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 41207C2D0DC for ; Thu, 26 Dec 2019 02:57:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16D0320828 for ; Thu, 26 Dec 2019 02:57:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1577329034; bh=rbkElJWAXkNtRfh891s+ZThXz0VfuU0P2LJA4L64enU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=MlUZJ1rktuhsNlDM3l1I3nFn6wqYgf25R664sGM0XtPmvhsGRWJWKlTp1e3E1kgOB U9BC/uVfsPOl2kTUVPf1cEYG5UOOpjGrwdGKBdAiAKQW7eJERqvFjDqOppj4LeVQip cljFKh4CAjjurp38ml+f2+tLXVJoNtVLAMdnn4mw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726943AbfLZC5N (ORCPT ); Wed, 25 Dec 2019 21:57:13 -0500 Received: from mail.kernel.org ([198.145.29.99]:54856 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726885AbfLZC5N (ORCPT ); Wed, 25 Dec 2019 21:57:13 -0500 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 6B667207FF; Thu, 26 Dec 2019 02:57:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1577329031; bh=rbkElJWAXkNtRfh891s+ZThXz0VfuU0P2LJA4L64enU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=kKgMG+jnL7SaYdWm7+P1acCEiRvKB+Xlg11reRfkuRWid8dPLiItX6YxmNwHTlyE+ JK/ObqfLtSonTmDp5/u2lAezNrOYEMJkIMVdREES6Hm5ymm67TYMsjFBMZqrjIOG2q FTWgUkD3KlGOo5Jo4KnkGs4Ox7BMmhRvhtmfLpB0= Date: Thu, 26 Dec 2019 11:57:07 +0900 From: Masami Hiramatsu To: Jisheng Zhang Cc: Catalin Marinas , Will Deacon , Steven Rostedt , Ingo Molnar , "Naveen N. Rao" , Anil S Keshavamurthy , "David S. Miller" , Mark Rutland , Jonathan Corbet , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-doc@vger.kernel.org" Subject: Re: [PATCH v7 3/3] arm64: implement KPROBES_ON_FTRACE Message-Id: <20191226115707.902545688aa90b34e2e550b3@kernel.org> In-Reply-To: <20191225173001.6c0e3fb2@xhacker.debian> References: <20191225172625.69811b3e@xhacker.debian> <20191225173001.6c0e3fb2@xhacker.debian> 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 Hi Jisheng, On Wed, 25 Dec 2019 09:44:21 +0000 Jisheng Zhang wrote: > KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it > eliminates the need for a trap, as well as the need to emulate or > single-step instructions. > > Tested on berlin arm64 platform. > > ~ # mount -t debugfs debugfs /sys/kernel/debug/ > ~ # cd /sys/kernel/debug/ > /sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events > > before the patch: > > /sys/kernel/debug # cat kprobes/list > ffffff801009fe28 k _do_fork+0x0 [DISABLED] > > after the patch: > > /sys/kernel/debug # cat kprobes/list > ffffff801009ff54 k _do_fork+0x0 [DISABLED][FTRACE] What happens if user puts a probe on _do_fork+4? Is that return -EILSEQ correctly? > > Signed-off-by: Jisheng Zhang > --- > .../debug/kprobes-on-ftrace/arch-support.txt | 2 +- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/ftrace.h | 1 + > arch/arm64/kernel/probes/Makefile | 1 + > arch/arm64/kernel/probes/ftrace.c | 78 +++++++++++++++++++ > 5 files changed, 82 insertions(+), 1 deletion(-) > create mode 100644 arch/arm64/kernel/probes/ftrace.c > > diff --git a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > index 4fae0464ddff..f9dd9dd91e0c 100644 > --- a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > +++ b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > @@ -9,7 +9,7 @@ > | alpha: | TODO | > | arc: | TODO | > | arm: | TODO | > - | arm64: | TODO | > + | arm64: | ok | > | c6x: | TODO | > | csky: | TODO | > | h8300: | TODO | > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index b1b4476ddb83..92b9882889ac 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -166,6 +166,7 @@ config ARM64 > select HAVE_STACKPROTECTOR > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES > + select