wasmer_vm/trap/traphandlers.rs
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// This file contains code from external sources.
// Attributions: https://github.com/wasmerio/wasmer/blob/main/docs/ATTRIBUTIONS.md
#![allow(static_mut_refs)]
//! WebAssembly trap handling, which is built on top of the lower-level
//! signalhandling mechanisms.
use crate::vmcontext::{VMFunctionContext, VMTrampoline};
use crate::{Trap, VMContext, VMFunctionBody};
use backtrace::Backtrace;
use core::ptr::{read, read_unaligned};
use corosensei::stack::DefaultStack;
use corosensei::trap::{CoroutineTrapHandler, TrapHandlerRegs};
use corosensei::{Coroutine, CoroutineResult, Yielder};
use scopeguard::defer;
use std::any::Any;
use std::cell::Cell;
use std::error::Error;
use std::io;
use std::mem;
#[cfg(unix)]
use std::mem::MaybeUninit;
use std::ptr::{self, NonNull};
use std::sync::atomic::{compiler_fence, AtomicPtr, AtomicUsize, Ordering};
use std::sync::Once;
use wasmer_types::TrapCode;
/// Configuration for the runtime VM
/// Currently only the stack size is configurable
pub struct VMConfig {
/// Optionnal stack size (in byte) of the VM. Value lower than 8K will be rounded to 8K.
pub wasm_stack_size: Option<usize>,
}
// TrapInformation can be stored in the "Undefined Instruction" itself.
// On x86_64, 0xC? select a "Register" for the Mod R/M part of "ud1" (so with no other bytes after)
// On Arm64, the udf alows for a 16bits values, so we'll use the same 0xC? to store the trapinfo
static MAGIC: u8 = 0xc0;
static DEFAULT_STACK_SIZE: AtomicUsize = AtomicUsize::new(1024 * 1024);
// Current definition of `ucontext_t` in the `libc` crate is incorrect
// on aarch64-apple-drawin so it's defined here with a more accurate definition.
#[repr(C)]
#[cfg(all(target_arch = "aarch64", target_os = "macos"))]
#[allow(non_camel_case_types)]
struct ucontext_t {
uc_onstack: libc::c_int,
uc_sigmask: libc::sigset_t,
uc_stack: libc::stack_t,
uc_link: *mut libc::ucontext_t,
uc_mcsize: usize,
uc_mcontext: libc::mcontext_t,
}
// Current definition of `ucontext_t` in the `libc` crate is not present
// on aarch64-unknown-freebsd so it's defined here.
#[repr(C)]
#[cfg(all(target_arch = "aarch64", target_os = "freebsd"))]
#[allow(non_camel_case_types)]
struct ucontext_t {
uc_sigmask: libc::sigset_t,
uc_mcontext: libc::mcontext_t,
uc_link: *mut ucontext_t,
uc_stack: libc::stack_t,
uc_flags: libc::c_int,
spare: [libc::c_int; 4],
}
#[cfg(all(
unix,
not(all(target_arch = "aarch64", target_os = "macos")),
not(all(target_arch = "aarch64", target_os = "freebsd"))
))]
use libc::ucontext_t;
/// Default stack size is 1MB.
pub fn set_stack_size(size: usize) {
DEFAULT_STACK_SIZE.store(size.clamp(8 * 1024, 100 * 1024 * 1024), Ordering::Relaxed);
}
cfg_if::cfg_if! {
if #[cfg(unix)] {
/// Function which may handle custom signals while processing traps.
pub type TrapHandlerFn<'a> = dyn Fn(libc::c_int, *const libc::siginfo_t, *const libc::c_void) -> bool + Send + Sync + 'a;
} else if #[cfg(target_os = "windows")] {
/// Function which may handle custom signals while processing traps.
pub type TrapHandlerFn<'a> = dyn Fn(*mut windows_sys::Win32::System::Diagnostics::Debug::EXCEPTION_POINTERS) -> bool + Send + Sync + 'a;
}
}
// Process an IllegalOpcode to see if it has a TrapCode payload
unsafe fn process_illegal_op(addr: usize) -> Option<TrapCode> {
let mut val: Option<u8> = None;
if cfg!(target_arch = "x86_64") {
val = if read(addr as *mut u8) & 0xf0 == 0x40
&& read((addr + 1) as *mut u8) == 0x0f
&& read((addr + 2) as *mut u8) == 0xb9
{
Some(read((addr + 3) as *mut u8))
} else if read(addr as *mut u8) == 0x0f && read((addr + 1) as *mut u8) == 0xb9 {
Some(read((addr + 2) as *mut u8))
} else {
None
}
}
if cfg!(target_arch = "aarch64") {
val = if read_unaligned(addr as *mut u32) & 0xffff0000 == 0 {
Some(read(addr as *mut u8))
} else {
None
}
}
match val.and_then(|val| {
if val & MAGIC == MAGIC {
Some(val & 0xf)
} else {
None
}
}) {
None => None,
Some(val) => match val {
0 => Some(TrapCode::StackOverflow),
1 => Some(TrapCode::HeapAccessOutOfBounds),
2 => Some(TrapCode::HeapMisaligned),
3 => Some(TrapCode::TableAccessOutOfBounds),
4 => Some(TrapCode::IndirectCallToNull),
5 => Some(TrapCode::BadSignature),
6 => Some(TrapCode::IntegerOverflow),
7 => Some(TrapCode::IntegerDivisionByZero),
8 => Some(TrapCode::BadConversionToInteger),
9 => Some(TrapCode::UnreachableCodeReached),
10 => Some(TrapCode::UnalignedAtomic),
_ => None,
},
}
}
cfg_if::cfg_if! {
if #[cfg(unix)] {
static mut PREV_SIGSEGV: MaybeUninit<libc::sigaction> = MaybeUninit::uninit();
static mut PREV_SIGBUS: MaybeUninit<libc::sigaction> = MaybeUninit::uninit();
static mut PREV_SIGILL: MaybeUninit<libc::sigaction> = MaybeUninit::uninit();
static mut PREV_SIGFPE: MaybeUninit<libc::sigaction> = MaybeUninit::uninit();
unsafe fn platform_init() {
let register = |slot: &mut MaybeUninit<libc::sigaction>, signal: i32| {
let mut handler: libc::sigaction = mem::zeroed();
// The flags here are relatively careful, and they are...
