linux-kernel - Re: [Patch v5 06/18] x86: pmu: Add asserts to warn inconsistent fixed events and counters

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Message-ID: <CALMp9eSEuA70itad7oQUo=Ak6MVJYLo4kG4zJwEXkiUG6MgdnA@mail.gmail.com>
Date: Thu, 22 Aug 2024 11:22:23 -0700
From: Jim Mattson <jmattson@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Mingwei Zhang <mizhang@...gle.com>, 
	Xiong Zhang <xiong.y.zhang@...el.com>, Zhenyu Wang <zhenyuw@...ux.intel.com>, 
	Like Xu <like.xu.linux@...il.com>, Jinrong Liang <cloudliang@...cent.com>, 
	Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [Patch v5 06/18] x86: pmu: Add asserts to warn inconsistent fixed
 events and counters

On Tue, Jul 2, 2024 at 7:12 PM Dapeng Mi <dapeng1.mi@...ux.intel.com> 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.
>
> Reviewed-by: Mingwei Zhang <mizhang@...gle.com>
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  x86/pmu.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index b4de2680..3e0bf3a2 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -113,8 +113,12 @@ 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 {
> +               unsigned int idx = cnt->ctr - MSR_CORE_PERF_FIXED_CTR0;
> +
> +               assert(idx < ARRAY_SIZE(fixed_events));

Won't this assertion result in a failure on bare metal, for CPUs
supporting fixed counter 3?

> +               return &fixed_events[idx];
> +       }
>
>         return (void*)0;
>  }
> @@ -740,6 +744,8 @@ int main(int ac, char **av)
>         printf("Fixed counters:      %d\n", pmu.nr_fixed_counters);
>         printf("Fixed counter width: %d\n", pmu.fixed_counter_width);
>
> +       assert(pmu.nr_fixed_counters <= ARRAY_SIZE(fixed_events));
> +

And this one as well?

>         apic_write(APIC_LVTPC, PMI_VECTOR);
>
>         check_counters();
> --
> 2.40.1
>