Re: [PATCH 2/2] kprobes/x86: Check for invalid ftrace location in __recover_probed_insn()

[Ingo Molnar <mingo@kernel.org>]

* Petr Mladek <pmladek@suse.cz> wrote:

> __recover_probed_insn() should always be called from an address where
> an instructions starts. The check for ftrace_location() might help to
> discover a potential inconsistency. Something goes terribly wrong when
> an address inside the ftrace location is checked. Let's BUG() in this case.
> 
> Suggested-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Signed-off-by: Petr Mladek <pmladek@suse.cz>
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> ---
>  arch/x86/kernel/kprobes/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 2f464b56766a..124577dcf768 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -228,6 +228,12 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
>  	kp = get_kprobe((void *)addr);
>  	faddr = ftrace_location(addr);
>  	/*
> +	 * Addresses inside the ftrace location are refused by
> +	 * arch_check_ftrace_location(). Something went terribly wrong
> +	 * if such an address is checked here.
> +	 */
> +	BUG_ON(faddr && faddr != addr);

Crashing the system with a BUG_ON() makes users very sad. 
Please use a construct like:

	if (WARN_ON(faddr && faddr != addr))
		return gently;

I've picked up your first patch.

Thanks,

	Ingo