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88691e9e CH |
1 | |
2 | ============= | |
3 | eBPF verifier | |
4 | ============= | |
5 | ||
6 | The safety of the eBPF program is determined in two steps. | |
7 | ||
8 | First step does DAG check to disallow loops and other CFG validation. | |
9 | In particular it will detect programs that have unreachable instructions. | |
10 | (though classic BPF checker allows them) | |
11 | ||
12 | Second step starts from the first insn and descends all possible paths. | |
13 | It simulates execution of every insn and observes the state change of | |
14 | registers and stack. | |
15 | ||
16 | At the start of the program the register R1 contains a pointer to context | |
17 | and has type PTR_TO_CTX. | |
18 | If verifier sees an insn that does R2=R1, then R2 has now type | |
19 | PTR_TO_CTX as well and can be used on the right hand side of expression. | |
20 | If R1=PTR_TO_CTX and insn is R2=R1+R1, then R2=SCALAR_VALUE, | |
21 | since addition of two valid pointers makes invalid pointer. | |
22 | (In 'secure' mode verifier will reject any type of pointer arithmetic to make | |
23 | sure that kernel addresses don't leak to unprivileged users) | |
24 | ||
25 | If register was never written to, it's not readable:: | |
26 | ||
27 | bpf_mov R0 = R2 | |
28 | bpf_exit | |
29 | ||
30 | will be rejected, since R2 is unreadable at the start of the program. | |
31 | ||
32 | After kernel function call, R1-R5 are reset to unreadable and | |
33 | R0 has a return type of the function. | |
34 | ||
35 | Since R6-R9 are callee saved, their state is preserved across the call. | |
36 | ||
37 | :: | |
38 | ||
39 | bpf_mov R6 = 1 | |
40 | bpf_call foo | |
41 | bpf_mov R0 = R6 | |
42 | bpf_exit | |
43 | ||
44 | is a correct program. If there was R1 instead of R6, it would have | |
45 | been rejected. | |
46 | ||
47 | load/store instructions are allowed only with registers of valid types, which | |
48 | are PTR_TO_CTX, PTR_TO_MAP, PTR_TO_STACK. They are bounds and alignment checked. | |
49 | For example:: | |
50 | ||
51 | bpf_mov R1 = 1 | |
52 | bpf_mov R2 = 2 | |
53 | bpf_xadd *(u32 *)(R1 + 3) += R2 | |
54 | bpf_exit | |
55 | ||
56 | will be rejected, since R1 doesn't have a valid pointer type at the time of | |
57 | execution of instruction bpf_xadd. | |
58 | ||
59 | At the start R1 type is PTR_TO_CTX (a pointer to generic ``struct bpf_context``) | |
60 | A callback is used to customize verifier to restrict eBPF program access to only | |
61 | certain fields within ctx structure with specified size and alignment. | |
62 | ||
63 | For example, the following insn:: | |
64 | ||
65 | bpf_ld R0 = *(u32 *)(R6 + 8) | |
66 | ||
67 | intends to load a word from address R6 + 8 and store it into R0 | |
68 | If R6=PTR_TO_CTX, via is_valid_access() callback the verifier will know | |
69 | that offset 8 of size 4 bytes can be accessed for reading, otherwise | |
70 | the verifier will reject the program. | |
71 | If R6=PTR_TO_STACK, then access should be aligned and be within | |
72 | stack bounds, which are [-MAX_BPF_STACK, 0). In this example offset is 8, | |
73 | so it will fail verification, since it's out of bounds. | |
74 | ||
75 | The verifier will allow eBPF program to read data from stack only after | |
76 | it wrote into it. | |
77 | ||
78 | Classic BPF verifier does similar check with M[0-15] memory slots. | |
79 | For example:: | |
80 | ||
81 | bpf_ld R0 = *(u32 *)(R10 - 4) | |
82 | bpf_exit | |
83 | ||
84 | is invalid program. | |
