Re: [PATCH] crypto: use timespec64 for jent_get_nstime

Stephan Mueller
2016-06-18T08:17:06Z

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@arndb.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