From ba9b2ede8a46eb7a2848b6683fe3f916e1bcd82d Mon Sep 17 00:00:00 2001 From: Dimitry Andric Date: Fri, 26 Jul 2019 18:49:20 +0000 Subject: [PATCH] Pull in r366369 from upstream llvm trunk (by Francis Visoiu Mistrih): [CodeGen][NFC] Simplify checks for stack protector index checking Use `hasStackProtectorIndex()` instead of `getStackProtectorIndex() >= 0`. Pull in r366371 from upstream llvm trunk (by Francis Visoiu Mistrih): [PEI] Don't re-allocate a pre-allocated stack protector slot The LocalStackSlotPass pre-allocates a stack protector and makes sure that it comes before the local variables on the stack. We need to make sure that later during PEI we don't re-allocate a new stack protector slot. If that happens, the new stack protector slot will end up being **after** the local variables that it should be protecting. Therefore, we would have two slots assigned for two different stack protectors, one at the top of the stack, and one at the bottom. Since PEI will overwrite the assigned slot for the stack protector, the load that is used to compare the value of the stack protector will use the slot assigned by PEI, which is wrong. For this, we need to check if the object is pre-allocated, and re-use that pre-allocated slot. Differential Revision: https://reviews.llvm.org/D64757 Pull in r367068 from upstream llvm trunk (by Francis Visoiu Mistrih): [CodeGen] Don't resolve the stack protector frame accesses until PEI Currently, stack protector loads and stores are resolved during LocalStackSlotAllocation (if the pass needs to run). When this is the case, the base register assigned to the frame access is going to be one of the vregs created during LocalStackSlotAllocation. This means that we are keeping a pointer to the stack protector slot, and we're using this pointer to load and store to it. In case register pressure goes up, we may end up spilling this pointer to the stack, which can be a security concern. Instead, leave it to PEI to resolve the frame accesses. In order to do that, we make all stack protector accesses go through frame index operands, then PEI will resolve this using an offset from sp/fp/bp. Differential Revision: https://reviews.llvm.org/D64759 Together, these fix a issue where the stack protection feature in LLVM's ARM backend can be rendered ineffective when the stack protector slot is re-allocated so that it appears after the local variables that it is meant to protect, leaving the function potentially vulnerable to a stack-based buffer overflow. Reported by: andrew Security: https://kb.cert.org/vuls/id/129209/ MFC after: 3 days --- .../lib/CodeGen/LocalStackSlotAllocation.cpp | 24 +++++++++++--- .../llvm/lib/CodeGen/PrologEpilogInserter.cpp | 33 ++++++++++++++----- 2 files changed, 44 insertions(+), 13 deletions(-) diff --git a/contrib/llvm/lib/CodeGen/LocalStackSlotAllocation.cpp b/contrib/llvm/lib/CodeGen/LocalStackSlotAllocation.cpp index 795028e97929..c2140994bbf1 100644 --- a/contrib/llvm/lib/CodeGen/LocalStackSlotAllocation.cpp +++ b/contrib/llvm/lib/CodeGen/LocalStackSlotAllocation.cpp @@ -200,19 +200,27 @@ void LocalStackSlotPass::calculateFrameObjectOffsets(MachineFunction &Fn) { // Make sure that the stack protector comes before the local variables on the // stack. SmallSet ProtectedObjs; - if (MFI.getStackProtectorIndex() >= 0) { + if (MFI.hasStackProtectorIndex()) { + int StackProtectorFI = MFI.getStackProtectorIndex(); + + // We need to make sure we didn't pre-allocate the stack protector when + // doing this. + // If we already have a stack protector, this will re-assign it to a slot + // that is **not** covering the protected objects. + assert(!MFI.isObjectPreAllocated(StackProtectorFI) && + "Stack protector pre-allocated in LocalStackSlotAllocation"); + StackObjSet LargeArrayObjs; StackObjSet SmallArrayObjs; StackObjSet AddrOfObjs; - AdjustStackOffset(MFI, MFI.getStackProtectorIndex(), Offset, - StackGrowsDown, MaxAlign); + AdjustStackOffset(MFI, StackProtectorFI, Offset, StackGrowsDown, MaxAlign); // Assign