85 | Though R10 is correct read-only register and has type PTR_TO_STACK | |
86 | and R10 - 4 is within stack bounds, there were no stores into that location. | |
87 | ||
88 | Pointer register spill/fill is tracked as well, since four (R6-R9) | |
89 | callee saved registers may not be enough for some programs. | |
90 | ||
91 | Allowed function calls are customized with bpf_verifier_ops->get_func_proto() | |
92 | The eBPF verifier will check that registers match argument constraints. | |
93 | After the call register R0 will be set to return type of the function. | |
94 | ||
95 | Function calls is a main mechanism to extend functionality of eBPF programs. | |
96 | Socket filters may let programs to call one set of functions, whereas tracing | |
97 | filters may allow completely different set. | |
98 | ||
99 | If a function made accessible to eBPF program, it needs to be thought through | |
100 | from safety point of view. The verifier will guarantee that the function is | |
101 | called with valid arguments. | |
102 | ||
103 | seccomp vs socket filters have different security restrictions for classic BPF. | |
104 | Seccomp solves this by two stage verifier: classic BPF verifier is followed | |
105 | by seccomp verifier. In case of eBPF one configurable verifier is shared for | |
106 | all use cases. | |
107 | ||
108 | See details of eBPF verifier in kernel/bpf/verifier.c | |
109 | ||
110 | Register value tracking | |
111 | ======================= | |
112 | ||
113 | In order to determine the safety of an eBPF program, the verifier must track | |
114 | the range of possible values in each register and also in each stack slot. | |
115 | This is done with ``struct bpf_reg_state``, defined in include/linux/ | |
116 | bpf_verifier.h, which unifies tracking of scalar and pointer values. Each | |
117 | register state has a type, which is either NOT_INIT (the register has not been | |
118 | written to), SCALAR_VALUE (some value which is not usable as a pointer), or a | |
119 | pointer type. The types of pointers describe their base, as follows: | |
120 | ||
121 | ||
122 | PTR_TO_CTX | |
123 | Pointer to bpf_context. | |
124 | CONST_PTR_TO_MAP | |
125 | Pointer to struct bpf_map. "Const" because arithmetic | |
126 | on these pointers is forbidden. | |
127 | PTR_TO_MAP_VALUE | |
128 | Pointer to the value stored in a map element. | |
129 | PTR_TO_MAP_VALUE_OR_NULL | |
130 | Either a pointer to a map value, or NULL; map accesses | |
131 | (see maps.rst) return this type, which becomes a | |
132 | PTR_TO_MAP_VALUE when checked != NULL. Arithmetic on | |
133 | these pointers is forbidden. | |
134 | PTR_TO_STACK | |
135 | Frame pointer. | |
136 | PTR_TO_PACKET | |
137 | skb->data. | |
138 | PTR_TO_PACKET_END | |
139 | skb->data + headlen; arithmetic forbidden. | |
140 | PTR_TO_SOCKET | |
141 | Pointer to struct bpf_sock_ops, implicitly refcounted. | |
142 | PTR_TO_SOCKET_OR_NULL | |
143 | Either a pointer to a socket, or NULL; socket lookup | |
144 | returns this type, which becomes a PTR_TO_SOCKET when | |
145 | checked != NULL. PTR_TO_SOCKET is reference-counted, | |
146 | so programs must release the reference through the | |
147 | socket release function before the end of the program. | |
148 | Arithmetic on these pointers is forbidden. | |
149 | ||
150 | However, a pointer may be offset from this base (as a result of pointer | |
151 | arithmetic), and this is tracked in two parts: the 'fixed offset' and 'variable | |
152 | offset'. The former is used when an exactly-known value (e.g. an immediate | |
