Subject: Re: [PATCH v1 09/10] lkdtm: Fix lkdtm_EXEC_RODATA()

From: Kees Cook <[email-masked]>
Date: Wed, 13 Oct 2021 00:09:16 -0700

On Mon, Oct 11, 2021 at 05:25:36PM +0200, Christophe Leroy wrote:
> Behind a location, lkdtm_EXEC_RODATA() executes a real function,
> not a copy of do_nothing().
> 
> So do it directly instead of using execute_location().

I don't understand this. Why does the next patch not fix this?

-Kees

> 
> And fix displayed addresses by dereferencing the function descriptors.
> 
> Signed-off-by: Christophe Leroy <[email-masked]>
> ---
>  drivers/misc/lkdtm/perms.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
> index 442d60ed25ef..da16564e1ecd 100644
> --- a/drivers/misc/lkdtm/perms.c
> +++ b/drivers/misc/lkdtm/perms.c
> @@ -153,7 +153,14 @@ void lkdtm_EXEC_VMALLOC(void)
>  
>  void lkdtm_EXEC_RODATA(void)
>  {
> -	execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
> +	pr_info("attempting ok execution at %px\n",
> +		dereference_symbol_descriptor(do_nothing));
> +	do_nothing();
> +
> +	pr_info("attempting bad execution at %px\n",
> +		dereference_symbol_descriptor(lkdtm_rodata_do_nothing));
> +	lkdtm_rodata_do_nothing();
> +	pr_err("FAIL: func returned\n");
>  }
>  
>  void lkdtm_EXEC_USERSPACE(void)
> -- 
> 2.31.1
> 

-- 
Kees Cook