https://github.com/malavikasamak updated
https://github.com/llvm/llvm-project/pull/112284
>From bf1f0b88c26cef3fd7eab40341558e1742c62321 Mon Sep 17 00:00:00 2001
From: MalavikaSamak <malavi...@apple.com>
Date: Fri, 11 Oct 2024 12:24:58 -0700
Subject: [PATCH] [Wunsafe-buffer-usage] False positives for & expression
indexing constant size array (arr[anything & 0])
Do not warn when a constant sized array is indexed with an expression that
contains bitwise and operation
involving constants and it always results in a bound safe access.
rdar://136684050
---
clang/lib/Analysis/UnsafeBufferUsage.cpp | 21 +++++++++++--
.../warn-unsafe-buffer-usage-array.cpp | 31 +++++++++++++++++++
2 files changed, 50 insertions(+), 2 deletions(-)
diff --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp
b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index c064aa30e8aed..3f2e66c03ebd7 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -462,8 +462,25 @@ AST_MATCHER(ArraySubscriptExpr, isSafeArraySubscript) {
// bug
if (ArrIdx.isNonNegative() && ArrIdx.getLimitedValue() < limit)
return true;
- }
- return false;
+ } else if (const auto *BE = dyn_cast<BinaryOperator>(IndexExpr)) {
+ 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())) ||
+ (!RHS->isValueDependent() &&
+ RHS->EvaluateAsInt(EVResult, Finder->getASTContext()))) {
+ llvm::APSInt result = EVResult.Val.getInt();
+ if (result.isNonNegative() && result.getLimitedValue() < limit)
+ return true;
+ }
+ return false;
+
+ } else
+ return false;
}
AST_MATCHER_P(CallExpr, hasNumArgs, unsigned, Num) {
diff --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp
b/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp
index e80b54b7c6967..c1f9bf4c05418 100644
--- a/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage-array.cpp
@@ -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}}
}
@@ -33,6 +35,35 @@ 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[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];
+}
+
+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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