153 | operand) is added to a pointer, while the latter is used for values which are | |
154 | not exactly known. The variable offset is also used in SCALAR_VALUEs, to track | |
155 | the range of possible values in the register. | |
156 | ||
157 | The verifier's knowledge about the variable offset consists of: | |
158 | ||
159 | * minimum and maximum values as unsigned | |
160 | * minimum and maximum values as signed | |
161 | ||
162 | * knowledge of the values of individual bits, in the form of a 'tnum': a u64 | |
163 | 'mask' and a u64 'value'. 1s in the mask represent bits whose value is unknown; | |
164 | 1s in the value represent bits known to be 1. Bits known to be 0 have 0 in both | |
165 | mask and value; no bit should ever be 1 in both. For example, if a byte is read | |
166 | into a register from memory, the register's top 56 bits are known zero, while | |
167 | the low 8 are unknown - which is represented as the tnum (0x0; 0xff). If we | |
168 | then OR this with 0x40, we get (0x40; 0xbf), then if we add 1 we get (0x0; | |
169 | 0x1ff), because of potential carries. | |
170 | ||
171 | Besides arithmetic, the register state can also be updated by conditional | |
172 | branches. For instance, if a SCALAR_VALUE is compared > 8, in the 'true' branch | |
173 | it will have a umin_value (unsigned minimum value) of 9, whereas in the 'false' | |
174 | branch it will have a umax_value of 8. A signed compare (with BPF_JSGT or | |
175 | BPF_JSGE) would instead update the signed minimum/maximum values. Information | |
176 | from the signed and unsigned bounds can be combined; for instance if a value is | |
177 | first tested < 8 and then tested s> 4, the verifier will conclude that the value | |
178 | is also > 4 and s< 8, since the bounds prevent crossing the sign boundary. | |
179 | ||
180 | PTR_TO_PACKETs with a variable offset part have an 'id', which is common to all | |
181 | pointers sharing that same variable offset. This is important for packet range | |
182 | checks: after adding a variable to a packet pointer register A, if you then copy | |
183 | it to another register B and then add a constant 4 to A, both registers will | |
184 | share the same 'id' but the A will have a fixed offset of +4. Then if A is | |
185 | bounds-checked and found to be less than a PTR_TO_PACKET_END, the register B is | |
186 | now known to have a safe range of at least 4 bytes. See 'Direct packet access', | |
187 | below, for more on PTR_TO_PACKET ranges. | |
188 | ||
189 | The 'id' field is also used on PTR_TO_MAP_VALUE_OR_NULL, common to all copies of | |
190 | the pointer returned from a map lookup. This means that when one copy is | |
191 | checked and found to be non-NULL, all copies can become PTR_TO_MAP_VALUEs. | |
192 | As well as range-checking, the tracked information is also used for enforcing | |
193 | alignment of pointer accesses. For instance, on most systems the packet pointer | |
194 | is 2 bytes after a 4-byte alignment. If a program adds 14 bytes to that to jump | |
195 | over the Ethernet header, then reads IHL and addes (IHL * 4), the resulting | |
196 | pointer will have a variable offset known to be 4n+2 for some n, so adding the 2 | |
197 | bytes (NET_IP_ALIGN) gives a 4-byte alignment and so word-sized accesses through | |
198 | that pointer are safe. | |
199 | The 'id' field is also used on PTR_TO_SOCKET and PTR_TO_SOCKET_OR_NULL, common | |
200 | to all copies of the pointer returned from a socket lookup. This has similar | |
