selftests/bpf: Add perf_event_read_sample test cases

It checks the perf event sample access with bpf_cast_to_kern_ctx().
It should access sample data only event->attr.sample_type allows.
Other fields might not be initialized.

  $ ./vmtest.sh ./test_progs -t perf_event_read_sample
  ...
  #135/1   perf_event_read_sample/perf_event_read_sample_ok:OK
  #135/2   perf_event_read_sample/perf_event_read_sample_invalid:OK
  #135     perf_event_read_sample:OK

Signed-off-by: Namhyung Kim <[email protected]>

Author: namhyung

tools/testing/selftests/bpf/prog_tests/perf_sample.c

@@ -0,0 +1,167 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <linux/perf_event.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+
+#include <test_progs.h>
+#include "test_perf_sample.skel.h"
+
+#ifndef noinline
+#define noinline __attribute__((noinline))
+#endif
+
+/* treat user-stack data as invalid (for testing only) */
+#define PERF_SAMPLE_INVALID  PERF_SAMPLE_STACK_USER
+
+#define PERF_MMAP_SIZE  8192
+#define DATA_MMAP_SIZE  4096
+
+static int perf_fd = -1;
+static void *perf_ringbuf;
+static struct test_perf_sample *skel;
+
+static int open_perf_event(u64 sample_flags)
+{
+	struct perf_event_attr attr = {
+		.type = PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_PAGE_FAULTS,
+		.sample_type = sample_flags,
+		.sample_period = 1,
+		.disabled = 1,
+		.size = sizeof(attr),
+	};
+	int fd;
+	void *ptr;
+
+	fd = syscall(SYS_perf_event_open, &attr, 0, -1, -1, 0);
+	if (!ASSERT_GT(fd, 0, "perf_event_open"))
+		return -1;
+
+	ptr = mmap(NULL, PERF_MMAP_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+	if (!ASSERT_NEQ(ptr, MAP_FAILED, "mmap")) {
+		close(fd);
+		return -1;
+	}
+
+	perf_fd = fd;
+	perf_ringbuf = ptr;
+
+	return 0;
+}
+
+static void close_perf_event(void)
+{
+	if (perf_fd == -1)
+		return;
+
+	munmap(perf_ringbuf, PERF_MMAP_SIZE);
+	close(perf_fd);
+
+	perf_fd = -1;
+	perf_ringbuf = NULL;
+}
+
+static noinline void *trigger_perf_event(void)
+{
+	int *buf = mmap(NULL, DATA_MMAP_SIZE, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
+
+	if (!ASSERT_NEQ(buf, MAP_FAILED, "mmap"))
+		return NULL;
+
+	ioctl(perf_fd, PERF_EVENT_IOC_ENABLE);
+
+	/* it should generate a page fault which triggers the perf_event */
+	*buf = 1;
+
+	ioctl(perf_fd, PERF_EVENT_IOC_DISABLE);
+
+	munmap(buf, DATA_MMAP_SIZE);
+
+	/* return the map address to check the sample addr */
+	return buf;
+}
+
+/* check if the perf ringbuf has a sample data */
+static int check_perf_event(void)
+{
+	struct perf_event_mmap_page *page = perf_ringbuf;
+	struct perf_event_header *hdr;
+
+	if (page->data_head == page->data_tail)
+		return 0;
+
+	hdr = perf_ringbuf + page->data_offset;
+
+	if (hdr->type != PERF_RECORD_SAMPLE)
+		return 0;
+
+	return 1;
+}
+
+static void setup_perf_sample_bpf_skel(void)
+{
+	struct bpf_link *link;
+
+	skel = test_perf_sample__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "test_perf_sample_open_and_load"))
+		return;
+
+	link = bpf_program__attach_perf_event(skel->progs.perf_sample_filter, perf_fd);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_perf_event"))
+		return;
+}
+
+static void clean_perf_sample_bpf_skel(void)
+{
+	test_perf_sample__detach(skel);
+	test_perf_sample__destroy(skel);
+}
+
+static void test_perf_event_read_sample_ok(void)
+{
+	u64 flags = PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR;
+	uintptr_t map_addr;
+
+	if (open_perf_event(flags) < 0)
+		return;
+	setup_perf_sample_bpf_skel();
+	map_addr = (uintptr_t)trigger_perf_event();
+
+	ASSERT_EQ(check_perf_event(), 1, "number of sample");
+	ASSERT_EQ(skel->bss->sample_addr, map_addr, "sample addr");
+	ASSERT_EQ((int)skel->bss->sample_pid, getpid(), "sample pid");
+	/* just assume the IP in (trigger_perf_event, +4096) */
+	ASSERT_GT(skel->bss->sample_ip, (uintptr_t)trigger_perf_event, "sample ip");
+	ASSERT_LT(skel->bss->sample_ip, (uintptr_t)trigger_perf_event + 4096, "sample ip");
+
+	clean_perf_sample_bpf_skel();
+	close_perf_event();
+}
+
+static void test_perf_event_read_sample_invalid(void)
+{
+	u64 flags = PERF_SAMPLE_INVALID;
+
+	if (open_perf_event(flags) < 0)
+		return;
+	setup_perf_sample_bpf_skel();
+	trigger_perf_event();
+
+	ASSERT_EQ(check_perf_event(), 0, "number of sample");
+
+	clean_perf_sample_bpf_skel();
+	close_perf_event();
+}
+
+void test_perf_event_read_sample(void)
+{
+	if (test__start_subtest("perf_event_read_sample_ok"))
+		test_perf_event_read_sample_ok();
+	if (test__start_subtest("perf_event_read_sample_invalid"))
+		test_perf_event_read_sample_invalid();
+}

tools/testing/selftests/bpf/progs/test_perf_sample.c

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2022 Google
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+unsigned long long sample_ip;
+unsigned long long sample_pid;
+unsigned long long sample_addr;
+
+void *bpf_cast_to_kern_ctx(void *) __ksym;
+
+#define SAMPLE_FLAGS  (PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR)
+
+SEC("perf_event")
+int perf_sample_filter(void *ctx)
+{
+	struct bpf_perf_event_data_kern *kctx;
+
+	kctx = bpf_cast_to_kern_ctx(ctx);
+
+	if ((kctx->event->attr.sample_type & SAMPLE_FLAGS) != SAMPLE_FLAGS)
+		return 0;
+
+	sample_ip = kctx->data->ip;
+	sample_pid = kctx->data->tid_entry.pid;
+	sample_addr = kctx->data->addr;
+
+	/* generate sample data */
+	return 1;
+}
+
+char _license[] SEC("license") = "GPL";