Line data Source code
1 : /* SPDX-License-Identifier: LGPL-2.1+ */
2 : #include <linux/bpf_insn.h>
3 :
4 : #include "bpf-devices.h"
5 : #include "bpf-program.h"
6 :
7 : #define PASS_JUMP_OFF 4096
8 :
9 0 : static int bpf_access_type(const char *acc) {
10 0 : int r = 0;
11 :
12 0 : assert(acc);
13 :
14 0 : for (; *acc; acc++)
15 0 : switch(*acc) {
16 0 : case 'r':
17 0 : r |= BPF_DEVCG_ACC_READ;
18 0 : break;
19 0 : case 'w':
20 0 : r |= BPF_DEVCG_ACC_WRITE;
21 0 : break;
22 0 : case 'm':
23 0 : r |= BPF_DEVCG_ACC_MKNOD;
24 0 : break;
25 0 : default:
26 0 : return -EINVAL;
27 : }
28 :
29 0 : return r;
30 : }
31 :
32 0 : int cgroup_bpf_whitelist_device(BPFProgram *prog, int type, int major, int minor, const char *acc) {
33 0 : struct bpf_insn insn[] = {
34 : BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 6), /* compare device type */
35 : BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
36 : BPF_ALU32_IMM(BPF_AND, BPF_REG_1, 0),
37 : BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 3), /* compare access type */
38 : BPF_JMP_IMM(BPF_JNE, BPF_REG_4, major, 2), /* compare major */
39 : BPF_JMP_IMM(BPF_JNE, BPF_REG_5, minor, 1), /* compare minor */
40 : BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
41 : };
42 : int r, access;
43 :
44 0 : assert(prog);
45 0 : assert(acc);
46 :
47 0 : access = bpf_access_type(acc);
48 0 : if (access <= 0)
49 0 : return -EINVAL;
50 :
51 0 : insn[2].imm = access;
52 :
53 0 : r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
54 0 : if (r < 0)
55 0 : log_error_errno(r, "Extending device control BPF program failed: %m");
56 :
57 0 : return r;
58 : }
59 :
60 0 : int cgroup_bpf_whitelist_major(BPFProgram *prog, int type, int major, const char *acc) {
61 0 : struct bpf_insn insn[] = {
62 : BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 5), /* compare device type */
63 : BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
64 : BPF_ALU32_IMM(BPF_AND, BPF_REG_1, 0),
65 : BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 2), /* compare access type */
66 : BPF_JMP_IMM(BPF_JNE, BPF_REG_4, major, 1), /* compare major */
67 : BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
68 : };
69 : int r, access;
70 :
71 0 : assert(prog);
72 0 : assert(acc);
73 :
74 0 : access = bpf_access_type(acc);
75 0 : if (access <= 0)
76 0 : return -EINVAL;
77 :
78 0 : insn[2].imm = access;
79 :
80 0 : r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
81 0 : if (r < 0)
82 0 : log_error_errno(r, "Extending device control BPF program failed: %m");
83 :
84 0 : return r;
85 : }
86 :
87 0 : int cgroup_bpf_whitelist_class(BPFProgram *prog, int type, const char *acc) {
88 0 : struct bpf_insn insn[] = {
89 : BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 5), /* compare device type */
90 : BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
91 : BPF_ALU32_IMM(BPF_AND, BPF_REG_1, 0),
92 : BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 1), /* compare access type */
93 : BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
94 : };
95 : int r, access;
96 :
97 0 : assert(prog);
98 0 : assert(acc);
99 :
100 0 : access = bpf_access_type(acc);
101 0 : if (access <= 0)
102 0 : return -EINVAL;
103 :
104 0 : insn[2].imm = access;
105 :
106 0 : r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
107 0 : if (r < 0)
108 0 : log_error_errno(r, "Extending device control BPF program failed: %m");
109 :
110 0 : return r;
111 : }
112 :
113 0 : int cgroup_init_device_bpf(BPFProgram **ret, CGroupDevicePolicy policy, bool whitelist) {
114 0 : struct bpf_insn pre_insn[] = {
115 : /* load device type to r2 */
116 : BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_1,
117 : offsetof(struct bpf_cgroup_dev_ctx, access_type)),
118 :
119 : /* load access type to r3 */
120 : BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1,
121 : offsetof(struct bpf_cgroup_dev_ctx, access_type)),
122 : BPF_ALU32_IMM(BPF_RSH, BPF_REG_3, 16),
123 :
124 : /* load major number to r4 */
125 : BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1,
126 : offsetof(struct bpf_cgroup_dev_ctx, major)),
127 :
128 : /* load minor number to r5 */
129 : BPF_LDX_MEM(BPF_W, BPF_REG_5, BPF_REG_1,
130 : offsetof(struct bpf_cgroup_dev_ctx, minor)),
131 : };
132 :
133 0 : _cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
134 : int r;
135 :
136 0 : assert(ret);
137 :
138 0 : if (policy == CGROUP_AUTO && !whitelist)
139 0 : return 0;
140 :
141 0 : r = bpf_program_new(BPF_PROG_TYPE_CGROUP_DEVICE, &prog);
142 0 : if (r < 0)
143 0 : return log_error_errno(r, "Loading device control BPF program failed: %m");
