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Date:   Mon, 19 Aug 2019 22:13:02 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Subject: Re: [PATCH 1/4] kprobes: adjust kprobe addr for KPROBES_ON_FTRACE
To:     Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        "David S. Miller" <davem@davemloft.net>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Jisheng Zhang <Jisheng.Zhang@synaptics.com>,
        =?iso-8859-1?q?Masami=0A?= Hiramatsu <mhiramat@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>
Cc:     "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>
References: <20190819192422.5ed79702@xhacker.debian>
        <20190819192505.483c0bf0@xhacker.debian>
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Jisheng Zhang wrote:
> For KPROBES_ON_FTRACE case, we need to adjust the kprobe's addr
> correspondingly.
> 
> Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.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;

I'm not sure what this is achieving, but looks wrong to me.

If you intend to have kprobes default to using ftrace entry for probing 
functions, consider over-riding kprobe_lookup_name() -- see powerpc 
variant for example.


- Naveen