security_bpf_map.c

 1// SPDX-License-Identifier: GPL-2.0-only
 2
 3#include "vmlinux.h"
 4#include <bpf/bpf_tracing.h>
 5#include <bpf/bpf_helpers.h>
 6
 7char _license[] SEC("license") = "GPL";
 8
 9#define EPERM 1 /* Operation not permitted */
10
11/* From include/linux/mm.h. */
12#define FMODE_WRITE	0x2
13
14struct map;
15
16struct {
17	__uint(type, BPF_MAP_TYPE_ARRAY);
18	__type(key, __u32);
19	__type(value, __u32);
20	__uint(max_entries, 1);
21} prot_status_map SEC(".maps");
22
23struct {
24	__uint(type, BPF_MAP_TYPE_HASH);
25	__type(key, __u32);
26	__type(value, __u32);
27	__uint(max_entries, 3);
28} prot_map SEC(".maps");
29
30struct {
31	__uint(type, BPF_MAP_TYPE_HASH);
32	__type(key, __u32);
33	__type(value, __u32);
34	__uint(max_entries, 3);
35} not_prot_map SEC(".maps");
36
37SEC("fmod_ret/security_bpf_map")
38int BPF_PROG(fmod_bpf_map, struct bpf_map *map, int fmode)
39{
40	__u32 key = 0;
41	__u32 *status_ptr = bpf_map_lookup_elem(&prot_status_map, &key);
42
43	if (!status_ptr || !*status_ptr)
44		return 0;
45
46	if (map == &prot_map) {
47		/* Allow read-only access */
48		if (fmode & FMODE_WRITE)
49			return -EPERM;
50	}
51
52	return 0;
53}
54
55/*
56 * This program keeps references to maps. This is needed to prevent
57 * optimizing them out.
58 */
59SEC("fentry/bpf_fentry_test1")
60int BPF_PROG(fentry_dummy1, int a)
61{
62	__u32 key = 0;
63	__u32 val1 = a;
64	__u32 val2 = a + 1;
65
66	bpf_map_update_elem(&prot_map, &key, &val1, BPF_ANY);
67	bpf_map_update_elem(&not_prot_map, &key, &val2, BPF_ANY);
68	return 0;
69}