[StackProtector] Introduce stack-protect-refinement pass to remove unnecessary protections. #150390
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| //===- StackProtectRefinement.h - Stack Protect Refinement ----------------===// | ||
| // | ||
| // 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 | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
| // | ||
| // Remove ssp attributes from functions where we can prove it is safe. | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #ifndef LLVM_TRANSFORMS_SCALAR_STACKPROTECTREFINEMENT_H | ||
| #define LLVM_TRANSFORMS_SCALAR_STACKPROTECTREFINEMENT_H | ||
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| #include "llvm/Analysis/StackSafetyAnalysis.h" | ||
| #include "llvm/IR/PassManager.h" | ||
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| namespace llvm { | ||
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| class BasicBlock; | ||
| class Function; | ||
| class Instruction; | ||
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| class StackProtectRefinementPass | ||
| : public PassInfoMixin<StackProtectRefinementPass> { | ||
| public: | ||
| PreservedAnalyses run(Module &M, ModuleAnalysisManager &MAM); | ||
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| private: | ||
| void processFunction(Function &F) const; | ||
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| const StackSafetyGlobalInfo *SSI; | ||
| }; | ||
| } // end namespace llvm | ||
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| #endif // LLVM_TRANSFORMS_SCALAR_STACKPROTECTREFINEMENT_H | ||
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,64 @@ | ||
| //===- StackProtectRefinement.cpp - Stack Protect Refinement --------------===// | ||
| // | ||
| // 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 | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #include "llvm/Transforms/Scalar/StackProtectRefinement.h" | ||
| #include "llvm/ADT/Statistic.h" | ||
| #include "llvm/IR/InstIterator.h" | ||
| #include "llvm/IR/Instructions.h" | ||
| #include "llvm/Support/CommandLine.h" | ||
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| using namespace llvm; | ||
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| #define DEBUG_TYPE "stack-protect-refinement" | ||
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| STATISTIC( | ||
| NumFuncsWithAllocaInst, | ||
| "Number of functions with an instruction to allocate memory on the stack"); | ||
| STATISTIC(NumFuncsWithRemovedStackProtectAttr, | ||
| "Number of functions with alloca and removed stack protect attr"); | ||
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| static cl::opt<bool> | ||
| UseStackSafety("optimize-ssp", cl::init(true), cl::Hidden, | ||
| cl::desc("Use Stack Safety analysis results")); | ||
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| void StackProtectRefinementPass::processFunction(Function &F) const { | ||
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| bool hasAlloca = false; | ||
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| for (auto &I : instructions(&F)) { | ||
| if (auto *AI = dyn_cast<AllocaInst>(&I)) { | ||
| hasAlloca = true; | ||
| if (!SSI->isSafe(*AI)) { | ||
|
There was a problem hiding this comment. If this is all the pass is doing, should this just be done directly in the SSP lowering pass? Stripping the attribute seems potentially dangerous. Suppose a later pass chooses to introduce a new unsafe alloca, which will now no longer be appropriately processed during lowering |
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| NumFuncsWithAllocaInst++; | ||
| return; | ||
| } | ||
| } | ||
| } | ||
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| if (hasAlloca) { | ||
| NumFuncsWithAllocaInst++; | ||
| NumFuncsWithRemovedStackProtectAttr++; | ||
| } | ||
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| F.removeFnAttr(Attribute::StackProtect); | ||
| F.removeFnAttr(Attribute::StackProtectStrong); | ||
| } | ||
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| PreservedAnalyses StackProtectRefinementPass::run(Module &M, | ||
| ModuleAnalysisManager &MAM) { | ||
| if (!UseStackSafety) | ||
| return PreservedAnalyses::all(); | ||
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| SSI = &MAM.getResult<StackSafetyGlobalAnalysis>(M); | ||
| for (Function &F : M) | ||
| if (F.hasFnAttribute(Attribute::StackProtect) || | ||
| F.hasFnAttribute(Attribute::StackProtectStrong)) | ||
| processFunction(F); | ||
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| return PreservedAnalyses::all(); | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,64 @@ | ||
| // RUN: clang -O2 -fstack-protector-strong -emit-llvm -S %s -o - | FileCheck %s | ||
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| __attribute__((noinline)) | ||
| int foo1(int *p) { | ||
| return p[10]; | ||
| } | ||
| int bar1() { | ||
| // CHECK-LABEL: define {{[^@]+}}@bar1 | ||
| // CHECK-SAME: () local_unnamed_addr #[[ATTR1:[0-9]+]] { | ||
| int x[128]; | ||
| return foo1(x); | ||
| } | ||
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| __attribute__((noinline)) | ||
| int foo2(int *p) { | ||
| return p[1000]; | ||
| } | ||
| int bar2() { | ||
| // CHECK-LABEL: define {{[^@]+}}@bar2 | ||
| // CHECK-SAME: () local_unnamed_addr #[[ATTR2:[0-9]+]] { | ||
| int x[128]; | ||
| return foo2(x); | ||
| } | ||
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| int k; | ||
| __attribute__((noinline)) | ||
| int foo3(int *p) { | ||
| return p[k]; | ||
| } | ||
| int bar3() { | ||
| // CHECK-LABEL: define {{[^@]+}}@bar3 | ||
| // CHECK-SAME: () local_unnamed_addr #[[ATTR3:[0-9]+]] { | ||
| int x[128]; | ||
| return foo3(x); | ||
| } | ||
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| __attribute__((noinline)) | ||
| int foo4(int *p); | ||
| int bar4() { | ||
| // CHECK-LABEL: define {{[^@]+}}@bar4 | ||
| // CHECK-SAME: () local_unnamed_addr #[[ATTR4:[0-9]+]] { | ||
| int x[128]; | ||
| return foo4(x); | ||
| } | ||
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| int bar5() { | ||
| // CHECK-LABEL: define {{[^@]+}}@bar5 | ||
| // CHECK-SAME: () local_unnamed_addr #[[ATTR5:[0-9]+]] { | ||
| int x[128]; | ||
| int i; | ||
| for (i = 0; i < 128; ++i) | ||
| x[i] = i; | ||
| return foo1(x); | ||
| } | ||
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| //. | ||
| // CHECK: attributes #[[ATTR1]] = | ||
| // CHECK-NOT: sspstrong | ||
| // CHECK: attributes #[[ATTR2]] = {{.* sspstrong}} | ||
| // CHECK: attributes #[[ATTR3]] = {{.* sspstrong}} | ||
| // CHECK: attributes #[[ATTR4]] = {{.* sspstrong}} | ||
| // CHECK: attributes #[[ATTR5]] = | ||
| // CHECK-NOT: sspstrong | ||
| //. |
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