//
// SA_SIGINFO gives us access to information like the program
// counter from where the fault happened.
//
// SA_ONSTACK allows us to handle signals on an alternate stack,
// so that the handler can run in response to running out of
// stack space on the main stack. Rust installs an alternate
// stack with sigaltstack, so we rely on that.
//
// SA_NODEFER allows us to reenter the signal handler if we
// crash while handling the signal, and fall through to the
// Breakpad handler by testing handlingSegFault.
handler.sa_flags = libc::SA_SIGINFO | libc::SA_NODEFER | libc::SA_ONSTACK;
handler.sa_sigaction = trap_handler as usize;
libc::sigemptyset(&mut handler.sa_mask);
if libc::sigaction(signal, &handler, slot.as_mut_ptr()) != 0 {
panic!(
"unable to install signal handler: {}",
io::Error::last_os_error(),
);
}
};
// Allow handling OOB with signals on all architectures
register(&mut PREV_SIGSEGV, libc::SIGSEGV);
// Handle `unreachable` instructions which execute `ud2` right now
register(&mut PREV_SIGILL, libc::SIGILL);
// x86 uses SIGFPE to report division by zero
if cfg!(target_arch = "x86") || cfg!(target_arch = "x86_64") {
register(&mut PREV_SIGFPE, libc::SIGFPE);
}
// On ARM, handle Unaligned Accesses.
// On Darwin, guard page accesses are raised as SIGBUS.
if cfg!(target_arch = "arm") || cfg!(target_vendor = "apple") {
register(&mut PREV_SIGBUS, libc::SIGBUS);
}
// This is necessary to support debugging under LLDB on Darwin.
// For more details see https://github.com/mono/mono/commit/8e75f5a28e6537e56ad70bf870b86e22539c2fb7
#[cfg(target_vendor = "apple")]
{
use mach2::exception_types::*;
use mach2::kern_return::*;
use mach2::port::*;
use mach2::thread_status::*;
use mach2::traps::*;
use mach2::mach_types::*;
extern "C" {
fn task_set_exception_ports(
task: task_t,
exception_mask: exception_mask_t,
new_port: mach_port_t,
behavior: exception_behavior_t,
new_flavor: thread_state_flavor_t,
) -> kern_return_t;
}
#[allow(non_snake_case)]
#[cfg(target_arch = "x86_64")]
let MACHINE_THREAD_STATE = x86_THREAD_STATE64;
#[allow(non_snake_case)]
#[cfg(target_arch = "aarch64")]
let MACHINE_THREAD_STATE = 6;
task_set_exception_ports(
mach_task_self(),
EXC_MASK_BAD_ACCESS | EXC_MASK_ARITHMETIC | EXC_MASK_BAD_INSTRUCTION,
MACH_PORT_NULL,
EXCEPTION_STATE_IDENTITY as exception_behavior_t,
MACHINE_THREAD_STATE,
);
}
}
unsafe extern "C" fn trap_handler(
signum: libc::c_int,
siginfo: *mut libc::siginfo_t,
context: *mut libc::c_void,
) {
let previous = match signum {
libc::SIGSEGV => &PREV_SIGSEGV,
libc::SIGBUS => &PREV_SIGBUS,
libc::SIGFPE => &PREV_SIGFPE,
libc::SIGILL => &PREV_SIGILL,
_ => panic!("unknown signal: {}", signum),
};
// We try to get the fault address associated to this signal
let maybe_fault_address = match signum {
libc::SIGSEGV | libc::SIGBUS => {
Some((*siginfo).si_addr() as usize)
}
_ => None,
};
let trap_code = match signum {
// check if it was cased by a UD and if the Trap info is a payload to it
libc::SIGILL => {
let addr = (*siginfo).si_addr() as usize;
process_illegal_op(addr)
}
_ => None,
};
let ucontext = &mut *(context as *mut ucontext_t);
let (pc, sp) = get_pc_sp(ucontext);
let handled = TrapHandlerContext::handle_trap(
pc,
sp,
maybe_fault_address,
trap_code,
|regs| update_context(ucontext, regs),
|handler| handler(signum, siginfo, context),
);
if handled {
return;
}
// This signal is not for any compiled wasm code we expect, so we
// need to forward the signal to the next handler. If there is no
// next handler (SIG_IGN or SIG_DFL), then it's time to crash. To do
// this, we set the signal back to its original disposition and
// return. This will cause the faulting op to be re-executed which
// will crash in the normal way. If there is a next handler, call
// it. It will either crash synchronously, fix up the instruction
// so that execution can continue and return, or trigger a crash by
// returning the signal to it's original disposition and returning.
