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[Cherry-pick] [Wunsafe-buffer-usage] False positives for & expression indexing constant size array (arr[anything & 0]) (#112284) #10105

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Merged
merged 1 commit into from
Feb 26, 2025
Merged

[Cherry-pick] [Wunsafe-buffer-usage] False positives for & expression indexing constant size array (arr[anything & 0]) (#112284) #10105

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19 changes: 19 additions & 0 deletions clang/lib/Analysis/UnsafeBufferUsage.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1053,6 +1053,25 @@ AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {
// bug
if (ArrIdx.isNonNegative() && ArrIdx.getLimitedValue() < limit)
return true;
} else if (const auto *BE = dyn_cast<BinaryOperator>(IndexExpr)) {
// For an integer expression `e` and an integer constant `n`, `e & n` and
// `n & e` are bounded by `n`:
if (BE->getOpcode() != BO_And)
return false;

const Expr *LHS = BE->getLHS();
const Expr *RHS = BE->getRHS();

if ((!LHS->isValueDependent() &&
LHS->EvaluateAsInt(EVResult,
Finder->getASTContext())) || // case: `n & e`
(!RHS->isValueDependent() &&
RHS->EvaluateAsInt(EVResult, Finder->getASTContext()))) { // `e & n`
llvm::APSInt result = EVResult.Val.getInt();
if (result.isNonNegative() && result.getLimitedValue() < limit)
return true;
}
return false;
}
return false;
}
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33 changes: 33 additions & 0 deletions clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp
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Expand Up @@ -18,7 +18,9 @@ void foo2(unsigned idx) {

struct Foo {
int member_buffer[10];
int x;
};

void foo2(Foo& f, unsigned idx) {
f.member_buffer[idx] = 0; // expected-warning{{unsafe buffer access}}
}
Expand All @@ -33,6 +35,37 @@ void constant_idx_safe0(unsigned idx) {
buffer[0] = 0;
}

int array[10]; // expected-warning {{'array' is an unsafe buffer that does not perform bounds checks}}

void masked_idx1(unsigned long long idx, Foo f) {
// Bitwise and operation
array[idx & 5] = 10; // no-warning
array[5 &idx] = 12; // no-warning
array[idx & 11 & 5] = 3; // no warning
array[idx & 11] = 20; // expected-note{{used in buffer access here}}
array[idx &=5]; // expected-note{{used in buffer access here}}
array[f.x & 5]; // no-warning
array[5 & f.x]; // no-warning
array[f.x & (-5)]; // expected-note{{used in buffer access here}}
}

typedef unsigned long long uint64_t;
typedef unsigned int uint32_t;
typedef unsigned char uint8_t;

void type_conversions(uint64_t idx1, uint32_t idx2, uint8_t idx3) {
array[(uint32_t)idx1 & 3];
array[idx2 & 3];
array[idx3 & 3];
}

int array2[5]; // expected-warning {{'array2' is an unsafe buffer that does not perform bounds checks}}

void masked_idx_safe(unsigned long long idx) {
array2[6 & 5]; // no warning
array2[6 & idx & (idx + 1) & 5]; // expected-note{{used in buffer access here}}
}

void constant_idx_unsafe(unsigned idx) {
int buffer[10]; // expected-warning{{'buffer' is an unsafe buffer that does not perform bounds checks}}
// expected-note@-1{{change type of 'buffer' to 'std::array' to label it for hardening}}
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