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Cranelift: Make heap_addr return calculated base + index + offset (#5231)

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* Cranelift: Make `heap_addr` return calculated `base + index + offset`

Rather than return just the `base + index`.

(Note: I've chosen to use the nomenclature "index" for the dynamic operand and
"offset" for the static immediate.)

This move the addition of the `offset` into `heap_addr`, instead of leaving it
for the subsequent memory operation, so that we can Spectre-guard the full
address, and not allow speculative execution to read the first 4GiB of memory.

Before this commit, we were effectively doing

    load(spectre_guard(base + index) + offset)

Now we are effectively doing

    load(spectre_guard(base + index + offset))

Finally, this also corrects `heap_addr`'s documented semantics to say that it
returns an address that will trap on access if `index + offset + access_size` is
out of bounds for the given heap, rather than saying that the `heap_addr` itself
will trap. This matches the implemented behavior for static memories, and after
https://github.com/bytecodealliance/wasmtime/pull/5190 lands (which is blocked
on this commit) will also match the implemented behavior for dynamic memories.

* Update heap_addr docs

* Factor out `offset + size` to a helper
This commit is contained in:
Nick Fitzgerald
2022-11-09 11:53:51 -08:00
committed by GitHub
parent 33a192556e
commit fc62d4ad65
39 changed files with 563 additions and 284 deletions
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22
cranelift/interpreter/src/step.rs
View File

@@ -119,10 +119,6 @@ where
}
// 32-bit
InstructionData::UnaryIeee32 { imm, .. } => DataValue::from(imm),
InstructionData::HeapAddr { imm, .. } => {
let imm: u32 = imm.into();
DataValue::from(imm as i32) // Note the switch from unsigned to signed.
}
InstructionData::Load { offset, .. }
| InstructionData::Store { offset, .. }
| InstructionData::StackLoad { offset, .. }
@@ -489,19 +485,27 @@ where
Opcode::SymbolValue => unimplemented!("SymbolValue"),
Opcode::TlsValue => unimplemented!("TlsValue"),
Opcode::HeapAddr => {
if let InstructionData::HeapAddr { heap, .. } = inst {
if let InstructionData::HeapAddr {
heap,
offset: imm_offset,
size,
..
} = inst
{
let addr_ty = inst_context.controlling_type().unwrap();
let offset = arg(0)?.into_int()? as u64;
let load_size = imm().into_int()? as u64;
let dyn_offset = arg(0)?.into_int()? as u64;
assign_or_memtrap({
AddressSize::try_from(addr_ty).and_then(|addr_size| {
// Attempt to build an address at the maximum possible offset
// for this load. If address generation fails we know it's out of bounds.
let bound_offset = (offset + load_size).saturating_sub(1);
let bound_offset =
(dyn_offset + u64::from(u32::from(imm_offset)) + u64::from(size))
.saturating_sub(1);
state.heap_address(addr_size, heap, bound_offset)?;
// Build the actual address
let addr = state.heap_address(addr_size, heap, offset)?;
let mut addr = state.heap_address(addr_size, heap, dyn_offset)?;
addr.offset += u64::from(u32::from(imm_offset));
let dv = DataValue::try_from(addr)?;
Ok(dv.into())
})