Introduce control flow speculation tracking pass for AArch64
The pass implements tracking of control flow miss-speculation into a "taint"
register. That taint register can then be used to mask off registers with
sensitive data when executing under miss-speculation, a.k.a. "transient
execution".
This pass is aimed at mitigating against SpectreV1-style vulnarabilities.
At the moment, it implements the tracking of miss-speculation of control
flow into a taint register, but doesn't implement a mechanism yet to then
use that taint register to mask off vulnerable data in registers (something
for a follow-on improvement). Possible strategies to mask out vulnerable
data that can be implemented on top of this are:
- speculative load hardening to automatically mask of data loaded
in registers.
- using intrinsics to mask of data in registers as indicated by the
programmer (see https://lwn.net/Articles/759423/).
For AArch64, the following implementation choices are made.
Some of these are different than the implementation choices made in
the similar pass implemented in X86SpeculativeLoadHardening.cpp, as
the instruction set characteristics result in different trade-offs.
- The speculation hardening is done after register allocation. With a
relative abundance of registers, one register is reserved (X16) to be
the taint register. X16 is expected to not clash with other register
reservation mechanisms with very high probability because:
. The AArch64 ABI doesn't guarantee X16 to be retained across any call.
. The only way to request X16 to be used as a programmer is through
inline assembly. In the rare case a function explicitly demands to
use X16/W16, this pass falls back to hardening against speculation
by inserting a DSB SYS/ISB barrier pair which will prevent control
flow speculation.
- It is easy to insert mask operations at this late stage as we have
mask operations available that don't set flags.
- The taint variable contains all-ones when no miss-speculation is detected,
and contains all-zeros when miss-speculation is detected. Therefore, when
masking, an AND instruction (which only changes the register to be masked,
no other side effects) can easily be inserted anywhere that's needed.
- The tracking of miss-speculation is done by using a data-flow conditional
select instruction (CSEL) to evaluate the flags that were also used to
make conditional branch direction decisions. Speculation of the CSEL
instruction can be limited with a CSDB instruction - so the combination of
CSEL + a later CSDB gives the guarantee that the flags as used in the CSEL
aren't speculated. When conditional branch direction gets miss-speculated,
the semantics of the inserted CSEL instruction is such that the taint
register will contain all zero bits.
One key requirement for this to work is that the conditional branch is
followed by an execution of the CSEL instruction, where the CSEL
instruction needs to use the same flags status as the conditional branch.
This means that the conditional branches must not be implemented as one
of the AArch64 conditional branches that do not use the flags as input
(CB(N)Z and TB(N)Z). This is implemented by ensuring in the instruction
selectors to not produce these instructions when speculation hardening
is enabled. This pass will assert if it does encounter such an instruction.
- On function call boundaries, the miss-speculation state is transferred from
the taint register X16 to be encoded in the SP register as value 0.
Future extensions/improvements could be:
- Implement this functionality using full speculation barriers, akin to the
x86-slh-lfence option. This may be more useful for the intrinsics-based
approach than for the SLH approach to masking.
Note that this pass already inserts the full speculation barriers if the
function for some niche reason makes use of X16/W16.
- no indirect branch misprediction gets protected/instrumented; but this
could be done for some indirect branches, such as switch jump tables.
Differential Revision: https://reviews.llvm.org/D54896
llvm-svn: 349456
diff --git a/llvm/lib/Target/AArch64/AArch64.h b/llvm/lib/Target/AArch64/AArch64.h
index 2f0d0bf..c36d935 100644
--- a/llvm/lib/Target/AArch64/AArch64.h
+++ b/llvm/lib/Target/AArch64/AArch64.h
@@ -39,6 +39,7 @@
CodeGenOpt::Level OptLevel);
FunctionPass *createAArch64StorePairSuppressPass();
FunctionPass *createAArch64ExpandPseudoPass();
+FunctionPass *createAArch64SpeculationHardeningPass();
FunctionPass *createAArch64LoadStoreOptimizationPass();
FunctionPass *createAArch64SIMDInstrOptPass();
ModulePass *createAArch64PromoteConstantPass();
@@ -68,6 +69,7 @@
void initializeAArch64ConditionOptimizerPass(PassRegistry&);
void initializeAArch64DeadRegisterDefinitionsPass(PassRegistry&);
void initializeAArch64ExpandPseudoPass(PassRegistry&);
+void initializeAArch64SpeculationHardeningPass(PassRegistry&);
void initializeAArch64LoadStoreOptPass(PassRegistry&);
void initializeAArch64SIMDInstrOptPass(PassRegistry&);
void initializeAArch64PreLegalizerCombinerPass(PassRegistry&);
diff --git a/llvm/lib/Target/AArch64/AArch64FastISel.cpp b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
index 7a7b0dd..47550ca 100644
--- a/llvm/lib/Target/AArch64/AArch64FastISel.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
@@ -2258,6 +2258,13 @@
/// Try to emit a combined compare-and-branch instruction.
