Repository navigation
Expand file tree
/
Copy pathinject.py
More file actions
executable file
·503 lines (420 loc) · 15.3 KB
/
Copy pathinject.py
File metadata and controls
executable file
·503 lines (420 loc) · 15.3 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
#!/usr/bin/env python
#
# This script generates a BPF program with structure inspired by trace.py. The
# generated program operates on PID-indexed stacks. Generally speaking,
# bookkeeping is done at every intermediate function kprobe/kretprobe to enforce
# the goal of "fail iff this call chain and these predicates".
#
# Top level functions(the ones at the end of the call chain) are responsible for
# creating the pid_struct and deleting it from the map in kprobe and kretprobe
# respectively.
#
# Intermediate functions(between should_fail_whatever and the top level
# functions) are responsible for updating the stack to indicate "I have been
# called and one of my predicate(s) passed" in their entry probes. In their exit
# probes, they do the opposite, popping their stack to maintain correctness.
# This implementation aims to ensure correctness in edge cases like recursive
# calls, so there's some additional information stored in pid_struct for that.
#
# At the bottom level function(should_fail_whatever), we do a simple check to
# ensure all necessary calls/predicates have passed before error injection.
#
# Note: presently there are a few hacks to get around various rewriter/verifier
# issues.
#
# Note: this tool requires:
# - CONFIG_BPF_KPROBE_OVERRIDE
#
# USAGE: inject [-h] [-I header] [-P probability] [-v] mode spec
#
# Copyright (c) 2018 Facebook, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 16-Mar-2018 Howard McLauchlan Created this.
import argparse
import re
from bcc import BPF
class Probe:
errno_mapping = {
"kmalloc": "-ENOMEM",
"bio": "-EIO",
}
@classmethod
def configure(cls, mode, probability):
cls.mode = mode
cls.probability = probability
def __init__(self, func, preds, length, entry):
# length of call chain
self.length = length
self.func = func
self.preds = preds
self.is_entry = entry
def _bail(self, err):
raise ValueError("error in probe '%s': %s" %
(self.spec, err))
def _get_err(self):
return Probe.errno_mapping[Probe.mode]
def _get_if_top(self):
# ordering guarantees that if this function is top, the last tup is top
chk = self.preds[0][1] == 0
if not chk:
return ""
if Probe.probability == 1:
early_pred = "false"
else:
early_pred = "bpf_get_prandom_u32() > %s" % str(int((1<<32)*Probe.probability))
# init the map
# dont do an early exit here so the singular case works automatically
# have an early exit for probability option
enter = """
/*
* Early exit for probability case
*/
if (%s)
return 0;
/*
* Top level function init map
*/
struct pid_struct p_struct = {0, 0};
m.insert(&pid, &p_struct);
""" % early_pred
# kill the entry
exit = """
/*
* Top level function clean up map
*/
m.delete(&pid);
"""
return enter if self.is_entry else exit
def _get_heading(self):
# we need to insert identifier and ctx into self.func
# gonna make a lot of formatting assumptions to make this work
left = self.func.find("(")
right = self.func.rfind(")")
# self.event and self.func_name need to be accessible
self.event = self.func[0:left]
self.func_name = self.event + ("_entry" if self.is_entry else "_exit")
func_sig = "struct pt_regs *ctx"
# assume theres something in there, no guarantee its well formed
if right > left + 1 and self.is_entry:
func_sig += ", " + self.func[left + 1:right]
return "int %s(%s)" % (self.func_name, func_sig)
def _get_entry_logic(self):
# there is at least one tup(pred, place) for this function
text = """
if (p->conds_met >= %s)
return 0;
if (p->conds_met == %s && %s) {
p->stack[%s] = p->curr_call;
p->conds_met++;
}"""
text = text % (self.length, self.preds[0][1], self.preds[0][0],
self.preds[0][1])
# for each additional pred
for tup in self.preds[1:]:
text += """
else if (p->conds_met == %s && %s) {
p->stack[%s] = p->curr_call;
p->conds_met++;
}
""" % (tup[1], tup[0], tup[1])
return text
