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shadowstack.ts
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696 lines (654 loc) · 22.6 KB
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/**
* @fileoverview Shadow stack instrumentation for a precise GC.
*
* Instruments function arguments and local assignments marked with a 'tostack'
* call to also do stores to a shadow stack of managed values only.
*
* Consider a simple call to a function looking like the following, taking
* managed arguments, plus assigning managed values to locals:
*
* function foo(a: Obj, b: Obj): Obj {
* let c = __tostack(a) // slot 2
* __collect()
* return b
* }
*
* foo(__tostack(a), __tostack(b)) // slot 0, 1
*
* At the call to `__collect()` the 32-bit stack frame of the function is:
*
* Offset | Value stored
* -------|----------------------------
* 0 | First managed argument 'a'
* 4 | Second managed argument 'b'
* -------|----------------------------
* 8 | First managed local 'c'
*
* We are splitting the frame in two halves as annotated since both halves are
* only known separately for indirect calls, with the first half becoming an
* extension of the calling function's stack frame by means of treating the
* arguments as if these were locals beyond the caller's `numLocals`. Function
* arguments stay a bit longer on the stack than usually, but we also don't have
* to modify the stack pointer pre-call at all this way. The caller's amended
* stack frame when assuming one managed local may look like this:
*
* Offset | Value stored
* -------|----------------------------
* 0 | First managed local '?'
* 4 | Extended with first managed argument 'a'
* 8 | Extended with second managed argument 'b'
*
* with the callee's stack frame becoming just:
*
* Offset | Value stored
* -------|----------------------------
* 0 | First managed local 'c'
*
* Instrumentation added below looks about like the following, with the stack
* growing downwards and 't' and 'r' being new temporary locals:
*
* // callee frameSize = 1 * sizeof<usize>()
* function foo(a: usize, b: usize): usize {
* memory.fill(__stack_pointer -= frameSize, 0, frameSize)
* store<usize>(__stack_pointer, c = a, 0 * sizeof<usize>())
* __collect()
* let r = b
* __stack_pointer += frameSize
* return r
* }
*
* // caller frameSize = (numLocalSlots + 2 [by extension]) * sizeof<usize>()
* (
* r = foo(
* ( t = a,
* store<usize>(__stack_pointer, t, (numLocalSlots + 0) * sizeof<usize>()),
* t ),
* ( t = b,
* store<usize>(__stack_pointer, t, (numLocalSlots + 1) * sizeof<usize>()),
* t )
* ),
* r
* )
*
* Also note that we have to `memory.fill` the second half because the first
* assignment to a local may happen at a later point within the function. The
* invariant we need to maintain for a precise GC is that it only sees zeroes
* or valid pointers, but never an invalid pointer left on the stack earlier.
* Since most frames are small, we unroll a sequence of `store`s up to a frame
* size of 16 bytes, and `memory.fill`, if available, beyond.
*
* @license Apache-2.0
*/
import {
Pass
} from "./pass";
import {
_BinaryenAddFunction,
_BinaryenAddFunctionExport,
_BinaryenCallGetNumOperands,
_BinaryenCallGetOperandAt,
_BinaryenCallGetTarget,
_BinaryenCallIndirectGetNumOperands,
_BinaryenCallIndirectGetOperandAt,
_BinaryenCallIndirectSetOperandAt,
_BinaryenCallSetOperandAt,
_BinaryenExportGetKind,
_BinaryenExportGetName,
_BinaryenExportGetValue,
_BinaryenExpressionGetId,
_BinaryenExpressionGetType,
_BinaryenFunctionGetBody,
_BinaryenFunctionGetName,
_BinaryenFunctionGetNumLocals,
_BinaryenFunctionGetNumVars,
_BinaryenFunctionGetParams,
_BinaryenFunctionGetResults,
_BinaryenFunctionGetVar,
_BinaryenFunctionSetBody,
_BinaryenGetExport,
_BinaryenGetFunction,
_BinaryenLocalSetGetIndex,
_BinaryenLocalSetGetValue,
_BinaryenLocalSetIsTee,
_BinaryenLocalSetSetValue,
_BinaryenRemoveExport,
_BinaryenRemoveFunction,
_BinaryenReturnGetValue,
_BinaryenReturnSetValue,
_free
} from "../glue/binaryen";
import {
ExpressionId,
ExpressionRef,
FunctionRef,
Index,
BinaryOp,
TypeRef,
allocPtrArray,
Module,
ExternalKind,
ExportRef,
expandType,
isConstZero,
} from "../module";
import {
Compiler,
Options
} from "../compiler";
import {
Feature
} from "../common";
import {
BuiltinNames
} from "../builtins";
import {
Source
} from "../ast";
type LocalIndex = Index;
type SlotIndex = Index;
type SlotMap = Map<LocalIndex,SlotIndex>;
type TempMap = Map<TypeRef,LocalIndex>;
/** Attempts to match the `__tostack(value)` pattern. Returns `value` if a match, otherwise `0`. */
function matchPattern(module: Module, expr: ExpressionRef): ExpressionRef {
let isFound = false;
while (
_BinaryenExpressionGetId(expr) == ExpressionId.Call &&
module.readStringCached(_BinaryenCallGetTarget(expr)) == BuiltinNames.tostack
) {
assert(_BinaryenCallGetNumOperands(expr) == 1);
expr = _BinaryenCallGetOperandAt(expr, 0);
isFound = true;
}
if (!isFound) return 0;
return expr;
}
/** Tests whether a `value` matched by `matchTostack` needs a slot. */
function needsSlot(value: ExpressionRef): bool {
switch (_BinaryenExpressionGetId(value)) {
// no need to stack null pointers
case ExpressionId.Const: return !isConstZero(value);
// note: can't omit a slot when assigning from another local since the other
// local might have shorter lifetime and become reassigned, say in a loop,
// then no longer holding on to the previous value in its stack slot.
