linux-kernel - Re: [PATCH v7 1/3] kprobes/ftrace: Use ftrace

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Date:   Wed, 25 Dec 2019 09:46:35 +0000
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Corbet <corbet@....net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v7 1/3] kprobes/ftrace: Use ftrace_location() when
 [dis]arming probes

On Wed, 25 Dec 2019 09:42:07 +0000 Jisheng Zhang wrote:
> 

oops, I missed "From: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>"

I will take care this point when posting new version.


> Ftrace location could include more than a single instruction in case
> of some architectures (powerpc64, for now). In this case, kprobe is
> permitted on any of those instructions, and uses ftrace infrastructure
> for functioning.
> 
> However, [dis]arm_kprobe_ftrace() uses the kprobe address when setting
> up ftrace filter IP. This won't work if the address points to any
> instruction apart from the one that has a branch to _mcount(). To
> resolve this, have [dis]arm_kprobe_ftrace() use ftrace_function() to
> identify the filter IP.
> 
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  kernel/kprobes.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 53534aa258a6..5c630b424e3a 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -986,9 +986,10 @@ static int prepare_kprobe(struct kprobe *p)
>  static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
>                                int *cnt)
>  {
> +       unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
>         int ret = 0;
> 
> -       ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 0, 0);
> +       ret = ftrace_set_filter_ip(ops, ftrace_ip, 0, 0);
>         if (ret) {
>                 pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
>                          p->addr, ret);
> @@ -1011,7 +1012,7 @@ static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
>          * At this point, sinec ops is not registered, we should be sefe from
>          * registering empty filter.
>          */
> -       ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
> +       ftrace_set_filter_ip(ops, ftrace_ip, 1, 0);
>         return ret;
>  }
> 
> @@ -1028,6 +1029,7 @@ static int arm_kprobe_ftrace(struct kprobe *p)
>  static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
>                                   int *cnt)
>  {
> +       unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
>         int ret = 0;
> 
>         if (*cnt == 1) {
> @@ -1038,7 +1040,7 @@ static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
> 
>         (*cnt)--;
> 
> -       ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
> +       ret = ftrace_set_filter_ip(ops, ftrace_ip, 1, 0);
>         WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
>                   p->addr, ret);
>         return ret;
> --
> 2.24.1
> 
> 
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