Hi Jiri,
On Tue, Nov 1, 2022 at 3:03 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> 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 ;-)
Sorry about that! :) I'll add the comment.
Thanks,
Namhyung
>
> > +
> > + 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
> >
