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//===- GlobalPtrAuthInfo.cpp - Analysis tools for ptrauth globals ---------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "llvm/IR/GlobalPtrAuthInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
using namespace llvm;
Expected<GlobalPtrAuthInfo> GlobalPtrAuthInfo::tryAnalyze(const Value *V) {
auto Invalid = [](const Twine &Reason) {
return make_error<StringError>(Reason, inconvertibleErrorCode());
};
auto &Ctx = V->getContext();
V = V->stripPointerCasts();
auto *GV = dyn_cast<GlobalVariable>(V);
if (!GV)
return Invalid("value isn't a global");
if (GV->getSection() != "llvm.ptrauth")
return Invalid("global isn't in section \"llvm.ptrauth\"");
if (!GV->hasInitializer())
return Invalid("global doesn't have an initializer");
auto *Init = GV->getInitializer();
auto *Ty = dyn_cast<StructType>(GV->getInitializer()->getType());
if (!Ty)
return Invalid("global isn't a struct");
auto *I64Ty = Type::getInt64Ty(Ctx);
auto *I32Ty = Type::getInt32Ty(Ctx);
auto *P0I8Ty = Type::getInt8PtrTy(Ctx);
// Check that the struct matches its expected shape:
// { i8*, i32, i64, i64 }
if (!Ty->isLayoutIdentical(
StructType::get(Ctx, {P0I8Ty, I32Ty, I64Ty, I64Ty})))
return Invalid("global doesn't have type '{ i8*, i32, i64, i64 }'");
auto *Key = dyn_cast<ConstantInt>(Init->getOperand(1));
if (!Key)
return Invalid("key isn't a constant integer");
auto *AddrDiscriminator = Init->getOperand(2);
if (!isa<ConstantInt>(AddrDiscriminator) &&
!isa<ConstantExpr>(AddrDiscriminator))
return Invalid("address discriminator isn't a constant integer or expr");
auto *Discriminator = dyn_cast<ConstantInt>(Init->getOperand(3));
if (!Discriminator)
return Invalid("discriminator isn't a constant integer");
return GlobalPtrAuthInfo(GV);
}
std::optional<GlobalPtrAuthInfo> GlobalPtrAuthInfo::analyze(const Value *V) {
if (auto PAIOrErr = tryAnalyze(V)) {
return *PAIOrErr;
} else {
consumeError(PAIOrErr.takeError());
return std::nullopt;
}
}
static bool areEquivalentAddrDiscriminators(const Value *V1, const Value *V2,
const DataLayout &DL) {
APInt V1Off(DL.getPointerSizeInBits(), 0);
APInt V2Off(DL.getPointerSizeInBits(), 0);
if (auto *V1Cast = dyn_cast<PtrToIntOperator>(V1))
V1 = V1Cast->getPointerOperand();
if (auto *V2Cast = dyn_cast<PtrToIntOperator>(V2))
V2 = V2Cast->getPointerOperand();
auto *V1Base = V1->stripAndAccumulateInBoundsConstantOffsets(DL, V1Off);
auto *V2Base = V2->stripAndAccumulateInBoundsConstantOffsets(DL, V2Off);
return V1Base == V2Base && V1Off == V2Off;
}
bool GlobalPtrAuthInfo::isCompatibleWith(const Value *Key,
const Value *Discriminator,
const DataLayout &DL) const {
// If the keys are different, there's no chance for this to be compatible.
if (Key != getKey())
return false;
// If the discriminators are the same, this is compatible iff there is no
// address discriminator.
if (Discriminator == getDiscriminator())
return getAddrDiscriminator()->isNullValue();
// If we dynamically blend the discriminator with the address discriminator,
// this is compatible.
if (auto *DiscBlend = dyn_cast<IntrinsicInst>(Discriminator)) {
if (DiscBlend->getIntrinsicID() == Intrinsic::ptrauth_blend &&
DiscBlend->getOperand(1) == getDiscriminator() &&
areEquivalentAddrDiscriminators(DiscBlend->getOperand(0),
getAddrDiscriminator(), DL))
return true;
}
// If we don't have a non-address discriminator, we don't need a blend in
// the first place: accept the address discriminator as the discriminator.
if (getDiscriminator()->isNullValue() &&
areEquivalentAddrDiscriminators(getAddrDiscriminator(), Discriminator,
DL))
return true;
// Otherwise, we don't know.
return false;
}
Constant *GlobalPtrAuthInfo::createWithSameSchema(Module &M,
Constant *Pointer) const {
return create(M, Pointer, const_cast<ConstantInt*>(getKey()),
const_cast<Constant*>(getAddrDiscriminator()),
const_cast<ConstantInt*>(getDiscriminator()));
}
Constant *GlobalPtrAuthInfo::create(Module &M, Constant *Pointer,
ConstantInt *Key,
Constant *AddrDiscriminator,
ConstantInt *Discriminator) {
auto CastPointer =
ConstantExpr::getBitCast(Pointer, Type::getInt8PtrTy(M.getContext()));
auto Init = ConstantStruct::getAnon({CastPointer, Key, AddrDiscriminator,
Discriminator}, /*packed*/ false);
// TODO: look for an existing global with the right setup?
auto GV = new GlobalVariable(M, Init->getType(), /*constant*/ true,
GlobalVariable::PrivateLinkage, Init);
GV->setSection("llvm.ptrauth");
auto Result = ConstantExpr::getBitCast(GV, Pointer->getType());
assert(analyze(Result).has_value() && "invalid ptrauth constant");
return Result;
}
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