bool AArch64FastISel::emitCompareAndBranch(const BranchInst *BI) {
+ // Speculation tracking/SLH assumes that optimized TB(N)Z/CB(N)Z instructions
+ // will not be produced, as they are conditional branch instructions that do
+ // not set flags.
+ if (FuncInfo.MF->getFunction().hasFnAttribute(
+ Attribute::SpeculativeLoadHardening))
+ return false;
+
assert(isa<CmpInst>(BI->getCondition()) && "Expected cmp instruction");
const CmpInst *CI = cast<CmpInst>(BI->getCondition());
CmpInst::Predicate Predicate = optimizeCmpPredicate(CI);
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 7b53941..cc10c96 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -4343,6 +4343,13 @@
SDValue Dest = Op.getOperand(4);
SDLoc dl(Op);
+ MachineFunction &MF = DAG.getMachineFunction();
+ // Speculation tracking/SLH assumes that optimized TB(N)Z/CB(N)Z instructions
+ // will not be produced, as they are conditional branch instructions that do
+ // not set flags.
+ bool ProduceNonFlagSettingCondBr =
+ !MF.getFunction().hasFnAttribute(Attribute::SpeculativeLoadHardening);
+
// Handle f128 first, since lowering it will result in comparing the return
// value of a libcall against zero, which is just what the rest of LowerBR_CC
// is expecting to deal with.
@@ -4385,7 +4392,7 @@
// If the RHS of the comparison is zero, we can potentially fold this
// to a specialized branch.
const ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(RHS);
- if (RHSC && RHSC->getZExtValue() == 0) {
+ if (RHSC && RHSC->getZExtValue() == 0 && ProduceNonFlagSettingCondBr) {
if (CC == ISD::SETEQ) {
// See if we can use a TBZ to fold in an AND as well.
// TBZ has a smaller branch displacement than CBZ. If the offset is
@@ -4428,7 +4435,7 @@
}
}
if (RHSC && RHSC->getSExtValue() == -1 && CC == ISD::SETGT &&
- LHS.getOpcode() != ISD::AND) {
+ LHS.getOpcode() != ISD::AND && ProduceNonFlagSettingCondBr) {
// Don't combine AND since emitComparison converts the AND to an ANDS
// (a.k.a. TST) and the test in the test bit and branch instruction
// becomes redundant. This would also increase register pressure.
@@ -10807,6 +10814,13 @@
static SDValue performBRCONDCombine(SDNode *N,
TargetLowering::DAGCombinerInfo &DCI,
SelectionDAG &DAG) {
+ MachineFunction &MF = DAG.getMachineFunction();
+ // Speculation tracking/SLH assumes that optimized TB(N)Z/CB(N)Z instructions
+ // will not be produced, as they are conditional branch instructions that do
+ // not set flags.
+ if (MF.getFunction().hasFnAttribute(Attribute::SpeculativeLoadHardening))
+ return SDValue();
+
if (SDValue NV = performCONDCombine(N, DCI, DAG, 2, 3))
N = NV.getNode();
SDValue Chain = N->getOperand(0);
diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index eddb349..10464ea 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -964,6 +964,13 @@
const MachineFunction &MF) const {
if (TargetInstrInfo::isSchedulingBoundary(MI, MBB, MF))
return true;
+ switch (MI.getOpcode()) {
+ case AArch64::DSB:
+ case AArch64::ISB:
+ // DSB and ISB also are scheduling barriers.
