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inject.py
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#!/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",
"alloc_page" : "true",
}
@classmethod
def configure(cls, mode, probability, count):
cls.mode = mode
cls.probability = probability
cls.count = count
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
# don't 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 there's 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)
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() + """
{
u32 overridden = 0;
int zero = 0;
u32* val;
val = count.lookup(&zero);
if (val)
overridden = *val;
/*
* preparation for predicate, if necessary
*/
%s
/*
* If this is the only call in the chain and predicate passes
*/
if (%s == 1 && %s && overridden < %s) {
count.atomic_increment(zero);
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 && overridden < %s) {
count.atomic_increment(zero);
bpf_override_return(ctx, %s);
}
return 0;
}"""
return text % (self.prep, self.length, pred, Probe.count,
self._get_err(), self.length - 1, pred, Probe.count,
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)",
"alloc_page": "should_fail_alloc_page(gfp_t gfp_mask, unsigned int order)",
}
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", choices=["kmalloc", "bio", "alloc_page"],
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")
parser.add_argument("-c", "--count", action="store", default=-1,
help="Number of fails before bypassing the override")
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.args.count)
# 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"
self.program += "BPF_ARRAY(count, u32, 1);\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:
try:
self.bpf.perf_buffer_poll()
except KeyboardInterrupt:
exit()
def run(self):
self._create_probes()
self._generate_program()
self._attach_probes()
self._main_loop()
if __name__ == "__main__":
Tool().run()