On Wed, Nov 8, 2017 at 8:00 AM, Arnd Bergmann <a...@arndb.de> wrote:
> I noticed that __getnstimeofday() is a rather odd interface, with
> a number of quirks:
>
> - The caller may come from NMI context, but the implementation is not NMI safe
> - The calling conventions are different from any other timekeeping functions
> - The naming doesn't fit into the 'ktime_get_*()' scheme
>
> This addresses the above issues by using a completely different
> method to get the time: ktime_get_real_fast_ns() is NMI safe and
> doesn't print a warning when called with the timekeeping suspended,
> and we can easily transform the result into a timespec structure. Since
> ktime_get_real_fast_ns() was not exported to modules, I also add the
> export.
>
> The behavior for the suspended case changes, we now return the time
> if we can find it out rather than setting it to zero. We could still
> change that but this would require exporting the 'timekeeping_suspended'
> to modules.
>
> I'm not trying to address y2038-safety at this point, but plan to
> do that later with a more complex patch.
>
> Cc: Kees Cook <keesc...@chromium.org>
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> ---
> It would be helpful to get this merged into v4.15-rc1, since I have
> some other cleanups that depend on this. Please have a look to see if
> this makes sense to you.
As long as this is sane to call when timekeeping is not running, I'm
happy to take the patch. Would you prefer I take this via pstore or do
you have another tree it should go through?
Acked-by: Kees Cook <keesc...@chromium.org>
-Kees
> ---
> fs/pstore/platform.c | 5 +----
> kernel/time/timekeeping.c | 1 +
> 2 files changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index ec7199e859d2..086e491faf04 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -482,10 +482,7 @@ void pstore_record_init(struct pstore_record *record,
> record->psi = psinfo;
>
> /* Report zeroed timestamp if called before timekeeping has resumed.
> */
> - if (__getnstimeofday(&record->time)) {
> - record->time.tv_sec = 0;
> - record->time.tv_nsec = 0;
> - }
> + record->time = ns_to_timespec(ktime_get_real_fast_ns());
> }
>
> /*
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 353f7bd1eeb0..198afa78bf69 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -528,6 +528,7 @@ u64 ktime_get_real_fast_ns(void)
> {
> return __ktime_get_real_fast_ns(&tk_fast_mono);
> }
> +EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns);
>
> /**
> * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
> --
> 2.9.0
>
--
Kees Cook
Pixel Security
