Re: [kvm-unit-tests Patch v3 03/11] x86: pmu: Add asserts to warn inconsistent fixed events and counters

[Jim Mattson]

On Tue, Jan 2, 2024 at 7:09 PM Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx> wrote:
>
> Current PMU code deosn't check whether PMU fixed counter number is
> larger than pre-defined fixed events. If so, it would cause memory
> access out of range.
>
> So add assert to warn this invalid case.
>
> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
> ---
>  x86/pmu.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index a13b8a8398c6..a42fff8d8b36 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -111,8 +111,12 @@ static struct pmu_event* get_counter_event(pmu_counter_t *cnt)
>                 for (i = 0; i < gp_events_size; i++)
>                         if (gp_events[i].unit_sel == (cnt->config & 0xffff))
>                                 return &gp_events[i];
> -       } else
> -               return &fixed_events[cnt->ctr - MSR_CORE_PERF_FIXED_CTR0];
> +       } else {
> +               int idx = cnt->ctr - MSR_CORE_PERF_FIXED_CTR0;
> +
> +               assert(idx < ARRAY_SIZE(fixed_events));
> +               return &fixed_events[idx];
> +       }
>
>         return (void*)0;
>  }
> @@ -245,6 +249,7 @@ static void check_fixed_counters(void)
>         };
>         int i;
>
> +       assert(pmu.nr_fixed_counters <= ARRAY_SIZE(fixed_events));
>         for (i = 0; i < pmu.nr_fixed_counters; i++) {
>                 cnt.ctr = fixed_events[i].unit_sel;
>                 measure_one(&cnt);
> @@ -266,6 +271,7 @@ static void check_counters_many(void)
>                         gp_events[i % gp_events_size].unit_sel;
>                 n++;
>         }
> +       assert(pmu.nr_fixed_counters <= ARRAY_SIZE(fixed_events));

Can we assert this just once, in main()?

>         for (i = 0; i < pmu.nr_fixed_counters; i++) {
>                 cnt[n].ctr = fixed_events[i].unit_sel;
>                 cnt[n].config = EVNTSEL_OS | EVNTSEL_USR;
> --
> 2.34.1
>