Re: [PATCH v7 3/4] vsprintf: Use hw RNG for ptr_key

[Steven Rostedt]

On Tue, 12 Jun 2018 10:39:13 +1000
"Tobin C. Harding" <me@xxxxxxxx> wrote:

> Currently we must wait for enough entropy to become available before
> hashed pointers can be printed.  We can remove this wait by using the
> hw RNG if available.
> 
> Use hw RNG to get keying material.
> 
> Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

-- Steve

> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Tobin C. Harding <me@xxxxxxxx>
> ---
>  lib/vsprintf.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index a48aaa79d352..c445f9f28760 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1675,8 +1675,16 @@ static struct random_ready_callback random_ready = {
>  
>  static int __init initialize_ptr_random(void)
>  {
> -	int ret = add_random_ready_callback(&random_ready);
> +	int key_size = sizeof(ptr_key);
> +	int ret;
> +
> +	/* Use hw RNG if available */
> +	if (get_random_bytes_arch(&ptr_key, key_size) == key_size) {
> +		static_branch_disable(&not_filled_random_ptr_key);
> +		return 0;
> +	}
>  
> +	ret = add_random_ready_callback(&random_ready);
>  	if (!ret) {
>  		return 0;
>  	} else if (ret == -EALREADY) {