bpf-developer-tutorial

// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
#include <vmlinux.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_core_read.h>
#include "execsnoop.bpf.h"

struct {
	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
	__uint(key_size, sizeof(u32));
	__uint(value_size, sizeof(u32));
} events SEC(".maps");

SEC("tracepoint/syscalls/sys_enter_execve")
int tracepoint__syscalls__sys_enter_execve(struct trace_event_raw_sys_enter* ctx)
{
	u64 id;
	pid_t pid, tgid;
	unsigned int ret;
	struct event event;
	struct task_struct *task;
	const char **args = (const char **)(ctx->args[1]);
	const char *argp;

	uid_t uid = (u32)bpf_get_current_uid_gid();
	int i;
	id = bpf_get_current_pid_tgid();
	pid = (pid_t)id;
	tgid = id >> 32;

	event.pid = tgid;
	event.uid = uid;
	task = (struct task_struct*)bpf_get_current_task();
	bpf_probe_read_str(&event.comm, sizeof(event.comm), task->comm);
	event.is_exit = false;
	bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, &event, sizeof(event));
	return 0;
}

SEC("tracepoint/syscalls/sys_exit_execve")
int tracepoint__syscalls__sys_exit_execve(struct trace_event_raw_sys_exit* ctx)
{
	u64 id;
	pid_t pid;
	int ret;
	struct event event;

	u32 uid = (u32)bpf_get_current_uid_gid();

	id = bpf_get_current_pid_tgid();
	pid = (pid_t)id;

	ret = ctx->ret;
	event.retval = ret;
	event.pid = pid;
	event.uid = uid;
	event.is_exit = true;
	bpf_get_current_comm(&event.comm, sizeof(event.comm));
	bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, &event, sizeof(event));
	return 0;
}

char LICENSE[] SEC("license") = "GPL";

这段代码定义了两个 eBPF 程序，一个用于捕获进程执行 execve 系统调用的入口，另一个用于捕获进程执行 execve 系统调用的出口。

在入口程序中，我们首先获取了当前进程的进程 ID 和用户 ID，然后通过 bpf_get_current_task 函数获取了当前进程的 task_struct 结构体，并通过 bpf_probe_read_str 函数读取了进程名称。最后，我们通过 bpf_perf_event_output 函数将进程执行事件输出到 perf buffer。

在出口程序中，我们首先获取了进程的进程 ID 和用户 ID，然后通过 bpf_get_current_comm 函数获取了进程的名称，最后通过 bpf_perf_event_output 函数将进程执行事件输出到 perf buffer。

使用这段代码，我们就可以捕获 Linux 内核中进程执行的事件。我们可以通过工具（例如 eunomia-bpf）来查看这些事件，并分析进程的执行情况。

Compile and Run

Compile:

docker run -it -v `pwd`/:/src/ yunwei37/ebpm:latest

Run:

$ sudo ./ecli run package.json

running and waiting for the ebpf events from perf event...
time pid ppid uid retval args_count args_size comm args 
23:07:35 32940 32783 1000 0 1 13 cat /usr/bin/cat 
23:07:43 32946 24577 1000 0 1 10 bash /bin/bash 
23:07:43 32948 32946 1000 0 1 18 lesspipe /usr/bin/lesspipe 
23:07:43 32949 32948 1000 0 2 36 basename /usr/bin/basename 
23:07:43 32951 32950 1000 0 2 35 dirname /usr/bin/dirname 
23:07:43 32952 32946 1000 0 2 22 dircolors /usr/bin/dircolors 
23:07:48 32953 32946 1000 0 2 25 ls /usr/bin/ls 
23:07:53 32957 32946 1000 0 2 17 sleep /usr/bin/sleep 
23:07:57 32959 32946 1000 0 1 17 oneko /usr/games/oneko

details in bcc

Demonstrations of execsnoop, the Linux eBPF/bcc version.

execsnoop traces the exec() syscall system-wide, and prints various details. Example output:

# ./execsnoop
COMM            PID    PPID   RET ARGS
bash             33161  24577    0 /bin/bash
lesspipe         33163  33161    0 /usr/bin/lesspipe
basename         33164  33163    0 /usr/bin/basename /usr/bin/lesspipe
dirname          33166  33165    0 /usr/bin/dirname /usr/bin/lesspipe
dircolors        33167  33161    0 /usr/bin/dircolors -b
ls               33172  33161    0 /usr/bin/ls --color=auto
top              33173  33161    0 /usr/bin/top
oneko            33174  33161    0 /usr/games/oneko
systemctl        33175  2975     0 /bin/systemctl is-enabled -q whoopsie.path
apport-checkrep  33176  2975     0 /usr/share/apport/apport-checkreports
apport-checkrep  33177  2975     0 /usr/share/apport/apport-checkreports --system
apport-checkrep  33178  2975     0 /usr/share/apport/apport-checkreports --system

This shows process information when exec system call is called.