let previous = &*previous.as_ptr();
if previous.sa_flags & libc::SA_SIGINFO != 0 {
mem::transmute::<
usize,
extern "C" fn(libc::c_int, *mut libc::siginfo_t, *mut libc::c_void),
>(previous.sa_sigaction)(signum, siginfo, context)
} else if previous.sa_sigaction == libc::SIG_DFL
{
libc::sigaction(signum, previous, ptr::null_mut());
} else if previous.sa_sigaction != libc::SIG_IGN {
mem::transmute::<usize, extern "C" fn(libc::c_int)>(
previous.sa_sigaction
)(signum)
}
}
unsafe fn get_pc_sp(context: &ucontext_t) -> (usize, usize) {
let (pc, sp);
cfg_if::cfg_if! {
if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "x86_64",
))] {
pc = context.uc_mcontext.gregs[libc::REG_RIP as usize] as usize;
sp = context.uc_mcontext.gregs[libc::REG_RSP as usize] as usize;
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "x86",
))] {
pc = context.uc_mcontext.gregs[libc::REG_EIP as usize] as usize;
sp = context.uc_mcontext.gregs[libc::REG_ESP as usize] as usize;
} else if #[cfg(all(target_os = "freebsd", target_arch = "x86"))] {
pc = context.uc_mcontext.mc_eip as usize;
sp = context.uc_mcontext.mc_esp as usize;
} else if #[cfg(all(target_os = "freebsd", target_arch = "x86_64"))] {
pc = context.uc_mcontext.mc_rip as usize;
sp = context.uc_mcontext.mc_rsp as usize;
} else if #[cfg(all(target_vendor = "apple", target_arch = "x86_64"))] {
pc = (*context.uc_mcontext).__ss.__rip as usize;
sp = (*context.uc_mcontext).__ss.__rsp as usize;
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "aarch64",
))] {
pc = context.uc_mcontext.pc as usize;
sp = context.uc_mcontext.sp as usize;
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "arm",
))] {
pc = context.uc_mcontext.arm_pc as usize;
sp = context.uc_mcontext.arm_sp as usize;
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
any(target_arch = "riscv64", target_arch = "riscv32"),
))] {
pc = context.uc_mcontext.__gregs[libc::REG_PC] as usize;
sp = context.uc_mcontext.__gregs[libc::REG_SP] as usize;
} else if #[cfg(all(target_vendor = "apple", target_arch = "aarch64"))] {
pc = (*context.uc_mcontext).__ss.__pc as usize;
sp = (*context.uc_mcontext).__ss.__sp as usize;
} else if #[cfg(all(target_os = "freebsd", target_arch = "aarch64"))] {
pc = context.uc_mcontext.mc_gpregs.gp_elr as usize;
sp = context.uc_mcontext.mc_gpregs.gp_sp as usize;
} else {
compile_error!("Unsupported platform");
}
};
(pc, sp)
}
unsafe fn update_context(context: &mut ucontext_t, regs: TrapHandlerRegs) {
cfg_if::cfg_if! {
if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "x86_64",
))] {
let TrapHandlerRegs { rip, rsp, rbp, rdi, rsi } = regs;
context.uc_mcontext.gregs[libc::REG_RIP as usize] = rip as i64;
context.uc_mcontext.gregs[libc::REG_RSP as usize] = rsp as i64;
context.uc_mcontext.gregs[libc::REG_RBP as usize] = rbp as i64;
context.uc_mcontext.gregs[libc::REG_RDI as usize] = rdi as i64;
context.uc_mcontext.gregs[libc::REG_RSI as usize] = rsi as i64;
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "x86",
))] {
let TrapHandlerRegs { eip, esp, ebp, ecx, edx } = regs;
context.uc_mcontext.gregs[libc::REG_EIP as usize] = eip as i32;
context.uc_mcontext.gregs[libc::REG_ESP as usize] = esp as i32;
context.uc_mcontext.gregs[libc::REG_EBP as usize] = ebp as i32;
context.uc_mcontext.gregs[libc::REG_ECX as usize] = ecx as i32;
context.uc_mcontext.gregs[libc::REG_EDX as usize] = edx as i32;
} else if #[cfg(all(target_vendor = "apple", target_arch = "x86_64"))] {
let TrapHandlerRegs { rip, rsp, rbp, rdi, rsi } = regs;
(*context.uc_mcontext).__ss.__rip = rip;
(*context.uc_mcontext).__ss.__rsp = rsp;
(*context.uc_mcontext).__ss.__rbp = rbp;
(*context.uc_mcontext).__ss.__rdi = rdi;
(*context.uc_mcontext).__ss.__rsi = rsi;
} else if #[cfg(all(target_os = "freebsd", target_arch = "x86"))] {
