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SubjectRe: [PATCH] time: create __getnstimeofday for WARNless calls
From
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(&timestamp);
> + /* Report zeroed timestamp if called before timekeeping has resumed. */
> + if (__getnstimeofday(&timestamp)) {
> + 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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