Messages in this thread | | | From | Kees Cook <> | Date | Fri, 10 Nov 2017 11:38:00 -0800 | Subject | Re: [PATCH] [v2] pstore: use ktime_get_real_fast_ns() instead of __getnstimeofday() |
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On Fri, Nov 10, 2017 at 7:25 AM, Arnd Bergmann <arnd@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, > one way to get there from NMI is > > NMI handler: > something bad > panic() > kmsg_dump() > pstore_dump() > pstore_record_init() > __getnstimeofday() > > - The calling conventions are different from any other timekeeping functions, > to deal with returning an error code during suspended timekeeping. > - 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 > has a reasonable behavior when timekeeping is suspended: it returns > the time at which it got suspended. > 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 slightly, we now return the > time if we can find it out rather than setting it to zero. As Thomas > Gleixner explained, this is still safe, as we won't attempt to > call into the clocksource driver that might be suspended > > 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 <keescook@chromium.org> > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > v2: improved changelog > --- > 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 e3c1332dfb4c..423159abd501 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 af139aa615ca..8f0d1857b78d 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -536,6 +536,7 @@ u64 ktime_get_coarse_real_fast_ns(void) > { > return __ktime_get_real_fast_ns(&tk_fast_mono, true); > } > +EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns);
I was going to add this to the pstore tree, but ktime_get_real_fast_ns() doesn't exist. In which tree is ktime_get_real_fast_ns() added? This should be carried there:
Acked-by: Kees Cook <keescook@chromium.org>
Thanks!
-Kees
> > /** > * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource. > -- > 2.9.0 >
-- Kees Cook Pixel Security
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