| From: David Engraf <david.engraf@sysgo.com> |
| Date: Tue, 19 Mar 2013 13:29:55 +0100 |
| Subject: hrtimer: Fix ktime_add_ns() overflow on 32bit architectures |
| |
| commit 51fd36f3fad8447c487137ae26b9d0b3ce77bb25 upstream. |
| |
| One can trigger an overflow when using ktime_add_ns() on a 32bit |
| architecture not supporting CONFIG_KTIME_SCALAR. |
| |
| When passing a very high value for u64 nsec, e.g. 7881299347898368000 |
| the do_div() function converts this value to seconds (7881299347) which |
| is still to high to pass to the ktime_set() function as long. The result |
| in is a negative value. |
| |
| The problem on my system occurs in the tick-sched.c, |
| tick_nohz_stop_sched_tick() when time_delta is set to |
| timekeeping_max_deferment(). The check for time_delta < KTIME_MAX is |
| valid, thus ktime_add_ns() is called with a too large value resulting in |
| a negative expire value. This leads to an endless loop in the ticker code: |
| |
| time_delta: 7881299347898368000 |
| expires = ktime_add_ns(last_update, time_delta) |
| expires: negative value |
| |
| This fix caps the value to KTIME_MAX. |
| |
| This error doesn't occurs on 64bit or architectures supporting |
| CONFIG_KTIME_SCALAR (e.g. ARM, x86-32). |
| |
| Signed-off-by: David Engraf <david.engraf@sysgo.com> |
| [jstultz: Minor tweaks to commit message & header] |
| Signed-off-by: John Stultz <john.stultz@linaro.org> |
| Signed-off-by: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| kernel/hrtimer.c | 4 ++++ |
| 1 file changed, 4 insertions(+) |
| |
| --- a/kernel/hrtimer.c |
| +++ b/kernel/hrtimer.c |
| @@ -298,6 +298,10 @@ ktime_t ktime_sub_ns(const ktime_t kt, u |
| } else { |
| unsigned long rem = do_div(nsec, NSEC_PER_SEC); |
| |
| + /* Make sure nsec fits into long */ |
| + if (unlikely(nsec > KTIME_SEC_MAX)) |
| + return (ktime_t){ .tv64 = KTIME_MAX }; |
| + |
| tmp = ktime_set((long)nsec, rem); |
| } |
| |