HAVE_KPROBES_ON_FTRACE > select HAVE_KRETPROBES > select HAVE_GENERIC_VDSO > select IOMMU_DMA if IOMMU_SUPPORT > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > index 91fa4baa1a93..875aeb839654 100644 > --- a/arch/arm64/include/asm/ftrace.h > +++ b/arch/arm64/include/asm/ftrace.h > @@ -20,6 +20,7 @@ > > /* The BL at the callsite's adjusted rec->ip */ > #define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE > +#define FTRACE_IP_EXTENSION MCOUNT_INSN_SIZE > > #define FTRACE_PLT_IDX 0 > #define FTRACE_REGS_PLT_IDX 1 > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile > index 8e4be92e25b1..4020cfc66564 100644 > --- a/arch/arm64/kernel/probes/Makefile > +++ b/arch/arm64/kernel/probes/Makefile > @@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \ > simulate-insn.o > obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \ > simulate-insn.o > +obj-$(CONFIG_KPROBES_ON_FTRACE) += ftrace.o > diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/ftrace.c > new file mode 100644 > index 000000000000..0643aa2dacdb > --- /dev/null > +++ b/arch/arm64/kernel/probes/ftrace.c > @@ -0,0 +1,78 @@ > +// SPDX-License-Identifier: GPL-2.0-or-later > +/* > + * Dynamic Ftrace based Kprobes Optimization > + * > + * Copyright (C) Hitachi Ltd., 2012 > + * Copyright (C) 2019 Jisheng Zhang > + * Synaptics Incorporated > + */ > + > +#include > + > +/* > + * In arm64 FTRACE_WITH_REGS implementation, we patch two nop instructions: > + * the lr saver and bl ftrace-entry. Both these instructions are claimed > + * by ftrace and we should allow probing on either instruction. No, the 2nd bl ftrace-entry must not be probed. The pair of lr-saver and bl ftrace-entry is tightly coupled. You can not decouple it. > + */ > +int arch_check_ftrace_location(struct kprobe *p) > +{ > + if (ftrace_location((unsigned long)p->addr)) > + p->flags |= KPROBE_FLAG_FTRACE; > + return 0; > +} Thus, this must return -EILSEQ if user puts a probe on the bl. > + > +/* Ftrace callback handler for kprobes -- called under preepmt disabed */ > +void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip, > + struct ftrace_ops *ops, struct pt_regs *regs) > +{ > + bool lr_saver = false; > + struct kprobe *p; > + struct kprobe_ctlblk *kcb; > + > + /* Preempt is disabled by ftrace */ > + p = get_kprobe((kprobe_opcode_t *)ip); > + if (!p) { > + p = get_kprobe((kprobe_opcode_t *)(ip - MCOUNT_INSN_SIZE)); > + if (unlikely(!p) || kprobe_disabled(p)) > + return; > + lr_saver = true; Then, this can be removed. > + } > + > + kcb = get_kprobe_ctlblk(); > + if (kprobe_running()) { > + kprobes_inc_nmissed_count(p); > + } else { > + unsigned long orig_ip = instruction_pointer(regs); > + > + if (lr_saver) > + ip -= MCOUNT_INSN_SIZE; Ditto. Thank you, > + instruction_pointer_set(regs, ip); > + __this_cpu_write(current_kprobe, p); > + kcb->kprobe_status = KPROBE_HIT_ACTIVE; > + if (!p->pre_handler || !p->pre_handler(p, regs)) { > + /* > + * Emulate singlestep (and also recover regs->pc) > + * as if there is a nop > + */ > + instruction_pointer_set(regs, > + (unsigned long)p->addr + MCOUNT_INSN_SIZE); > + if (unlikely(p->post_handler)) { > + kcb->kprobe_status = KPROBE_HIT_SSDONE; > + p->post_handler(p, regs, 0); > + } > + instruction_pointer_set(regs, orig_ip); > + } > + /* > + * If pre_handler returns !0, it changes regs->pc. We have to > + * skip emulating post_handler. > + */ > + __this_cpu_write(current_kprobe, NULL); > + } > +} > +NOKPROBE_SYMBOL(kprobe_ftrace_handler); > + > +int arch_prepare_kprobe_ftrace(struct kprobe *p) > +{ > + p->ainsn.api.insn = NULL; > + return 0; > +} > -- > 2.24.1 > -- Masami Hiramatsu