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Rewrite for recursive safety

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This commit rewrites the runtime crate to provide safety in the face
of recursive calls to the guest. The basic principle is that
`GuestMemory` is now a trait which dynamically returns the
pointer/length pair. This also has an implicit contract (hence the
`unsafe` trait) that the pointer/length pair point to a valid list of
bytes in host memory "until something is reentrant".

After this changes the various suite of `Guest*` types were rewritten.
`GuestRef` and `GuestRefMut` were both removed since they cannot safely
exist. The `GuestPtrMut` type was removed for simplicity, and the final
`GuestPtr` type subsumes `GuestString` and `GuestArray`. This means
that there's only one guest pointer type, `GuestPtr<'a, T>`, where `'a`
is the borrow into host memory, basically borrowing the `GuestMemory`
trait object itself.

Some core utilities are exposed on `GuestPtr`, but they're all 100%
safe. Unsafety is now entirely contained within a few small locations:

* Implementations of the `GuestType` for primitive types (e.g. `i8`,
  `u8`, etc) use `unsafe` to read/write memory. The `unsafe` trait of
  `GuestMemory` though should prove that they're safe.

* `GuestPtr<'_, str>` has a method which validates utf-8 contents, and
  this requires `unsafe` internally to read all the bytes. This is
  guaranteed to be safe however given the contract of `GuestMemory`.

And that's it! Everything else is a bunch of safe combinators all built
up on the various utilities provided by `GuestPtr`. The general idioms
are roughly the same as before, with various tweaks here and there. A
summary of expected idioms are:

* For small values you'd `.read()` or `.write()` very quickly. You'd
  pass around the type itself.

* For strings, you'd pass `GuestPtr<'_, str>` down to the point where
  it's actually consumed. At that moment you'd either decide to copy it
  out (a safe operation) or you'd get a raw view to the string (an
  unsafe operation) and assert that you won't call back into wasm while
  you're holding that pointer.

* Arrays are similar to strings, passing around `GuestPtr<'_, [T]>`.
  Arrays also have a `iter()` method which yields an iterator of
  `GuestPtr<'_, T>` for convenience.

Overall there's still a lot of missing documentation on the runtime
crate specifically around the safety of the `GuestMemory` trait as well
as how the utilities/methods are expected to be used. Additionally
there's utilities which aren't currently implemented which would be easy
to implement. For example there's no method to copy out a string or a
slice, although that would be pretty easy to add.

In any case I'm curious to get feedback on this approach and see what
y'all think!
This commit is contained in:
Alex Crichton
2020-03-04 10:21:34 -08:00
parent 3764204250
commit ca9f33b6d9
28 changed files with 751 additions and 2013 deletions
Download Patch File Download Diff File Expand all files Collapse all files

