assemblyscript/src/passes/shadowstack.ts at main · AssemblyScript/assemblyscript · GitHub

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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));

}

assemblyscript/src/passes/shadowstack.ts at main · AssemblyScript/assemblyscript · GitHub

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assemblyscript/src/passes/shadowstack.ts at main · AssemblyScript/assemblyscript · GitHub

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