def _generate_entry(self):
prog = self._get_heading() + """
{
u32 pid = bpf_get_current_pid_tgid();
%s
struct pid_struct *p = m.lookup(&pid);
if (!p)
return 0;
/*
* preparation for predicate, if necessary
*/
%s
/*
* Generate entry logic
*/
%s
p->curr_call++;
return 0;
}"""
prog = prog % (self._get_if_top(), self.prep, self._get_entry_logic())
return prog
# only need to check top of stack
def _get_exit_logic(self):
text = """
if (p->conds_met < 1 || p->conds_met >= %s)
return 0;
if (p->stack[p->conds_met - 1] == p->curr_call)
p->conds_met--;
"""
return text % str(self.length + 1)
def _generate_exit(self):
prog = self._get_heading() + """
{
u32 pid = bpf_get_current_pid_tgid();
struct pid_struct *p = m.lookup(&pid);
if (!p)
return 0;
p->curr_call--;
/*
* Generate exit logic
*/
%s
%s
return 0;
}"""
prog = prog % (self._get_exit_logic(), self._get_if_top())
return prog
# Special case for should_fail_whatever
def _generate_bottom(self):
pred = self.preds[0][0]
text = self._get_heading() + """
{
/*
* preparation for predicate, if necessary
*/
%s
/*
* If this is the only call in the chain and predicate passes
*/
if (%s == 1 && %s) {
bpf_override_return(ctx, %s);
return 0;
}
u32 pid = bpf_get_current_pid_tgid();
struct pid_struct *p = m.lookup(&pid);
if (!p)
return 0;
/*
* If all conds have been met and predicate passes
*/
if (p->conds_met == %s && %s)
bpf_override_return(ctx, %s);
return 0;
}"""
return text % (self.prep, self.length, pred, self._get_err(),
self.length - 1, pred, self._get_err())
# presently parses and replaces STRCMP
# STRCMP exists because string comparison is inconvenient and somewhat buggy
# https://github.com/iovisor/bcc/issues/1617
def _prepare_pred(self):
self.prep = ""
for i in range(len(self.preds)):
new_pred = ""
pred = self.preds[i][0]
place = self.preds[i][1]
start, ind = 0, 0
while start < len(pred):
ind = pred.find("STRCMP(", start)
if ind == -1:
break
new_pred += pred[start:ind]
# 7 is len("STRCMP(")
start = pred.find(")", start + 7) + 1
# then ind ... start is STRCMP(...)
ptr, literal = pred[ind + 7:start - 1].split(",")
literal = literal.strip()
# x->y->z, some string literal
# we make unique id with place_ind
uuid = "%s_%s" % (place, ind)
unique_bool = "is_true_%s" % uuid
self.prep += """
char *str_%s = %s;
bool %s = true;\n""" % (uuid, ptr.strip(), unique_bool)
check = "\t%s &= *(str_%s++) == '%%s';\n" % (unique_bool, uuid)
for ch in literal:
self.prep += check % ch
self.prep += check % r'\0'
new_pred += unique_bool
new_pred += pred[start:]
self.preds[i] = (new_pred, place)
def generate_program(self):
# generate code to work around various rewriter issues
self._prepare_pred()
# special case for bottom
if self.preds[-1][1] == self.length - 1:
return self._generate_bottom()
return self._generate_entry() if self.is_entry else self._generate_exit()
def attach(self, bpf):
if self.is_entry:
bpf.attach_kprobe(event=self.event,
fn_name=self.func_name)
else:
bpf.attach_kretprobe(event=self.event,
fn_name=self.func_name)
class Tool:
examples ="""
EXAMPLES:
# ./inject.py kmalloc -v 'SyS_mount()'
Fails all calls to syscall mount
# ./inject.py kmalloc -v '(true) => SyS_mount()(true)'
Explicit rewriting of above
# ./inject.py kmalloc -v 'mount_subtree() => btrfs_mount()'
Fails btrfs mounts only
# ./inject.py kmalloc -v 'd_alloc_parallel(struct dentry *parent, const struct \\
qstr *name)(STRCMP(name->name, 'bananas'))'
Fails dentry allocations of files named 'bananas'
# ./inject.py kmalloc -v -P 0.01 'SyS_mount()'
Fails calls to syscall mount with 1% probability
"""
# add cases as necessary
error_injection_mapping = {
"kmalloc": "should_failslab(struct kmem_cache *s, gfp_t gfpflags)",
"bio": "should_fail_bio(struct bio *bio)",
}
def __init__(self):
parser = argparse.ArgumentParser(description="Fail specified kernel" +
" functionality when call chain and predicates are met",
formatter_class=argparse.RawDescriptionHelpFormatter,
epilog=Tool.examples)
parser.add_argument(dest="mode", ch
8000
oices=['kmalloc','bio'],
help="indicate which base kernel function to fail")
