linux-kernel - Re: [PATCH] crypto: use timespec64 for jent_get

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Message-ID: <1639786.8E0M9GixOz@positron.chronox.de>
Date:	Sat, 18 Jun 2016 10:16:59 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>, y2038@...ts.linaro.org,
	Kees Cook <keescook@...omium.org>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: use timespec64 for jent_get_nstime

Am Freitag, 17. Juni 2016, 17:59:41 schrieb Arnd Bergmann:

Hi Arnd,

> The jent_get_nstime() function uses __getnstimeofday() to get
> something similar to a 64-bit nanosecond counter. As we want
> to get rid of struct timespec to fix the y2038 overflow,
> this patch changes the code to use __getnstimeofday64()
> instead, which returns a timespec64 structure.
> 
> Nothing changes about the algorithm, but it looks like it
> might be better to use
> 
>  *out = ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec;
> 
> or even
> 
>  *out = ktime_get_raw_fast_ns();
> 
> to get an actual nanosecond value and avoid the predictable
> jitter that happens at the end of a second. Checking whether
> or not this would be good needs investigation by someone who
> understands the code better than me.

I will test it.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  crypto/jitterentropy-kcapi.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
> index 597cedd3531c..82ac44eff20d 100644
> --- a/crypto/jitterentropy-kcapi.c
> +++ b/crypto/jitterentropy-kcapi.c
> @@ -89,7 +89,7 @@ void jent_memcpy(void *dest, const void *src, unsigned int
> n)
> 
>  void jent_get_nstime(__u64 *out)
>  {
> -	struct timespec ts;
> +	struct timespec64 ts;
>  	__u64 tmp = 0;
> 
>  	tmp = random_get_entropy();
> @@ -98,9 +98,11 @@ void jent_get_nstime(__u64 *out)
>  	 * If random_get_entropy does not return a value (which is possible 
on,
>  	 * for example, MIPS), invoke __getnstimeofday
>  	 * hoping that there are timers we can work with.
> +	 *
> +	 * should we have a __ktime_get_ns() instead?
>  	 */
>  	if ((0 == tmp) &&
> -	   (0 == __getnstimeofday(&ts))) {
> +	   (0 == __getnstimeofday64(&ts))) {
>  		tmp = ts.tv_sec;
>  		tmp = tmp << 32;
>  		tmp = tmp | ts.tv_nsec;


Ciao
Stephan