201 | behaviour to the handling for PTR_TO_MAP_VALUE_OR_NULL->PTR_TO_MAP_VALUE, but | |
202 | it also handles reference tracking for the pointer. PTR_TO_SOCKET implicitly | |
203 | represents a reference to the corresponding ``struct sock``. To ensure that the | |
204 | reference is not leaked, it is imperative to NULL-check the reference and in | |
205 | the non-NULL case, and pass the valid reference to the socket release function. | |
206 | ||
207 | Direct packet access | |
208 | ==================== | |
209 | ||
210 | In cls_bpf and act_bpf programs the verifier allows direct access to the packet | |
211 | data via skb->data and skb->data_end pointers. | |
212 | Ex:: | |
213 | ||
214 | 1: r4 = *(u32 *)(r1 +80) /* load skb->data_end */ | |
215 | 2: r3 = *(u32 *)(r1 +76) /* load skb->data */ | |
216 | 3: r5 = r3 | |
217 | 4: r5 += 14 | |
218 | 5: if r5 > r4 goto pc+16 | |
219 | R1=ctx R3=pkt(id=0,off=0,r=14) R4=pkt_end R5=pkt(id=0,off=14,r=14) R10=fp | |
220 | 6: r0 = *(u16 *)(r3 +12) /* access 12 and 13 bytes of the packet */ | |
221 | ||
222 | this 2byte load from the packet is safe to do, since the program author | |
223 | did check ``if (skb->data + 14 > skb->data_end) goto err`` at insn #5 which | |
224 | means that in the fall-through case the register R3 (which points to skb->data) | |
225 | has at least 14 directly accessible bytes. The verifier marks it | |
226 | as R3=pkt(id=0,off=0,r=14). | |
227 | id=0 means that no additional variables were added to the register. | |
228 | off=0 means that no additional constants were added. | |
229 | r=14 is the range of safe access which means that bytes [R3, R3 + 14) are ok. | |
230 | Note that R5 is marked as R5=pkt(id=0,off=14,r=14). It also points | |
231 | to the packet data, but constant 14 was added to the register, so | |
232 | it now points to ``skb->data + 14`` and accessible range is [R5, R5 + 14 - 14) | |
233 | which is zero bytes. | |
234 | ||
235 | More complex packet access may look like:: | |
236 | ||
237 | ||
238 | R0=inv1 R1=ctx R3=pkt(id=0,off=0,r=14) R4=pkt_end R5=pkt(id=0,off=14,r=14) R10=fp | |
239 | 6: r0 = *(u8 *)(r3 +7) /* load 7th byte from the packet */ | |
240 | 7: r4 = *(u8 *)(r3 +12) | |
241 | 8: r4 *= 14 | |
242 | 9: r3 = *(u32 *)(r1 +76) /* load skb->data */ | |
243 | 10: r3 += r4 | |
244 | 11: r2 = r1 | |
245 | 12: r2 <<= 48 | |
246 | 13: r2 >>= 48 | |
247 | 14: r3 += r2 | |
248 | 15: r2 = r3 | |
249 | 16: r2 += 8 | |
250 | 17: r1 = *(u32 *)(r1 +80) /* load skb->data_end */ | |
251 | 18: if r2 > r1 goto pc+2 | |
252 | R0=inv(id=0,umax_value=255,var_off=(0x0; 0xff)) R1=pkt_end R2=pkt(id=2,off=8,r=8) R3=pkt(id=2,off=0,r=8) R4=inv(id=0,umax_value=3570,var_off=(0x0; 0xfffe)) R5=pkt(id=0,off=14,r=14) R10=fp | |
253 | 19: r1 = *(u8 *)(r3 +4) | |
254 | ||
255 | The state of the register R3 is R3=pkt(id=2,off=0,r=8) | |
256 | id=2 means that two ``r3 += rX`` instructions were seen, so r3 points to some | |
257 | offset within a packet and since the program author did | |
258 | ``if (r3 + 8 > r1) goto err`` at insn #18, the safe range is [R3, R3 + 8). | |
259 | The verifier only allows 'add'/'sub' operations on packet registers. Any other | |
260 | operation will set the register state to 'SCALAR_VALUE' and it won't be | |
261 | available for direct packet access. | |
262 | ||
263 | Operation ``r3 += rX`` may overflow and become less than original skb->data, | |
264 | therefore the verifier has to prevent that. So when it sees ``r3 += rX`` | |