+ return true;
+ default:;
+ }
return isSEHInstruction(MI);
}
diff --git a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
index 90258cc..6cbfb6a 100644
--- a/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
@@ -788,16 +788,36 @@
const unsigned CondReg = I.getOperand(0).getReg();
MachineBasicBlock *DestMBB = I.getOperand(1).getMBB();
- if (selectCompareBranch(I, MF, MRI))
+ // Speculation tracking/SLH assumes that optimized TB(N)Z/CB(N)Z
+ // instructions will not be produced, as they are conditional branch
+ // instructions that do not set flags.
+ bool ProduceNonFlagSettingCondBr =
+ !MF.getFunction().hasFnAttribute(Attribute::SpeculativeLoadHardening);
+ if (ProduceNonFlagSettingCondBr && selectCompareBranch(I, MF, MRI))
return true;
- auto MIB = BuildMI(MBB, I, I.getDebugLoc(), TII.get(AArch64::TBNZW))
- .addUse(CondReg)
- .addImm(/*bit offset=*/0)
- .addMBB(DestMBB);
+ if (ProduceNonFlagSettingCondBr) {
+ auto MIB = BuildMI(MBB, I, I.getDebugLoc(), TII.get(AArch64::TBNZW))
+ .addUse(CondReg)
+ .addImm(/*bit offset=*/0)
+ .addMBB(DestMBB);
- I.eraseFromParent();
- return constrainSelectedInstRegOperands(*MIB.getInstr(), TII, TRI, RBI);
+ I.eraseFromParent();
+ return constrainSelectedInstRegOperands(*MIB.getInstr(), TII, TRI, RBI);
+ } else {
+ auto CMP = BuildMI(MBB, I, I.getDebugLoc(), TII.get(AArch64::ANDSWri))
+ .addDef(AArch64::WZR)
+ .addUse(CondReg)
+ .addImm(1);
+ constrainSelectedInstRegOperands(*CMP.getInstr(), TII, TRI, RBI);
+ auto Bcc =
+ BuildMI(MBB, I, I.getDebugLoc(), TII.get(AArch64::Bcc))
+ .addImm(AArch64CC::EQ)
+ .addMBB(DestMBB);
+
+ I.eraseFromParent();
+ return constrainSelectedInstRegOperands(*Bcc.getInstr(), TII, TRI, RBI);
+ }
}
case TargetOpcode::G_BRINDIRECT: {
diff --git a/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp b/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
index 55631bc..96ae45a 100644
--- a/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64RegisterInfo.cpp
@@ -203,6 +203,10 @@
if (hasBasePointer(MF))
markSuperRegs(Reserved, AArch64::W19);
+ // SLH uses register W16/X16 as the taint register.
+ if (MF.getFunction().hasFnAttribute(Attribute::SpeculativeLoadHardening))
+ markSuperRegs(Reserved, AArch64::W16);
+
assert(checkAllSuperRegsMarked(Reserved));
return Reserved;
}
diff --git a/llvm/lib/Target/AArch64/AArch64SpeculationHardening.cpp b/llvm/lib/Target/AArch64/AArch64SpeculationHardening.cpp
new file mode 100644
index 0000000..1f8ef5e
--- /dev/null
+++ b/llvm/lib/Target/AArch64/AArch64SpeculationHardening.cpp
@@ -0,0 +1,368 @@
+//===- AArch64SpeculationHardening.cpp - Harden Against Missspeculation --===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains a pass to insert code to mitigate against side channel
+// vulnerabilities that may happen under control flow miss-speculation.
+//
+// The pass implements tracking of control flow miss-speculation into a "taint"
+// register. That taint register can then be used to mask off registers with
+// sensitive data when executing under miss-speculation, a.k.a. "transient
+// execution".
+// This pass is aimed at mitigating against SpectreV1-style vulnarabilities.
+//
+// At the moment, it implements the tracking of miss-speculation of control
+// flow into a taint register, but doesn't implement a mechanism yet to then
+// use that taint register to mask of vulnerable data in registers (something
+// for a follow-on improvement). Possible strategies to mask out vulnerable
+// data that can be implemented on top of this are:
+// - speculative load hardening to automatically mask of data loaded
+// in registers.
+// - using intrinsics to mask of data in registers as indicated by the
+// programmer (see https://lwn.net/Articles/759423/).
+//
+// For AArch64, the following implementation choices are made below.
+// Some of these are different than the implementation choices made in
+// the similar pass implemented in X86SpeculativeLoadHardening.cpp, as
+// the instruction set characteristics result in different trade-offs.
