linux-kernel - Re: [PATCH v3] kprobes: Forbid probing on trampoline and bpf prog

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Date:   Tue, 2 Aug 2022 08:28:57 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Chen Zhongjin <chenzhongjin@...wei.com>
Cc:     <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
        <naveen.n.rao@...ux.ibm.com>, <anil.s.keshavamurthy@...el.com>,
        <davem@...emloft.net>, <mhiramat@...nel.org>,
        <peterz@...radead.org>, <mingo@...nel.org>, <ast@...nel.org>,
        <daniel@...earbox.net>
Subject: Re: [PATCH v3] kprobes: Forbid probing on trampoline and bpf prog

On Mon, 1 Aug 2022 11:37:19 +0800
Chen Zhongjin <chenzhongjin@...wei.com> wrote:

> kernel_text_address returns ftrace_trampoline, kprobe_insn_slot
> and bpf_text_address as kprobe legal address.
> 
> These text are removable and changeable without any notifier to
> kprobes. Probing on them can trigger some unexpected behavior[1].
> 
> Considering that jump_label and static_call text are already be
> forbiden to probe, kernel_text_address should be replaced with
> core_kernel_text and is_module_text_address to check other text
> which is unsafe to kprobe.
> 
> [1] https://lkml.org/lkml/2022/7/26/1148
> 
> Fixes: 5b485629ba0d ("kprobes, extable: Identify kprobes trampolines as kernel text area")
> Fixes: 74451e66d516 ("bpf: make jited programs visible in traces")
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>

Thanks! this looks good to me.

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


> ---
> v2 -> v3:
> Remove '-next' carelessly added in title.
> 
> v1 -> v2:
> Check core_kernel_text and is_module_text_address rather than
> only kprobe_insn.
> Also fix title and commit message for this. See old patch at [1].
> ---
>  kernel/kprobes.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index f214f8c088ed..80697e5e03e4 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1560,7 +1560,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  	preempt_disable();
>  
>  	/* Ensure it is not in reserved area nor out of text */
> -	if (!kernel_text_address((unsigned long) p->addr) ||
> +	if (!(core_kernel_text((unsigned long) p->addr) ||
> +	    is_module_text_address((unsigned long) p->addr)) ||
>  	    within_kprobe_blacklist((unsigned long) p->addr) ||
>  	    jump_label_text_reserved(p->addr, p->addr) ||
>  	    static_call_text_reserved(p->addr, p->addr) ||
> -- 
> 2.17.1
> 


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