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[AddressSanitizer] Remove memory effects from functions (llvm#130495)
If left as-is, subsequent optimizations might utilize the possible memory effects and optimize-out the instrumentation. Think of the following case: ``` store i8 4, ptr %shadow call void @llvm.lifetime.start.p0(i64 4, ptr %local) %28 = call void @foo(ptr %local) store i8 -8, ptr %shadow call void @llvm.lifetime.end.p0(i64 4, ptr %local) ``` where `foo` is an external function with `memory(argmem: write)`. A pass such as DeadStoreElimination is allowed to remove the initial store, which might fail sanitizer checks within `foo`. My first attempt was to add a `memory(readwrite)` at the call-site level, but unfortunately the current implementation of `getMemoryEffects` doesn't exactly give it "precedence" as specified, but rather restricts the access specified by the call-site and not the other way around as well.
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‎llvm/include/llvm/Transforms/Instrumentation/AddressSanitizerCommon.h

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Original file line numberDiff line numberDiff line change
@@ -58,6 +58,12 @@ void getAddressSanitizerParams(const Triple &TargetTriple, int LongSize,
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bool IsKasan, uint64_t *ShadowBase,
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int *MappingScale, bool *OrShadowOffset);
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/// Remove memory attributes that are incompatible with the instrumentation
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/// added by AddressSanitizer and HWAddressSanitizer.
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/// \p ReadsArgMem - indicates whether function arguments may be read by
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/// instrumentation and require removing `writeonly` attributes.
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void removeASanIncompatibleFnAttributes(Function &F, bool ReadsArgMem);
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} // namespace llvm
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#endif

‎llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

Lines changed: 42 additions & 0 deletions
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@@ -612,6 +612,45 @@ void getAddressSanitizerParams(const Triple &TargetTriple, int LongSize,
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*OrShadowOffset = Mapping.OrShadowOffset;
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}
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void removeASanIncompatibleFnAttributes(Function &F, bool ReadsArgMem) {
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// Sanitizer checks read from shadow, which invalidates memory(argmem: *).
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//
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// This is not only true for sanitized functions, because AttrInfer can
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// infer those attributes on libc functions, which is not true if those
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// are instrumented (Android) or intercepted.
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//
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// We might want to model ASan shadow memory more opaquely to get rid of
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// this problem altogether, by hiding the shadow memory write in an
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// intrinsic, essentially like in the AArch64StackTagging pass. But that's
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// for another day.
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// The API is weird. `onlyReadsMemory` actually means "does not write", and
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// `onlyWritesMemory` actually means "does not read". So we reconstruct
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// "accesses memory" && "does not read" <=> "writes".
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bool Changed = false;
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if (!F.doesNotAccessMemory()) {
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bool WritesMemory = !F.onlyReadsMemory();
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bool ReadsMemory = !F.onlyWritesMemory();
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if ((WritesMemory && !ReadsMemory) || F.onlyAccessesArgMemory()) {
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F.removeFnAttr(Attribute::Memory);
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Changed = true;
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}
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}
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if (ReadsArgMem) {
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for (Argument &A : F.args()) {
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if (A.hasAttribute(Attribute::WriteOnly)) {
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A.removeAttr(Attribute::WriteOnly);
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Changed = true;
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}
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}
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}
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if (Changed) {
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// nobuiltin makes sure later passes don't restore assumptions about
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// the function.
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F.addFnAttr(Attribute::NoBuiltin);
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}
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}
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ASanAccessInfo::ASanAccessInfo(int32_t Packed)
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: Packed(Packed),
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AccessSizeIndex((Packed >> kAccessSizeIndexShift) & kAccessSizeIndexMask),
@@ -2732,6 +2771,9 @@ int ModuleAddressSanitizer::GetAsanVersion(const Module &M) const {
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bool ModuleAddressSanitizer::instrumentModule(Module &M) {
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initializeCallbacks(M);
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for (Function &F : M)
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removeASanIncompatibleFnAttributes(F, /*ReadsArgMem=*/false);
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// Create a module constructor. A destructor is created lazily because not all
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// platforms, and not all modules need it.
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if (ConstructorKind == AsanCtorKind::Global) {

