Re: [bpf-next v2 08/10] bpf: Implement bpf_prog_test_run for perf event programs

Stanislav Fomichev
2019-06-25T20:12:24Z

On 06/25, Krzesimir Nowak wrote:
> As an input, test run for perf event program takes struct
> bpf_perf_event_data as ctx_in and struct bpf_perf_event_value as
> data_in. For an output, it basically ignores ctx_out and data_out.
>
> The implementation sets an instance of struct bpf_perf_event_data_kern
> in such a way that the BPF program reading data from context will
> receive what we passed to the bpf prog test run in ctx_in. Also BPF
> program can call bpf_perf_prog_read_value to receive what was passed
> in data_in.
>
> Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
> ---
> kernel/trace/bpf_trace.c | 107 ++++++++++++++++++
> .../bpf/verifier/perf_event_sample_period.c | 8 ++
> 2 files changed, 115 insertions(+)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index c102c240bb0b..2fa49ea8a475 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -16,6 +16,8 @@
>
> #include <asm/tlb.h>
>
> +#include <trace/events/bpf_test_run.h>
> +
> #include "trace_probe.h"
> #include "trace.h"
>
> @@ -1160,7 +1162,112 @@ const struct bpf_verifier_ops perf_event_verifier_ops = {
> .convert_ctx_access = pe_prog_convert_ctx_access,
> };
>
> +static int pe_prog_test_run(struct bpf_prog *prog,
> + const union bpf_attr *kattr,
> + union bpf_attr __user *uattr)
> +{
> + void __user *ctx_in = u64_to_user_ptr(kattr->test.ctx_in);
> + void __user *data_in = u64_to_user_ptr(kattr->test.data_in);
> + u32 data_size_in = kattr->test.data_size_in;
> + u32 ctx_size_in = kattr->test.ctx_size_in;
> + u32 repeat = kattr->test.repeat;
> + u32 retval = 0, duration = 0;
> + int err = -EINVAL;
> + u64 time_start, time_spent = 0;
> + int i;
> + struct perf_sample_data sample_data = {0, };
> + struct perf_event event = {0, };
> + struct bpf_perf_event_data_kern real_ctx = {0, };
> + struct bpf_perf_event_data fake_ctx = {0, };
> + struct bpf_perf_event_value value = {0, };
> +
> + if (ctx_size_in != sizeof(fake_ctx))
> + goto out;
> + if (data_size_in != sizeof(value))
> + goto out;
> +
> + if (copy_from_user(&fake_ctx, ctx_in, ctx_size_in)) {
> + err = -EFAULT;
> + goto out;
> + }
Move this to net/bpf/test_run.c? I have a bpf_ctx_init helper to deal
with ctx input, might save you some code above wrt ctx size/etc.

> + if (copy_from_user(&value, data_in, data_size_in)) {
> + err = -EFAULT;
> + goto out;
> + }
> +
> + real_ctx.regs = &fake_ctx.regs;
> + real_ctx.data = &sample_data;
> + real_ctx.event = &event;
> + perf_sample_data_init(&sample_data, fake_ctx.addr,
> + fake_ctx.sample_period);
> + event.cpu = smp_processor_id();
> + event.oncpu = -1;
> + event.state = PERF_EVENT_STATE_OFF;
> + local64_set(&event.count, value.counter);
> + event.total_time_enabled = value.enabled;
> + event.total_time_running = value.running;
> + /* make self as a leader - it is used only for checking the
> + * state field
> + */
> + event.group_leader = &event;
> +
> + /* slightly changed copy pasta from bpf_test_run() in
> + * net/bpf/test_run.c
> + */
> + if (!repeat)
> + repeat = 1;
> +
> + rcu_read_lock();
> + preempt_disable();
> + time_start = ktime_get_ns();
> + for (i = 0; i < repeat; i++) {
Any reason for not using bpf_test_run?

> + retval = BPF_PROG_RUN(prog, &real_ctx);
> +
> + if (signal_pending(current)) {
> + err = -EINTR;
> + preempt_enable();
> + rcu_read_unlock();
> + goto out;
> + }
> +
> + if (need_resched()) {
> + time_spent += ktime_get_ns() - time_start;
> + preempt_enable();
> + rcu_read_unlock();
> +
> + cond_resched();
> +
> + rcu_read_lock();
> + preempt_disable();
> + time_start = ktime_get_ns();
> + }
> + }
> + time_spent += ktime_get_ns() - time_start;
> + preempt_enable();
> + rcu_read_unlock();
> +
> + do_div(time_spent, repeat);
> + duration = time_spent > U32_MAX ? U32_MAX : (u32)time_spent;
> + /* end of slightly changed copy pasta from bpf_test_run() in
> + * net/bpf/test_run.c
> + */
> +
> + if (copy_to_user(&uattr->test.retval, &retval, sizeof(retval))) {
> + err = -EFAULT;
> + goto out;
> + }
> + if (copy_to_user(&uattr->test.duration, &duration, sizeof(duration))) {
> + err = -EFAULT;
> + goto out;
> + }
Can BPF program modify fake_ctx? Do we need/want to copy it back?

> + err = 0;
> +out:
> + trace_bpf_test_finish(&err);
> + return err;
> +}
> +
> const struct bpf_prog_ops perf_event_prog_ops = {
> + .test_run = pe_prog_test_run,
> };
>
> static DEFINE_MUTEX(bpf_event_mutex);
> diff --git a/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c b/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c
> index 471c1a5950d8..16e9e5824d14 100644
> --- a/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c
> +++ b/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c
This should probably go in another patch.

> @@ -13,6 +13,8 @@
> },
> .result = ACCEPT,
> .prog_type = BPF_PROG_TYPE_PERF_EVENT,
> + .ctx_len = sizeof(struct bpf_perf_event_data),
> + .data_len = sizeof(struct bpf_perf_event_value),
> },
> {
> "check bpf_perf_event_data->sample_period half load permitted",
> @@ -29,6 +31,8 @@
> },
> .result = ACCEPT,
> .prog_type = BPF_PROG_TYPE_PERF_EVENT,
> + .ctx_len = sizeof(struct bpf_perf_event_data),
> + .data_len = sizeof(struct bpf_perf_event_value),
> },
> {
> "check bpf_perf_event_data->sample_period word load permitted",
> @@ -45,6 +49,8 @@
> },
> .result = ACCEPT,
> .prog_type = BPF_PROG_TYPE_PERF_EVENT,
> + .ctx_len = sizeof(struct bpf_perf_event_data),
> + .data_len = sizeof(struct bpf_perf_event_value),
> },
> {
> "check bpf_perf_event_data->sample_period dword load permitted",
> @@ -56,4 +62,6 @@
> },
> .result = ACCEPT,
> .prog_type = BPF_PROG_TYPE_PERF_EVENT,
> + .ctx_len = sizeof(struct bpf_perf_event_data),
> + .data_len = sizeof(struct bpf_perf_event_value),
> },
> --
> 2.20.1
>