linux-kernel - Re: [PATCH -tip v2] kprobes: Prohibit probing on BUG() and WARN() address

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Date:   Wed, 4 Sep 2019 08:29:03 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip v2] kprobes: Prohibit probing on BUG() and WARN()
 address

On Tue,  3 Sep 2019 20:08:21 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Since BUG() and WARN() may use a trap (e.g. UD2 on x86) to
> get the address where the BUG() has occurred, kprobes can not
> do single-step out-of-line that instruction. So prohibit
> probing on such address.
> 
> Without this fix, if someone put a kprobe on WARN(), the
> kernel will crash with invalid opcode error instead of
> outputing warning message, because kernel can not find
> correct bug address.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> ---
>   Changes in v2:
>    - Add find_bug() stub function for !CONFIG_GENERIC_BUG
>    - Cast the p->addr to unsigned long.
> ---
>  include/linux/bug.h |    5 +++++
>  kernel/kprobes.c    |    3 ++-
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bug.h b/include/linux/bug.h
> index fe5916550da8..f639bd0122f3 100644
> --- a/include/linux/bug.h
> +++ b/include/linux/bug.h
> @@ -47,6 +47,11 @@ void generic_bug_clear_once(void);
>  
>  #else	/* !CONFIG_GENERIC_BUG */
>  
> +static inline void *find_bug(unsigned long bugaddr)
> +{
> +	return NULL;
> +}
> +
>  static inline enum bug_trap_type report_bug(unsigned long bug_addr,
>  					    struct pt_regs *regs)
>  {
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 452151e79535..5bdf47190f09 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1514,7 +1514,8 @@ static int check_kprobe_address_safe(struct kprobe *p,
>  	/* Ensure it is not in reserved area nor out of text */
>  	if (!kernel_text_address((unsigned long) p->addr) ||
>  	    within_kprobe_blacklist((unsigned long) p->addr) ||
> -	    jump_label_text_reserved(p->addr, p->addr)) {
> +	    jump_label_text_reserved(p->addr, p->addr) ||
> +	    find_bug((unsigned long) p->addr)) {
>  		ret = -EINVAL;
>  		goto out;
>  	}