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💢 Package unknown hostcall panics into termination details #572

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Jul 30, 2020
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💢 Package unknown hostcall panics into termination details #572

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1 change: 1 addition & 0 deletions lucet-runtime/include/lucet_types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@ enum lucet_terminated_reason {
lucet_terminated_reason_borrow_error,
lucet_terminated_reason_provided,
lucet_terminated_reason_remote,
lucet_terminated_reason_other_panic,
};

enum lucet_trapcode {
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13 changes: 10 additions & 3 deletions lucet-runtime/lucet-runtime-internals/src/c_api.rs
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Expand Up @@ -309,15 +309,21 @@ pub mod lucet_result {
},
TerminationDetails::Provided(p) => lucet_terminated {
reason: lucet_terminated_reason::Provided,
provided: p
provided: *p
.downcast_ref()
.map(|CTerminationDetails { details }| *details)
.unwrap_or(ptr::null_mut()),
.map(|CTerminationDetails { details }| details)
.unwrap_or(&ptr::null_mut()),
},
TerminationDetails::Remote => lucet_terminated {
reason: lucet_terminated_reason::Remote,
provided: std::ptr::null_mut(),
},
TerminationDetails::OtherPanic(p) => lucet_terminated {
reason: lucet_terminated_reason::OtherPanic,
// double box the panic payload so that the pointer passed to FFI
// land is thin
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took a moment to remember that non-thin-pointer types don't have FFI-stable layouts. That's what's going on here, right?

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Exactly; Box::into_raw(x) where x is Box<dyn T> returns a *mut dyn T, which is two machine pointers wide for the vtable, so casting it to *mut c_void to store in the struct would be Bad. The extra box makes the returned raw pointer have the type *mut Box<dyn T>, which is fine because the vtable pointer is then stored in the box on the heap.

provided: Box::into_raw(Box::new(p)) as *mut _,
},
},
},
},
Expand Down Expand Up @@ -372,6 +378,7 @@ pub mod lucet_result {
BorrowError,
Provided,
Remote,
OtherPanic,
}

#[repr(C)]
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20 changes: 20 additions & 0 deletions lucet-runtime/lucet-runtime-internals/src/instance.rs
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Expand Up @@ -1284,6 +1284,25 @@ pub enum TerminationDetails {
Provided(Box<dyn Any + 'static>),
/// The instance was terminated by its `KillSwitch`.
Remote,
/// A panic occurred during a hostcall other than the specialized panic used to implement
/// Lucet runtime features.
///
/// Panics are raised by the Lucet runtime in order to unwind the hostcall before jumping back
/// to the host context for any of the reasons described by the variants of this type. The panic
/// payload in that case is a already a `TerminationDetails` value.
///
/// This variant is created when any type other than `TerminationDetails` is the payload of a
/// panic arising during a hostcall, meaning it was not intentionally raised by the Lucet
/// runtime.
///
/// The panic payload contained in this variant should be rethrown using
/// [`resume_unwind`](https://doc.rust-lang.org/std/panic/fn.resume_unwind.html) once returned
/// to the host context.
///
/// Note that this variant will be removed once cross-FFI unwinding support lands in
/// [Rust](https://github.com/rust-lang/rfcs/pull/2945) and
/// [Lucet](https://github.com/bytecodealliance/lucet/pull/254).
OtherPanic(Box<dyn Any + Send + 'static>),
}

impl TerminationDetails {
Expand Down Expand Up @@ -1334,6 +1353,7 @@ impl std::fmt::Debug for TerminationDetails {
TerminationDetails::YieldTypeMismatch => write!(f, "YieldTypeMismatch"),
TerminationDetails::Provided(_) => write!(f, "Provided(Any)"),
TerminationDetails::Remote => write!(f, "Remote"),
TerminationDetails::OtherPanic(_) => write!(f, "OtherPanic(Any)"),
}
}
}
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11 changes: 5 additions & 6 deletions lucet-runtime/lucet-runtime-macros/src/lib.rs
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Expand Up @@ -111,12 +111,11 @@ pub fn lucet_hostcall(_attr: TokenStream, item: TokenStream) -> TokenStream {
match res {
Ok(res) => res,
Err(e) => {
match e.downcast::<#termination_details>() {
Ok(details) => {
#vmctx_mod::Vmctx::from_raw(vmctx_raw).terminate_no_unwind(*details)
},
Err(e) => std::panic::resume_unwind(e),
}
let details = match e.downcast::<#termination_details>() {
Ok(details) => *details,
Err(e) => #termination_details::OtherPanic(e),
};
#vmctx_mod::Vmctx::from_raw(vmctx_raw).terminate_no_unwind(details)
}
}
})
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52 changes: 51 additions & 1 deletion lucet-runtime/lucet-runtime-tests/src/guest_fault.rs
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Expand Up @@ -28,6 +28,14 @@ macro_rules! guest_fault_common_defs {
123
}

pub struct OtherPanicPayload;

#[lucet_hostcall]
#[no_mangle]
pub fn raise_other_panic(_vmctx: &Vmctx) {
panic!(OtherPanicPayload);
}

pub static mut RECOVERABLE_PTR: *mut libc::c_char = std::ptr::null_mut();

#[no_mangle]
Expand Down Expand Up @@ -55,6 +63,17 @@ macro_rules! guest_fault_common_defs {
}
}

extern "C" fn raise_other_panic_main(vmctx: *const lucet_vmctx) {
extern "C" {
// actually is defined in this file
fn raise_other_panic(vmctx: *const lucet_vmctx);
}
unsafe {
raise_other_panic(vmctx);
std::hint::unreachable_unchecked();
}
}

extern "C" fn infinite_loop(_vmctx: *const lucet_vmctx) {
loop {}
}
Expand Down Expand Up @@ -156,6 +175,10 @@ macro_rules! guest_fault_common_defs {
"hostcall_main",
FunctionPointer::from_usize(hostcall_main as usize),
))
.with_export_func(MockExportBuilder::new(
"raise_other_panic_main",
FunctionPointer::from_usize(raise_other_panic_main as usize),
))
.with_export_func(MockExportBuilder::new(
"infinite_loop",
FunctionPointer::from_usize(infinite_loop as usize),
Expand Down Expand Up @@ -622,7 +645,8 @@ macro_rules! guest_fault_tests {
test_nonex(|| {
let module = mock_traps_module();
let region =
<TestRegion as RegionCreate>::create(1, &Limits::default()).expect("region can be created");
<TestRegion as RegionCreate>::create(1, &Limits::default())
.expect("region can be created");
let mut inst = region
.new_instance(module)
.expect("instance can be created");
Expand All @@ -648,6 +672,32 @@ macro_rules! guest_fault_tests {
});
}

#[test]
fn raise_other_panic() {
test_nonex(|| {
let module = mock_traps_module();
let region =
<TestRegion as RegionCreate>::create(1, &Limits::default())
.expect("region can be created");
let mut inst = region
.new_instance(module)
.expect("instance can be created");

match inst.run("raise_other_panic_main", &[]) {
Err(Error::RuntimeTerminated(TerminationDetails::OtherPanic(payload))) => {
assert!(payload.is::<crate::common::OtherPanicPayload>());
}
res => panic!("unexpected result: {:?}", res),
}

// after a fault, can reset and run a normal function; in practice we would
// want to reraise the panic most of the time, but this should still work
inst.reset().expect("instance resets");

run_onetwothree(&mut inst);
});
}

#[test]
fn fatal_continue_signal_handler() {
fn signal_handler_continue(
Expand Down