+// - The speculation hardening is done after register allocation. With a
+// relative abundance of registers, one register is reserved (X16) to be
+// the taint register. X16 is expected to not clash with other register
+// reservation mechanisms with very high probability because:
+// . The AArch64 ABI doesn't guarantee X16 to be retained across any call.
+// . The only way to request X16 to be used as a programmer is through
+// inline assembly. In the rare case a function explicitly demands to
+// use X16/W16, this pass falls back to hardening against speculation
+// by inserting a DSB SYS/ISB barrier pair which will prevent control
+// flow speculation.
+// - It is easy to insert mask operations at this late stage as we have
+// mask operations available that don't set flags.
+// - The taint variable contains all-ones when no miss-speculation is detected,
+// and contains all-zeros when miss-speculation is detected. Therefore, when
+// masking, an AND instruction (which only changes the register to be masked,
+// no other side effects) can easily be inserted anywhere that's needed.
+// - The tracking of miss-speculation is done by using a data-flow conditional
+// select instruction (CSEL) to evaluate the flags that were also used to
+// make conditional branch direction decisions. Speculation of the CSEL
+// instruction can be limited with a CSDB instruction - so the combination of
+// CSEL + a later CSDB gives the guarantee that the flags as used in the CSEL
+// aren't speculated. When conditional branch direction gets miss-speculated,
+// the semantics of the inserted CSEL instruction is such that the taint
+// register will contain all zero bits.
+// One key requirement for this to work is that the conditional branch is
+// followed by an execution of the CSEL instruction, where the CSEL
+// instruction needs to use the same flags status as the conditional branch.
+// This means that the conditional branches must not be implemented as one
+// of the AArch64 conditional branches that do not use the flags as input
+// (CB(N)Z and TB(N)Z). This is implemented by ensuring in the instruction
+// selectors to not produce these instructions when speculation hardening
+// is enabled. This pass will assert if it does encounter such an instruction.
+// - On function call boundaries, the miss-speculation state is transferred from
+// the taint register X16 to be encoded in the SP register as value 0.
+//
+// Future extensions/improvements could be:
+// - Implement this functionality using full speculation barriers, akin to the
+// x86-slh-lfence option. This may be more useful for the intrinsics-based
+// approach than for the SLH approach to masking.
+// Note that this pass already inserts the full speculation barriers if the
+// function for some niche reason makes use of X16/W16.
+// - no indirect branch misprediction gets protected/instrumented; but this
+// could be done for some indirect branches, such as switch jump tables.
+//===----------------------------------------------------------------------===//
+
+#include "AArch64InstrInfo.h"
+#include "AArch64Subtarget.h"
+#include "Utils/AArch64BaseInfo.h"
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineOperand.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/DebugLoc.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/CodeGen.h"
+#include "llvm/Target/TargetMachine.h"
+#include <cassert>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "aarch64-speculation-hardening"
+
+#define AARCH64_SPECULATION_HARDENING_NAME "AArch64 speculation hardening pass"
+
+namespace {
+
+class AArch64SpeculationHardening : public MachineFunctionPass {
+public:
+ const TargetInstrInfo *TII;
+ const TargetRegisterInfo *TRI;
+
+ static char ID;
+
+ AArch64SpeculationHardening() : MachineFunctionPass(ID) {
+ initializeAArch64SpeculationHardeningPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnMachineFunction(MachineFunction &Fn) override;
+
+ StringRef getPassName() const override {
+ return AARCH64_SPECULATION_HARDENING_NAME;
+ }
+
+private:
+ unsigned MisspeculatingTaintReg;
+ bool UseControlFlowSpeculationBarrier;
+
+ bool functionUsesHardeningRegister(MachineFunction &MF) const;
+ bool instrumentControlFlow(MachineBasicBlock &MBB);
+ bool endsWithCondControlFlow(MachineBasicBlock &MBB, MachineBasicBlock *&TBB,
+ MachineBasicBlock *&FBB,
+ AArch64CC::CondCode &CondCode) const;
+ void insertTrackingCode(MachineBasicBlock &SplitEdgeBB,
+ AArch64CC::CondCode &CondCode, DebugLoc DL) const;
+ void insertSPToRegTaintPropagation(MachineBasicBlock *MBB,
+ MachineBasicBlock::iterator MBBI) const;
+ void insertRegToSPTaintPropagation(MachineBasicBlock *MBB,
+ MachineBasicBlock::iterator MBBI,
+ unsigned TmpReg) const;
+};
+
+} // end anonymous namespace
+
+char AArch64SpeculationHardening::ID = 0;
+
+INITIALIZE_PASS(AArch64SpeculationHardening, "aarch64-speculation-hardening",
+ AARCH64_SPECULATION_HARDENING_NAME, false, false)
+
+bool AArch64SpeculationHardening::endsWithCondControlFlow(
+ MachineBasicBlock &MBB, MachineBasicBlock *&TBB, MachineBasicBlock *&FBB,
+ AArch64CC::CondCode &CondCode) const {
+ SmallVector<MachineOperand, 1> analyzeBranchCondCode;
+ if (TII->analyzeBranch(MBB, TBB, FBB, analyzeBranchCondCode, false))
+ return false;
+
+ // Ignore if the BB ends in an unconditional branch/fall-through.