92
tests/pointers.rs
View File

@@ -1,5 +1,5 @@
use proptest::prelude::*;
use wiggle_runtime::{GuestError, GuestPtr, GuestPtrMut, GuestRefMut, GuestType};
use wiggle_runtime::{GuestError, GuestMemory, GuestPtr};
use wiggle_test::{impl_errno, HostMemory, MemArea, WasiCtx};
wiggle::from_witx!({
@@ -10,49 +10,52 @@ wiggle::from_witx!({
impl_errno!(types::Errno);
impl pointers::Pointers for WasiCtx {
fn pointers_and_enums(
fn pointers_and_enums<'a>(
&self,
input1: types::Excuse,
input2_ptr: GuestPtrMut<types::Excuse>,
input3_ptr: GuestPtr<types::Excuse>,
input4_ptr_ptr: GuestPtrMut<GuestPtr<types::Excuse>>,
input2_ptr: GuestPtr<'a, types::Excuse>,
input3_ptr: GuestPtr<'a, types::Excuse>,
input4_ptr_ptr: GuestPtr<'a, GuestPtr<'a, types::Excuse>>,
) -> Result<(), types::Errno> {
println!("BAZ input1 {:?}", input1);
// Read enum value from mutable:
let mut input2_ref: GuestRefMut<types::Excuse> = input2_ptr.as_ref_mut().map_err(|e| {
let input2: types::Excuse = input2_ptr.read().map_err(|e| {
eprintln!("input2_ptr error: {}", e);
types::Errno::InvalidArg
})?;
let input2: types::Excuse = *input2_ref;
println!("input2 {:?}", input2);
// Read enum value from immutable ptr:
let input3 = *input3_ptr.as_ref().map_err(|e| {
let input3 = input3_ptr.read().map_err(|e| {
eprintln!("input3_ptr error: {}", e);
types::Errno::InvalidArg
})?;
println!("input3 {:?}", input3);
// Write enum to mutable ptr:
*input2_ref = input3;
input2_ptr.write(input3).map_err(|e| {
eprintln!("input2_ptr error: {}", e);
types::Errno::InvalidArg
})?;
println!("wrote to input2_ref {:?}", input3);
// Read ptr value from mutable ptr:
let input4_ptr: GuestPtr<types::Excuse> = GuestType::read(&input4_ptr_ptr.as_immut())
.map_err(|e| {
eprintln!("input4_ptr_ptr error: {}", e);
types::Errno::InvalidArg
})?;
let input4_ptr: GuestPtr<types::Excuse> = input4_ptr_ptr.read().map_err(|e| {
eprintln!("input4_ptr_ptr error: {}", e);
types::Errno::InvalidArg
})?;
// Read enum value from that ptr:
let input4: types::Excuse = *input4_ptr.as_ref().map_err(|e| {
let input4: types::Excuse = input4_ptr.read().map_err(|e| {
eprintln!("input4_ptr error: {}", e);
types::Errno::InvalidArg
})?;
println!("input4 {:?}", input4);
// Write ptr value to mutable ptr:
input4_ptr_ptr.write(&input2_ptr.as_immut());
input4_ptr_ptr.write(input2_ptr).map_err(|e| {
eprintln!("input4_ptr_ptr error: {}", e);
types::Errno::InvalidArg
})?;
Ok(())
}
@@ -123,37 +126,32 @@ impl PointersAndEnumsExercise {
.boxed()
}
pub fn test(&self) {
let mut ctx = WasiCtx::new();
let mut host_memory = HostMemory::new();
let mut guest_memory = host_memory.guest_memory();
let ctx = WasiCtx::new();
let host_memory = HostMemory::new();
*guest_memory
.ptr_mut(self.input2_loc.ptr)
.expect("input2 ptr")
.as_ref_mut()
.expect("input2 ref_mut") = self.input2;
host_memory
.ptr(self.input2_loc.ptr)
.write(self.input2)
.expect("input2 ref_mut");
*guest_memory
.ptr_mut(self.input3_loc.ptr)
.expect("input3 ptr")
.as_ref_mut()
.expect("input3 ref_mut") = self.input3;
host_memory
.ptr(self.input3_loc.ptr)
.write(self.input3)
.expect("input3 ref_mut");
*guest_memory
.ptr_mut(self.input4_loc.ptr)
.expect("input4 ptr")
.as_ref_mut()
.expect("input4 ref_mut") = self.input4;
host_memory
.ptr(self.input4_loc.ptr)
.write(self.input4)
.expect("input4 ref_mut");
*guest_memory
.ptr_mut(self.input4_ptr_loc.ptr)
.expect("input4 ptr ptr")
.as_ref_mut()
.expect("input4 ptr ref_mut") = self.input4_loc.ptr;
host_memory
.ptr(self.input4_ptr_loc.ptr)
.write(self.input4_loc.ptr)
.expect("input4 ptr ref_mut");
let e = pointers::pointers_and_enums(
&mut ctx,
&mut guest_memory,
&ctx,
&host_memory,
self.input1.into(),
self.input2_loc.ptr as i32,
self.input3_loc.ptr as i32,
@@ -162,10 +160,9 @@ impl PointersAndEnumsExercise {
assert_eq!(e, types::Errno::Ok.into(), "errno");
// Implementation of pointers_and_enums writes input3 to the input2_loc:
let written_to_input2_loc: i32 = *guest_memory
let written_to_input2_loc: i32 = host_memory
.ptr(self.input2_loc.ptr)
.expect("input2 ptr")
.as_ref()
.read()
.expect("input2 ref");
assert_eq!(
@@ -175,10 +172,9 @@ impl PointersAndEnumsExercise {
);
// Implementation of pointers_and_enums writes input2_loc to input4_ptr_loc:
let written_to_input4_ptr: u32 = *guest_memory
let written_to_input4_ptr: u32 = host_memory
.ptr(self.input4_ptr_loc.ptr)
.expect("input4_ptr_loc ptr")
.as_ref()
.read()
.expect("input4_ptr_loc ref");
assert_eq!(