144 :
145 0 : if (policy == CGROUP_CLOSED || whitelist) {
146 0 : r = bpf_program_add_instructions(prog, pre_insn, ELEMENTSOF(pre_insn));
147 0 : if (r < 0)
148 0 : return log_error_errno(r, "Extending device control BPF program failed: %m");
149 : }
150 :
151 0 : *ret = TAKE_PTR(prog);
152 :
153 0 : return 0;
154 : }
155 :
156 0 : int cgroup_apply_device_bpf(Unit *u, BPFProgram *prog, CGroupDevicePolicy policy, bool whitelist) {
157 0 : struct bpf_insn post_insn[] = {
158 : /* return DENY */
159 : BPF_MOV64_IMM(BPF_REG_0, 0),
160 : BPF_JMP_A(1),
161 :
162 : };
163 :
164 0 : struct bpf_insn exit_insn[] = {
165 : /* else return ALLOW */
166 : BPF_MOV64_IMM(BPF_REG_0, 1),
167 : BPF_EXIT_INSN()
168 : };
169 :
170 0 : _cleanup_free_ char *path = NULL;
171 : int r;
172 :
173 0 : if (!prog) {
174 : /* Remove existing program. */
175 0 : u->bpf_device_control_installed = bpf_program_unref(u->bpf_device_control_installed);
176 0 : return 0;
177 : }
178 :
179 0 : if (policy != CGROUP_STRICT || whitelist) {
180 : size_t off;
181 :
182 0 : r = bpf_program_add_instructions(prog, post_insn, ELEMENTSOF(post_insn));
183 0 : if (r < 0)
184 0 : return log_error_errno(r, "Extending device control BPF program failed: %m");
185 :
186 : /* Fixup PASS_JUMP_OFF jump offsets. */
187 0 : for (off = 0; off < prog->n_instructions; off++) {
188 0 : struct bpf_insn *ins = &prog->instructions[off];
189 :
190 0 : if (ins->code == (BPF_JMP | BPF_JA) && ins->off == PASS_JUMP_OFF)
191 0 : ins->off = prog->n_instructions - off - 1;
192 : }
193 : } else
194 : /* Explicitly forbid everything. */
195 0 : exit_insn[0].imm = 0;
196 :
197 0 : r = bpf_program_add_instructions(prog, exit_insn, ELEMENTSOF(exit_insn));
198 0 : if (r < 0)
199 0 : return log_error_errno(r, "Extending device control BPF program failed: %m");
200 :
201 0 : r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, NULL, &path);
202 0 : if (r < 0)
203 0 : return log_error_errno(r, "Failed to determine cgroup path: %m");
204 :
205 0 : r = bpf_program_cgroup_attach(prog, BPF_CGROUP_DEVICE, path, BPF_F_ALLOW_MULTI);
206 0 : if (r < 0)
207 0 : return log_error_errno(r, "Attaching device control BPF program to cgroup %s failed: %m", path);
208 :
209 : /* Unref the old BPF program (which will implicitly detach it) right before attaching the new program. */
210 0 : u->bpf_device_control_installed = bpf_program_unref(u->bpf_device_control_installed);
211 :
212 : /* Remember that this BPF program is installed now. */
213 0 : u->bpf_device_control_installed = bpf_program_ref(prog);
214 :
215 0 : return 0;
216 : }
217 :
218 11 : int bpf_devices_supported(void) {
219 11 : struct bpf_insn trivial[] = {
220 : BPF_MOV64_IMM(BPF_REG_0, 1),
221 : BPF_EXIT_INSN()
222 : };
223 :
224 11 : _cleanup_(bpf_program_unrefp) BPFProgram *program = NULL;
225 : static int supported = -1;
226 : int r;
227 :
228 : /* Checks whether BPF device controller is supported. For this, we check five things:
229 : *
230 : * a) whether we are privileged
231 : * b) whether the unified hierarchy is being used
232 : * c) the BPF implementation in the kernel supports BPF_PROG_TYPE_CGROUP_DEVICE programs, which we require
233 : */
234 :
235 11 : if (supported >= 0)
236 6 : return supported;
237 :
238 5 : if (geteuid() != 0) {
239 5 : log_debug("Not enough privileges, BPF device control is not supported.");
240 5 : return supported = 0;
241 : }
242 :
243 0 : r = cg_unified_controller(SYSTEMD_CGROUP_CONTROLLER);
244 0 : if (r < 0)
245 0 : return log_error_errno(r, "Can't determine whether the unified hierarchy is used: %m");
246 0 : if (r == 0) {
247 0 : log_debug("Not running with unified cgroups, BPF device control is not supported.");
248 0 : return supported = 0;
249 : }
250 :
251 0 : r = bpf_program_new(BPF_PROG_TYPE_CGROUP_DEVICE, &program);
252 0 : if (r < 0) {
253 0 : log_debug_errno(r, "Can't allocate CGROUP DEVICE BPF program, BPF device control is not supported: %m");
254 0 : return supported = 0;
255 : }
256 :
257 0 : r = bpf_program_add_instructions(program, trivial, ELEMENTSOF(trivial));
258 0 : if (r < 0) {
259 0 : log_debug_errno(r, "Can't add trivial instructions to CGROUP DEVICE BPF program, BPF device control is not supported: %m");
260 0 : return supported = 0;
261 : }
262 :
263 0 : r = bpf_program_load_kernel(program, NULL, 0);
264 0 : if (r < 0) {
265 0 : log_debug_errno(r, "Can't load kernel CGROUP DEVICE BPF program, BPF device control is not supported: %m");
266 0 : return supported = 0;
267 : }
268 :
269 0 : return supported = 1;
270 : }
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