linux-kernel - Re: [PATCH] kprobes: Rollback kprobe flags on failed arm

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Message-Id: <20220604000312.69f42c92e932152da256c2bb@kernel.org>
Date:   Sat, 4 Jun 2022 00:03:12 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Chuang <nashuiliang@...il.com>
Cc:     Jingren Zhou <zhoujingren@...iglobal.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>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kprobes: Rollback kprobe flags on failed arm_kprobe

Hi Chuang,

On Thu,  2 Jun 2022 15:32:59 +0800
Chuang <nashuiliang@...il.com> wrote:

> From: Chuang Wang <nashuiliang@...il.com>
> 
> In aggrprobe scenes, if arm_kprobe() returns an error(e.g. livepatch and
> kprobe are using the same function X), kprobe flags, while has been
> modified to ~KPROBE_FLAG_DISABLED, is not rollled back.
> 
> Then, __disable_kprobe() will be failed in __unregister_kprobe_top(),
> the kprobe list will be not removed from aggrprobe, memory leaks or
> illegal pointers will be caused.
> 
> WARN disarm_kprobe:
>  Failed to disarm kprobe-ftrace at 00000000c729fdbc (-2)
>  RIP: 0010:disarm_kprobe+0xcc/0x110
>  Call Trace:
>   __disable_kprobe+0x78/0x90
>   __unregister_kprobe_top+0x13/0x1b0
>   ? _cond_resched+0x15/0x30
>   unregister_kprobes+0x32/0x80
>   unregister_kprobe+0x1a/0x20
> 
> Illegal Pointers:
>  BUG: unable to handle kernel paging request at 0000000000656369
>  RIP: 0010:__get_valid_kprobe+0x69/0x90
>  Call Trace:
>   register_kprobe+0x30/0x60
>   __register_trace_kprobe.part.7+0x8b/0xc0
>   create_local_trace_kprobe+0xd2/0x130
>   perf_kprobe_init+0x83/0xd0

Oops, thanks for reporting!
 
> Signed-off-by: Chuang Wang <nashuiliang@...il.com>
> Signed-off-by: Jingren Zhou <zhoujingren@...iglobal.com>

This should go to stable, so add below tag. (No need to CC to stable)

Fixes: 12310e343755 ("kprobes: Propagate error from arm_kprobe_ftrace()")
Cc: stable@...r.kernel.org

And could you also update this patch as below?

> ---
>  kernel/kprobes.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index f214f8c088ed..96c75e23113c 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -2422,8 +2422,10 @@ int enable_kprobe(struct kprobe *kp)
>  	if (!kprobes_all_disarmed && kprobe_disabled(p)) {
>  		p->flags &= ~KPROBE_FLAG_DISABLED;
>  		ret = arm_kprobe(p);
> -		if (ret)
> +		if (ret) {
>  			p->flags |= KPROBE_FLAG_DISABLED;

Here, can you add a check?

	if (p != kp) 

> +			kp->flags |= KPROBE_FLAG_DISABLED;

Thus is is clear that this is corresponding to
---
        if (p != kp)
                kp->flags &= ~KPROBE_FLAG_DISABLED;
---

Thank you,

> +		}
>  	}
>  out:
>  	mutex_unlock(&kprobe_mutex);
> -- 
> 2.34.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>