linux-kernel - Re: [PATCH V2] x86/ftrace: Make sure that ftrace trampolines are not RWX

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Date:   Thu, 25 May 2017 19:46:04 +0200
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH V2] x86/ftrace: Make sure that ftrace trampolines are not
 RWX

On Thu, May 25, 2017 at 10:57:51AM +0200, Thomas Gleixner wrote:
> ftrace use module_alloc() to allocate trampoline pages. The mapping of
> module_alloc() is RWX, which makes sense as the memory is written to right
> after allocation. But nothing makes these pages RO after writing to them.
> 
> Add proper set_memory_rw/ro() calls to protect the trampolines after
> modification.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/kernel/ftrace.c |   20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -689,8 +689,12 @@ static inline void *alloc_tramp(unsigned
>  {
>  	return module_alloc(size);
>  }
> -static inline void tramp_free(void *tramp)
> +static inline void tramp_free(void *tramp, int size)
>  {
> +	int npages = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +
> +	set_memory_nx((unsigned long)tramp, npages);
> +	set_memory_rw((unsigned long)tramp, npages);
>  	module_memfree(tramp);
>  }

Can/should module_memfree() just do this for users? With Masami's fix that'd
be 2 users already.

   Luis