linux-kernel - Re: [PATCH v3] sched: Fix out-of-bound access in uclamp

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Message-ID: <YJAMfE/cV8zL4tHJ@hirez.programming.kicks-ass.net>
Date:   Mon, 3 May 2021 16:45:16 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Quentin Perret <qperret@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Qais Yousef <qais.yousef@....com>,
        Android Kernel Team <kernel-team@...roid.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>
Subject: Re: [PATCH v3] sched: Fix out-of-bound access in uclamp

On Mon, May 03, 2021 at 12:55:34PM +0200, Dietmar Eggemann wrote:
> On 30/04/2021 17:27, Vincent Guittot wrote:
> > On Fri, 30 Apr 2021 at 17:14, Quentin Perret <qperret@...gle.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@....com>
> >> Signed-off-by: Quentin Perret <qperret@...gle.com>
> > 
> > Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>

> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>

Thanks!