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/*
* 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 36 bytes.
static_assert(sizeof(size_t) == 4, "Cannot handle size_t != 4 bytes");
static const size_t fake_params_count = 36 / 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 (unsigned long& 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;
}
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