let TrapHandlerRegs { eip, esp, ebp, ecx, edx } = regs;
context.uc_mcontext.mc_eip = eip as libc::register_t;
context.uc_mcontext.mc_esp = esp as libc::register_t;
context.uc_mcontext.mc_ebp = ebp as libc::register_t;
context.uc_mcontext.mc_ecx = ecx as libc::register_t;
context.uc_mcontext.mc_edx = edx as libc::register_t;
} else if #[cfg(all(target_os = "freebsd", target_arch = "x86_64"))] {
let TrapHandlerRegs { rip, rsp, rbp, rdi, rsi } = regs;
context.uc_mcontext.mc_rip = rip as libc::register_t;
context.uc_mcontext.mc_rsp = rsp as libc::register_t;
context.uc_mcontext.mc_rbp = rbp as libc::register_t;
context.uc_mcontext.mc_rdi = rdi as libc::register_t;
context.uc_mcontext.mc_rsi = rsi as libc::register_t;
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "aarch64",
))] {
let TrapHandlerRegs { pc, sp, x0, x1, x29, lr } = regs;
context.uc_mcontext.pc = pc;
context.uc_mcontext.sp = sp;
context.uc_mcontext.regs[0] = x0;
context.uc_mcontext.regs[1] = x1;
context.uc_mcontext.regs[29] = x29;
context.uc_mcontext.regs[30] = lr;
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
target_arch = "arm",
))] {
let TrapHandlerRegs {
pc,
r0,
r1,
r7,
r11,
r13,
r14,
cpsr_thumb,
cpsr_endian,
} = regs;
context.uc_mcontext.arm_pc = pc;
context.uc_mcontext.arm_r0 = r0;
context.uc_mcontext.arm_r1 = r1;
context.uc_mcontext.arm_r7 = r7;
context.uc_mcontext.arm_fp = r11;
context.uc_mcontext.arm_sp = r13;
context.uc_mcontext.arm_lr = r14;
if cpsr_thumb {
context.uc_mcontext.arm_cpsr |= 0x20;
} else {
context.uc_mcontext.arm_cpsr &= !0x20;
}
if cpsr_endian {
context.uc_mcontext.arm_cpsr |= 0x200;
} else {
context.uc_mcontext.arm_cpsr &= !0x200;
}
} else if #[cfg(all(
any(target_os = "linux", target_os = "android"),
any(target_arch = "riscv64", target_arch = "riscv32"),
))] {
let TrapHandlerRegs { pc, ra, sp, a0, a1, s0 } = regs;
context.uc_mcontext.__gregs[libc::REG_PC] = pc as libc::c_ulong;
context.uc_mcontext.__gregs[libc::REG_RA] = ra as libc::c_ulong;
context.uc_mcontext.__gregs[libc::REG_SP] = sp as libc::c_ulong;
context.uc_mcontext.__gregs[libc::REG_A0] = a0 as libc::c_ulong;
context.uc_mcontext.__gregs[libc::REG_A0 + 1] = a1 as libc::c_ulong;
context.uc_mcontext.__gregs[libc::REG_S0] = s0 as libc::c_ulong;
} else if #[cfg(all(target_vendor = "apple", target_arch = "aarch64"))] {
let TrapHandlerRegs { pc, sp, x0, x1, x29, lr } = regs;
(*context.uc_mcontext).__ss.__pc = pc;
(*context.uc_mcontext).__ss.__sp = sp;
(*context.uc_mcontext).__ss.__x[0] = x0;
(*context.uc_mcontext).__ss.__x[1] = x1;
(*context.uc_mcontext).__ss.__fp = x29;
(*context.uc_mcontext).__ss.__lr = lr;
} else if #[cfg(all(target_os = "freebsd", target_arch = "aarch64"))] {
let TrapHandlerRegs { pc, sp, x0, x1, x29, lr } = regs;
context.uc_mcontext.mc_gpregs.gp_elr = pc as libc::register_t;
context.uc_mcontext.mc_gpregs.gp_sp = sp as libc::register_t;
context.uc_mcontext.mc_gpregs.gp_x[0] = x0 as libc::register_t;
context.uc_mcontext.mc_gpregs.gp_x[1] = x1 as libc::register_t;
context.uc_mcontext.mc_gpregs.gp_x[29] = x29 as libc::register_t;
context.uc_mcontext.mc_gpregs.gp_x[30] = lr as libc::register_t;
} else {
compile_error!("Unsupported platform");
}
};
}
} else if #[cfg(target_os = "windows")] {
use windows_sys::Win32::System::Diagnostics::Debug::{
AddVectoredExceptionHandler,
CONTEXT,
EXCEPTION_CONTINUE_EXECUTION,
EXCEPTION_CONTINUE_SEARCH,
EXCEPTION_POINTERS,
};
use windows_sys::Win32::Foundation::{
EXCEPTION_ACCESS_VIOLATION,
EXCEPTION_ILLEGAL_INSTRUCTION,
EXCEPTION_INT_DIVIDE_BY_ZERO,
EXCEPTION_INT_OVERFLOW,
EXCEPTION_STACK_OVERFLOW,
};
unsafe fn platform_init() {
// our trap handler needs to go first, so that we can recover from
// wasm faults and continue execution, so pass `1` as a true value
// here.
