summary refs log tree commit diff
path: root/ripple/minitrace/src/main.rs
blob: 811f6a9d1114992afdd4c9d08cc629e6fa934c44 (plain)
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
// SPDX-FileCopyrightText: edef <edef@unfathomable.blue>
// SPDX-FileCopyrightText: V <v@unfathomable.blue>
// SPDX-License-Identifier: OSL-3.0

use {
	crate::{
		pidfd::PidFd,
		syscall_abi::{AtFlags, DirFd, MapFlags, SyscallEntry},
	},
	anyhow::{bail, Context, Result},
	bitflags::bitflags,
	nix::{
		libc,
		sys::{
			personality::{self, Persona},
			ptrace,
			resource::{self, Resource as HostResource},
			signal::Signal as HostSignal,
			wait::{waitpid, WaitPidFlag, WaitStatus},
		},
		unistd::Pid,
	},
	std::{
		env,
		ffi::CString,
		fmt::Debug,
		fs::{self, File},
		io::{self, BufRead, Seek, SeekFrom},
		os::unix::process::CommandExt,
		process::Command,
	},
};

mod maps_file;
mod pidfd;
mod syscall_abi;

// 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,
	mem: File,
	pidfd: PidFd,
}

impl Drop for Process {
	fn drop(&mut self) {
		if let Err(err) = self.terminate() {
			eprintln!("{err}");
		}
	}
}

impl Process {
	fn spawn(cmd: &mut Command) -> Result<Process> {
		unsafe {
			cmd.pre_exec(|| {
				// disable ASLR
				let mut persona = personality::get()?;
				persona.insert(Persona::ADDR_NO_RANDOMIZE);
				personality::set(persona)?;

				// set stack limit (to guarantee top-down address space layout)
				resource::setrlimit(
					HostResource::RLIMIT_STACK,
					Some(
						// not a particularly meaningful number,
						// just plucked from the author's system
						8 * 1024 * 1024,
					),
					Some(
						128 * 1024 * 1024
						// guard page
						- 4096,
					),
				)?;

				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(_, HostSignal::SIGTRAP) => {}
			status => bail!("unexpected child state: {status:?}"),
		}

		let pidfd = PidFd::open(tgid.as_pid()).context("Couldn't open child pidfd")?;

		Ok(Process {
			tgid,
			mem: File::open(format!("/proc/{}/mem", tgid.0))
				.context("Couldn't open child memory")?,
			pidfd,
		})
	}

	fn terminate(&self) -> Result<()> {
		match self.pidfd.kill(HostSignal::SIGKILL) {
			Ok(()) | Err(nix::Error::ESRCH) => Ok(()),
			Err(err) => Err(anyhow::Error::from(err).context("Couldn't terminate child")),
		}
	}

	fn read_mem_cstr(&self, ptr: u64) -> Result<CString> {
		let mut mem = io::BufReader::new(&self.mem);
		mem.seek(SeekFrom::Start(ptr))?;
		let mut buf = vec![];
		mem.read_until(0, &mut buf)?;

		Ok(CString::from_vec_with_nul(buf).expect("logic error"))
	}

	fn read_mappings(&self) -> Result<Vec<maps_file::Mapping>> {
		let pid = self.tgid.as_pid();
		let contents = fs::read_to_string(format!("/proc/{pid}/maps"))?;

		// TODO(edef): consult /proc/$pid/map_files/* for pathnames, since /proc/$pid/maps is unreliable with odd paths
		// we'll want to verify the two against each other, just to be sure they're congruent

		let mut mappings = contents
			.lines()
			.map(maps_file::parse_mapping_line)
			.collect::<Result<_, _>>()?;

		for &mut maps_file::Mapping {
			start,
			end,
			ref mut pathname,
			..
		} in &mut mappings
		{
			if pathname.starts_with('[') && pathname.ends_with(']') {
				// these won't exist in map_files
				continue;
			}

			let map_path = format!("/proc/{pid}/map_files/{start:x}-{end:x}");
			let target = fs::read_link(&map_path)
				.with_context(|| {
					format!("Cannot readlink({map_path:?}) (expected target: {pathname:?})")
				})?
				.into_os_string()
				.into_string()
				.expect("path is not valid UTF-8");
			assert_eq!(*pathname, maps_file::escape_path(&target), "escaping bug?");
			*pathname = target;
		}

		Ok(mappings)
	}

	fn dump_mappings(&self) -> Result<()> {
		let mappings = self.read_mappings()?;
		let mut mappings = mappings.iter().peekable();
		let mut segments = vec![];

		while let Some(mut last) = mappings.next() {
			let mut segment = vec![];
			segment.push(last);
			while let Some(&next) = mappings.peek() {
				if last.dev != next.dev || last.inode != next.inode {
					// not the same file
					break;
				}
				if last.end != next.start || last.offset + last.end - last.start != next.offset {
					// not contiguous
					break;
				}
				last = mappings.next().unwrap();
				segment.push(last);
			}
			segments.push(segment);
		}

		println!("{:#?}", segments);
		Ok(())
	}
}

#[derive(Debug, Clone)]
enum EntryExit {
	/// Process is about to enter a syscall
	Entry(SyscallEntry),
	/// Process is about to exit a syscall
	Exit(SyscallEntry, i64),
}

fn main() -> Result<()> {
	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.env_clear();
		cmd
	})?;

	process.dump_mappings()?;

	let options = ptrace::Options::PTRACE_O_TRACESYSGOOD
		| ptrace::Options::PTRACE_O_TRACECLONE
		| ptrace::Options::PTRACE_O_EXITKILL;
	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 = match SyscallEntry::from_regs(&process, regs) {
					Ok(entry) => entry,
					Err(err) => panic!("{err}"),
				};

				if !check_syscall(&entry) {
					panic!("invalid syscall {entry:?}");
				}

				match entry {
					SyscallEntry::times { .. } => {}
					_ => println!("{entry:?}"),
				}

				syscall_state = Some(EntryExit::Entry(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;
			}
			(syscall_state, status) => {
				panic!("unknown status {status:?} with syscall_state = {syscall_state:?}")
			}
		}
	}

	Ok(())
}

fn check_syscall(entry: &SyscallEntry) -> bool {
	match *entry {
		SyscallEntry::mmap {
			addr,
			len: _,
			prot: _,
			flags,
			fd,
			off,
		} => {
			if addr % 4096 != 0 {
				return false;
			}

			match fd {
				None => flags.contains(MapFlags::ANONYMOUS) && off == 0,
				Some(_) => {
					flags.intersection(MapFlags::PRIVATE | MapFlags::ANONYMOUS) == MapFlags::PRIVATE
				}
			}
		}
		SyscallEntry::mprotect { addr, len, prot: _ } => addr % 4096 == 0 && len % 4096 == 0,
		SyscallEntry::openat {
			dfd,
			filename: _,
			flags: _,
			mode: _,
		} => dfd == DirFd::Cwd,
		SyscallEntry::newfstatat {
			dfd,
			ref filename,
			statbuf: _,
			flags,
		} => {
			match (dfd, filename.as_bytes()) {
				(_, b"") if !flags.contains(AtFlags::EMPTY_PATH) => {
					// empty path without AT_EMPTY_PATH
					false
				}
				(DirFd::Cwd, _) | (_, b"") => true,
				_ => false,
			}
		}
		_ => true,
	}
}