Re: [kvm-unit-tests patch v6 05/18] x86: pmu: Enlarge cnt[] length to 48 in check_counters_many()

Sean Christopherson
2025-02-14T21:06:56Z

On Sat, Sep 14, 2024, Dapeng Mi wrote:
> Considering there are already 8 GP counters and 4 fixed counters on
> latest Intel processors, like Sapphire Rapids. The original cnt[] array
> length 10 is definitely not enough to cover all supported PMU counters on
> these new processors even through currently KVM only supports 3 fixed
> counters at most. This would cause out of bound memory access and may trigger
> false alarm on PMU counter validation
>
> It's probably more and more GP and fixed counters are introduced in the
> future and then directly extends the cnt[] array length to 48 once and
> for all. Base on the layout of IA32_PERF_GLOBAL_CTRL and
> IA32_PERF_GLOBAL_STATUS, 48 looks enough in near feature.
>
> Reviewed-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> ---
> x86/pmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index a0268db8..b4de2680 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -255,7 +255,7 @@ static void check_fixed_counters(void)
>
> static void check_counters_many(void)
> {
> - pmu_counter_t cnt[10];
> + pmu_counter_t cnt[48];

ARGH. Since the *entire* purpose of increasing the size is to guard against
buffer overflow, add an assert that the loop doesn't overflow.

> int i, n;
>
> for (i = 0, n = 0; n < pmu.nr_gp_counters; i++) {
> --
> 2.40.1
>