}
return true;
}
/** Instruments a module with a shadow stack for precise GC. */
export class ShadowStackPass extends Pass {
/** Stack frame slots, per function. */
slotMaps: Map<FunctionRef, SlotMap> = new Map();
/** Temporary locals, per function. */
tempMaps: Map<FunctionRef, TempMap> = new Map();
/** Exports (with managed operands) map. */
exportMap: Map<string,i32[]> = new Map();
/** Compiler reference. */
compiler: Compiler;
constructor(compiler: Compiler) {
super(compiler.module);
this.compiler = compiler;
}
/** Compiler options. */
get options(): Options { return this.compiler.options; }
/** Target pointer type. */
get ptrType(): TypeRef { return this.options.sizeTypeRef; }
/** Target pointer size. */
get ptrSize(): i32 { return this.ptrType == TypeRef.I64 ? 8 : 4; }
/** Target pointer addition operation. */
get ptrBinaryAdd(): BinaryOp { return this.ptrType == TypeRef.I64 ? BinaryOp.AddI64 : BinaryOp.AddI32; }
/** Target pointer subtraction operation. */
get ptrBinarySub(): BinaryOp { return this.ptrType == TypeRef.I64 ? BinaryOp.SubI64 : BinaryOp.SubI32; }
/** Gets a constant with the specified value of the target pointer type. */
ptrConst(value: i32): ExpressionRef {
return this.ptrType == TypeRef.I64
? this.module.i64(value)
: this.module.i32(value);
}
/** Notes the presence of a slot for the specified (imaginary) local, returning the slot index. */
noteSlot(func: FunctionRef, localIndex: Index): i32 {
let slotMap: SlotMap;
if (this.slotMaps.has(func)) {
slotMap = changetype<SlotMap>(this.slotMaps.get(func));
if (slotMap.has(localIndex)) {
return changetype<i32>(slotMap.get(localIndex));
}
} else {
slotMap = new Map();
this.slotMaps.set(func, slotMap);
}
let slotIndex = slotMap.size;
slotMap.set(localIndex, slotIndex);
return slotIndex;
}
/** Notes the presence of an exported function taking managed operands. */
noteExport(name: string, managedOperandIndices: i32[]): void {
if (!managedOperandIndices.length) return;
this.exportMap.set(name, managedOperandIndices);
}
/** Gets a shared temporary local of the given type in the specified functions. */
getSharedTemp(func: FunctionRef, type: TypeRef): Index {
let tempMap: TempMap;
if (this.tempMaps.has(func)) {
tempMap = changetype<TempMap>(this.tempMaps.get(func));
if (tempMap.has(type)) {
return changetype<Index>(tempMap.get(type));
}
} else {
tempMap = new Map();
this.tempMaps.set(func, tempMap);
}
let numLocals = _BinaryenFunctionGetNumLocals(func);
let localIndex = numLocals + tempMap.size;
tempMap.set(type, localIndex);
return localIndex;
}
/** Makes an expression modifying the stack pointer by the given offset. */
makeStackOffset(offset: i32): ExpressionRef {
assert(offset != 0);
let module = this.module;
let expr = module.global_set(BuiltinNames.stack_pointer,
module.binary(offset >= 0 ? this.ptrBinaryAdd : this.ptrBinarySub,
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
this.ptrConst(abs(offset))
)
);
if (offset > 0) return expr;
return module.block(null, [
expr,
this.makeStackCheck()
], TypeRef.None);
}
/** Makes a sequence of expressions zeroing the stack frame. */
makeStackFill(frameSize: i32, stmts: ExpressionRef[]): void {
assert(frameSize > 0);
let module = this.module;
if (this.options.hasFeature(Feature.BulkMemory) && frameSize > 16) {
stmts.push(
module.memory_fill(
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
module.i32(0), // TODO: Wasm64 also i32?
