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

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 25 Jun 2019 13:12:20 -0700

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 <[email-masked]>
> ---
>  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
>