265 | instruction and rX is more than 16-bit value, any subsequent bounds-check of r3 | |
266 | against skb->data_end will not give us 'range' information, so attempts to read | |
267 | through the pointer will give "invalid access to packet" error. | |
268 | ||
269 | Ex. after insn ``r4 = *(u8 *)(r3 +12)`` (insn #7 above) the state of r4 is | |
270 | R4=inv(id=0,umax_value=255,var_off=(0x0; 0xff)) which means that upper 56 bits | |
271 | of the register are guaranteed to be zero, and nothing is known about the lower | |
272 | 8 bits. After insn ``r4 *= 14`` the state becomes | |
273 | R4=inv(id=0,umax_value=3570,var_off=(0x0; 0xfffe)), since multiplying an 8-bit | |
274 | value by constant 14 will keep upper 52 bits as zero, also the least significant | |
275 | bit will be zero as 14 is even. Similarly ``r2 >>= 48`` will make | |
276 | R2=inv(id=0,umax_value=65535,var_off=(0x0; 0xffff)), since the shift is not sign | |
277 | extending. This logic is implemented in adjust_reg_min_max_vals() function, | |
278 | which calls adjust_ptr_min_max_vals() for adding pointer to scalar (or vice | |
279 | versa) and adjust_scalar_min_max_vals() for operations on two scalars. | |
280 | ||
281 | The end result is that bpf program author can access packet directly | |
282 | using normal C code as:: | |
283 | ||
284 | void *data = (void *)(long)skb->data; | |
285 | void *data_end = (void *)(long)skb->data_end; | |
286 | struct eth_hdr *eth = data; | |
287 | struct iphdr *iph = data + sizeof(*eth); | |
288 | struct udphdr *udp = data + sizeof(*eth) + sizeof(*iph); | |
289 | ||
290 | if (data + sizeof(*eth) + sizeof(*iph) + sizeof(*udp) > data_end) | |
291 | return 0; | |
292 | if (eth->h_proto != htons(ETH_P_IP)) | |
293 | return 0; | |
294 | if (iph->protocol != IPPROTO_UDP || iph->ihl != 5) | |
295 | return 0; | |
296 | if (udp->dest == 53 || udp->source == 9) | |
297 | ...; | |
298 | ||
299 | which makes such programs easier to write comparing to LD_ABS insn | |
300 | and significantly faster. | |
301 | ||
302 | Pruning | |
303 | ======= | |
304 | ||
305 | The verifier does not actually walk all possible paths through the program. For | |
306 | each new branch to analyse, the verifier looks at all the states it's previously | |
307 | been in when at this instruction. If any of them contain the current state as a | |
308 | subset, the branch is 'pruned' - that is, the fact that the previous state was | |
309 | accepted implies the current state would be as well. For instance, if in the | |
310 | previous state, r1 held a packet-pointer, and in the current state, r1 holds a | |
311 | packet-pointer with a range as long or longer and at least as strict an | |
312 | alignment, then r1 is safe. Similarly, if r2 was NOT_INIT before then it can't | |
313 | have been used by any path from that point, so any value in r2 (including | |
314 | another NOT_INIT) is safe. The implementation is in the function regsafe(). | |
315 | Pruning considers not only the registers but also the stack (and any spilled | |
316 | registers it may hold). They must all be safe for the branch to be pruned. | |
317 | This is implemented in states_equal(). | |
318 | ||
319 | Understanding eBPF verifier messages | |
320 | ==================================== | |
321 | ||
322 | The following are few examples of invalid eBPF programs and verifier error | |
323 | messages as seen in the log: | |
324 | ||
325 | Program with unreachable instructions:: | |
326 | ||
327 | static struct bpf_insn prog[] = { | |
