samples/bpf/tracex5_kern.c

/* Copyright (c) 2015 PLUMgrid, http://plumgrid.com
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#include <linux/ptrace.h>
#include <linux/version.h>
#include <uapi/linux/bpf.h>
#include <uapi/linux/seccomp.h>
#include "bpf_helpers.h"

#define PROG(F) SEC("kprobe/"__stringify(F)) int bpf_func_##F

struct bpf_map_def SEC("maps") progs = {
	.type = BPF_MAP_TYPE_PROG_ARRAY,
	.key_size = sizeof(u32),
	.value_size = sizeof(u32),
	.max_entries = 1024,
};

SEC("kprobe/seccomp_phase1")
int bpf_prog1(struct pt_regs *ctx)
{
	struct seccomp_data sd = {};

	bpf_probe_read(&sd, sizeof(sd), (void *)ctx->di);

	/* dispatch into next BPF program depending on syscall number */
	bpf_tail_call(ctx, &progs, sd.nr);

	/* fall through -> unknown syscall */
	if (sd.nr >= __NR_getuid && sd.nr <= __NR_getsid) {
		char fmt[] = "syscall=%d (one of get/set uid/pid/gid)\n";
		bpf_trace_printk(fmt, sizeof(fmt), sd.nr);
	}
	return 0;
}

/* we jump here when syscall number == __NR_write */
PROG(__NR_write)(struct pt_regs *ctx)
{
	struct seccomp_data sd = {};

	bpf_probe_read(&sd, sizeof(sd), (void *)ctx->di);
	if (sd.args[2] == 512) {
		char fmt[] = "write(fd=%d, buf=%p, size=%d)\n";
		bpf_trace_printk(fmt, sizeof(fmt),
				 sd.args[0], sd.args[1], sd.args[2]);
	}
	return 0;
}

PROG(__NR_read)(struct pt_regs *ctx)
{
	struct seccomp_data sd = {};

	bpf_probe_read(&sd, sizeof(sd), (void *)ctx->di);
	if (sd.args[2] > 128 && sd.args[2] <= 1024) {
		char fmt[] = "read(fd=%d, buf=%p, size=%d)\n";
		bpf_trace_printk(fmt, sizeof(fmt),
				 sd.args[0], sd.args[1], sd.args[2]);
	}
	return 0;
}

PROG(__NR_mmap)(struct pt_regs *ctx)
{
	char fmt[] = "mmap\n";
	bpf_trace_printk(fmt, sizeof(fmt));
	return 0;
}

char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = LINUX_VERSION_CODE;