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More shadow bugs/fixes #218

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merged 3 commits into from
Dec 9, 2024
Merged

More shadow bugs/fixes #218

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c50ffd2
Fix incorrect byte-size computation.
vext01 Dec 9, 2024
3b05bdc
Remove unnecessary cast.
vext01 Dec 9, 2024
339994b
Crash when encountering calls we've not thought about.
vext01 Dec 9, 2024
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13 changes: 8 additions & 5 deletions llvm/lib/Transforms/Yk/ShadowStack.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -142,8 +142,8 @@ class YkShadowStack : public ModulePass {
}
}
Builder.SetInsertPoint(&I);
auto AllocaSizeInBits = AI.getAllocationSizeInBits(DL);
if (!AllocaSizeInBits) {
auto AllocaSizeInBytes = AI.getAllocationSize(DL);
if (!AllocaSizeInBytes) {
// YKFIXME: Deal with functions where the stack size isn't know at
// compile time, e.g. when `alloca` is used.
Context.emitError("Unable to add shadow stack: function has "
Expand All @@ -153,7 +153,6 @@ class YkShadowStack : public ModulePass {
// Calculate this `AllocaInst`s size, aligning its pointer if
// necessary, and create a replacement pointer into the shadow
// stack.
size_t AllocaSize = *AllocaSizeInBits / sizeof(uintptr_t);
size_t Align = AI.getAlign().value();
Offset = int((Offset + (Align - 1)) / Align) * Align;
if (Offset == 0) {
Expand All @@ -168,11 +167,10 @@ class YkShadowStack : public ModulePass {
Int8Ty, SSPtr, {ConstantInt::get(Int32Ty, Offset)}, "",
cast<Instruction>(&AI));
Builder.SetInsertPoint(GEP);
Builder.CreateBitCast(GEP, AI.getAllocatedType()->getPointerTo());
cast<Value>(I).replaceAllUsesWith(GEP);
}
RemoveAllocas.push_back(cast<Instruction>(&AI));
Offset += AllocaSize;
Offset += *AllocaSizeInBytes;
} else if (isa<CallInst>(I)) {
// When we see a call, we need make space for a new stack frame. We
// do this by simply adjusting the pointer stored in the global
Expand Down Expand Up @@ -228,6 +226,11 @@ class YkShadowStack : public ModulePass {
Builder.CreateStore(GEP, GShadowStackPtr);
Builder.SetInsertPoint(I.getNextNonDebugInstruction());
Builder.CreateStore(SSPtr, GShadowStackPtr);
} else if (isa<CallBase>(I)) {
// FIXME: There are other call-like instructions (e.g. `invoke`,
// `callbr`) that we will need to think about when they arise.
Context.emitError("Unimplemented shadow stack allocation");
return false;
}
}
}
Expand Down
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