‎llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

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@@ -594,6 +594,11 @@ void HWAddressSanitizer::initializeModule() {
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LLVM_DEBUG(dbgs() << "Init " << M.getName() << "\n");
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TargetTriple = Triple(M.getTargetTriple());
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// HWASan may do short granule checks on function arguments read from the
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// argument memory (last byte of the granule), which invalidates writeonly.
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for (Function &F : M.functions())
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removeASanIncompatibleFnAttributes(F, /*ReadsArgMem=*/true);
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// x86_64 currently has two modes:
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// - Intel LAM (default)
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// - pointer aliasing (heap only)

‎llvm/test/Instrumentation/AddressSanitizer/AMDGPU/asan_instrument_mem_intrinsics.ll

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -186,7 +186,7 @@ declare void @llvm.memset.p5.i32(ptr addrspace(5) nocapture writeonly, i8, i32,
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define void @test_mem_intrinsic_memcpy(ptr %dest0,ptr %src0,ptr addrspace(1) %dest1,ptr addrspace(1) %src1,ptr addrspace(2) %dest2,ptr addrspace(2) %src2,ptr addrspace(3) %dest3,ptr addrspace(3) %src3,ptr addrspace(4) %dest4,ptr addrspace(4) %src4,ptr addrspace(5) %dest5,ptr addrspace(5) %src5) #0 {
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entry:
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;CHECK: define void @test_mem_intrinsic_memcpy(ptr [[DEST0:%.*]], ptr [[SRC0:%.*]], ptr addrspace(1) [[DEST1:%.*]], ptr addrspace(1) [[SRC1:%.*]], ptr addrspace(2) [[DEST2:%.*]], ptr addrspace(2) [[SRC2:%.*]], ptr addrspace(3) [[DEST3:%.*]], ptr addrspace(3) [[SRC3:%.*]], ptr addrspace(4) [[DEST4:%.*]], ptr addrspace(4) [[SRC4:%.*]], ptr addrspace(5) [[DEST5:%.*]], ptr addrspace(5) [[SRC5:%.*]]) #2 {
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;CHECK: define void @test_mem_intrinsic_memcpy(ptr [[DEST0:%.*]], ptr [[SRC0:%.*]], ptr addrspace(1) [[DEST1:%.*]], ptr addrspace(1) [[SRC1:%.*]], ptr addrspace(2) [[DEST2:%.*]], ptr addrspace(2) [[SRC2:%.*]], ptr addrspace(3) [[DEST3:%.*]], ptr addrspace(3) [[SRC3:%.*]], ptr addrspace(4) [[DEST4:%.*]], ptr addrspace(4) [[SRC4:%.*]], ptr addrspace(5) [[DEST5:%.*]], ptr addrspace(5) [[SRC5:%.*]]){{.*}} {
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;CHECK-NEXT: entry:
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;CHECK-NEXT: [[VR0:%.*]] = call ptr @__asan_memcpy(ptr [[DEST0]], ptr [[SRC0]], i64 64)
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;CHECK-NEXT: [[VR1:%.*]] = addrspacecast ptr addrspace(1) [[SRC1]] to ptr
@@ -469,7 +469,7 @@ entry:
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define void @test_mem_intrinsic_memmove(ptr %dest0,ptr %src0,ptr addrspace(1) %dest1,ptr addrspace(1) %src1,ptr addrspace(2) %dest2,ptr addrspace(2) %src2,ptr addrspace(3) %dest3,ptr addrspace(3) %src3,ptr addrspace(4) %dest4,ptr addrspace(4) %src4,ptr addrspace(5) %dest5,ptr addrspace(5) %src5) #0 {
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entry:
