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Date: Mon, 23 May 2022 13:30:13 -0700 From: Kees Cook <keescook@...omium.org> To: Johannes Weiner <hannes@...xchg.org> Cc: Suren Baghdasaryan <surenb@...gle.com>, 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>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH] sched/psi: Bounds-check state iterator against NR_PSI_STATES On Mon, May 23, 2022 at 10:19:22AM -0400, Johannes Weiner wrote: > On Fri, May 20, 2022 at 09:58:26AM -0700, Kees Cook 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> > > --- > > 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]++; > > This is a very hot path, it runs for every nested cgroup on every task > switch, wakeup and sleep. We should avoid unnecessary instructions and > branches if we can help it at all. > > Does the below patch address the warning for you? I can't test it > myself, because I'm not getting it with gcc version 12.1.0. It's also > odd that it didn't warn you about the loop over `clear' a few lines > up, which ostensibly has the same "problem". It seems this is a GCC 12 bug. Array indexes that have been used with a shift end up miscalculated when building also with -fsanitize=shift (i.e. allmodconfig): https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105679 > > --- > > diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h > index c7fe7c089718..113861343733 100644 > --- a/include/linux/psi_types.h > +++ b/include/linux/psi_types.h > @@ -41,6 +41,7 @@ enum psi_task_count { > #define TSK_RUNNING (1 << NR_RUNNING) > #define TSK_ONCPU (1 << NR_ONCPU) > #define TSK_MEMSTALL_RUNNING (1 << NR_MEMSTALL_RUNNING) > +#define TSK_MASK ((1U << NR_PSI_TASK_COUNTS) - 1) > > /* Resources that workloads could be stalled on */ > enum psi_res { > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > index a4fa3aadfcba..fb7fd40af337 100644 > --- a/kernel/sched/psi.c > +++ b/kernel/sched/psi.c > @@ -804,6 +804,8 @@ void psi_task_change(struct task_struct *task, int clear, int set) > void *iter = NULL; > u64 now; > > + WARN_ON_ONCE((clear|set) & ~TSK_MASK); > + > if (!task->pid) > return; I'll give this a spin. Thanks! -Kees -- Kees Cook
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