if AddVectoredExceptionHandler(1, Some(exception_handler)).is_null() {
panic!("failed to add exception handler: {}", io::Error::last_os_error());
}
}
unsafe extern "system" fn exception_handler(
exception_info: *mut EXCEPTION_POINTERS
) -> i32 {
// Check the kind of exception, since we only handle a subset within
// wasm code. If anything else happens we want to defer to whatever
// the rest of the system wants to do for this exception.
let record = &*(*exception_info).ExceptionRecord;
if record.ExceptionCode != EXCEPTION_ACCESS_VIOLATION &&
record.ExceptionCode != EXCEPTION_ILLEGAL_INSTRUCTION &&
record.ExceptionCode != EXCEPTION_STACK_OVERFLOW &&
record.ExceptionCode != EXCEPTION_INT_DIVIDE_BY_ZERO &&
record.ExceptionCode != EXCEPTION_INT_OVERFLOW
{
return EXCEPTION_CONTINUE_SEARCH;
}
// FIXME: this is what the previous C++ did to make sure that TLS
// works by the time we execute this trap handling code. This isn't
// exactly super easy to call from Rust though and it's not clear we
// necessarily need to do so. Leaving this here in case we need this
// in the future, but for now we can probably wait until we see a
// strange fault before figuring out how to reimplement this in
// Rust.
//
// if (!NtCurrentTeb()->Reserved1[sThreadLocalArrayPointerIndex]) {
// return EXCEPTION_CONTINUE_SEARCH;
// }
let context = &mut *(*exception_info).ContextRecord;
let (pc, sp) = get_pc_sp(context);
// We try to get the fault address associated to this exception.
let maybe_fault_address = match record.ExceptionCode {
EXCEPTION_ACCESS_VIOLATION => Some(record.ExceptionInformation[1]),
EXCEPTION_STACK_OVERFLOW => Some(sp),
_ => None,
};
let trap_code = match record.ExceptionCode {
// check if it was cased by a UD and if the Trap info is a payload to it
EXCEPTION_ILLEGAL_INSTRUCTION => {
process_illegal_op(pc)
}
_ => None,
};
// This is basically the same as the unix version above, only with a
// few parameters tweaked here and there.
let handled = TrapHandlerContext::handle_trap(
pc,
sp,
maybe_fault_address,
trap_code,
|regs| update_context(context, regs),
|handler| handler(exception_info),
);
if handled {
EXCEPTION_CONTINUE_EXECUTION
} else {
EXCEPTION_CONTINUE_SEARCH
}
}
unsafe fn get_pc_sp(context: &CONTEXT) -> (usize, usize) {
let (pc, sp);
cfg_if::cfg_if! {
if #[cfg(target_arch = "x86_64")] {
pc = context.Rip as usize;
sp = context.Rsp as usize;
} else if #[cfg(target_arch = "x86")] {
pc = context.Rip as usize;
sp = context.Rsp as usize;
} else {
compile_error!("Unsupported platform");
}
};
(pc, sp)
}
unsafe fn update_context(context: &mut CONTEXT, regs: TrapHandlerRegs) {
cfg_if::cfg_if! {
if #[cfg(target_arch = "x86_64")] {
let TrapHandlerRegs { rip, rsp, rbp, rdi, rsi } = regs;
context.Rip = rip;
context.Rsp = rsp;
context.Rbp = rbp;
context.Rdi = rdi;
context.Rsi = rsi;
} else if #[cfg(target_arch = "x86")] {
let TrapHandlerRegs { eip, esp, ebp, ecx, edx } = regs;
context.Eip = eip;
context.Esp = esp;
context.Ebp = ebp;
context.Ecx = ecx;
context.Edx = edx;
} else {
compile_error!("Unsupported platform");
}
};
}
}
}
/// This function is required to be called before any WebAssembly is entered.
/// This will configure global state such as signal handlers to prepare the
/// process to receive wasm traps.
///
/// This function must not only be called globally once before entering
/// WebAssembly but it must also be called once-per-thread that enters
/// WebAssembly. Currently in wasmer's integration this function is called on
/// creation of a `Store`.
pub fn init_traps() {
static INIT: Once = Once::new();
INIT.call_once(|| unsafe {
platform_init();
});
}
/// Raises a user-defined trap immediately.
///
/// This function performs as-if a wasm trap was just executed, only the trap
/// has a dynamic payload associated with it which is user-provided. This trap
/// payload is then returned from `catch_traps` below.
///
/// # Safety
///
/// Only safe to call when wasm code is on the stack, aka `catch_traps` must
/// have been previous called and not yet returned.
/// Additionally no Rust destructors may be on the stack.
/// They will be skipped and not executed.
pub unsafe fn raise_user_trap(data: Box<dyn Error + Send + Sync>) -> ! {
unwind_with(UnwindReason::UserTrap(data))
}
/// Raises a trap from inside library code immediately.
///
/// This function performs as-if a wasm trap was just executed. This trap
/// payload is then returned from `catch_traps` below.
///
/// # Safety
///
/// Only safe to call when wasm code is on the stack, aka `catch_traps` must
/// have been previous called and not yet returned.
/// Additionally no Rust destructors may be on the stack.
/// They will be skipped and not executed.
pub unsafe fn raise_lib_trap(trap: Trap) -> ! {
unwind_with(UnwindReason::LibTrap(trap))
}
/// Carries a Rust panic across wasm code and resumes the panic on the other
/// side.
