/
protect_unix.rs
234 lines (207 loc) 路 7.21 KB
/
protect_unix.rs
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//! Installing signal handlers allows us to handle traps and out-of-bounds memory
//! accesses that occur when runniing WebAssembly.
//!
//! This code is inspired by: https://github.com/pepyakin/wasmtime/commit/625a2b6c0815b21996e111da51b9664feb174622
//!
//! When a WebAssembly module triggers any traps, we perform recovery here.
//!
//! This module uses TLS (thread-local storage) to track recovery information. Since the four signals we're handling
//! are very special, the async signal unsafety of Rust's TLS implementation generally does not affect the correctness here
//! unless you have memory unsafety elsewhere in your code.
//!
use libc::{c_int, c_void, siginfo_t};
use nix::sys::signal::{
sigaction, SaFlags, SigAction, SigHandler, SigSet, Signal, SIGBUS, SIGFPE, SIGILL, SIGSEGV,
SIGTRAP,
};
use std::any::Any;
use std::cell::{Cell, RefCell, UnsafeCell};
use std::collections::HashMap;
use std::ptr;
use std::sync::Arc;
use std::sync::Once;
use wasmer_runtime_core::codegen::BkptInfo;
use wasmer_runtime_core::typed_func::WasmTrapInfo;
extern "C" fn signal_trap_handler(
signum: ::nix::libc::c_int,
siginfo: *mut siginfo_t,
ucontext: *mut c_void,
) {
unsafe {
match Signal::from_c_int(signum) {
Ok(SIGTRAP) => {
let (_, ip) = get_faulting_addr_and_ip(siginfo as _, ucontext);
let bkpt_map = BKPT_MAP.with(|x| x.borrow().last().map(|x| x.clone()));
if let Some(bkpt_map) = bkpt_map {
if let Some(ref x) = bkpt_map.get(&(ip as usize)) {
(x)(BkptInfo {});
return;
}
}
}
_ => {}
}
do_unwind(signum, siginfo as _, ucontext);
}
}
extern "C" {
pub fn setjmp(env: *mut c_void) -> c_int;
fn longjmp(env: *mut c_void, val: c_int) -> !;
}
pub unsafe fn install_sighandler() {
let sa = SigAction::new(
SigHandler::SigAction(signal_trap_handler),
SaFlags::SA_ONSTACK,
SigSet::empty(),
);
sigaction(SIGFPE, &sa).unwrap();
sigaction(SIGILL, &sa).unwrap();
sigaction(SIGSEGV, &sa).unwrap();
sigaction(SIGBUS, &sa).unwrap();
sigaction(SIGTRAP, &sa).unwrap();
}
const SETJMP_BUFFER_LEN: usize = 27;
pub static SIGHANDLER_INIT: Once = Once::new();
thread_local! {
pub static SETJMP_BUFFER: UnsafeCell<[c_int; SETJMP_BUFFER_LEN]> = UnsafeCell::new([0; SETJMP_BUFFER_LEN]);
pub static CAUGHT_ADDRESSES: Cell<(*const c_void, *const c_void)> = Cell::new((ptr::null(), ptr::null()));
pub static CURRENT_EXECUTABLE_BUFFER: Cell<*const c_void> = Cell::new(ptr::null());
pub static TRAP_EARLY_DATA: Cell<Option<Box<dyn Any>>> = Cell::new(None);
pub static BKPT_MAP: RefCell<Vec<Arc<HashMap<usize, Box<Fn(BkptInfo) + Send + Sync + 'static>>>>> = RefCell::new(Vec::new());
}
pub unsafe fn trigger_trap() -> ! {
let jmp_buf = SETJMP_BUFFER.with(|buf| buf.get());
longjmp(jmp_buf as *mut c_void, 0)
}
pub enum CallProtError {
Trap(WasmTrapInfo),
Error(Box<dyn Any>),
}
pub fn call_protected<T>(f: impl FnOnce() -> T) -> Result<T, CallProtError> {
unsafe {
let jmp_buf = SETJMP_BUFFER.with(|buf| buf.get());
let prev_jmp_buf = *jmp_buf;
SIGHANDLER_INIT.call_once(|| {
install_sighandler();
});
let signum = setjmp(jmp_buf as *mut _);
if signum != 0 {
*jmp_buf = prev_jmp_buf;
if let Some(data) = TRAP_EARLY_DATA.with(|cell| cell.replace(None)) {
Err(CallProtError::Error(data))
} else {
// let (faulting_addr, _inst_ptr) = CAUGHT_ADDRESSES.with(|cell| cell.get());
// let signal = match Signal::from_c_int(signum) {
// Ok(SIGFPE) => "floating-point exception",
// Ok(SIGILL) => "illegal instruction",
// Ok(SIGSEGV) => "segmentation violation",
// Ok(SIGBUS) => "bus error",
// Err(_) => "error while getting the Signal",
// _ => "unknown trapped signal",
// };
// // When the trap-handler is fully implemented, this will return more information.
