Messages in this thread | | | Subject | Re: [PATCH v3] sched: Fix out-of-bound access in uclamp | From | Dietmar Eggemann <> | Date | Mon, 3 May 2021 12:55:34 +0200 |
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On 30/04/2021 17:27, Vincent Guittot wrote: > On Fri, 30 Apr 2021 at 17:14, Quentin Perret <qperret@google.com> wrote: >> >> Util-clamp places tasks in different buckets based on their clamp values >> for performance reasons. However, the size of buckets is currently >> computed using a rounding division, which can lead to an off-by-one >> error in some configurations. >> >> For instance, with 20 buckets, the bucket size will be 1024/20=51. A >> task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly, >> correct indexes are in range [0,19], hence leading to an out of bound >> memory access. >> >> Clamp the bucket id to fix the issue. >> >> Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting") >> Suggested-by: Qais Yousef <qais.yousef@arm.com> >> Signed-off-by: Quentin Perret <qperret@google.com> > > Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
I forgot that config UCLAMP_BUCKETS_COUNT is in range 5 ... 20.
So the error is bound to [-2 ... 5] (13/79, 20/51). I agree that we can live with that.
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
>> --- >> Changes in v3: >> - Keep rounding div to improve fairness (Vincent) >> --- >> kernel/sched/core.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 98191218d891..c12ec648423e 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -928,7 +928,7 @@ DEFINE_STATIC_KEY_FALSE(sched_uclamp_used); >> >> static inline unsigned int uclamp_bucket_id(unsigned int clamp_value) >> { >> - return clamp_value / UCLAMP_BUCKET_DELTA; >> + return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1); >> } >> >> static inline unsigned int uclamp_none(enum uclamp_id clamp_id) >> -- >> 2.31.1.527.g47e6f16901-goog >>
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