Recover safely from WebAssembly-generated traps

This commit is contained in:
losfair 2018-11-24 19:40:29 +08:00 committed by Lachlan Sneff
parent 4015fb6193
commit 227a3ee6d6
4 changed files with 60 additions and 31 deletions

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@ -28,6 +28,7 @@ use structopt::StructOpt;
mod macros;
pub mod apis;
pub mod common;
mod recovery;
pub mod sighandler;
#[cfg(test)]
mod spectests;
@ -95,9 +96,7 @@ fn execute_wasm(wasm_path: PathBuf) -> Result<(), String> {
Some(&webassembly::Export::Function(index)) => index,
_ => panic!("Main function not found"),
});
let main: extern "C" fn(&webassembly::Instance) =
get_instance_function!(instance, func_index);
main(&instance);
instance.start_func(func_index).unwrap();
}
Ok(())

41
src/recovery.rs Normal file
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@ -0,0 +1,41 @@
//! When a WebAssembly module triggers any traps, we perform recovery here.
use std::cell::UnsafeCell;
extern "C" {
fn setjmp(env: *mut ::nix::libc::c_void) -> ::nix::libc::c_int;
fn longjmp(env: *mut ::nix::libc::c_void, val: ::nix::libc::c_int) -> !;
}
const SETJMP_BUFFER_LEN: usize = 27;
thread_local! {
static SETJMP_BUFFER: UnsafeCell<[::nix::libc::c_int; SETJMP_BUFFER_LEN]> = UnsafeCell::new([0; SETJMP_BUFFER_LEN]);
}
/// Calls a function with longjmp receiver installed. The function must be compiled from WebAssembly;
/// Otherwise, the behavior is undefined.
pub unsafe fn protected_call<T, R>(f: fn(T) -> R, p: T) -> Result<R, i32> {
let jmp_buf = SETJMP_BUFFER.with(|buf| buf.get());
let prev_jmp_buf = *jmp_buf;
let signum = setjmp(jmp_buf as *mut ::nix::libc::c_void);
if signum != 0 {
*jmp_buf = prev_jmp_buf;
Err(signum)
} else {
let ret = f(p);
*jmp_buf = prev_jmp_buf;
Ok(ret)
}
}
/// Unwinds to last protected_call.
pub unsafe fn do_unwind(signum: i32) -> ! {
let jmp_buf = SETJMP_BUFFER.with(|buf| buf.get());
if *jmp_buf == [0; SETJMP_BUFFER_LEN] {
::std::process::abort();
}
longjmp(jmp_buf as *mut ::nix::libc::c_void, signum)
}

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@ -4,12 +4,11 @@
//!
//! Please read more about this here: https://github.com/CraneStation/wasmtime/issues/15
//! This code is inspired by: https://github.com/pepyakin/wasmtime/commit/625a2b6c0815b21996e111da51b9664feb174622
use super::recovery;
use nix::sys::signal::{
sigaction, SaFlags, SigAction, SigHandler, SigSet, Signal, SIGBUS, SIGFPE, SIGILL, SIGSEGV,
sigaction, SaFlags, SigAction, SigHandler, SigSet, SIGBUS, SIGFPE, SIGILL, SIGSEGV,
};
static mut SETJMP_BUFFER: [::nix::libc::c_int; 27] = [0; 27];
pub unsafe fn install_sighandler() {
let sa = SigAction::new(
SigHandler::Handler(signal_trap_handler),
@ -20,29 +19,10 @@ pub unsafe fn install_sighandler() {
sigaction(SIGILL, &sa).unwrap();
sigaction(SIGSEGV, &sa).unwrap();
sigaction(SIGBUS, &sa).unwrap();
let signum = setjmp((&mut SETJMP_BUFFER[..]).as_mut_ptr() as *mut ::nix::libc::c_void);
if signum != 0 {
let signal = Signal::from_c_int(signum).unwrap();
match signal {
SIGFPE => panic!("floating-point exception"),
SIGILL => panic!("illegal instruction"),
SIGSEGV => panic!("segmentation violation"),
SIGBUS => panic!("bus error"),
_ => panic!("signal error: {:?}", signal),
};
}
}
extern "C" {
fn setjmp(env: *mut ::nix::libc::c_void) -> ::nix::libc::c_int;
fn longjmp(env: *mut ::nix::libc::c_void, val: ::nix::libc::c_int);
}
extern "C" fn signal_trap_handler(signum: ::nix::libc::c_int) {
unsafe {
longjmp(
(&mut SETJMP_BUFFER).as_mut_ptr() as *mut ::nix::libc::c_void,
signum,
);
recovery::do_unwind(signum);
}
}

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@ -22,6 +22,7 @@ use std::slice;
use std::sync::Arc;
use super::super::common::slice::{BoundedSlice, UncheckedSlice};
use super::super::recovery;
use super::errors::ErrorKind;
use super::import_object::{ImportObject, ImportValue};
use super::math_intrinsics;
@ -225,7 +226,8 @@ impl Instance {
// let r = *Arc::from_raw(isa_ptr);
compile_function(&*options.isa, function_body).unwrap()
// unimplemented!()
}).collect();
})
.collect();
for compiled_func in compiled_funcs.into_iter() {
let CompiledFunction {
@ -475,7 +477,8 @@ impl Instance {
&mem[..],
mem.current as usize * LinearMemory::WASM_PAGE_SIZE,
)
}).collect();
})
.collect();
let globals_pointer: GlobalsSlice = globals[..].into();
let data_pointers = DataPointers {
@ -513,10 +516,16 @@ impl Instance {
get_function_addr(&func_index, &self.import_functions, &self.functions)
}
pub fn start(&self) {
if let Some(func_index) = self.start_func {
pub fn start_func(&self, func_index: FuncIndex) -> Result<(), i32> {
let func: fn(&Instance) = get_instance_function!(&self, func_index);
func(self)
unsafe { recovery::protected_call(func, self) }
}
pub fn start(&self) -> Result<(), i32> {
if let Some(func_index) = self.start_func {
self.start_func(func_index)
} else {
panic!("start func not found")
}
}