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SubjectRe: System crash with perf_fuzzer (kernel: 5.0.0-rc3)
On Wed, Jan 30, 2019 at 07:36:48PM +0100, Jiri Olsa wrote:

SNIP

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 280a72b3a553..22ec63a0782e 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4969,6 +4969,26 @@ static void __perf_event_period(struct perf_event *event,
> }
> }
>
> +static int check_period(struct perf_event *event, u64 value)
> +{
> + u64 sample_period_attr = event->attr.sample_period;
> + u64 sample_period_hw = event->hw.sample_period;
> + int ret;
> +
> + if (event->attr.freq) {
> + event->attr.sample_freq = value;
> + } else {
> + event->attr.sample_period = value;
> + event->hw.sample_period = value;
> + }

hm, I think we need to check the period without changing the event,
because we don't disable pmu, so it might get picked up by bts code

will check

jirka

> +
> + ret = event->pmu->check_period(event);
> +
> + event->attr.sample_period = sample_period_attr;
> + event->hw.sample_period = sample_period_hw;
> + return ret;
> +}
> +
> static int perf_event_period(struct perf_event *event, u64 __user *arg)
> {
> u64 value;
> @@ -4985,6 +5005,9 @@ static int perf_event_period(struct perf_event *event, u64 __user *arg)
> if (event->attr.freq && value > sysctl_perf_event_sample_rate)
> return -EINVAL;
>
> + if (check_period(event, value))
> + return -EINVAL;
> +
> event_function_call(event, __perf_event_period, &value);
>
> return 0;
> @@ -9601,6 +9624,11 @@ static int perf_pmu_nop_int(struct pmu *pmu)
> return 0;
> }
>
> +static int perf_event_nop_int(struct perf_event *event)
> +{
> + return 0;
> +}
> +
> static DEFINE_PER_CPU(unsigned int, nop_txn_flags);
>
> static void perf_pmu_start_txn(struct pmu *pmu, unsigned int flags)
> @@ -9901,6 +9929,9 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
> pmu->pmu_disable = perf_pmu_nop_void;
> }
>
> + if (!pmu->check_period)
> + pmu->check_period = perf_event_nop_int;
> +
> if (!pmu->event_idx)
> pmu->event_idx = perf_event_idx_default;
>
> --
> 2.17.2
>

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