+ if (analyzeBranchCondCode.empty())
+ return false;
+
+ // If the BB ends with a single conditional branch, FBB will be set to
+ // nullptr (see API docs for TII->analyzeBranch). For the rest of the
+ // analysis we want the FBB block to be set always.
+ assert(TBB != nullptr);
+ if (FBB == nullptr)
+ FBB = MBB.getFallThrough();
+
+ // If both the true and the false condition jump to the same basic block,
+ // there isn't need for any protection - whether the branch is speculated
+ // correctly or not, we end up executing the architecturally correct code.
+ if (TBB == FBB)
+ return false;
+
+ assert(MBB.succ_size() == 2);
+ // translate analyzeBranchCondCode to CondCode.
+ assert(analyzeBranchCondCode.size() == 1 && "unknown Cond array format");
+ CondCode = AArch64CC::CondCode(analyzeBranchCondCode[0].getImm());
+ return true;
+}
+
+void AArch64SpeculationHardening::insertTrackingCode(
+ MachineBasicBlock &SplitEdgeBB, AArch64CC::CondCode &CondCode,
+ DebugLoc DL) const {
+ if (UseControlFlowSpeculationBarrier) {
+ // insert full control flow speculation barrier (DSB SYS + ISB)
+ BuildMI(SplitEdgeBB, SplitEdgeBB.begin(), DL, TII->get(AArch64::ISB))
+ .addImm(0xf);
+ BuildMI(SplitEdgeBB, SplitEdgeBB.begin(), DL, TII->get(AArch64::DSB))
+ .addImm(0xf);
+ } else {
+ BuildMI(SplitEdgeBB, SplitEdgeBB.begin(), DL, TII->get(AArch64::CSELXr))
+ .addDef(MisspeculatingTaintReg)
+ .addUse(MisspeculatingTaintReg)
+ .addUse(AArch64::XZR)
+ .addImm(CondCode);
+ SplitEdgeBB.addLiveIn(AArch64::NZCV);
+ }
+}
+
+bool AArch64SpeculationHardening::instrumentControlFlow(
+ MachineBasicBlock &MBB) {
+ LLVM_DEBUG(dbgs() << "Instrument control flow tracking on MBB: " << MBB);
+
+ bool Modified = false;
+ MachineBasicBlock *TBB = nullptr;
+ MachineBasicBlock *FBB = nullptr;
+ AArch64CC::CondCode CondCode;
+
+ if (!endsWithCondControlFlow(MBB, TBB, FBB, CondCode)) {
+ LLVM_DEBUG(dbgs() << "... doesn't end with CondControlFlow\n");
+ } else {
+ // Now insert:
+ // "CSEL MisSpeculatingR, MisSpeculatingR, XZR, cond" on the True edge and
+ // "CSEL MisSpeculatingR, MisSpeculatingR, XZR, Invertcond" on the False
+ // edge.