///
/// # Safety
///
/// Only safe to call when wasm code is on the stack, aka `catch_traps` must
/// have been previously called and not returned. Additionally no Rust destructors may be on the
/// stack. They will be skipped and not executed.
pub unsafe fn resume_panic(payload: Box<dyn Any + Send>) -> ! {
unwind_with(UnwindReason::Panic(payload))
}
/// Call the wasm function pointed to by `callee`.
///
/// * `vmctx` - the callee vmctx argument
/// * `caller_vmctx` - the caller vmctx argument
/// * `trampoline` - the jit-generated trampoline whose ABI takes 4 values, the
/// callee vmctx, the caller vmctx, the `callee` argument below, and then the
/// `values_vec` argument.
/// * `callee` - the third argument to the `trampoline` function
/// * `values_vec` - points to a buffer which holds the incoming arguments, and to
/// which the outgoing return values will be written.
///
/// # Safety
///
/// Wildly unsafe because it calls raw function pointers and reads/writes raw
/// function pointers.
pub unsafe fn wasmer_call_trampoline(
trap_handler: Option<*const TrapHandlerFn<'static>>,
config: &VMConfig,
vmctx: VMFunctionContext,
trampoline: VMTrampoline,
callee: *const VMFunctionBody,
values_vec: *mut u8,
) -> Result<(), Trap> {
catch_traps(trap_handler, config, move || {
mem::transmute::<
unsafe extern "C" fn(
*mut VMContext,
*const VMFunctionBody,
*mut wasmer_types::RawValue,
),
extern "C" fn(VMFunctionContext, *const VMFunctionBody, *mut u8),
>(trampoline)(vmctx, callee, values_vec);
})
}
/// Catches any wasm traps that happen within the execution of `closure`,
/// returning them as a `Result`.
///
/// # Safety
///
/// Highly unsafe since `closure` won't have any dtors run.
pub unsafe fn catch_traps<F, R: 'static>(
trap_handler: Option<*const TrapHandlerFn<'static>>,
config: &VMConfig,
closure: F,
) -> Result<R, Trap>
where
F: FnOnce() -> R + 'static,
{
// Ensure that per-thread initialization is done.
lazy_per_thread_init()?;
let stack_size = config
.wasm_stack_size
.unwrap_or_else(|| DEFAULT_STACK_SIZE.load(Ordering::Relaxed));
on_wasm_stack(stack_size, trap_handler, closure).map_err(UnwindReason::into_trap)
}
// We need two separate thread-local variables here:
// - YIELDER is set within the new stack and is used to unwind back to the root
// of the stack from inside it.
// - TRAP_HANDLER is set from outside the new stack and is solely used from
// signal handlers. It must be atomic since it is used by signal handlers.
//
// We also do per-thread signal stack initialization on the first time
// TRAP_HANDLER is accessed.
thread_local! {
static YIELDER: Cell<Option<NonNull<Yielder<(), UnwindReason>>>> = const { Cell::new(None) };
static TRAP_HANDLER: AtomicPtr<TrapHandlerContext> = const { AtomicPtr::new(ptr::null_mut()) };
}
/// Read-only information that is used by signal handlers to handle and recover
/// from traps.
#[allow(clippy::type_complexity)]
struct TrapHandlerContext {
inner: *const u8,
handle_trap: fn(
*const u8,
usize,
usize,
Option<usize>,
Option<TrapCode>,
&mut dyn FnMut(TrapHandlerRegs),
) -> bool,
custom_trap: Option<*const TrapHandlerFn<'static>>,
}
struct TrapHandlerContextInner<T> {
/// Information about the currently running coroutine. This is used to
/// reset execution to the root of the coroutine when a trap is handled.
coro_trap_handler: CoroutineTrapHandler<Result<T, UnwindReason>>,
}
impl TrapHandlerContext {
/// Runs the given function with a trap handler context. The previous
/// trap handler context is preserved and restored afterwards.
fn install<T, R>(
custom_trap: Option<*const TrapHandlerFn<'static>>,
coro_trap_handler: CoroutineTrapHandler<Result<T, UnwindReason>>,
f: impl FnOnce() -> R,
) -> R {
// Type-erase the trap handler function so that it can be placed in TLS.
fn func<T>(
ptr: *const u8,
pc: usize,
sp: usize,
maybe_fault_address: Option<usize>,
trap_code: Option<TrapCode>,
update_regs: &mut dyn FnMut(TrapHandlerRegs),
) -> bool {
unsafe {
(*(ptr as *const TrapHandlerContextInner<T>)).handle_trap(
pc,
sp,
maybe_fault_address,
trap_code,
update_regs,
)
}
}
let inner = TrapHandlerContextInner { coro_trap_handler };
let ctx = Self {
inner: &inner as *const _ as *const u8,
handle_trap: func::<T>,
custom_trap,
};
compiler_fence(Ordering::Release);
let prev = TRAP_HANDLER.with(|ptr| {
let prev = ptr.load(Ordering::Relaxed);
ptr.store(&ctx as *const Self as *mut Self, Ordering::Relaxed);
prev
});
defer! {
TRAP_HANDLER.with(|ptr| ptr.store(prev, Ordering::Relaxed));
compiler_fence(Ordering::Acquire);
}
f()
}
/// Attempts to handle the trap if it's a wasm trap.