parser.add_argument(metavar="spec", dest="spec",
help="specify call chain")
parser.add_argument("-I", "--include", action="append",
metavar="header",
help="additional header files to include in the BPF program")
parser.add_argument("-P", "--probability", default=1,
metavar="probability", type=float,
help="probability that this call chain will fail")
parser.add_argument("-v", "--verbose", action="store_true",
help="print BPF program")
self.args = parser.parse_args()
self.program = ""
self.spec = self.args.spec
self.map = {}
self.probes = []
self.key = Tool.error_injection_mapping[self.args.mode]
# create_probes and associated stuff
def _create_probes(self):
self._parse_spec()
Probe.configure(self.args.mode, self.args.probability)
# self, func, preds, total, entry
# create all the pair probes
for fx, preds in self.map.items():
# do the enter
self.probes.append(Probe(fx, preds, self.length, True))
if self.key == fx:
continue
# do the exit
self.probes.append(Probe(fx, preds, self.length, False))
def _parse_frames(self):
# sentinel
data = self.spec + '\0'
start, count = 0, 0
frames = []
cur_frame = []
i = 0
last_frame_added = 0
while i < len(data):
# improper input
if count < 0:
raise Exception("Check your parentheses")
c = data[i]
count += c == '('
count -= c == ')'
if not count:
if c == '\0' or (c == '=' and data[i + 1] == '>'):
# This block is closing a chunk. This means cur_frame must
# have something in it.
if not cur_frame:
raise Exception("Cannot parse spec, missing parens")
if len(cur_frame) == 2:
frame = tuple(cur_frame)
elif cur_frame[0][0] == '(':
frame = self.key, cur_frame[0]
else:
frame = cur_frame[0], '(true)'
frames.append(frame)
del cur_frame[:]
i += 1
start = i + 1
elif c == ')':
cur_frame.append(data[start:i + 1].strip())
start = i + 1
last_frame_added = start
i += 1
# We only permit spaces after the last frame
if self.spec[last_frame_added:].strip():
raise Exception("Invalid characters found after last frame");
# improper input
if count:
raise Exception("Check your parentheses")
return frames
def _parse_spec(self):
frames = self._parse_frames()
frames.reverse()
absolute_order = 0
for f in frames:
# default case
func, pred = f[0], f[1]
if not self._validate_predicate(pred):
raise Exception("Invalid predicate")
if not self._validate_identifier(func):
raise Exception("Invalid function identifier")
tup = (pred, absolute_order)
if func not in self.map:
self.map[func] = [tup]
else:
self.map[func].append(tup)
absolute_order += 1
if self.key not in self.map:
self.map[self.key] = [('(true)', absolute_order)]
absolute_order += 1
self.length = absolute_order
def _validate_identifier(self, func):
# We've already established paren balancing. We will only look for
# identifier validity here.
paren_index = func.find("(")
potential_id = func[:paren_index]
pattern = '[_a-zA-z][_a-zA-Z0-9]*$'
if re.match(pattern, potential_id):
return True
return False
def _validate_predicate(self, pred):
if len(pred) > 0 and pred[0] == "(":
open = 1
for i in range(1, len(pred)):
if pred[i] == "(":
open += 1
elif pred[i] == ")":
open -= 1
if open != 0:
# not well formed, break
return False
return True
def _def_pid_struct(self):
text = """
struct pid_struct {
u64 curr_call; /* book keeping to handle recursion */
u64 conds_met; /* stack pointer */
u64 stack[%s];
};
""" % self.length
return text
def _attach_probes(self):
self.bpf = BPF(text=self.program)
for p in self.probes:
p.attach(self.bpf)
def _generate_program(self):
# leave out auto includes for now
self.program += '#include <linux/mm.h>\n'
for include in (self.args.include or []):
self.program += "#include <%s>\n" % include
self.program += self._def_pid_struct()
self.program += "BPF_HASH(m, u32, struct pid_struct);\n"
for p in self.probes:
self.program += p.generate_program() + "\n"
if self.args.verbose:
print(self.program)
def _main_loop(self):
while True:
self.bpf.perf_buffer_poll()
def run(self):
self._create_probes()
self._generate_program()
self._attach_probes()
self._main_loop()
if __name__ == "__main__":
Tool().run()