328 | BPF_EXIT_INSN(), | |
329 | BPF_EXIT_INSN(), | |
330 | }; | |
331 | ||
43429ea7 | 332 | Error:: |
88691e9e CH |
333 | |
334 | unreachable insn 1 | |
335 | ||
336 | Program that reads uninitialized register:: | |
337 | ||
338 | BPF_MOV64_REG(BPF_REG_0, BPF_REG_2), | |
339 | BPF_EXIT_INSN(), | |
340 | ||
341 | Error:: | |
342 | ||
343 | 0: (bf) r0 = r2 | |
344 | R2 !read_ok | |
345 | ||
346 | Program that doesn't initialize R0 before exiting:: | |
347 | ||
348 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_1), | |
349 | BPF_EXIT_INSN(), | |
350 | ||
351 | Error:: | |
352 | ||
353 | 0: (bf) r2 = r1 | |
354 | 1: (95) exit | |
355 | R0 !read_ok | |
356 | ||
357 | Program that accesses stack out of bounds:: | |
358 | ||
359 | BPF_ST_MEM(BPF_DW, BPF_REG_10, 8, 0), | |
360 | BPF_EXIT_INSN(), | |
361 | ||
362 | Error:: | |
363 | ||
364 | 0: (7a) *(u64 *)(r10 +8) = 0 | |
365 | invalid stack off=8 size=8 | |
366 | ||
367 | Program that doesn't initialize stack before passing its address into function:: | |
368 | ||
369 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), | |
370 | BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), | |
371 | BPF_LD_MAP_FD(BPF_REG_1, 0), | |
372 | BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), | |
373 | BPF_EXIT_INSN(), | |
374 | ||
375 | Error:: | |
376 | ||
377 | 0: (bf) r2 = r10 | |
378 | 1: (07) r2 += -8 | |
379 | 2: (b7) r1 = 0x0 | |
380 | 3: (85) call 1 | |
381 | invalid indirect read from stack off -8+0 size 8 | |
382 | ||
383 | Program that uses invalid map_fd=0 while calling to map_lookup_elem() function:: | |
384 | ||
385 | BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), | |
386 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), | |
387 | BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), | |
388 | BPF_LD_MAP_FD(BPF_REG_1, 0), | |
389 | BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), | |
390 | BPF_EXIT_INSN(), | |
391 | ||
392 | Error:: | |
393 | ||
394 | 0: (7a) *(u64 *)(r10 -8) = 0 | |
395 | 1: (bf) r2 = r10 | |
396 | 2: (07) r2 += -8 | |
397 | 3: (b7) r1 = 0x0 | |
398 | 4: (85) call 1 | |
399 | fd 0 is not pointing to valid bpf_map | |
400 | ||
401 | Program that doesn't check return value of map_lookup_elem() before accessing | |
402 | map element:: | |
403 | ||
404 | BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), | |
405 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), | |
406 | BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), | |
407 | BPF_LD_MAP_FD(BPF_REG_1, 0), | |
408 | BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), | |
409 | BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 0), | |
410 | BPF_EXIT_INSN(), | |
411 | ||
412 | Error:: | |
413 | ||
414 | 0: (7a) *(u64 *)(r10 -8) = 0 | |
415 | 1: (bf) r2 = r10 | |
416 | 2: (07) r2 += -8 | |
417 | 3: (b7) r1 = 0x0 | |
418 | 4: (85) call 1 | |
419 | 5: (7a) *(u64 *)(r0 +0) = 0 | |
420 | R0 invalid mem access 'map_value_or_null' | |
421 | ||
422 | Program that correctly checks map_lookup_elem() returned value for NULL, but | |
423 | accesses the memory with incorrect alignment:: | |
424 | ||
425 | BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), | |
426 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), | |
427 | BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), | |
428 | BPF_LD_MAP_FD(BPF_REG_1, 0), | |
429 | BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), | |
430 | BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1), | |
