linux-hardening - Re: [PATCH] sched/psi: Bounds-check state iterator against NR_PSI

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Date:   Fri, 20 May 2022 10:09:20 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] sched/psi: Bounds-check state iterator against NR_PSI_STATES

On Fri, May 20, 2022 at 9:58 AM Kees Cook <keescook@...omium.org> wrote:
>
> GCC 12 cannot tell that "t" will be bounded by NR_PSI_STATES, which could
> lead to walking off the end of the tasks array, which is NR_PSI_STATES in
> size. Explicitly bounds-check "t" as part of the loop.
>
> In file included from ../kernel/sched/build_utility.c:97:
> ../kernel/sched/psi.c: In function 'psi_group_change':
> ../kernel/sched/psi.c:730:38: warning: array subscript 32 is above array bounds of 'unsigned int[5]' [-Warray-bounds]
>   730 |                         groupc->tasks[t]++;
>       |                         ~~~~~~~~~~~~~^~~
> In file included from ../include/linux/psi.h:6,
>                  from ../kernel/sched/build_utility.c:36:
> ../include/linux/psi_types.h:84:22: note: while referencing 'tasks'
>    84 |         unsigned int tasks[NR_PSI_TASK_COUNTS];
>       |                      ^~~~~
> ../kernel/sched/psi.c:730:38: warning: array subscript 32 is above array bounds of 'unsigned int[5]' [-Warray-bounds]
>   730 |                         groupc->tasks[t]++;
>       |                         ~~~~~~~~~~~~~^~~
> ../include/linux/psi_types.h:84:22: note: while referencing 'tasks'
>    84 |         unsigned int tasks[NR_PSI_TASK_COUNTS];
>       |                      ^~~~~
>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

> ---
>  kernel/sched/psi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index a337f3e35997..827f16a79936 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -725,7 +725,7 @@ static void psi_group_change(struct psi_group *group, int cpu,
>                 }
>         }
>
> -       for (t = 0; set; set &= ~(1 << t), t++)
> +       for (t = 0; set && t < ARRAY_SIZE(groupc->tasks); set &= ~(1 << t), t++)
>                 if (set & (1 << t))
>                         groupc->tasks[t]++;
>
> --
> 2.32.0
>