unsafe fn handle_trap(
pc: usize,
sp: usize,
maybe_fault_address: Option<usize>,
trap_code: Option<TrapCode>,
mut update_regs: impl FnMut(TrapHandlerRegs),
call_handler: impl Fn(&TrapHandlerFn<'static>) -> bool,
) -> bool {
let ptr = TRAP_HANDLER.with(|ptr| ptr.load(Ordering::Relaxed));
if ptr.is_null() {
return false;
}
let ctx = &*ptr;
// Check if this trap is handled by a custom trap handler.
if let Some(trap_handler) = ctx.custom_trap {
if call_handler(&*trap_handler) {
return true;
}
}
(ctx.handle_trap)(
ctx.inner,
pc,
sp,
maybe_fault_address,
trap_code,
&mut update_regs,
)
}
}
impl<T> TrapHandlerContextInner<T> {
unsafe fn handle_trap(
&self,
pc: usize,
sp: usize,
maybe_fault_address: Option<usize>,
trap_code: Option<TrapCode>,
update_regs: &mut dyn FnMut(TrapHandlerRegs),
) -> bool {
// Check if this trap occurred while executing on the Wasm stack. We can
// only recover from traps if that is the case.
if !self.coro_trap_handler.stack_ptr_in_bounds(sp) {
return false;
}
let signal_trap = trap_code.or_else(|| {
maybe_fault_address.map(|addr| {
if self.coro_trap_handler.stack_ptr_in_bounds(addr) {
TrapCode::StackOverflow
} else {
TrapCode::HeapAccessOutOfBounds
}
})
});
// Don't try to generate a backtrace for stack overflows: unwinding
// information is often not precise enough to properly describe what is
// happenning during a function prologue, which can lead the unwinder to
// read invalid memory addresses.
//
// See: https://github.com/rust-lang/backtrace-rs/pull/357
let backtrace = if signal_trap == Some(TrapCode::StackOverflow) {
Backtrace::from(vec![])
} else {
Backtrace::new_unresolved()
};
// Set up the register state for exception return to force the
// coroutine to return to its caller with UnwindReason::WasmTrap.
let unwind = UnwindReason::WasmTrap {
backtrace,
signal_trap,
pc,
};
let regs = self
.coro_trap_handler
.setup_trap_handler(move || Err(unwind));
update_regs(regs);
true
}
}
enum UnwindReason {
/// A panic caused by the host
Panic(Box<dyn Any + Send>),
/// A custom error triggered by the user
UserTrap(Box<dyn Error + Send + Sync>),
/// A Trap triggered by a wasm libcall
LibTrap(Trap),
/// A trap caused by the Wasm generated code
WasmTrap {
backtrace: Backtrace,
pc: usize,
signal_trap: Option<TrapCode>,
},
}
impl UnwindReason {
fn into_trap(self) -> Trap {
match self {
Self::UserTrap(data) => Trap::User(data),
Self::LibTrap(trap) => trap,
Self::WasmTrap {
backtrace,
pc,
signal_trap,
} => Trap::wasm(pc, backtrace, signal_trap),
Self::Panic(panic) => std::panic::resume_unwind(panic),
}
}
}
unsafe fn unwind_with(reason: UnwindReason) -> ! {
let yielder = YIELDER
.with(|cell| cell.replace(None))
.expect("not running on Wasm stack");
yielder.as_ref().suspend(reason);
// on_wasm_stack will forcibly reset the coroutine stack after yielding.
unreachable!();
}
/// Runs the given function on a separate stack so that its stack usage can be
/// bounded. Stack overflows and other traps can be caught and execution
/// returned to the root of the stack.
fn on_wasm_stack<F: FnOnce() -> T + 'static, T: 'static>(
stack_size: usize,
trap_handler: Option<*const TrapHandlerFn<'static>>,
f: F,
) -> Result<T, UnwindReason> {
// Allocating a new stack is pretty expensive since it involves several
// system calls. We therefore keep a cache of pre-allocated stacks which
// allows them to be reused multiple times.
// FIXME(Amanieu): We should refactor this to avoid the lock.
lazy_static::lazy_static! {
static ref STACK_POOL: crossbeam_queue::SegQueue<DefaultStack> = crossbeam_queue::SegQueue::new();
}
let stack = STACK_POOL
.pop()
.unwrap_or_else(|| DefaultStack::new(stack_size).unwrap());
let mut stack = scopeguard::guard(stack, |stack| STACK_POOL.push(stack));
// Create a coroutine with a new stack to run the function on.
let mut coro = Coroutine::with_stack(&mut *stack, move |yielder, ()| {
// Save the yielder to TLS so that it can be used later.
YIELDER.with(|cell| cell.set(Some(yielder.into())));
Ok(f())
});
// Ensure that YIELDER is reset on exit even if the coroutine panics,
defer! {
YIELDER.with(|cell| cell.set(None));
}
// Set up metadata for the trap handler for the duration of the coroutine
// execution. This is restored to its previous value afterwards.
TrapHandlerContext::install(trap_handler, coro.trap_handler(), || {
match coro.resume(()) {
CoroutineResult::Yield(trap) => {
// This came from unwind_with which requires that there be only
// Wasm code on the stack.
unsafe {
coro.force_reset();
}
Err(trap)
}
CoroutineResult::Return(result) => result,
}
})
}
/// When executing on the Wasm stack, temporarily switch back to the host stack
/// to perform an operation that should not be constrainted by the Wasm stack
/// limits.