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;CHECK: define void @test_mem_intrinsic_memmove(ptr [[DEST0:%.*]], ptr [[SRC0:%.*]], ptr addrspace(1) [[DEST1:%.*]], ptr addrspace(1) [[SRC1:%.*]], ptr addrspace(2) [[DEST2:%.*]], ptr addrspace(2) [[SRC2:%.*]], ptr addrspace(3) [[DEST3:%.*]], ptr addrspace(3) [[SRC3:%.*]], ptr addrspace(4) [[DEST4:%.*]], ptr addrspace(4) [[SRC4:%.*]], ptr addrspace(5) [[DEST5:%.*]], ptr addrspace(5) [[SRC5:%.*]]) #2 {
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;CHECK: define void @test_mem_intrinsic_memmove(ptr [[DEST0:%.*]], ptr [[SRC0:%.*]], ptr addrspace(1) [[DEST1:%.*]], ptr addrspace(1) [[SRC1:%.*]], ptr addrspace(2) [[DEST2:%.*]], ptr addrspace(2) [[SRC2:%.*]], ptr addrspace(3) [[DEST3:%.*]], ptr addrspace(3) [[SRC3:%.*]], ptr addrspace(4) [[DEST4:%.*]], ptr addrspace(4) [[SRC4:%.*]], ptr addrspace(5) [[DEST5:%.*]], ptr addrspace(5) [[SRC5:%.*]]){{.*}} {
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;CHECK-NEXT: entry:
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;CHECK-NEXT: [[VR0:%.*]] = call ptr @__asan_memmove(ptr [[DEST0]], ptr [[SRC0]], i64 64)
475475
;CHECK-NEXT: [[VR1:%.*]] = addrspacecast ptr addrspace(1) [[SRC1]] to ptr
@@ -753,7 +753,7 @@ entry:
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define void @test_mem_intrinsic_memset(ptr %ptr0,ptr addrspace(1) %ptr1,ptr addrspace(2) %ptr2,ptr addrspace(3) %ptr3,ptr addrspace(4) %ptr4,ptr addrspace(5) %ptr5) #0{
755755
entry:
756-
;CHECK: define void @test_mem_intrinsic_memset(ptr [[PTR0:%.*]], ptr addrspace(1) [[PTR1:%.*]], ptr addrspace(2) [[PTR2:%.*]], ptr addrspace(3) [[PTR3:%.*]], ptr addrspace(4) [[PTR4:%.*]], ptr addrspace(5) [[PTR5:%.*]]) #2 {
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;CHECK: define void @test_mem_intrinsic_memset(ptr [[PTR0:%.*]], ptr addrspace(1) [[PTR1:%.*]], ptr addrspace(2) [[PTR2:%.*]], ptr addrspace(3) [[PTR3:%.*]], ptr addrspace(4) [[PTR4:%.*]], ptr addrspace(5) [[PTR5:%.*]]){{.*}} {
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;CHECK-NEXT: entry:
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;CHECK-NEXT: [[VR0:%.*]] = call ptr @__asan_memset(ptr [[PTR0]], i32 1, i64 128)
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;CHECK-NEXT: [[VR1:%.*]] = addrspacecast ptr addrspace(1) [[PTR1]] to ptr

‎llvm/test/Instrumentation/AddressSanitizer/remove-memory-effects.ll

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,20 @@
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; Remove possible memory effects from functions that are invalidated by
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; AddressSanitizer instrumentation.
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; RUN: opt -passes='asan<use-after-scope>' -S %s | FileCheck %s
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; CHECK: @foo(ptr writeonly) #[[ATTRS_FOO:[0-9]+]]
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declare void @foo(ptr writeonly) memory(argmem: write)
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; CHECK: @bar() #[[ATTRS_BAR:[0-9]+]]
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define void @bar() sanitize_address {
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entry:
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%x = alloca i32, align 4
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call void @llvm.lifetime.start.p0(i64 4, ptr %x)
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call void @foo(ptr %x)
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call void @llvm.lifetime.end.p0(i64 4, ptr %x)
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ret void
17+
}
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; CHECK: attributes #[[ATTRS_FOO]] = { nobuiltin }
20+
; CHECK: attributes #[[ATTRS_BAR]] = { sanitize_address }

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