this.ptrConst(frameSize)
)
);
} else {
let remain = frameSize;
while (remain >= 8) {
// store<i64>(__stack_pointer, 0, frameSize - remain)
stmts.push(
module.store(8,
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
module.i64(0),
TypeRef.I64,
frameSize - remain
)
);
remain -= 8;
}
if (remain) {
assert(remain == 4);
// store<i32>(__stack_pointer, 0, frameSize - remain)
stmts.push(
module.store(4,
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
module.i32(0),
TypeRef.I32,
frameSize - remain
)
);
}
}
}
private hasStackCheckFunction: bool = false;
/** Makes a check that the current stack pointer is valid. */
makeStackCheck(): ExpressionRef {
let module = this.module;
if (!this.hasStackCheckFunction) {
this.hasStackCheckFunction = true;
module.addFunction("~stack_check", TypeRef.None, TypeRef.None, null,
module.if(
module.binary(BinaryOp.LtI32,
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
module.global_get(BuiltinNames.data_end, this.ptrType)
),
this.compiler.makeStaticAbort(
this.compiler.ensureStaticString("stack overflow"),
Source.native
)
)
);
}
return module.call("~stack_check", null, TypeRef.None);
}
private updateCallOperands(operands: ExpressionRef[]): i32 {
let module = this.module;
let numSlots = 0;
for (let i = 0, k = operands.length; i < k; ++i) {
let operand = operands[i];
let match = matchPattern(module, operand);
if (!match) continue;
if (!needsSlot(match)) {
operands[i] = match;
continue;
}
let currentFunction = this.currentFunction;
let numLocals = _BinaryenFunctionGetNumLocals(currentFunction);
let slotIndex = this.noteSlot(currentFunction, numLocals + this.callSlotOffset + numSlots);
let temp = this.getSharedTemp(currentFunction, this.ptrType);
let stmts = new Array<ExpressionRef>();
// t = value
stmts.push(
module.local_set(temp, match, false)
);
// store<usize>(__stack_pointer, t, slotIndex * ptrSize)
stmts.push(
module.store(this.ptrSize,
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
module.local_get(temp, this.ptrType),
this.ptrType, slotIndex * this.ptrSize
)
);
// -> t
stmts.push(
module.local_get(temp, this.ptrType)
);
operands[i] = module.block(null, stmts, this.ptrType);
++numSlots;
}
return numSlots;
}
/** Slot offset accounting for nested calls. */
private callSlotOffset: i32 = 0;
/** Slot offset stack in nested calls. */
private callSlotStack: i32[] = new Array();
/** @override */
visitCallPre(call: ExpressionRef): void {
let numOperands = _BinaryenCallGetNumOperands(call);
let operands = new Array<ExpressionRef>(numOperands);
for (let i: Index = 0; i < numOperands; ++i) {
operands[i] = _BinaryenCallGetOperandAt(call, i);
}
let numSlots = this.updateCallOperands(operands);
for (let i = 0, k = operands.length; i < k; ++i) {
_BinaryenCallSetOperandAt(call, i, operands[i]);
}
if (numSlots) {
// Reserve these slots for us so nested calls use their own
this.callSlotOffset += numSlots;
}
this.callSlotStack.push(numSlots);
}
/** @override */
visitCall(call: ExpressionRef): void {
let numSlots = this.callSlotStack.pop();
if (numSlots) this.callSlotOffset -= numSlots;
}
/** @override */
visitCallIndirectPre(callIndirect: ExpressionRef): void {
let numOperands = _BinaryenCallIndirectGetNumOperands(callIndirect);
let operands = new Array<ExpressionRef>(numOperands);
for (let i: Index = 0; i < numOperands; ++i) {
operands[i] = _BinaryenCallIndirectGetOperandAt(callIndirect, i);
}
let numSlots = this.updateCallOperands(operands);
for (let i = 0, k = operands.length; i < k; ++i) {
_BinaryenCallIndirectSetOperandAt(callIndirect, i, operands[i]);
}
if (numSlots) {
// Reserve these slots for us so nested calls use their own
this.callSlotOffset += numSlots;
}
this.callSlotStack.push(numSlots);
}
/** @override */
visitCallIndirect(callIndirect: ExpressionRef): void {
