Messages in this thread | | | Date | Thu, 13 Dec 2012 10:17:18 -0800 | Subject | Re: [PATCH] time: create __getnstimeofday for WARNless calls | From | Kees Cook <> |
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John, any feedback on this?
Thanks,
-Kees
On Mon, Nov 19, 2012 at 10:26 AM, Kees Cook <keescook@chromium.org> wrote: > The pstore RAM backend can get called during resume, and must be defensive > against a suspended time source. Expose getnstimeofday logic that returns > an error instead of a WARN. This can be detected and the timestamp can > be zeroed out. > > Reported-by: Doug Anderson <dianders@chromium.org> > Cc: John Stultz <johnstul@us.ibm.com> > Cc: Anton Vorontsov <anton.vorontsov@linaro.org> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > fs/pstore/ram.c | 10 +++++++--- > include/linux/time.h | 1 + > kernel/time/timekeeping.c | 29 ++++++++++++++++++++++++----- > 3 files changed, 32 insertions(+), 8 deletions(-) > > diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c > index 1a4f6da..dacfe78 100644 > --- a/fs/pstore/ram.c > +++ b/fs/pstore/ram.c > @@ -168,12 +168,16 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type, > static size_t ramoops_write_kmsg_hdr(struct persistent_ram_zone *prz) > { > char *hdr; > - struct timeval timestamp; > + struct timespec timestamp; > size_t len; > > - do_gettimeofday(×tamp); > + /* Report zeroed timestamp if called before timekeeping has resumed. */ > + if (__getnstimeofday(×tamp)) { > + timestamp.tv_sec = 0; > + timestamp.tv_nsec = 0; > + } > hdr = kasprintf(GFP_ATOMIC, RAMOOPS_KERNMSG_HDR "%lu.%lu\n", > - (long)timestamp.tv_sec, (long)timestamp.tv_usec); > + (long)timestamp.tv_sec, (long)(timestamp.tv_nsec / 1000)); > WARN_ON_ONCE(!hdr); > len = hdr ? strlen(hdr) : 0; > persistent_ram_write(prz, hdr, len); > diff --git a/include/linux/time.h b/include/linux/time.h > index 4d358e9..0015aea 100644 > --- a/include/linux/time.h > +++ b/include/linux/time.h > @@ -158,6 +158,7 @@ extern int do_setitimer(int which, struct itimerval *value, > struct itimerval *ovalue); > extern unsigned int alarm_setitimer(unsigned int seconds); > extern int do_getitimer(int which, struct itimerval *value); > +extern int __getnstimeofday(struct timespec *tv); > extern void getnstimeofday(struct timespec *tv); > extern void getrawmonotonic(struct timespec *ts); > extern void getnstime_raw_and_real(struct timespec *ts_raw, > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index e424970..84820dc 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -220,19 +220,18 @@ static void timekeeping_forward_now(struct timekeeper *tk) > } > > /** > - * getnstimeofday - Returns the time of day in a timespec > + * __getnstimeofday - Returns the time of day in a timespec. > * @ts: pointer to the timespec to be set > * > - * Returns the time of day in a timespec. > + * Updates the time of day in the timespec. > + * Returns 0 on success, or -ve when suspended (timespec will be undefined). > */ > -void getnstimeofday(struct timespec *ts) > +int __getnstimeofday(struct timespec *ts) > { > struct timekeeper *tk = &timekeeper; > unsigned long seq; > s64 nsecs = 0; > > - WARN_ON(timekeeping_suspended); > - > do { > seq = read_seqbegin(&tk->lock); > > @@ -243,6 +242,26 @@ void getnstimeofday(struct timespec *ts) > > ts->tv_nsec = 0; > timespec_add_ns(ts, nsecs); > + > + /* > + * Do not bail out early, in case there were callers still using > + * the value, even in the face of the WARN_ON. > + */ > + if (unlikely(timekeeping_suspended)) > + return -EAGAIN; > + return 0; > +} > +EXPORT_SYMBOL(__getnstimeofday); > + > +/** > + * getnstimeofday - Returns the time of day in a timespec. > + * @ts: pointer to the timespec to be set > + * > + * Returns the time of day in a timespec (WARN if suspended). > + */ > +void getnstimeofday(struct timespec *ts) > +{ > + WARN_ON(__getnstimeofday(ts)); > } > EXPORT_SYMBOL(getnstimeofday); > > -- > 1.7.9.5 > > > -- > Kees Cook > Chrome OS Security
-- Kees Cook Chrome OS Security
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