Subject: [PATCH bpf-next v2 7/9] samples/bpf: add a test for bpf_get_stack helper

From: Yonghong Song <[email-masked]>
Date: Wed, 18 Apr 2018 09:54:42 -0700

The test attached a kprobe program to kernel function sys_write.
It tested to get stack for user space, kernel space and user
space with build_id request. It also tested to get user
and kernel stack into the same buffer with back-to-back
bpf_get_stack helper calls.

Whenever the kernel stack is available, the user space
application will check to ensure that sys_write/SyS_write
is part of the stack.

Signed-off-by: Yonghong Song <[email-masked]>
---
 samples/bpf/Makefile               |   4 +
 samples/bpf/trace_get_stack_kern.c |  86 +++++++++++++++++++++
 samples/bpf/trace_get_stack_user.c | 150 +++++++++++++++++++++++++++++++++++++
 3 files changed, 240 insertions(+)
 create mode 100644 samples/bpf/trace_get_stack_kern.c
 create mode 100644 samples/bpf/trace_get_stack_user.c

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 4d6a6ed..94e7b10 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -44,6 +44,7 @@ hostprogs-y += xdp_monitor
 hostprogs-y += xdp_rxq_info
 hostprogs-y += syscall_tp
 hostprogs-y += cpustat
+hostprogs-y += trace_get_stack
 
 # Libbpf dependencies
 LIBBPF := ../../tools/lib/bpf/bpf.o ../../tools/lib/bpf/nlattr.o
@@ -95,6 +96,7 @@ xdp_monitor-objs := bpf_load.o $(LIBBPF) xdp_monitor_user.o
 xdp_rxq_info-objs := bpf_load.o $(LIBBPF) xdp_rxq_info_user.o
 syscall_tp-objs := bpf_load.o $(LIBBPF) syscall_tp_user.o
 cpustat-objs := bpf_load.o $(LIBBPF) cpustat_user.o
+trace_get_stack-objs := bpf_load.o $(LIBBPF) trace_get_stack_user.o
 
 # Tell kbuild to always build the programs
 always := $(hostprogs-y)
@@ -148,6 +150,7 @@ always += xdp_rxq_info_kern.o
 always += xdp2skb_meta_kern.o
 always += syscall_tp_kern.o
 always += cpustat_kern.o
+always += trace_get_stack_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
@@ -193,6 +196,7 @@ HOSTLOADLIBES_xdp_monitor += -lelf
 HOSTLOADLIBES_xdp_rxq_info += -lelf
 HOSTLOADLIBES_syscall_tp += -lelf
 HOSTLOADLIBES_cpustat += -lelf
+HOSTLOADLIBES_trace_get_stack += -lelf
 
 # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
 #  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
diff --git a/samples/bpf/trace_get_stack_kern.c b/samples/bpf/trace_get_stack_kern.c
new file mode 100644
index 0000000..665e4ad
--- /dev/null
+++ b/samples/bpf/trace_get_stack_kern.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/ptrace.h>
+#include <linux/version.h>
+#include <uapi/linux/bpf.h>
+#include "bpf_helpers.h"
+
+/* Permit pretty deep stack traces */
+#define MAX_STACK 100
+struct stack_trace_t {
+	int pid;
+	int kern_stack_size;
+	int user_stack_size;
+	int user_stack_buildid_size;
+	u64 kern_stack[MAX_STACK];
+	u64 user_stack[MAX_STACK];
+	struct bpf_stack_build_id user_stack_buildid[MAX_STACK];
+};
+
+struct bpf_map_def SEC("maps") perfmap = {
+	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
+	.key_size = sizeof(int),
+	.value_size = sizeof(u32),
+	.max_entries = 2,
+};
+
+struct bpf_map_def SEC("maps") stackdata_map = {
+	.type = BPF_MAP_TYPE_PERCPU_ARRAY,
+	.key_size = sizeof(u32),
+	.value_size = sizeof(struct stack_trace_t),
+	.max_entries = 1,
+};
+
+struct bpf_map_def SEC("maps") rawdata_map = {
+	.type = BPF_MAP_TYPE_PERCPU_ARRAY,
+	.key_size = sizeof(u32),
+	.value_size = MAX_STACK * sizeof(u64) * 2,
+	.max_entries = 1,
+};
+
+SEC("kprobe/sys_write")
+int bpf_prog1(struct pt_regs *ctx)
+{
+	int max_len, max_buildid_len, usize, ksize, total_size;
+	struct stack_trace_t *data;
+	void *raw_data;
+	u32 key = 0;
+
+	data = bpf_map_lookup_elem(&stackdata_map, &key);
+	if (!data)
+		return 0;
+
+	max_len = MAX_STACK * sizeof(u64);
+	max_buildid_len = MAX_STACK * sizeof(struct bpf_stack_build_id);
+	data->pid = bpf_get_current_pid_tgid();
+	data->kern_stack_size = bpf_get_stack(ctx, data->kern_stack,
+					      max_len, 0);
+	data->user_stack_size = bpf_get_stack(ctx, data->user_stack, max_len,
+					    BPF_F_USER_STACK);
+	data->user_stack_buildid_size = bpf_get_stack(
+		ctx, data->user_stack_buildid, max_buildid_len,
+		BPF_F_USER_STACK | BPF_F_USER_BUILD_ID);
+	bpf_perf_event_output(ctx, &perfmap, 0, data, sizeof(*data));
+
+	/* write both kernel and user stacks to the same buffer */
+	raw_data = bpf_map_lookup_elem(&rawdata_map, &key);
+	if (!raw_data)
+		return 0;
+
+	usize = bpf_get_stack(ctx, raw_data, max_len, BPF_F_USER_STACK);
+	if (usize < 0)
+		return 0;
+
+	ksize = bpf_get_stack(ctx, raw_data + usize, max_len - usize, 0);
+	if (ksize < 0)
+		return 0;
+
+	total_size = usize + ksize;
+	if (total_size > 0 && total_size <= max_len)
+		bpf_perf_event_output(ctx, &perfmap, 0, raw_data, total_size);
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
+u32 _version SEC("version") = LINUX_VERSION_CODE;
diff --git a/samples/bpf/trace_get_stack_user.c b/samples/bpf/trace_get_stack_user.c
new file mode 100644
index 0000000..f64f5a5
--- /dev/null
+++ b/samples/bpf/trace_get_stack_user.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <linux/perf_event.h>
+#include <linux/bpf.h>
+#include <errno.h>
+#include <assert.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <time.h>
+#include <signal.h>
+#include "libbpf.h"
+#include "bpf_load.h"
+#include "perf-sys.h"
+
+static int pmu_fd;
+
+#define MAX_CNT 10ull
+#define MAX_STACK 100
+struct stack_trace_t {
+	int pid;
+	int kern_stack_size;
+	int user_stack_size;
+	int user_stack_buildid_size;
+	__u64 kern_stack[MAX_STACK];
+	__u64 user_stack[MAX_STACK];
+	struct bpf_stack_build_id user_stack_buildid[MAX_STACK];
+};
+
+static void print_bpf_output(void *data, int size)
+{
+	struct stack_trace_t *e = data;
+	int i, num_stack;
+	static __u64 cnt;
+	bool found = false;
+
+	cnt++;
+
+	if (size < sizeof(struct stack_trace_t)) {
+		__u64 *raw_data = data;
+
+		num_stack = size / sizeof(__u64);
+		printf("sample size = %d, raw stack\n\t", size);
+		for (i = 0; i < num_stack; i++) {
+			struct ksym *ks = ksym_search(raw_data[i]);
+
+			printf("0x%llx ", raw_data[i]);
+			if (ks && (strcmp(ks->name, "sys_write") == 0 ||
+				   strcmp(ks->name, "SyS_write") == 0))
+				found = true;
+		}
+		printf("\n");
+	} else {
+		printf("sample size = %d, pid %d\n", size, e->pid);
+		if (e->kern_stack_size > 0) {
+			num_stack = e->kern_stack_size / sizeof(__u64);
+			printf("\tkernel_stack(%d): ", num_stack);
+			for (i = 0; i < num_stack; i++) {
+				struct ksym *ks = ksym_search(e->kern_stack[i]);
+
+				printf("0x%llx ", e->kern_stack[i]);
+				if (ks && (strcmp(ks->name, "sys_write") == 0 ||
+					   strcmp(ks->name, "SyS_write") == 0))
+					found = true;
+			}
+			printf("\n");
+		}
+		if (e->user_stack_size > 0) {
+			num_stack = e->user_stack_size / sizeof(__u64);
+			printf("\tuser_stack(%d): ", num_stack);
+			for (i = 0; i < num_stack; i++)
+				printf("0x%llx ", e->user_stack[i]);
+			printf("\n");
+		}
+		if (e->user_stack_buildid_size > 0) {
+			num_stack = e->user_stack_buildid_size /
+				    sizeof(struct bpf_stack_build_id);
+			printf("\tuser_stack_buildid(%d): ", num_stack);
+			for (i = 0; i < num_stack; i++) {
+				int j;
+
+				printf("(%d, 0x", e->user_stack_buildid[i].status);
+				for (j = 0; j < BPF_BUILD_ID_SIZE; j++)
+					printf("%02x", e->user_stack_buildid[i].build_id[i]);
+				printf(", %llx) ", e->user_stack_buildid[i].offset);
+			}
+			printf("\n");
+		}
+	}
+	if (!found) {
+		printf("received %lld events, kern symbol not found, exiting ...\n", cnt);
+		kill(0, SIGINT);
+	}
+
+	if (cnt == MAX_CNT) {
+		printf("received max %lld events, exiting ...\n", cnt);
+		kill(0, SIGINT);
+	}
+}
+
+static void test_bpf_perf_event(void)
+{
+	struct perf_event_attr attr = {
+		.sample_type = PERF_SAMPLE_RAW,
+		.type = PERF_TYPE_SOFTWARE,
+		.config = PERF_COUNT_SW_BPF_OUTPUT,
+	};
+	int key = 0;
+
+	pmu_fd = sys_perf_event_open(&attr, -1/*pid*/, 0/*cpu*/, -1/*group_fd*/, 0);
+
+	assert(pmu_fd >= 0);
+	assert(bpf_map_update_elem(map_fd[0], &key, &pmu_fd, BPF_ANY) == 0);
+	ioctl(pmu_fd, PERF_EVENT_IOC_ENABLE, 0);
+}
+
+static void action(void)
+{
+	FILE *f;
+
+	f = popen("taskset 1 dd if=/dev/zero of=/dev/null", "r");
+	(void) f;
+}
+
+int main(int argc, char **argv)
+{
+	char filename[256];
+
+	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+	if (load_kallsyms()) {
+		printf("failed to process /proc/kallsyms\n");
+		return 2;
+	}
+
+	if (load_bpf_file(filename)) {
+		printf("%s", bpf_log_buf);
+		return 1;
+	}
+
+	test_bpf_perf_event();
+	return perf_event_poller(pmu_fd, action, print_bpf_output);
+}
-- 
2.9.5