let numSlots = this.callSlotStack.pop();
if (numSlots) this.callSlotOffset -= numSlots;
}
/** @override */
visitLocalSet(localSet: ExpressionRef): void {
let module = this.module;
let value = _BinaryenLocalSetGetValue(localSet);
let match = matchPattern(module, value);
if (!match) return;
if (!needsSlot(match)) {
_BinaryenLocalSetSetValue(localSet, match);
return;
}
let index = _BinaryenLocalSetGetIndex(localSet);
let slotIndex = this.noteSlot(this.currentFunction, index);
let stmts = new Array<ExpressionRef>();
// store<usize>(__stack_pointer, local = match, slotIndex * ptrSize)
stmts.push(
module.store(this.ptrSize,
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
module.local_tee(index, match, false),
this.ptrType, slotIndex * this.ptrSize
)
);
if (_BinaryenLocalSetIsTee(localSet)) {
// -> local
stmts.push(
module.local_get(index, this.ptrType)
);
this.replaceCurrent(module.flatten(stmts, this.ptrType));
} else {
this.replaceCurrent(module.flatten(stmts, TypeRef.None));
}
}
/** Updates a function with additional locals etc. */
updateFunction(funcRef: FunctionRef): void {
let name = _BinaryenFunctionGetName(funcRef);
let params = _BinaryenFunctionGetParams(funcRef);
let results = _BinaryenFunctionGetResults(funcRef);
let body = assert(_BinaryenFunctionGetBody(funcRef));
let numVars = _BinaryenFunctionGetNumVars(funcRef);
let vars = new Array<TypeRef>();
for (let i: Index = 0; i < numVars; ++i) {
vars[i] = _BinaryenFunctionGetVar(funcRef, i);
}
let tempMaps = this.tempMaps;
if (tempMaps.has(funcRef)) {
let tempMap = changetype<TempMap>(tempMaps.get(funcRef));
for (let _keys = Map_keys(tempMap), i = 0, k = _keys.length; i < k; ++i) {
vars.push(_keys[i]);
}
}
let moduleRef = this.module.ref;
_BinaryenRemoveFunction(moduleRef, name);
let cArr = allocPtrArray(vars);
let newFuncRef = _BinaryenAddFunction(moduleRef, name, params, results, cArr, vars.length, body);
if (this.options.sourceMap || this.options.debugInfo) {
let func = this.compiler.program.searchFunctionByRef(newFuncRef);
if (func) func.addDebugInfo(this.module, newFuncRef);
}
_free(cArr);
}
/** Updates a function export taking managed arguments. */
updateExport(exportRef: ExportRef, managedOperandIndices: i32[]): void {
let module = this.module;
let moduleRef = module.ref;
assert(_BinaryenExportGetKind(exportRef) == ExternalKind.Function);
let internalNameRef = _BinaryenExportGetValue(exportRef);
let internalName = module.readStringCached(internalNameRef)!;
let externalNameRef = _BinaryenExportGetName(exportRef);
let funcRef = _BinaryenGetFunction(moduleRef, internalNameRef);
let params = _BinaryenFunctionGetParams(funcRef);
let paramTypes = expandType(params);
let numParams = paramTypes.length;
let results = _BinaryenFunctionGetResults(funcRef);
let numLocals = numParams;
let vars = new Array<TypeRef>();
let numSlots = assert(managedOperandIndices.length);
let frameSize = numSlots * this.ptrSize;
let wrapperName = "export:" + internalName;
let wrapperNameRef = module.allocStringCached(wrapperName);
if (_BinaryenGetFunction(moduleRef, wrapperNameRef) == 0) {
let stmts = new Array<ExpressionRef>();
// __stack_pointer -= frameSize
stmts.push(
this.makeStackOffset(-frameSize)
);
for (let slotIndex = 0; slotIndex < numSlots; ++slotIndex) {
// store<usize>(__stack_pointer, $local, slotIndex * ptrSize)
stmts.push(
module.store(this.ptrSize,
module.global_get(BuiltinNames.stack_pointer, this.ptrType),
module.local_get(managedOperandIndices[slotIndex], this.ptrType),
this.ptrType, slotIndex * this.ptrSize
)
);
}
let forwardedOperands = new Array<ExpressionRef>(numParams);
for (let i = 0; i < numParams; ++i) {
forwardedOperands[i] = module.local_get(i, paramTypes[i]);
}
if (results != TypeRef.None) {
let tempIndex = numLocals++;
vars.push(results);
// t = original(...)
