linux-kernel - Re: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON

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Date:   Tue, 20 Aug 2019 09:01:30 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "David S. Miller" <davem@...emloft.net>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE

Hi Jisheng,

On Mon, 19 Aug 2019 11:36:09 +0000
Jisheng Zhang <Jisheng.Zhang@...aptics.com> wrote:

> For KPROBES_ON_FTRACE case, we need to adjust the kprobe's addr
> correspondingly.

No, I think you have misunderstood what the ftrace_call_adjust() does.
Ftrace's rec->ip is already adjusted when initializing it. Kprobes
checks the list after initialized (adjusted). So you don't need to
adjust it again.

BTW, this type of hidden adjustment should be avoided by design.
If you find user specifies wrong address, return error instead of
adjust it silently.

Thank you,

> 
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> ---
>  kernel/kprobes.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 9873fc627d61..f8400753a8a9 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1560,6 +1560,9 @@ int register_kprobe(struct kprobe *p)
>  	addr = kprobe_addr(p);
>  	if (IS_ERR(addr))
>  		return PTR_ERR(addr);
> +#ifdef CONFIG_KPROBES_ON_FTRACE
> +	addr = (kprobe_opcode_t *)ftrace_call_adjust((unsigned long)addr);
> +#endif
>  	p->addr = addr;
>  
>  	ret = check_kprobe_rereg(p);
> -- 
> 2.23.0.rc1
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>