On Mon, Oct 31, 2022 at 10:23:38PM -0700, Namhyung Kim wrote:
> To allow bpf overflow handler to access the perf sample data, it needs to
> prepare missing but requested data before calling the handler.
>
> I'm taking a conservative approach to allow a list of sample formats only
> instead of allowing them all. For now, IP and ADDR data are allowed and
> I think it's good enough to build and verify general BPF-based sample
> filters for perf events.
>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
> ---
> kernel/events/core.c | 40 +++++++++++++++++++++++++++++++---------
> 1 file changed, 31 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index aefc1e08e015..519f30c33a24 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7329,8 +7329,10 @@ void perf_prepare_sample(struct perf_event_header *header,
> filtered_sample_type = sample_type & ~data->sample_flags;
> __perf_event_header__init_id(header, data, event, filtered_sample_type);
>
> - if (sample_type & (PERF_SAMPLE_IP | PERF_SAMPLE_CODE_PAGE_SIZE))
> - data->ip = perf_instruction_pointer(regs);
> + if (sample_type & (PERF_SAMPLE_IP | PERF_SAMPLE_CODE_PAGE_SIZE)) {
> + if (filtered_sample_type & PERF_SAMPLE_IP)
> + data->ip = perf_instruction_pointer(regs);
> + }
>
> if (sample_type & PERF_SAMPLE_CALLCHAIN) {
> int size = 1;
> @@ -10006,6 +10008,32 @@ static void perf_event_free_filter(struct perf_event *event)
> }
>
> #ifdef CONFIG_BPF_SYSCALL
> +static void bpf_prepare_sample(struct bpf_prog *prog,
> + struct perf_event *event,
> + struct perf_sample_data *data,
> + struct pt_regs *regs)
> +{
> + u64 filtered_sample_type;
> +
> + filtered_sample_type = event->attr.sample_type & ~data->sample_flags;
could we add the same comment in here as is in perf_prepare_sample
/*
* Clear the sample flags that have already been done by the
* PMU driver.
*/
it took me while to recall while we set addr to 0 in here ;-)
thanks,
jirka
> +
> + if (prog->call_get_stack &&
> + (filtered_sample_type & PERF_SAMPLE_CALLCHAIN)) {
> + data->callchain = perf_callchain(event, regs);
> + data->sample_flags |= PERF_SAMPLE_CALLCHAIN;
> + }
> +
> + if (filtered_sample_type & PERF_SAMPLE_IP) {
> + data->ip = perf_instruction_pointer(regs);
> + data->sample_flags |= PERF_SAMPLE_IP;
> + }
> +
> + if (filtered_sample_type & PERF_SAMPLE_ADDR) {
> + data->addr = 0;
> + data->sample_flags |= PERF_SAMPLE_ADDR;
> + }
> +}
> +
> static void bpf_overflow_handler(struct perf_event *event,
> struct perf_sample_data *data,
> struct pt_regs *regs)
> @@ -10023,13 +10051,7 @@ static void bpf_overflow_handler(struct perf_event *event,
> rcu_read_lock();
> prog = READ_ONCE(event->prog);
> if (prog) {
> - if (prog->call_get_stack &&
> - (event->attr.sample_type & PERF_SAMPLE_CALLCHAIN) &&
> - !(data->sample_flags & PERF_SAMPLE_CALLCHAIN)) {
> - data->callchain = perf_callchain(event, regs);
> - data->sample_flags |= PERF_SAMPLE_CALLCHAIN;
> - }
> -
> + bpf_prepare_sample(prog, event, data, regs);
> ret = bpf_prog_run(prog, &ctx);
> }
> rcu_read_unlock();
> --
> 2.38.1.273.g43a17bfeac-goog
>