stmts.push(
module.local_set(tempIndex,
module.call(internalName, forwardedOperands, results),
false // internal
)
);
// __stack_pointer += frameSize
stmts.push(
this.makeStackOffset(+frameSize)
);
// -> t
stmts.push(
module.local_get(tempIndex, results)
);
} else {
// original(...)
stmts.push(
module.call(internalName, forwardedOperands, results)
);
// __stack_pointer += frameSize
stmts.push(
this.makeStackOffset(+frameSize)
);
}
let cArr = allocPtrArray(vars);
_BinaryenAddFunction(moduleRef, wrapperNameRef, params, results, cArr, vars.length,
module.block(null, stmts, results)
);
_free(cArr);
}
_BinaryenRemoveExport(moduleRef, externalNameRef);
_BinaryenAddFunctionExport(moduleRef, wrapperNameRef, externalNameRef);
}
/** @override */
walkModule(): void {
// Run the pass normally
super.walkModule();
// Instrument returns in functions utilizing stack slots
let module = this.module;
let instrumentReturns = new InstrumentReturns(this);
for (let _keys = Map_keys(this.slotMaps), i = 0, k = _keys.length; i < k; ++i) {
let func = _keys[i];
let slotMap = changetype<SlotMap>(this.slotMaps.get(func));
let frameSize = slotMap.size * this.ptrSize;
// Instrument function returns
instrumentReturns.frameSize = frameSize;
instrumentReturns.walkFunction(func);
// Instrument function entry
let stmts = new Array<ExpressionRef>();
// __stack_pointer -= frameSize
stmts.push(
this.makeStackOffset(-frameSize)
);
// memory.fill(__stack_pointer, 0, frameSize)
this.makeStackFill(frameSize, stmts);
// Handle implicit return
let body = _BinaryenFunctionGetBody(func);
let bodyType = _BinaryenExpressionGetType(body);
if (bodyType == TypeRef.Unreachable) {
// body
stmts.push(
body
);
} else if (bodyType == TypeRef.None) {
// body
stmts.push(
body
);
// __stack_pointer += frameSize
stmts.push(
this.makeStackOffset(+frameSize)
);
} else {
let temp = this.getSharedTemp(func, bodyType);
// t = body
stmts.push(
module.local_set(temp, body, false)
);
// __stack_pointer += frameSize
stmts.push(
this.makeStackOffset(+frameSize)
);
// -> t
stmts.push(
module.local_get(temp, bodyType)
);
}
_BinaryenFunctionSetBody(func, module.flatten(stmts, bodyType));
}
// Update functions we added more locals to
// TODO: _BinaryenFunctionAddVar ?
for (let _keys = Map_keys(this.tempMaps), i = 0, k = _keys.length; i < k; ++i) {
this.updateFunction(_keys[i]);
}
// Update exports taking managed arguments
let exportMap = this.exportMap;
for (let _keys = Map_keys(exportMap), i = 0, k = _keys.length; i < k; ++i) {
let exportName = _keys[i];
let exportRef = _BinaryenGetExport(module.ref, module.allocStringCached(exportName));
let managedOperandIndices = changetype<i32[]>(exportMap.get(exportName));
this.updateExport(exportRef, managedOperandIndices);
}
}
}
/** Companion pass instrumenting `return` statements to restore the stack frame. */
class InstrumentReturns extends Pass {
/** Parent pass. */
parentPass: ShadowStackPass;
/** Frame size of the current function being processed. */
frameSize: i32 = 0;
constructor(shadowStack: ShadowStackPass) {
super(shadowStack.module);
this.parentPass = shadowStack;
}
/** @override */
visitReturn(ret: ExpressionRef): void {
assert(this.frameSize);
let module = this.module;
let value = _BinaryenReturnGetValue(ret);
let stmts = new Array<ExpressionRef>();
if (value) {
let returnType = _BinaryenExpressionGetType(value);
if (returnType == TypeRef.Unreachable) return;
let temp = this.parentPass.getSharedTemp(this.currentFunction, returnType);
// t = value
stmts.push(
module.local_set(temp, value, false)
);
// __stack_pointer += frameSize
stmts.push(
this.parentPass.makeStackOffset(+this.frameSize)
);
// return t
_BinaryenReturnSetValue(ret, module.local_get(temp, returnType));
} else {
// __stack_pointer += frameSize
stmts.push(
this.parentPass.makeStackOffset(+this.frameSize)
);
// return
}
stmts.push(
ret
);
this.replaceCurrent(module.flatten(stmts, TypeRef.Unreachable));
}
}