+ AArch64CC::CondCode InvCondCode = AArch64CC::getInvertedCondCode(CondCode);
+
+ MachineBasicBlock *SplitEdgeTBB = MBB.SplitCriticalEdge(TBB, *this);
+ MachineBasicBlock *SplitEdgeFBB = MBB.SplitCriticalEdge(FBB, *this);
+
+ assert(SplitEdgeTBB != nullptr);
+ assert(SplitEdgeFBB != nullptr);
+
+ DebugLoc DL;
+ if (MBB.instr_end() != MBB.instr_begin())
+ DL = (--MBB.instr_end())->getDebugLoc();
+
+ insertTrackingCode(*SplitEdgeTBB, CondCode, DL);
+ insertTrackingCode(*SplitEdgeFBB, InvCondCode, DL);
+
+ LLVM_DEBUG(dbgs() << "SplitEdgeTBB: " << *SplitEdgeTBB << "\n");
+ LLVM_DEBUG(dbgs() << "SplitEdgeFBB: " << *SplitEdgeFBB << "\n");
+ Modified = true;
+ }
+
+ // Perform correct code generation around function calls and before returns.
+ {
+ SmallVector<MachineInstr *, 4> ReturnInstructions;
+ SmallVector<MachineInstr *, 4> CallInstructions;
+
+ for (MachineInstr &MI : MBB) {
+ if (MI.isReturn())
+ ReturnInstructions.push_back(&MI);
+ else if (MI.isCall())
+ CallInstructions.push_back(&MI);
+ }
+
+ Modified |=
+ (ReturnInstructions.size() > 0) || (CallInstructions.size() > 0);
+
+ for (MachineInstr *Return : ReturnInstructions)
+ insertRegToSPTaintPropagation(Return->getParent(), Return, AArch64::X17);
+ for (MachineInstr *Call : CallInstructions) {
+ // Just after the call:
+ MachineBasicBlock::iterator i = Call;
+ i++;
+ insertSPToRegTaintPropagation(Call->getParent(), i);
+ // Just before the call:
+ insertRegToSPTaintPropagation(Call->getParent(), Call, AArch64::X17);
+ }
+ }
+
+ return Modified;
+}
+
+void AArch64SpeculationHardening::insertSPToRegTaintPropagation(
+ MachineBasicBlock *MBB, MachineBasicBlock::iterator MBBI) const {
+ // If full control flow speculation barriers are used, emit a control flow
+ // barrier to block potential miss-speculation in flight coming in to this
+ // function.
+ if (UseControlFlowSpeculationBarrier) {
+ // insert full control flow speculation barrier (DSB SYS + ISB)
+ BuildMI(*MBB, MBBI, DebugLoc(), TII->get(AArch64::DSB)).addImm(0xf);
+ BuildMI(*MBB, MBBI, DebugLoc(), TII->get(AArch64::ISB)).addImm(0xf);
+ return;
+ }
+
+ // CMP SP, #0 === SUBS xzr, SP, #0
+ BuildMI(*MBB, MBBI, DebugLoc(), TII->get(AArch64::SUBSXri))
+ .addDef(AArch64::XZR)
+ .addUse(AArch64::SP)
+ .addImm(0)
+ .addImm(0); // no shift
+ // CSETM x16, NE === CSINV x16, xzr, xzr, EQ
+ BuildMI(*MBB, MBBI, DebugLoc(), TII->get(AArch64::CSINVXr))
+ .addDef(MisspeculatingTaintReg)
+ .addUse(AArch64::XZR)
+ .addUse(AArch64::XZR)
+ .addImm(AArch64CC::EQ);
+}
+
+void AArch64SpeculationHardening::insertRegToSPTaintPropagation(
+ MachineBasicBlock *MBB, MachineBasicBlock::iterator MBBI,
+ unsigned TmpReg) const {
+ // If full control flow speculation barriers are used, there will not be
+ // miss-speculation when returning from this function, and therefore, also
+ // no need to encode potential miss-speculation into the stack pointer.
+ if (UseControlFlowSpeculationBarrier)
+ return;
+
+ // mov Xtmp, SP === ADD Xtmp, SP, #0
+ BuildMI(*MBB, MBBI, DebugLoc(), TII->get(AArch64::ADDXri))
+ .addDef(TmpReg)
+ .addUse(AArch64::SP)
+ .addImm(0)
+ .addImm(0); // no shift
+ // and Xtmp, Xtmp, TaintReg === AND Xtmp, Xtmp, TaintReg, #0
+ BuildMI(*MBB, MBBI, DebugLoc(), TII->get(AArch64::ANDXrs))
+ .addDef(TmpReg, RegState::Renamable)
+ .addUse(TmpReg, RegState::Kill | RegState::Renamable)
+ .addUse(MisspeculatingTaintReg, RegState::Kill)
+ .addImm(0);
+ // mov SP, Xtmp === ADD SP, Xtmp, #0
+ BuildMI(*MBB, MBBI, DebugLoc(), TII->get(AArch64::ADDXri))
+ .addDef(AArch64::SP)
+ .addUse(TmpReg, RegState::Kill)
+ .addImm(0)
+ .addImm(0); // no shift
+}
+
+bool AArch64SpeculationHardening::functionUsesHardeningRegister(
+ MachineFunction &MF) const {
+ for (MachineBasicBlock &MBB : MF) {
+ for (MachineInstr &MI : MBB) {
+ // treat function calls specially, as the hardening register does not
+ // need to remain live across function calls.