USAGE message:

usage: execsnoop [-h] [-T] [-t] [-x] [--cgroupmap CGROUPMAP]
                       [--mntnsmap MNTNSMAP] [-u USER] [-q] [-n NAME]
                       [-l LINE] [-U] [--max-args MAX_ARGS]
                       
Trace exec() syscalls

options:
  -h, --help            show this help message and exit
  -T, --time            include time column on output (HH:MM:SS)
  -t, --timestamp       include timestamp on output
  -x, --fails           include failed exec()s
  --cgroupmap CGROUPMAP
                        trace cgroups in this BPF map only
  --mntnsmap MNTNSMAP   trace mount namespaces in this BPF map only
  -u USER, --uid USER   trace this UID only
  -q, --quote           Add quotemarks (") around arguments.
  -n NAME, --name NAME  only print commands matching this name (regex), any
                        arg
  -l LINE, --line LINE  only print commands where arg contains this line
                        (regex)
  -U, --print-uid       print UID column
  --max-args MAX_ARGS   maximum number of arguments parsed and displayed,
                        defaults to 20
                        
examples:
    ./execsnoop           # trace all exec() syscalls
    ./execsnoop -x        # include failed exec()s
    ./execsnoop -T        # include time (HH:MM:SS)
    ./execsnoop -U        # include UID
    ./execsnoop -u 1000   # only trace UID 1000
    ./execsnoop -u user   # get user UID and trace only them
    ./execsnoop -t        # include timestamps
    ./execsnoop -q        # add "quotemarks" around arguments
    ./execsnoop -n main   # only print command lines containing "main"
    ./execsnoop -l tpkg   # only print command where arguments contains "tpkg"
    ./execsnoop --cgroupmap mappath  # only trace cgroups in this BPF map
    ./execsnoop --mntnsmap mappath   # only trace mount namespaces in the map

The -T and -t option include time and timestamps on output:

# ./execsnoop -T -t
TIME     TIME(s) PCOMM            PID    PPID   RET ARGS
23:35:25 4.335   bash             33360  24577    0 /bin/bash
23:35:25 4.338   lesspipe         33361  33360    0 /usr/bin/lesspipe
23:35:25 4.340   basename         33362  33361    0 /usr/bin/basename /usr/bin/lesspipe
23:35:25 4.342   dirname          33364  33363    0 /usr/bin/dirname /usr/bin/lesspipe
23:35:25 4.347   dircolors        33365  33360    0 /usr/bin/dircolors -b
23:35:40 19.327  touch            33367  33366    0 /usr/bin/touch /run/udev/gdm-machine-has-hardware-gpu
23:35:40 19.329  snap-device-hel  33368  33366    0 /usr/lib/snapd/snap-device-helper change snap_firefox_firefox /devices/pci0000:00/0000:00:02.0/drm/card0 226:0
23:35:40 19.331  snap-device-hel  33369  33366    0 /usr/lib/snapd/snap-device-helper change snap_firefox_geckodriver /devices/pci0000:00/0000:00:02.0/drm/card0 226:0
23:35:40 19.332  snap-device-hel  33370  33366    0 /usr/lib/snapd/snap-device-helper change snap_snap-store_snap-store /devices/pci0000:00/0000:00:02.0/drm/card0 226:0

The -u option filtering UID:

# ./execsnoop -Uu 1000
UID   PCOMM            PID    PPID   RET ARGS
1000  bash             33604  24577    0 /bin/bash
1000  lesspipe         33606  33604    0 /usr/bin/lesspipe
1000  basename         33607  33606    0 /usr/bin/basename /usr/bin/lesspipe
1000  dirname          33609  33608    0 /usr/bin/dirname /usr/bin/lesspipe
1000  dircolors        33610  33604    0 /usr/bin/dircolors -b
1000  sleep            33615  33604    0 /usr/bin/sleep
1000  sleep            33616  33604    0 /usr/bin/sleep 1
1000  clear            33617  33604    0 /usr/bin/clear

Report bugs to https://github.com/iovisor/bcc/tree/master/libbpf-tools.

README.md Unescape Escape

eBPF 入门实践教程七：捕获进程执行/退出时间，通过 perf event array 向用户态打印输出

execsnoop

Compile and Run

details in bcc

README.md