///
/// This is particularly important since the usage of the Wasm stack is under
/// the control of untrusted code. Malicious code could artificially induce a
/// stack overflow in the middle of a sensitive host operations (e.g. growing
/// a memory) which would be hard to recover from.
pub fn on_host_stack<F: FnOnce() -> T, T>(f: F) -> T {
// Reset YIEDER to None for the duration of this call to indicate that we
// are no longer on the Wasm stack.
let yielder_ptr = YIELDER.with(|cell| cell.replace(None));
// If we are already on the host stack, execute the function directly. This
// happens if a host function is called directly from the API.
let yielder = match yielder_ptr {
Some(ptr) => unsafe { ptr.as_ref() },
None => return f(),
};
// Restore YIELDER upon exiting normally or unwinding.
defer! {
YIELDER.with(|cell| cell.set(yielder_ptr));
}
// on_parent_stack requires the closure to be Send so that the Yielder
// cannot be called from the parent stack. This is not a problem for us
// since we don't expose the Yielder.
struct SendWrapper<T>(T);
unsafe impl<T> Send for SendWrapper<T> {}
let wrapped = SendWrapper(f);
yielder.on_parent_stack(move || {
let wrapped = wrapped;
(wrapped.0)()
})
}
#[cfg(windows)]
pub fn lazy_per_thread_init() -> Result<(), Trap> {
// We need additional space on the stack to handle stack overflow
// exceptions. Rust's initialization code sets this to 0x5000 but this
// seems to be insufficient in practice.
use windows_sys::Win32::System::Threading::SetThreadStackGuarantee;
if unsafe { SetThreadStackGuarantee(&mut 0x10000) } == 0 {
panic!("failed to set thread stack guarantee");
}
Ok(())
}
/// A module for registering a custom alternate signal stack (sigaltstack).
///
/// Rust's libstd installs an alternate stack with size `SIGSTKSZ`, which is not
/// always large enough for our signal handling code. Override it by creating
/// and registering our own alternate stack that is large enough and has a guard
/// page.
#[cfg(unix)]
pub fn lazy_per_thread_init() -> Result<(), Trap> {
use std::ptr::null_mut;
thread_local! {
/// Thread-local state is lazy-initialized on the first time it's used,
/// and dropped when the thread exits.
static TLS: Tls = unsafe { init_sigstack() };
}
/// The size of the sigaltstack (not including the guard, which will be
/// added). Make this large enough to run our signal handlers.
const MIN_STACK_SIZE: usize = 16 * 4096;
enum Tls {
OutOfMemory,
Allocated {
mmap_ptr: *mut libc::c_void,
mmap_size: usize,
},
BigEnough,
}
unsafe fn init_sigstack() -> Tls {
// Check to see if the existing sigaltstack, if it exists, is big
// enough. If so we don't need to allocate our own.
let mut old_stack = mem::zeroed();
let r = libc::sigaltstack(ptr::null(), &mut old_stack);
assert_eq!(r, 0, "learning about sigaltstack failed");
if old_stack.ss_flags & libc::SS_DISABLE == 0 && old_stack.ss_size >= MIN_STACK_SIZE {
return Tls::BigEnough;
}
// ... but failing that we need to allocate our own, so do all that
// here.
let page_size: usize = region::page::size();
let guard_size = page_size;
let alloc_size = guard_size + MIN_STACK_SIZE;
let ptr = libc::mmap(
null_mut(),
alloc_size,
libc::PROT_NONE,
libc::MAP_PRIVATE | libc::MAP_ANON,
-1,
0,
);
if ptr == libc::MAP_FAILED {
return Tls::OutOfMemory;
}
// Prepare the stack with readable/writable memory and then register it
// with `sigaltstack`.
let stack_ptr = (ptr as usize + guard_size) as *mut libc::c_void;
let r = libc::mprotect(
stack_ptr,
MIN_STACK_SIZE,
libc::PROT_READ | libc::PROT_WRITE,
);
assert_eq!(r, 0, "mprotect to configure memory for sigaltstack failed");
let new_stack = libc::stack_t {
ss_sp: stack_ptr,
ss_flags: 0,
ss_size: MIN_STACK_SIZE,
};
let r = libc::sigaltstack(&new_stack, ptr::null_mut());
assert_eq!(r, 0, "registering new sigaltstack failed");
Tls::Allocated {
mmap_ptr: ptr,
mmap_size: alloc_size,
}
}
// Ensure TLS runs its initializer and return an error if it failed to
// set up a separate stack for signal handlers.
return TLS.with(|tls| {
if let Tls::OutOfMemory = tls {
Err(Trap::oom())
} else {
Ok(())
}
});
impl Drop for Tls {
fn drop(&mut self) {
let (ptr, size) = match self {
Self::Allocated {
mmap_ptr,
mmap_size,
} => (*mmap_ptr, *mmap_size),
_ => return,
};
unsafe {
// Deallocate the stack memory.
let r = libc::munmap(ptr, size);
debug_assert_eq!(r, 0, "munmap failed during thread shutdown");
}
}
}
}