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// SPDX-FileCopyrightText: edef <edef@unfathomable.blue>
// SPDX-License-Identifier: OSL-3.0
use {
anyhow::{bail, Context},
nix::{
libc,
sys::{
personality::{self, Persona},
ptrace,
signal::Signal,
wait::{waitpid, WaitPidFlag, WaitStatus},
},
unistd::Pid,
},
std::{env, os::unix::process::CommandExt, process::Command},
};
// TODO(edef): consider implementing this in terms of TID?
// tgids are a strict subset of tids
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
struct Tgid(pub libc::pid_t);
impl Tgid {
fn as_pid(&self) -> Pid {
Pid::from_raw(self.0)
}
}
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
struct Tid(pub libc::pid_t);
impl Tid {
fn as_pid(&self) -> Pid {
Pid::from_raw(self.0)
}
}
#[derive(Debug)]
struct Process {
tgid: Tgid,
}
impl Process {
fn spawn(cmd: &mut Command) -> anyhow::Result<Process> {
unsafe {
cmd.pre_exec(|| {
ptrace::traceme()?;
Ok(())
});
}
let child = cmd.spawn()?;
// the thread group leader's TID is equal to the TGID
let tgid = Tgid(child.id() as _);
match waitpid(tgid.as_pid(), None).context("Couldn't waitpid on fresh child")? {
WaitStatus::Stopped(_, Signal::SIGTRAP) => {}
status => bail!("unexpected child state: {:?}", status),
}
Ok(Process { tgid })
}
}
#[derive(Debug, Copy, Clone)]
struct SyscallEntry {
number: u64,
// rdi, rsi, rdx, rcx, r8, r9
args: [u64; 6],
}
impl SyscallEntry {
fn from_regs(regs: libc::user_regs_struct) -> SyscallEntry {
SyscallEntry {
number: regs.orig_rax,
args: [regs.rdi, regs.rsi, regs.rdx, regs.rcx, regs.r8, regs.r9],
}
}
}
#[derive(Debug, Copy, Clone)]
enum EntryExit {
/// Process is about to enter a syscall
Entry(SyscallEntry),
/// Process is about to exit a syscall
Exit(SyscallEntry, i64),
}
fn main() -> anyhow::Result<()> {
// disable ASLR
let mut persona = personality::get()?;
persona.insert(Persona::ADDR_NO_RANDOMIZE);
personality::set(persona)?;
let process = Process::spawn(&mut {
let mut args = env::args();
// drop argv[0]
args.next();
let mut cmd = Command::new(args.next().unwrap());
for arg in args {
cmd.arg(arg);
}
cmd
})?;
let options = ptrace::Options::PTRACE_O_TRACESYSGOOD | ptrace::Options::PTRACE_O_TRACECLONE;
ptrace::setoptions(process.tgid.as_pid(), options)?;
// this is always equal to tgid for now,
// but I'm keeping this separate so it's obvious what has to be tgid
let tid = Tid(process.tgid.0);
let mut syscall_state: Option<EntryExit> = None;
loop {
ptrace::syscall(tid.as_pid(), None)?;
if let Some(EntryExit::Exit(..)) = syscall_state {
// syscall has completed now
syscall_state = None;
}
let status = waitpid(tid.as_pid(), Some(WaitPidFlag::__WALL))?;
match (syscall_state, status) {
(None, WaitStatus::PtraceSyscall(event_tid)) => {
let event_tid = Tid(event_tid.as_raw());
assert_eq!(tid, event_tid);
let regs = ptrace::getregs(event_tid.as_pid())?;
let entry = SyscallEntry::from_regs(regs);
syscall_state = Some(EntryExit::Entry(entry));
if !check_syscall(entry) {
ptrace::kill(event_tid.as_pid())?;
panic!("unsupported syscall {:?}", entry);
}
}
(Some(EntryExit::Entry(entry)), WaitStatus::PtraceSyscall(event_tid)) => {
let event_tid = Tid(event_tid.as_raw());
assert_eq!(tid, event_tid);
let regs = ptrace::getregs(event_tid.as_pid())?;
let ret = regs.rax as i64;
syscall_state = Some(EntryExit::Exit(entry, ret));
}
(_, WaitStatus::Exited(event_tid, _)) => {
let event_tid = Tid(event_tid.as_raw());
assert_eq!(tid, event_tid);
// TODO(edef): this only works for main thread
break;
}
_ => panic!(
"unknown status {:?} with syscall_state = {:?}",
status, syscall_state
),
}
}
Ok(())
}
fn check_syscall(entry: SyscallEntry) -> bool {
match entry.number {
// read
0 => {}
// write
1 => {}
// close
3 => {}
// mmap
9 => {
let [_addr, _len, _prot, flags, fd, _off] = entry.args;
if fd != !0 {
return flags & (libc::MAP_PRIVATE as u64) != 0;
} else {
return flags & (libc::MAP_ANON as u64) != 0;
}
}
// mprotect
10 => {}
// brk
12 => {}
// rt_sigaction
13 => {}
// ioctl
16 => match entry.args[1] {
// TCGETS
0x5401 | 0x5413 => {}
_ => return false,
},
// pread64
17 => {}
// access
21 => {}
// getcwd
79 => {}
// readlink
89 => {}
// sysinfo
99 => {}
// times
100 => {}
// arch_prctl
158 => match entry.args[0] {
// ARCH_SET_FS
0x1002 => {}
_ => return false,
},
// exit_group
231 => {}
// openat
257 => {}
// newfstatat
262 => {}
// prlimit64
302 => {
// pid = 0
if entry.args[0] != 0 {
return false;
}
match entry.args[1] as u32 {
libc::RLIMIT_AS | libc::RLIMIT_STACK | libc::RLIMIT_RSS => {}
_ => return false,
}
}
_ => return false,
}
true
}
|
