linux-kernel - Re: [PATCH 1/3] jump_label: Warn on failed jump

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Date:   Wed, 14 Feb 2018 12:01:12 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jason Baron <jbaron@...mai.com>, Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 1/3] jump_label: Warn on failed jump_label patch

On Wed, 14 Feb 2018 10:40:41 -0600
Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> When the jump label code encounters an address which isn't recognized by
> kernel_text_address(), it just silently fails.
> 
> This can be dangerous because jump labels are used in a variety of
> places, and are generally expected to work.  Convert the silent failure
> to a warning.

I made ftrace function tracing work on init code, can we do the same
with tracepoints (aka jump labels)?

But I have to say that this goes with my argument that there exists
tracepoints in the kernel that nobody cares about ;-)

-- Steve

> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  kernel/jump_label.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/jump_label.c b/kernel/jump_label.c
> index b4517095db6a..c71fb7cdfc41 100644
> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -370,8 +370,12 @@ static void __jump_label_update(struct static_key *key,
>  		 * kernel_text_address() verifies we are not in core kernel
>  		 * init code, see jump_label_invalidate_module_init().
>  		 */
> -		if (entry->code && kernel_text_address(entry->code))
> -			arch_jump_label_transform(entry, jump_label_type(entry));
> +		if (entry->code) {
> +			if (kernel_text_address(entry->code))
> +				arch_jump_label_transform(entry, jump_label_type(entry));
> +			else
> +				WARN_ONCE(1, "can't patch jump_label at %pS", (void *)entry->code);
> +		}
>  	}
>  }
>