On Thu, Dec 20, 2012 at 3:43 AM, Thomas Gleixner <t...@linutronix.de> wrote:
> On Mon, 17 Dec 2012, John Stultz wrote:
>> From: Kees Cook <keesc...@chromium.org>
>>
>> Hey Thomas,
>> Wanted to see if maybe there was still time for this for 3.8?
>> thanks
>> -john
>>
>> 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.
>
> Shouldn't we zero out the time stamp in the core code ?
It wasn't clear to me if the raw/wrong value should be available to a
caller when they got the EAGAIN. Since pstore is the only known user
of this, I'm fine moving the zeroing into the timekeeping core.
-Kees
>
> Thanks,
>
> tglx
>
>> Reported-by: Doug Anderson <diand...@chromium.org>
>> Cc: Anton Vorontsov <anton.voront...@linaro.org>
>> Cc: Thomas Gleixner <t...@linutronix.de>
>> Signed-off-by: Kees Cook <keesc...@chromium.org>
>> Signed-off-by: John Stultz <john.stu...@linaro.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 4c7de02..dfc7f87 100644
>> --- a/kernel/time/timekeeping.c
>> +++ b/kernel/time/timekeeping.c
>> @@ -214,19 +214,18 @@ 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);
>>
>> @@ -237,6 +236,26 @@ 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
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