" is not needed here. Thank you, > return; > > @@ -33,6 +53,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, > */ > regs->nip -= MCOUNT_INSN_SIZE; > > + if (mflr_kprobe) > + regs->nip -= MCOUNT_INSN_SIZE; > + > __this_cpu_write(current_kprobe, p); > kcb->kprobe_status = KPROBE_HIT_ACTIVE; > if (!p->pre_handler || !p->pre_handler(p, regs)) { > @@ -45,6 +68,8 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip, > kcb->kprobe_status = KPROBE_HIT_SSDONE; > p->post_handler(p, regs, 0); > } > + if (mflr_kprobe) > + regs->nip += MCOUNT_INSN_SIZE; > } > /* > * If pre_handler returns !0, it changes regs->nip. We have to > @@ -57,6 +82,11 @@ NOKPROBE_SYMBOL(kprobe_ftrace_handler); > > int arch_prepare_kprobe_ftrace(struct kprobe *p) > { > + if ((unsigned long)p->addr & 0x03) { > + printk("Attempt to register kprobe at an unaligned address\n"); > + return -EILSEQ; > + } > + > p->ainsn.insn = NULL; > p->ainsn.boostable = -1; > return 0; > -- > 2.22.0 > -- Masami Hiramatsu