431 | BPF_ST_MEM(BPF_DW, BPF_REG_0, 4, 0), | |
432 | BPF_EXIT_INSN(), | |
433 | ||
434 | Error:: | |
435 | ||
436 | 0: (7a) *(u64 *)(r10 -8) = 0 | |
437 | 1: (bf) r2 = r10 | |
438 | 2: (07) r2 += -8 | |
439 | 3: (b7) r1 = 1 | |
440 | 4: (85) call 1 | |
441 | 5: (15) if r0 == 0x0 goto pc+1 | |
442 | R0=map_ptr R10=fp | |
443 | 6: (7a) *(u64 *)(r0 +4) = 0 | |
444 | misaligned access off 4 size 8 | |
445 | ||
446 | Program that correctly checks map_lookup_elem() returned value for NULL and | |
447 | accesses memory with correct alignment in one side of 'if' branch, but fails | |
448 | to do so in the other side of 'if' branch:: | |
449 | ||
450 | BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0), | |
451 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), | |
452 | BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), | |
453 | BPF_LD_MAP_FD(BPF_REG_1, 0), | |
454 | BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem), | |
455 | BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2), | |
456 | BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 0), | |
457 | BPF_EXIT_INSN(), | |
458 | BPF_ST_MEM(BPF_DW, BPF_REG_0, 0, 1), | |
459 | BPF_EXIT_INSN(), | |
460 | ||
461 | Error:: | |
462 | ||
463 | 0: (7a) *(u64 *)(r10 -8) = 0 | |
464 | 1: (bf) r2 = r10 | |
465 | 2: (07) r2 += -8 | |
466 | 3: (b7) r1 = 1 | |
467 | 4: (85) call 1 | |
468 | 5: (15) if r0 == 0x0 goto pc+2 | |
469 | R0=map_ptr R10=fp | |
470 | 6: (7a) *(u64 *)(r0 +0) = 0 | |
471 | 7: (95) exit | |
472 | ||
473 | from 5 to 8: R0=imm0 R10=fp | |
474 | 8: (7a) *(u64 *)(r0 +0) = 1 | |
475 | R0 invalid mem access 'imm' | |
476 | ||
477 | Program that performs a socket lookup then sets the pointer to NULL without | |
478 | checking it:: | |
479 | ||
480 | BPF_MOV64_IMM(BPF_REG_2, 0), | |
481 | BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_2, -8), | |
482 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), | |
483 | BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), | |
484 | BPF_MOV64_IMM(BPF_REG_3, 4), | |
485 | BPF_MOV64_IMM(BPF_REG_4, 0), | |
486 | BPF_MOV64_IMM(BPF_REG_5, 0), | |
487 | BPF_EMIT_CALL(BPF_FUNC_sk_lookup_tcp), | |
488 | BPF_MOV64_IMM(BPF_REG_0, 0), | |
489 | BPF_EXIT_INSN(), | |
490 | ||
491 | Error:: | |
492 | ||
493 | 0: (b7) r2 = 0 | |
494 | 1: (63) *(u32 *)(r10 -8) = r2 | |
495 | 2: (bf) r2 = r10 | |
496 | 3: (07) r2 += -8 | |
497 | 4: (b7) r3 = 4 | |
498 | 5: (b7) r4 = 0 | |
499 | 6: (b7) r5 = 0 | |
500 | 7: (85) call bpf_sk_lookup_tcp#65 | |
501 | 8: (b7) r0 = 0 | |
502 | 9: (95) exit | |
503 | Unreleased reference id=1, alloc_insn=7 | |
504 | ||
505 | Program that performs a socket lookup but does not NULL-check the returned | |
506 | value:: | |
507 | ||
508 | BPF_MOV64_IMM(BPF_REG_2, 0), | |
509 | BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_2, -8), | |
510 | BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), | |
511 | BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8), | |
512 | BPF_MOV64_IMM(BPF_REG_3, 4), | |
513 | BPF_MOV64_IMM(BPF_REG_4, 0), | |
514 | BPF_MOV64_IMM(BPF_REG_5, 0), | |
515 | BPF_EMIT_CALL(BPF_FUNC_sk_lookup_tcp), | |
516 | BPF_EXIT_INSN(), | |
517 | ||
518 | Error:: | |
519 | ||
520 | 0: (b7) r2 = 0 | |
521 | 1: (63) *(u32 *)(r10 -8) = r2 | |
522 | 2: (bf) r2 = r10 | |
523 | 3: (07) r2 += -8 | |
524 | 4: (b7) r3 = 4 | |
525 | 5: (b7) r4 = 0 | |
526 | 6: (b7) r5 = 0 | |
527 | 7: (85) call bpf_sk_lookup_tcp#65 | |
528 | 8: (95) exit | |
529 | Unreleased reference id=1, alloc_insn=7 |