// Err(RuntimeError::Trap {
// msg: format!("unknown trap at {:p} - {}", faulting_addr, signal).into(),
// }
// .into())
Err(CallProtError::Trap(WasmTrapInfo::Unknown))
}
} else {
let ret = f(); // TODO: Switch stack?
*jmp_buf = prev_jmp_buf;
Ok(ret)
}
}
}
/// Unwinds to last protected_call.
pub unsafe fn do_unwind(signum: i32, siginfo: *const c_void, ucontext: *const c_void) -> ! {
// Since do_unwind is only expected to get called from WebAssembly code which doesn't hold any host resources (locks etc.)
// itself, accessing TLS here is safe. In case any other code calls this, it often indicates a memory safety bug and you should
// temporarily disable the signal handlers to debug it.
let jmp_buf = SETJMP_BUFFER.with(|buf| buf.get());
if *jmp_buf == [0; SETJMP_BUFFER_LEN] {
::std::process::abort();
}
CAUGHT_ADDRESSES.with(|cell| cell.set(get_faulting_addr_and_ip(siginfo, ucontext)));
longjmp(jmp_buf as *mut ::nix::libc::c_void, signum)
}
#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
unsafe fn get_faulting_addr_and_ip(
siginfo: *const c_void,
ucontext: *const c_void,
) -> (*const c_void, *const c_void) {
use libc::{ucontext_t, RIP};
#[allow(dead_code)]
#[repr(C)]
struct siginfo_t {
si_signo: i32,
si_errno: i32,
si_code: i32,
si_addr: u64,
// ...
}
let siginfo = siginfo as *const siginfo_t;
let si_addr = (*siginfo).si_addr;
let ucontext = ucontext as *const ucontext_t;
let rip = (*ucontext).uc_mcontext.gregs[RIP as usize];
(si_addr as _, rip as _)
}
#[cfg(all(target_os = "macos", target_arch = "x86_64"))]
unsafe fn get_faulting_addr_and_ip(
siginfo: *const c_void,
ucontext: *const c_void,
) -> (*const c_void, *const c_void) {
#[allow(dead_code)]
#[repr(C)]
struct ucontext_t {
uc_onstack: u32,
uc_sigmask: u32,
uc_stack: libc::stack_t,
uc_link: *const ucontext_t,
uc_mcsize: u64,
uc_mcontext: *const mcontext_t,
}
#[repr(C)]
struct exception_state {
trapno: u16,
cpu: u16,
err: u32,
faultvaddr: u64,
}
#[repr(C)]
struct regs {
rax: u64,
rbx: u64,
rcx: u64,
rdx: u64,
rdi: u64,
rsi: u64,
rbp: u64,
rsp: u64,
r8: u64,
r9: u64,
r10: u64,
r11: u64,
r12: u64,
r13: u64,
r14: u64,
r15: u64,
rip: u64,
rflags: u64,
cs: u64,
fs: u64,
gs: u64,
}
#[allow(dead_code)]
#[repr(C)]
struct mcontext_t {
es: exception_state,
ss: regs,
// ...
}
let siginfo = siginfo as *const siginfo_t;
let si_addr = (*siginfo).si_addr;
let ucontext = ucontext as *const ucontext_t;
let rip = (*(*ucontext).uc_mcontext).ss.rip;
(si_addr, rip as _)
}