+ if (MI.isCall())
+ continue;
+ if (MI.readsRegister(MisspeculatingTaintReg, TRI) ||
+ MI.modifiesRegister(MisspeculatingTaintReg, TRI))
+ return true;
+ }
+ }
+ return false;
+}
+
+bool AArch64SpeculationHardening::runOnMachineFunction(MachineFunction &MF) {
+ if (!MF.getFunction().hasFnAttribute(Attribute::SpeculativeLoadHardening))
+ return false;
+
+ MisspeculatingTaintReg = AArch64::X16;
+ TII = MF.getSubtarget().getInstrInfo();
+ TRI = MF.getSubtarget().getRegisterInfo();
+ bool Modified = false;
+
+ UseControlFlowSpeculationBarrier = functionUsesHardeningRegister(MF);
+
+ // Instrument control flow speculation tracking, if requested.
+ LLVM_DEBUG(
+ dbgs()
+ << "***** AArch64SpeculationHardening - track control flow *****\n");
+
+ // 1. Add instrumentation code to function entry and exits.
+ SmallVector<MachineBasicBlock *, 2> EntryBlocks;
+ EntryBlocks.push_back(&MF.front());
+ for (const LandingPadInfo &LPI : MF.getLandingPads())
+ EntryBlocks.push_back(LPI.LandingPadBlock);
+ for (auto Entry : EntryBlocks)
+ insertSPToRegTaintPropagation(
+ Entry, Entry->SkipPHIsLabelsAndDebug(Entry->begin()));
+
+ // 2. Add instrumentation code to every basic block.
+ for (auto &MBB : MF)
+ Modified |= instrumentControlFlow(MBB);
+
+ return Modified;
+}
+
+/// \brief Returns an instance of the pseudo instruction expansion pass.
+FunctionPass *llvm::createAArch64SpeculationHardeningPass() {
+ return new AArch64SpeculationHardening();
+}
diff --git a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
index 32c8534..4e01652 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
@@ -177,6 +177,7 @@
initializeFalkorHWPFFixPass(*PR);
initializeFalkorMarkStridedAccessesLegacyPass(*PR);
initializeLDTLSCleanupPass(*PR);
+ initializeAArch64SpeculationHardeningPass(*PR);
}
//===----------------------------------------------------------------------===//
@@ -550,6 +551,16 @@
if (TM->getOptLevel() != CodeGenOpt::None) {
if (EnableLoadStoreOpt)
addPass(createAArch64LoadStoreOptimizationPass());
+ }
+
+ // The AArch64SpeculationHardeningPass destroys dominator tree and natural
+ // loop info, which is needed for the FalkorHWPFFixPass and also later on.
+ // Therefore, run the AArch64SpeculationHardeningPass before the
+ // FalkorHWPFFixPass to avoid recomputing dominator tree and natural loop
+ // info.
+ addPass(createAArch64SpeculationHardeningPass());
+
+ if (TM->getOptLevel() != CodeGenOpt::None) {
if (EnableFalkorHWPFFix)
addPass(createFalkorHWPFFixPass());
}
diff --git a/llvm/lib/Target/AArch64/CMakeLists.txt b/llvm/lib/Target/AArch64/CMakeLists.txt
index 9c8c1d0..7778882 100644
--- a/llvm/lib/Target/AArch64/CMakeLists.txt
+++ b/llvm/lib/Target/AArch64/CMakeLists.txt
@@ -52,6 +52,7 @@
AArch64RegisterBankInfo.cpp
AArch64RegisterInfo.cpp
AArch64SelectionDAGInfo.cpp
+ AArch64SpeculationHardening.cpp
AArch64StorePairSuppress.cpp
AArch64Subtarget.cpp
AArch64TargetMachine.cpp