linux-kernel - Re: [PATCH v3 3/3] module: Make __tracepoints

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Message-ID: <20190410161112.540017d9@gandalf.local.home>
Date:   Wed, 10 Apr 2019 16:11:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
        keescook@...omium.org, mathieu.desnoyers@...icios.com,
        Jessica Yu <jeyu@...nel.org>,
        kernel-hardening@...ts.openwall.com, kernel-team@...roid.com,
        rcu@...r.kernel.org
Subject: Re: [PATCH v3 3/3] module: Make __tracepoints_ptrs as read-only

On Wed, 10 Apr 2019 15:57:08 -0400
"Joel Fernandes (Google)" <joel@...lfernandes.org> wrote:

> This series hardens the tracepoints in modules by making the array of
> pointers referring to the tracepoints as read-only. This array is needed
> during module unloading to verify that the tracepoint is quiescent.
> There is no reason for the array to be to be writable after init, and
> can cause security or other hidden bugs. Mark these as ro_after_init.
> 
> Suggested-by: paulmck@...ux.vnet.ibm.com
> Suggested-by: keescook@...omium.org
> Suggested-by: mathieu.desnoyers@...icios.com
> Cc: rostedt@...dmis.org
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> ---
>  kernel/module.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 8b9631e789f0..be980aaa8804 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3320,6 +3320,12 @@ static const char * const ro_after_init_sections[] = {
>  	 * by the SRCU notifiers
>  	 */
>  	"___srcu_struct_ptrs",
> +
> +	/*
> +	 * Array of tracepoint pointers used for checking if tracepoints are
> +	 * quiescent during unloading.
> +	 */
> +	"__tracepoints_ptrs",

Do we ever modify the __tracepoint_ptrs section? I know the jump_label
sections are sorted on load, which means they need to be writable
during init, but if __tracepoint_ptrs is not sorted or touched during
load, why not just put them in the rodata section to begin with?

-- Steve

>  };
>  
>  static struct module *layout_and_allocate(struct load_info *info, int flags)