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
|
/*
* Copyright (c) 2021, Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Format.h>
#include <AK/Random.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>
#include <AK/Vector.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <syscall.h>
static bool is_deadly_syscall(int fn)
{
return fn == SC_exit || fn == SC_fork || fn == SC_sigreturn || fn == SC_exit_thread;
}
static bool is_unfuzzable_syscall(int fn)
{
return fn == SC_dump_backtrace || fn == SC_munmap || fn == SC_kill || fn == SC_killpg;
}
static bool is_nosys_syscall(int fn)
{
return fn == SC_futex || fn == SC_emuctl;
}
static bool is_bad_idea(int fn, const size_t* direct_sc_args, const size_t* fake_sc_params, const char* some_string)
{
switch (fn) {
case SC_mprotect:
// This would mess with future tests or crash the fuzzer.
return direct_sc_args[0] == (size_t)fake_sc_params || direct_sc_args[0] == (size_t)some_string;
case SC_read:
case SC_readv:
// FIXME: Known bug: https://github.com/SerenityOS/serenity/issues/5328
return direct_sc_args[0] == 1;
case SC_write:
case SC_writev:
// FIXME: Known bug: https://github.com/SerenityOS/serenity/issues/5328
return direct_sc_args[0] == 0;
case SC_pledge:
// Equivalent to pledge(nullptr, _), which would kill the fuzzer.
return direct_sc_args[0] == (size_t)fake_sc_params && fake_sc_params[1] == 0;
default:
return false;
}
}
static void do_systematic_tests()
{
int rc;
for (int i = 0; i < Syscall::Function::__Count; ++i) {
dbgln("Testing syscall #{} ({})", i, Syscall::to_string((Syscall::Function)i));
if (is_deadly_syscall(i)) {
dbgln("(skipping deadly syscall)");
continue;
}
// This is pure torture
rc = syscall(Syscall::Function(i), 0xc0000001, 0xc0000002, 0xc0000003);
VERIFY(rc != -ENOSYS || is_nosys_syscall(i));
}
// Finally, test invalid syscalls:
dbgln("Testing syscall #{} (n+1)", (int)Syscall::Function::__Count);
rc = syscall(Syscall::Function::__Count, 0xc0000001, 0xc0000002, 0xc0000003);
VERIFY(rc == -ENOSYS);
dbgln("Testing syscall #-1");
rc = syscall(Syscall::Function(-1), 0xc0000001, 0xc0000002, 0xc0000003);
VERIFY(rc == -ENOSYS);
}
static void randomize_from(size_t* buffer, size_t len, const Vector<size_t>& values)
{
for (size_t i = 0; i < len; ++i) {
buffer[i] = values[get_random_uniform(values.size())];
}
}
// The largest SC_*_params struct is SC_mmap_params with 9 size_ts (36 bytes on x86, 72 on x86_64).
static constexpr size_t fake_params_count = sizeof(Syscall::SC_mmap_params) / sizeof(size_t);
static void do_weird_call(size_t attempt, int syscall_fn, size_t arg1, size_t arg2, size_t arg3, size_t* fake_params)
{
// Report to dbg what we're about to do, in case it's interesting:
StringBuilder builder;
builder.appendff("#{}: Calling {}({:p}, {:p}, {:p}) with {:p} containing [",
attempt, Syscall::to_string((Syscall::Function)syscall_fn), arg1, arg2, arg3, fake_params);
for (size_t i = 0; i < fake_params_count; ++i) {
if (i != 0)
builder.append(", ");
builder.appendff("{:p}", fake_params[i]);
}
builder.append("]");
dbgln("{}", builder.build());
// Actually do the syscall ('fake_params' is passed indirectly, if any of arg1, arg2, or arg3 point to it.
int rc = syscall(Syscall::Function(syscall_fn), arg1, arg2, arg3);
VERIFY(rc != -ENOSYS || is_nosys_syscall(syscall_fn));
}
static void do_random_tests()
{
// Make it less likely to kill ourselves due to sys$alarm(1):
{
struct sigaction act_ignore = { { SIG_IGN }, 0, 0 };
int rc = sigaction(SIGALRM, &act_ignore, nullptr);
VERIFY(rc == 0);
}
// Note that we will also make lots of syscalls for randomness and debugging.
const size_t fuzz_syscall_count = 10000;
size_t direct_sc_args[3] = { 0 };
// Isolate to a separate region to make corruption less likely, because we will write to it:
auto* fake_sc_params = reinterpret_cast<size_t*>(mmap(nullptr, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON | MAP_RANDOMIZED, 0, 0));
const char* some_string = "Hello, world!";
Vector<size_t> interesting_values = {
0,
1,
reinterpret_cast<size_t>(some_string),
strlen(some_string),
reinterpret_cast<size_t>(fake_sc_params),
0xc0000000,
0xc0000000 - PAGE_SIZE,
0xffffffff,
};
dbgln("Doing a few random syscalls with:");
for (const auto& interesting_value : interesting_values) {
dbgln(" {0} ({0:p})", interesting_value);
}
for (size_t i = 0; i < fuzz_syscall_count; ++i) {
// Construct a nice syscall:
int syscall_fn = get_random_uniform(Syscall::Function::__Count);
randomize_from(direct_sc_args, array_size(direct_sc_args), interesting_values);
randomize_from(fake_sc_params, fake_params_count, interesting_values);
if (is_deadly_syscall(syscall_fn)
|| is_unfuzzable_syscall(syscall_fn)
|| is_bad_idea(syscall_fn, direct_sc_args, fake_sc_params, some_string)) {
// Retry, and don't count towards syscall limit.
--i;
continue;
}
do_weird_call(i, syscall_fn, direct_sc_args[0], direct_sc_args[1], direct_sc_args[2], fake_sc_params);
}
}
int main()
{
do_systematic_tests();
do_random_tests();
// If the Kernel survived, pass.
printf("PASS\n");
return 0;
}
|
