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[wasm] Fix for getelema1 crash in specific scenarios #87246

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merged 4 commits into from
Jun 8, 2023
Merged

[wasm] Fix for getelema1 crash in specific scenarios #87246

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d1bc570
Fix for getelema1 crash in specific scenarios
kg Jun 8, 2023
bdc3dfb
Check more of the zero page for nonzero data
kg Jun 8, 2023
e7dde46
Overhaul trace local variable naming and reuse
kg Jun 8, 2023
422e0b7
Restore old leave-on-stack behavior
kg Jun 8, 2023
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33 changes: 24 additions & 9 deletions src/mono/wasm/runtime/jiterpreter-support.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ import { WasmOpcode, WasmSimdOpcode } from "./jiterpreter-opcodes";
import { MintOpcode } from "./mintops";
import cwraps from "./cwraps";
import { mono_log_error, mono_log_info } from "./logging";
import { localHeapViewU8 } from "./memory";
import { localHeapViewU8, localHeapViewU32 } from "./memory";
import { utf8ToString } from "./strings";

export const maxFailures = 2,
Expand Down Expand Up @@ -1531,9 +1531,9 @@ export function try_append_memset_fast(builder: WasmBuilder, localOffset: number
if (value !== 0)
return false;

const destLocal = destOnStack ? "math_lhs32" : "pLocals";
const destLocal = destOnStack ? "memop_dest" : "pLocals";
if (destOnStack)
builder.local("math_lhs32", WasmOpcode.set_local);
builder.local(destLocal, WasmOpcode.set_local);

let offset = destOnStack ? 0 : localOffset;

Expand Down Expand Up @@ -1616,8 +1616,9 @@ export function try_append_memmove_fast(
return false;

if (addressesOnStack) {
destLocal = destLocal || "math_lhs32";
srcLocal = srcLocal || "math_rhs32";
destLocal = destLocal || "memop_dest";
srcLocal = srcLocal || "memop_src";
// Stack layout is [..., dest, src]
builder.local(srcLocal, WasmOpcode.set_local);
builder.local(destLocal, WasmOpcode.set_local);
} else if (!destLocal || !srcLocal) {
Expand Down Expand Up @@ -1784,6 +1785,8 @@ export function bytesFromHex(hex: string): Uint8Array {
return bytes;
}

let observedTaintedZeroPage : boolean | undefined;

export function isZeroPageReserved(): boolean {
// FIXME: This check will always return true on worker threads.
// Right now the jiterpreter is disabled when threading is active, so that's not an issue.
Expand All @@ -1793,14 +1796,26 @@ export function isZeroPageReserved(): boolean {
if (!cwraps.mono_wasm_is_zero_page_reserved())
return false;

// If we ever saw garbage written to the zero page, never use it
if (observedTaintedZeroPage === true)
return false;

// Determine whether emscripten's stack checker or some other troublemaker has
// written junk at the start of memory. The previous cwraps call will have
// checked whether the stack starts at zero or not (on the main thread).
// We can't do this in the C helper because emcc/asan might be checking pointers.
return (Module.HEAPU32[0] === 0) &&
(Module.HEAPU32[1] === 0) &&
(Module.HEAPU32[2] === 0) &&
(Module.HEAPU32[3] === 0);
const heapU32 = localHeapViewU32();
for (let i = 0; i < 8; i++) {
if (heapU32[i] !== 0) {
if (observedTaintedZeroPage === false)
mono_log_error(`Zero page optimizations are enabled but garbage appeared in memory at address ${i * 4}: ${heapU32[i]}`);
observedTaintedZeroPage = true;
return false;
}
}

observedTaintedZeroPage = false;
return true;
}

export type JiterpreterOptions = {
Expand Down
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