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Subject: Re: [PATCH] arm64/kprobe: add support for KPROBES_ON_FTRACE
To:     <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
CC:     <will@kernel.org>, <catalin.marinas@arm.com>,
        <mhiramat@kernel.org>, <naveen.n.rao@linux.ibm.com>,
        <sandeepa.s.prabhu@gmail.com>, <bobo.shaobowang@huawei.com>
References: <20191223123828.39543-1-cj.chengjian@huawei.com>
From:   "chengjian (D)" <cj.chengjian@huawei.com>
Message-ID: <a7c7b8f0-126e-a755-43ee-d384de74e43e@huawei.com>
Date:   Mon, 23 Dec 2019 20:39:10 +0800
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I am SORRY.

I searched on patchwork and found this :

arm64: implement KPROBES_ON_FTRACE

https://lore.kernel.org/patchwork/patch/1169445/

So please ignore my EMAIL.

Thank you.

---- Cheng Jian


On 2019/12/23 20:38, Cheng Jian wrote:
> Allow KPROBES to use the ftrace infrastructure.
> This depends on HAVE_DYNAMIC_FTRACE_WITH_REGS
> which introduce by :
>          commit 3b23e4991fb6 ("arm64: implement ftrace with regs")
>
> Based on the x86 code by Masami.
>
> With:
>          # cd /sys/kernel/debug/tracing
>          # echo 'p _do_fork+0x4' > kprobe_events
>
> before patch:
> 	# cat ../kprobes/list
>          sh: write error: Invalid argument
>
> after patch:
> 	# cat ../kprobes/list
>          ffffa00016aa9d4c  k  _do_fork+0x4    [FTRACE]
>
> Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
> ---
>   .../debug/kprobes-on-ftrace/arch-support.txt  |  2 +-
>   arch/arm64/Kconfig                            |  1 +
>   arch/arm64/kernel/probes/Makefile             |  2 +
>   arch/arm64/kernel/probes/ftrace.c             | 65 +++++++++++++++++++
>   4 files changed, 69 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..d613be9c2346 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -144,6 +144,7 @@ config ARM64
>   	select HAVE_DYNAMIC_FTRACE
>   	select HAVE_DYNAMIC_FTRACE_WITH_REGS \
>   		if $(cc-option,-fpatchable-function-entry=2)
> +	select HAVE_KPROBES_ON_FTRACE if HAVE_DYNAMIC_FTRACE_WITH_REGS
>   	select HAVE_EFFICIENT_UNALIGNED_ACCESS
>   	select HAVE_FAST_GUP
>   	select HAVE_FTRACE_MCOUNT_RECORD
> diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile
> index 8e4be92e25b1..45a9d916a47d 100644
> --- a/arch/arm64/kernel/probes/Makefile
> +++ b/arch/arm64/kernel/probes/Makefile
> @@ -4,3 +4,5 @@ obj-$(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..f89bfaa3e5f3
> --- /dev/null
> +++ b/arch/arm64/kernel/probes/ftrace.c
> @@ -0,0 +1,65 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Dynamic Ftrace based Kprobes Optimization
> + *
> + * Copyright (C) Hitachi Ltd., 2012
> + * Copyright (C) 2019 Huawei Inc.
> + * Copyright 2019 Cheng Jian <cj.chengjian@huawei.com>
> + */
> +#include <linux/kprobes.h>
> +#include <linux/ptrace.h>
> +#include <linux/hardirq.h>
> +#include <linux/preempt.h>
> +#include <linux/ftrace.h>
> +
> +
> +/* Ftrace callback handler for kprobes -- called under preepmt disabed */
> +void kprobe_ftrace_handler(unsigned long pc, unsigned long parent_pc,
> +			   struct ftrace_ops *ops, struct pt_regs *regs)
> +{
> +	struct kprobe *p;
> +	struct kprobe_ctlblk *kcb;
> +
> +	/* Preempt is disabled by ftrace */
> +	p = get_kprobe((kprobe_opcode_t *)pc);
> +	if (unlikely(!p) || kprobe_disabled(p))
> +		return;
> +
> +	kcb = get_kprobe_ctlblk();
> +	if (kprobe_running()) {
> +		kprobes_inc_nmissed_count(p);
> +	} else {
> +		/*
> +		 * On ARM64, recg->pc is *before* this instruction for the
> +		 * pre handler.
> +		 */
> +		regs->pc -= MCOUNT_INSN_SIZE;
> +
> +		__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->ip)
> +			 * as if there is a nop
> +			 */
> +			regs->pc += MCOUNT_INSN_SIZE;
> +			if (unlikely(p->post_handler)) {
> +				kcb->kprobe_status = KPROBE_HIT_SSDONE;
> +				p->post_handler(p, regs, 0);
> +			}
> +		}
> +		/*
> +		 * If pre_handler returns !0, it changes regs->ip. 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;
> +}