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Subject[PATCH] sched/psi: Bounds-check state iterator against NR_PSI_STATES
Date
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@cmpxchg.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
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
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