large stack objects first. for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) { if (MFI.isDeadObjectIndex(i)) continue; - if (MFI.getStackProtectorIndex() == (int)i) + if (StackProtectorFI == (int)i) continue; switch (MFI.getObjectSSPLayout(i)) { @@ -344,6 +352,14 @@ bool LocalStackSlotPass::insertFrameReferenceRegisters(MachineFunction &Fn) { assert(MFI.isObjectPreAllocated(FrameIdx) && "Only pre-allocated locals expected!"); + // We need to keep the references to the stack protector slot through frame + // index operands so that it gets resolved by PEI rather than this pass. + // This avoids accesses to the stack protector though virtual base + // registers, and forces PEI to address it using fp/sp/bp. + if (MFI.hasStackProtectorIndex() && + FrameIdx == MFI.getStackProtectorIndex()) + continue; + LLVM_DEBUG(dbgs() << "Considering: " << MI); unsigned idx = 0; diff --git a/contrib/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/contrib/llvm/lib/CodeGen/PrologEpilogInserter.cpp index 23754e487a18..5438334277f1 100644 --- a/contrib/llvm/lib/CodeGen/PrologEpilogInserter.cpp +++ b/contrib/llvm/lib/CodeGen/PrologEpilogInserter.cpp @@ -845,18 +845,26 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &MF) { // Make sure that the stack protector comes before the local variables on the // stack. SmallSet ProtectedObjs; - if (MFI.getStackProtectorIndex() >= 0) { + if (MFI.hasStackProtectorIndex()) { + int StackProtectorFI = MFI.getStackProtectorIndex(); StackObjSet LargeArrayObjs; StackObjSet SmallArrayObjs; StackObjSet AddrOfObjs; - AdjustStackOffset(MFI, MFI.getStackProtectorIndex(), StackGrowsDown, - Offset, MaxAlign, Skew); + // If we need a stack protector, we need to make sure that + // LocalStackSlotPass didn't already allocate a slot for it. + // If we are told to use the LocalStackAllocationBlock, the stack protector + // is expected to be already pre-allocated. + if (!MFI.getUseLocalStackAllocationBlock()) + AdjustStackOffset(MFI, StackProtectorFI, StackGrowsDown, Offset, MaxAlign, + Skew); + else if (!MFI.isObjectPreAllocated(MFI.getStackProtectorIndex())) + llvm_unreachable( + "Stack protector not pre-allocated by LocalStackSlotPass."); // Assign large stack objects first. for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) { - if (MFI.isObjectPreAllocated(i) && - MFI.getUseLocalStackAllocationBlock()) + if (MFI.isObjectPreAllocated(i) && MFI.getUseLocalStackAllocationBlock()) continue; if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex) continue; @@ -864,8 +872,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &MF) { continue; if (MFI.isDeadObjectIndex(i)) continue; - if (MFI.getStackProtectorIndex() == (int)i || - EHRegNodeFrameIndex == (int)i) + if (StackProtectorFI == (int)i || EHRegNodeFrameIndex == (int)i) continue; switch (MFI.getObjectSSPLayout(i)) { @@ -884,6 +891,15 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &MF) { llvm_unreachable("Unexpected SSPLayoutKind."); } + // We expect **all** the protected stack objects to be pre-allocated by + // LocalStackSlotPass. If it turns out that PEI still has to allocate some + // of them, we may end up messing up the expected order of the objects. + if (MFI.getUseLocalStackAllocationBlock() && + !(LargeArrayObjs.empty() && SmallArrayObjs.empty() && + AddrOfObjs.empty())) + llvm_unreachable("Found protected stack objects not pre-allocated by " + "LocalStackSlotPass."); + AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown, Offset, MaxAlign, Skew); AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown, @@ -905,8 +921,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &MF) { continue; if (MFI.isDeadObjectIndex(i)) continue; - if (MFI.getStackProtectorIndex() == (int)i || - EHRegNodeFrameIndex == (int)i) + if (MFI.getStackProtectorIndex() == (int)i || EHRegNodeFrameIndex == (int)i) continue; if (ProtectedObjs.count(i)) continue;